FRAMEWORK FOR THE

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FRAMEWORK FOR THE
ENVIRONMENTAL MANAGEMENT
OF OFFSHORE DISCHARGE
OF
DRILLING FLUID ON CUTTINGS
ISSUES PAPER
MARCH 1998
CONTENTS
Executive Summary 1
1.Introduction 1
2.Drilling Fluid Technology 3
3.Environmental Behaviour of Drilling Fluids 3
3.1 Environmental Issues 3
3.1.1 Toxicity 4
3.1.2 Persistence and Biodegradability 4
3.1.3 Bioaccumulation/Bioconcentration 5
3.1.4 Smothering Effects 5
3.1.5 Organic Enrichment and Anoxia 6
3.1.6 Leaching of Non-Water based Drilling Fluids 6
3.1.7 Tainting of Fish 6
3.2 Field Studies 6
4.Drilling Fluid and Cuttings Management 7
4.1 Evaluation of Disposal Options 7
4.2 Management Framework 9
5.Future Direction 11
6.Conclusion 14
7.References 16
Appendices
Appendix A - Classification of Drilling Fluids
A1 Water Based Fluids
A2 Non-Water Based Fluids
17
17
17
Appendix B - Technical Requirements for Using Non-Water Based Drilling Fluids 19
Appendix C - Field Studies
C1 Findings From Australian Studies
C2 Overseas Findings
23
23
26
Framework for the Environmental Management of Drilling Fluids on Cuttings in Australia, March 1998 Page 1
EXECUTIVE SUMMARY
Most countries of the world have determined that offshore drilling operations, subject to appropriate
management arrangements and regulatory control, can be conducted in an environmentally acceptable manner.
Australia, being lightly explored, experiences much less drilling activity than elsewhere in the world. Overall
environmental impacts associated with this activity in Australian waters are minimal, but localised impacts
may occur in some circumstances. APPEA has developed a framework for the environmental management of
drilling fluids on cuttings to ensure that the marine discharge of drilling fluid on cuttings is within
environmentally acceptable limits.
The majority of exploration and development drilling programs in Australia use and discharge water based
drilling fluids, however there are occasions when technical drilling requirements mean that non-water based
fluids must be used.
The framework is location and activity specific, acknowledging that a case by case assessment for discharge is
required because of the differences in environmental sensitivity of receiving environments, the variable
oceanographic conditions and the available products and technologies. The framework includes a habitat
sensitivity rating for the major Australian offshore prospective basins.
Worldwide studies have generally shown that the marine discharge of drilling fluid on cuttings creates a
minimal, short term zone of effect. The recovery time varies depending on the volume discharged, the local
oceanographic conditions, the biodegradability of the base fluid used and the treatment before discharge. This
zone of effect can be predicted by dispersion modelling.
Additional research to examine and understand the direct and indirect impacts of marine discharge of drilling
fluids on cuttings is proposed, to progressively improve the environmental performance of offshore drilling.
Seabed monitoring programs have been undertaken by a number of Australian companies, and the proposed
studies will be designed to extend and add value to those existing programs.
Where drilling programs in sensitive locations require non-water based fluids, the environmental risk can be
higher. In which case the implementation of less cost-effective disposal options such as re-injection or
transport to shore may be warranted.
1. Introduction
Australia is one of a small number of nations fortunate to be endowed with significant petroleum resources.
These resources, together with a wide range of other natural resources, have substantially underpinned
Australias high standard of living and contribute significantly to the nations economy and competitive
advantage in world trade. The wise use of these resources can sustain Australias economy well into the
future.
According to the Australian Bureau of Agriculture and Resource Economics Australia is 74 per cent self-
sufficient in petroleum liquids and in terms of total energy production, including gas, Australia is
approximately 99 per cent self sufficient. With continued growth in Australias economy and population, the
demand for petroleum and its products will grow accordingly. This increases the urgency to explore and
develop oil and gas reserves in order to limit Australias dependency on petroleum imports.
The Australian petroleum exploration and production industry has a sound environmental record and is
committed to responsible environmental management. The industry has attracted attention in recent times due
to increased public awareness of environmental issues and the communitys concern about the potential effects
of the industry on the environment. Much of this attention has been focussed on regulators. Current
regulatory approaches seek to place greater responsibility onto the companies, while developing reporting and
assessment systems that provide the confidence and assurance that environmental outcomes and performance
Framework for the Environmental Management of Drilling Fluids on Cuttings in Australia, March 1998 Page 2
are acceptable. Regulator and management decisions must rely on a sound scientific basis, and a consistent
and transparent process must be employed across all State and Commonwealth jurisdictions.
Australia differs from more intensely explored areas such as the North Sea in a number of ways. Figure 1
shows the relative levels of drilling activity in offshore Australia and the North Sea. Environmental concerns,
testing protocols, standards, regulatory arrangements, and other controls developed for countries with more
intense activity may not be directly applicable or relevant to Australian conditions. Approaches developed
elsewhere need to be assessed for their relevance and usefulness particularly from an environmental
perspective. The North Sea experience dominated by the use of non-water based drilling fluids, cold water
temperatures, and low dispersion rates contrasts with the situation in Australia.
Figure 1: Number of Wells Drilled Offshore
In Australia water based fluids are the predominant fluid used, with non-water based fluids usually employed
only for the bottom section of a well and in areas of technical complexity. Non-water based fluids are
separated from cuttings, retained on board and returned to shore for recycling at the end of the drilling
program. As part of the rotary drilling operations, the drilled cuttings are continuously discharged overboard
after separation by vibrating screens (shale shakers) from recirculated drilling fluids, and to a lesser extent,
centrifuges, desanders and/or mudcleaners. Some drilling fluid remains adhered to the cuttings, which are
flushed with seawater through a direct overboard drain. The majority of the drilling fluid is not adhered to the
cuttings and is continuously recycled during the well program to make efficient use of the drilling fluid.
Marine discharge of drill cuttings is permitted in most areas of the world, subject to local controls to ensure
environmental protection. Recent concerns, particularly in the North Sea, over the impact of marine discharge
of drilling fluid on cuttings has led to the closer examination of the types of drill fluids used and discharge
practices.
In order to develop appropriate regulatory and management arrangements, Australia must evaluate its own
situation and requirements before following the lead of some other countries. Banning the use and/or
discharge of particular types of drilling fluids may be environmentally unnecessary and impose additional
costs on industry. Industry and regulators need to examine ways of managing the treatment and disposal of
drilling fluids on cuttings with regard to the local environmental implications and effects. Research in the
areas of dispersion, bioaccumulation and toxicity should be undertaken using Australian conditions and
species in various Australian locations, as the regional environments are highly variable.
0
50
100
150
200
250
300
350
400
1991 1992 1993 1994 1995 1996 1991 1992 1993 1994 1995 1996
Number of Wells Drilled
Exploration
Appraisal
Devel opment
NORTH SEA
AUSTRALIA
Framework for the Environmental Management of Drilling Fluids on Cuttings in Australia, March 1998 Page 3
The Australian oil and gas exploration and production industry has a sound environmental record and is
committed to responsible and continuous improvement in environmental management. Consistent and
acceptable regulatory management arrangements for the discharge of drilling fluids on cuttings need to be
developed in collaboration with industry and government to produce safe, environmentally responsible and
cost-effective outcomes.
This paper provides a management framework for the discharge of drilling cuttings with adhered drilling fluid
(drilling fluid on cuttings), and demonstrates the Australian oil and gas exploration and production industry
is committed to minimising the environmental impact of drilling activity.
2. Drilling Fluid Technology
Drilling fluids play an essential role in providing for safe and efficient drilling by:
i) maintaining pressure on the formations;
ii) removing cuttings from the borehole;
iii) protecting and supporting the borehole wall;
iv) protecting permeable zones from damage; and
v) cooling and lubricating the drill bit and drill string.
There are two broad groups of drilling fluids currently in use in Australia: water based fluids and non-water
based fluids (Appendix A). Water based fluids are the base fluid for most drilling programs in Australia,
however there are occasions when technical drilling requirements mean that non-water based fluids need to be
used. Technical requirements for using non-water based drilling fluids are presented in Appendix B. Non-
water based fluids are used in drilling conditions which require greater stabilisation of the borehole, lubricity,
and/or resistance to thermal degradation than can be provided by water based fluids. The use of non-water
based drilling fluids generally reduces drilling time and technical difficulties which has implications for
improved safety on a drilling rig through better well control and reduced exposure time of rig crews, and
consequentially lower environmental risks for a drilling operation.
There are several categories of non-water based drilling fluids, many of which are environmentally benign,
which are under active development and improvement. One category, synthetic based fluids were developed to
provide the drilling performance of traditional diesel or mineral oil based fluids when drilling under demanding
conditions, and to provide improved environmental behaviour, especially with respect to persistence in the
marine environment. The term synthetic as applied to synthetic based fluids means material produced by the
chemical reaction of specific, purified chemical feedstock, as opposed to the traditional base fluids such as
diesel and mineral oil which are derived from crude oil solely through physical separation processes. A
classification of the types of drilling fluids is provided in Appendix A.
3. Environmental Aspects of Drilling Fluids
3.1 Environmental Issues
The primary concern overseas is the level of non-water based drilling fluids adhered to drilling cuttings
discharged to the marine environment. The main environmental issues associated with the discharge of
cuttings contaminated with these fluids to the marine environment are:
 toxicity to marine biota;
 fate, persistence and biodegradability;
 bioaccumulation / bioconcentration by marine biota;
 smothering effects of accumulated drill cuttings on the marine biota;
 organic enrichment and sediment anoxia;
 leaching of non-water based drilling fluids into the water column; and
 tainting of commercially exploited demersal fish stocks.

Framework for the Environmental Management of Drilling Fluids on Cuttings in Australia, March 1998 Page 4
3.1.1 Toxicity

Acute ecotoxicity testing is commonly used to predict the toxicity of drilling fluids in the marine environment.
Marine species are exposed to a range of test concentrations under laboratory conditions to determine the
LC50 of the test substance using established protocols for drilling fluids. The LC50 is the concentration of
the test substance which results in the mortality of 50 percent of the test population over a given period of
time. The results are compared against the toxicity grades (Hinwood et al., 1994) shown in Table 3.1.

Table 3.1 Classification of Toxicity Grades

Toxicity Rating
LC50 Value (mg/l)
Very toxic <1
Toxic 1 - 100
Moderately toxic 100 - 1,000
Slightly toxic 1000 - 10,000
Almost non-toxic 10,000 - 100,000
Non-toxic >100,000
Source: Hinwood et al, 1994

The non-water based drilling fluids currently used in drilling operations in Australia, offshore United States
and the North Sea range from slightly toxic to non-toxic, depending on the test organisms used. This low
toxicity can be attributed to two factors: the low solubility of non-water based drilling fluids in the water
column; and their low to negligible concentrations of aromatic hydrocarbons, which are the principal source of
environmental toxicity.

In relatively shallow and/or low energy marine and coastal environments, cuttings piles may accumulate on the
sea floor. Testing for toxicity to benthic organisms is therefore routinely conducted for non-water based
drilling fluids used in the North Sea. The most commonly selected test species is the amphipod Corophium
volutator which is intimately associated with sediments, has limited mobility and high sensitivity to
contaminants. Current non-water based drilling fluids which have undergone the Corophium volutator
sediment reworker ecotoxicity test have rated as slightly toxic against the values in Table 3.1. Exploration
drilling, usually one-off wells, does not generally create cuttings piles other than in exceptional shallow or low
energy environments.

3.1.2 Persistence and Biodegradability

The persistence and extent of cuttings piles and their subsequent degradation are of primary concern in the
marine discharge of drill cuttings containing non-water based drilling fluids. One of the initial objectives of
the development of synthetic based fluids was to maximise the rate of biodegradation to minimise potential
environmental impacts, primarily by increasing the rate of recovery of the benthic fauna. However, actually
quantifying biodegradation rates has proved problematic due to the range of factors affecting the rates both in
the laboratory and in the field. This has lead to the biodegradation of non-water based drilling fluids being
studied in four types of experiments: standard laboratory tests; solid phase tests; simulated seabed tests; and
by field seabed monitoring.

Results of biodegradation testing have shown that:
 non-water based fluids exhibit a range of degradation rates. Under comparable conditions, esters
seem to degrade most rapidly. The relative difference in degradation rates between base fluids
depends on the test protocol being used;
 degradation rates are inversely proportional to the non-water based drilling fluid concentration in the
sediments;
Framework for the Environmental Management of Drilling Fluids on Cuttings in Australia, March 1998 Page 5
 degradation occurs more rapidly in aerobic conditions than in anaerobic conditions;
 the sediment type (eg. sand versus mud) is a determinant of degradation rate; and
 full evaluation of degradation should address rates under both anaerobic conditions (as might be
found in the main part of cuttings piles if they are formed) and aerobic conditions (as may apply to
more dispersed or remobilised cuttings accumulations).
Oxygen availability is a key factor determining the rate of biodegradation of non-water based drilling fluids in
the marine environment. The physical and chemical characteristics of cuttings piles are dependent on the
nature of the drilling operation (multi well or single well), the type, amount and concentration of non-water
based drilling fluid on cuttings, the water depth, seabed temperatures and local energetics of the environment
where discharges are occurring. These factors coupled with the dispersion and remobilisation effects of
cuttings (such as cyclones and wave or current action) must be considered in determining the spatial extent of
any observed impact, the period elapsing before community recovery and the overall environmental effects.
As such, persistence and effects (and hence community recovery) can only be accurately assessed on a case by
case basis, preferably with regional field studies to provide an appropriate regional context to assess wider
impacts.
3.1.3 Bioaccumulation / Bioconcentration
Bioaccumulation is the uptake and retention of xenobiotics (substances which are not natural components of
the environment) by organisms from their immediate environment.
The bioaccumulation potential is the ratio of the equilibrium concentrations of the dissolved substances in a
two phase system consisting of two largely immiscible solvents (n-octanol and water) indicated as LogPow.
Substances with LogPow > 3 and molecular weight <600 have a tendency to bioaccumulate, but most experts
agree that a substance with LogPow >7 will not bioaccumulate in aquatic species because the particles will be
too large to move past the aqueous diffusion layer which is present at the water/gill interface.
Bioconcentration is the process by which there is a net accumulation of a chemical from water into the aquatic
organism resulting from simultaneous uptake and elimination (depuration). Bioconcentration is typically
determined by exposing the blue mussel Mytilus edulis to saturated aqueous concentrations of the test material
under a flow through condition for 10 days and then allowing them to depurate in clean water for a further 20
days.
The bioaccumulation and bioconcentration of chemicals and drilling fluids by marine biota can have
significant ecological consequences especially when it is biomagnified through the food chain ie. pollutants are
accumulated at greater amounts up the food chain with more serious consequences for higher organisms such
as birds and marine predators.
Generally, synthetic drilling fluids have a high n-octanol/water partition coefficient (LogPow) and are not
expected to bioaccumulate in aquatic life.
Both bioaccumulation and bioconcentration testing is routinely conducted for new drilling fluids entering the
market, with results supporting the view that the fluids have limited potential to bioconcentrate in aquatic
organisms.
3.1.4 Smothering Effects
When drill cuttings are discharged to the seabed during drilling operations the cuttings may accumulate in
close proximity to the discharge point. The thickness and shape of the cuttings pile is dependant on the
amount and rate of drill cuttings discharge, the depth of water and the prevailing oceanographic conditions
such as current speed and direction.
Framework for the Environmental Management of Drilling Fluids on Cuttings in Australia, March 1998 Page 6
The benthic biota immediately below the point of cuttings discharge can be physically smothered, regardless of
the nature of the cuttings (water based or non-water based fluid). Recovery is dependent on the type of
community affected, the physical structure and persistence of the cuttings pile itself, the presence and nature of
any toxic components within the pile, and the availability of colonising organisms.
3.1.5 Organic Enrichment and Anoxia
The rapid depletion of oxygen through the microbial breakdown of organic matter associated with the
discharge of drilling fluid on cuttings can cause anoxic conditions within, or adjacent to, the cuttings pile.
Anoxic conditions may also result from burial of organic material by sediment redistribution and may retard
the recovery of certain marine species.
3.1.6 Leaching of Non-Water Based Drilling Fluids
Some non-water based drilling fluids may persist long enough within cuttings piles, and in time may leach into
the water column and potentially effect marine biota. The rate of leaching is dependant on the drilling fluid
type, its persistence, solubility, manner of burial and prevailing oceanographic conditions. Studies such as
Delvigne (1996) and Stagg and McIntosh (1996) have shown that exposure of fish to low tox oil based fluids,
both treated and untreated, resulted in limited leaching of hydrocarbons, and no leaching of metals.
3.1.7 Tainting of Fish
It was originally assumed in the North Sea that fish, particularly those that are bottom dwellers or feed on the
seabed, could be tainted by oily substances associated with the discharge of drill cuttings. It has since been
shown that such tainting of fish is unlikely.
3.2.Field Studies
Field studies provide the most realistic assessment of the effects of the discharge of non-water based drilling
fluids. However, for studies to be comparable the testing protocols must be consistent. Caution must be taken
when comparing overseas results with those in Australia, as different locations have different dispersion and
biodegradation rates due to:
i) type and quantity of drilling fluids discharged; and
ii) chemical and physical characteristics of the receiving environment.
In 1985, the Paris Commission Working Group on oil pollution produced agreed facts on the impacts of oil
based fluids on the marine environment. These findings, based on field studies and reported by Davies et al.
(1988), were:
 water based and oil based drill cuttings can have an adverse effect on the seabed biological community;
 the major impact on the seabed biological community was confined to within a 500m safety zone and
associated primarily with burial under the cuttings pile on the seabed;
 surrounding the area of major impact is a transition zone, generally within 200 - 1,000m, in which lesser
biological effects are detected; and
 elevated hydrocarbon concentrations due to the oil based muds were observed beyond the areas of
biological effects up to a distance of 4,000m in the direction of the prevailing current.

It is important to note that the agreed facts were based on multiple well drilling operations in the northern
portion of the North Sea. The facts were not so clearly defined for single well exploration sites, or from the
UK Sector of the southern North, where according to Davies et al. (1988) depths are shallower, current
regimes stronger, sediment characteristics more variable and a smaller number of wells are drilled from any
one installation. Such situations are more typical of Australian drilling operations.

Framework for the Environmental Management of Drilling Fluids on Cuttings in Australia, March 1998 Page 7
It has been shown that the main biological effect of discharged oil based drill cuttings is confined to within
500m for development drilling and 250m for single well sites, and is associated primarily with burial under the
mound of cuttings on the seabed (Poley & Wilkinson, 1983; Davies et al., 1984).

Seabed survey results for new generation non-water based drilling fluids are slowly becoming available. The
results demonstrate that these fluids have an effect on the seabed in the immediate vicinity of the discharge,
and that there is rapid recovery on completion of drilling related to the physical dispersion and the degradation
of the base fluid.

Table 3.2 provides a summary of field studies currently in progress, or completed, in Australian waters.
Selected findings from field studies in Australia and overseas are presented in Appendix C.

4. Drilling fluids on Cuttings Management

4.1 Evaluation of Disposal Options

Most oil and gas operators today develop and implement an environmental management system (EMS) for all
operations which is in line with international standards. Through the adoption and implementation of an EMS,
potential environmental impacts and consequences are identified, managed and minimised where possible.

In the process of drilling exploration and development wells, drill cuttings are generated and brought to the
surface. When assessing the most appropriate means for disposal, all options must be considered and
weighted to achieve the safest, most environmentally responsible and cost-effective outcome.

Options for the disposal of cuttings include marine discharge, injection or discharge into wellbores or sub-
surface formations, or transport of waste to shore for treatment and disposal. These practices entail their own
environmental effects, costs and many may be limited by practical and technical considerations. Using
onshore methods of disposal requires that the material be transported to the site, which will increase the risks
to the environment and personnel safety through handling, shipping and transport.

Operators recognise the potential environmental impacts of discharging non-water based drilling fluid and the
associated cuttings to the marine environment, and aim to minimise the volume of fluid discharged through:
 the containment and bunding of the drilling floor and rig deck;
 the containment of all chemical storage areas;
 locking of all dump valves;
 the installation of catchment drains, particularly on the rig floor and in the mud pits;
 the installation of a suction cleaning system to collect any spillage;
 the utilisation of solids control equipment to minimise the amount of drilling fluid retained on the
cuttings, as far as practicable, prior to discharge;
 the implementation of strict fluid handling procedures throughout the operation;
 the review of operations to ensure they are meeting environmental management procedures;
 monitoring the volume of drilling fluid retained on the cuttings;
 personnel training in the handling, storage and use of drilling fluids; and
 mass balance calculations through the drilling program.
Framework for the Environmental Management of Drilling Fluids on Cuttings in Australia, March 1998 Page 8
Table 3.2 Summary of Studies Currently in Progress or Completed in Australian Waters.
Fluid Name
(Generic/Specific)
#Wells/
Water Depth/
Drilling Period
Location#Stations/
Replicate/
Controls
Habitat Parameters Sampling Frequency Status Operator
LTO / Shellsol
DMA
Single / 80m / - NWS
Wanaea
8 / 5:2 / 2 Unconsolidated
sediment
Biota, TPH, Metals, Grain Size,
TOC, SiO
2
, CaCO
3
Baseline, +1 year, +3 years Baseline, +1 year,
completed
Woodside Offshore
Petroleum Pty Ltd
EMO / XPO7 Single / 78m / - NWS
Lynx 1a
10 / 2:0 / 2 Unconsolidated
sediment
TPH, Metals Cessation of drilling, +10 months Cessation completed,
analysing 10 month survey
Woodside Offshore
Petroleum Pty Ltd
OBM / LTO 11 / - NWS
North
Rankin
12 / 3:2 / 2 Unconsolidated
sediment
Biota, TPH, PAH, Grain Size,
CaCO
3
Cessation of drilling, additional
sampling to be determined
Cessation completed Woodside Offshore
Petroleum Pty Ltd
LTO / EMO
HDF 200 / XP07
Sarapan
15 / 130m / - NWS
Goodwyn
12 / 3:2 / 2 Unconsolidated
sediment
Biota, TPH, PAH, Grain Size,
CaCO
3
Baseline, additional sampling to be
determined
Baseline completed Woodside Offshore
Petroleum Pty Ltd
Petrofree / Ester 7 / 69m / 1 year Bass Strait
Fortescue
6 / 2 / 3 Unconsolidated
sediment
Biota, TPH, esters, grin size,
barium
Baseline, +½ yr during, +1 yr end,
+½ yr after, +1 yr after
completed Esso Australia Ltd.
WBM / KCl/PHPA
Glycol
42 / 61m / 4 years Bass Strait
West Tuna
10 / 2 / -
6
Unconsolidated
sediment
Biota, TPH, grain size barium Baseline (x2), +2 yrs during, +4
yrs during, +1 yr after
Baseline (2), completed Esso Australia Ltd.
WBM / KCl/PHPA - / 60m / - Otway
Basin
Minerva 2a
- Unconsolidated
sediment
Grain size, Biota, Heavy Metals,
TPH, radionuclides
Baseline, post drilling, +3 months,
+1 year
BHP Petroleum Pty Ltd
SBM-(IO) /
Novaplus
- / 27m / - Timor Sea
Buffalo 1
-
Halimeda gravels
Grain size, biota, heavy metals,
TPH, C
16
, C
18
Baseline,
+ 4 months
BHP Petroleum Pty Ltd
WBM 2 / - / - Exmouth
Gulf
Mydas &
Hawksbill
7 / 4 / 3 Unconsolidated
sediment
Biota, TPH, PAH, metals, grain
size
Baseline, post drilling, +6 months,
+12 months, +18 months, +2 years
Complete Apache Energy Limited
WBM 4 / 80m / 1 year NWS
East Spar
5 / 3 / 3 Unconsolidated
sediment
Biota, TPH, PAH, metals, grain
size
Annual Monitoring 1 and 2 year post drilling
complete
Apache Energy Limited
WBM 12 / 50m / 2 years NWS
Stag
42 / 36 / 4 Unconsolidated
sediment
Biota, TPH, PAH, metals, grain
size
Baseline, +6 years, +12 years Baseline complete Apache Energy Limited
LTO - Low Tox Oil Based Fluid WBM - Water based mud TOC - Total Organic Carbon NWS - Northwest Shelf
EMO - Enhanced Mineral Oil SBM - Synthetic based fluid PAH - Polycyclic Aromatic Hydrocarbon
OBM - Oil based fluid NWS -North West Shelf TPH - Total Petroleum Hydrocarbon
Data current as at October 1997
Framework for the Environmental Management of Drilling Fluids on Cuttings in Australia, March 1998 Page 9
4.2 Management Framework
APPEA has developed a framework for the environmental management of drilling fluid on cuttings which is
region specific, recognising the major prospective offshore basins in Australia. The framework evaluates the
sensitivity of various habitats in each region, and recommends buffer zones for individual habitats.
Research into the effects of marine discharge of drilling fluid on cuttings indicates the existence of a transition
zone which is either difficult to detect or is of marginal size (Chandler et al., 1995 and Davies et al., 1988).
The APPEA definition of buffer zones is based on conclusions from studies such as these and those carried out
in Australia which indicate that for:
i) Single Well Operations
 major contamination and community effects are limited to
within approximately 250 metres, and in many cases the
zone of effect either not detectable or is of marginal size;
 beyond 250 metres, it is difficult to detect any community
effects; and
 elevated concentrations of heavy metals and/or
hydrocarbons associated with drilling fluids are generally
not detected beyond 1,000 metres.

ii) Multiple Well Operations
 major community effects are limited to within
approximately 500 metres of the point of discharge;
 community changes with varying degree of severity have
been reported up to 2 kilometres;
 the biota is not affected beyond 2 kilometres; and
 elevated concentrations of heavy metals and/or
hydrocarbons associated with drilling muds are generally
contained within 2 kilometres of the point of discharge,
however, traces of contaminants below community effect
levels have been reported up to 10 kilometres from the point
of discharge.

Given the relatively localised effect of drill cutting discharges, APPEA recommends that the criteria detailed in
Table 4.1 should apply for determining the appropriate cuttings discharge distances from significant and
potentially sensitive marine habitats.

Where discharge of drilling fluid on cuttings is constrained due to environmental sensitivity and the nature of
the drilling fluid, alternative methods of disposal or cuttings treatment should be investigated and employed to
ensure environmental impacts are acceptable.

Tables 4.2 to 4.7 classify regional marine habitats and their significance/sensitivity in Australias major
hydrocarbon provinces. Site surveys should be conducted in areas where the significance or sensitivity of the
resources is uncertain.

Framework for the Environmental Management of Drilling Fluids on Cuttings in Australia, March 1998 Page 10
Table 4.1 Acceptable Distance from Habitats for Discharge of Drilling Fluid on Cuttings


Drilling Fluid**

Significance / Sensitivity of Habitat / Feature

High Medium Low
water based
> 300m* Cuttings discharge permitted Cuttings discharge permitted
ester based
> 500m* Cuttings discharge permitted Cuttings discharge permitted
other synthetic based
> 1km* > 1km* Cuttings discharge permitted
enhanced mineral oil
> 2.5km* > 2.5km* Cuttings discharge permitted
low tox oil based
> 5.0km*
#
> 2.5km*
#
Cuttings discharge permitted#
mineral oil based
No discharge Discharge constrained
+
Discharge constrained
+

* Drill cutting discharge may be undertaken closer subject to risk being demonstrated to be low through the modelling of drill
cutting dispersion scenarios. Alternative disposal methods may be appropriate for areas of high sensitivity, such as in the
immediate vicinity of coral reefs.


#
Drill cutting discharge may be undertaken subject to risk being demonstrated to be low through the process of drill cutting
dispersion modelling with subsequent seabed monitoring verification.


+
Drill cuttings discharge not permitted if concentration of adhered drilling fluid on cuttings exceeds 1%
v
/
v

** Definitions are provide in Appendix A.

Table 4.2 Classification of Regional Habitats - North West Shelf

Marine Habitat / Seabed Feature Significance /
Sensitivity
Rationale
Coral patch reefs High Productive and diverse habitats.
Coral fringing and barrier reefs High Productive and diverse habitats.
Shallow subtidal pavements (<30m) Low / Medium Productive habitats, supporting corals gorgonians
sponges, algae, seagrass. Possible turtle & dugong
feeding areas. Sensitivity variable depending on
extent of biotic cover and sand veneer.
Deep subtidal pavements (>30m) Low Generally low biotic cover without macrophytes and
scleractinean corals.
Intertidal pavements High Productive habitats, possible turtle & dugong feeding
areas, cuttings may persist in crevices rock pools and
impact associated biota.
Seagrass beds (mid-dense) High Fish & prawn nursery areas, possible turtle & dugong
feeding areas.
Unconsolidated subtidal sediments Low Widespread habitats, low diversity, rapid recovery.
Sandy beach and spits Medium Possible burial and persistence of oily cuttings,
important mollusc habitat.
Intertidal sand/mud flats High Possible impact on invertebrates - flow on effects to
shore and migratory birds.
Mangroves High Oily cuttings may accumulate and persist in burrows
& root channels. Anoxic conditions may form and
impact associated fauna and possibly mangroves.
Aquacultural leases High Potential for accumulation of contaminants,
lethal/sublethal effects and economic impact.
Defined and designated fish/prawn
nursery areas
High Potential for accumulation of contaminants,
lethal/sublethal effects and economic impact.
Framework for the Environmental Management of Drilling Fluids on Cuttings in Australia, March 1998 Page 11

Table 4.3 Classification of Regional Habitats - Timor Sea

Marine Habitat / Seabed Feature Significance /
Sensitivity
Rationale
Reef crests (where coral present) High Productive and diverse habitats.
Reef slope (< 70m) Low / Medium Supports variable cover of corals, gorgonians, and
sponges. Steep slopes and strong currents will
prevent cutting accumulation.
Reef slope (> 70m) Low Generally low biotic cover without macrophytes and
scleractinean corals.
Reef flat - sparse Halimeda/rubble
assemblage
Low Widespread habitat, low biotic cover, high energy
environment.
Reef flat - Halimeda/sponge/coral
assemblage
Low / Medium Relatively productive and diverse habitat. Sensitivity
varies according to degree of biotic cover.
Inter-reef plateaus Low Sparse biotic cover.
Deep unconsolidated sediments Low Widespread habitat.

Table 4.4 Classification of Regional Habitats - Bass Strait

Marine Habitat / Seabed Feature Significance /
Sensitivity
Rationale
Unconsolidated subtidal sediments Low Widespread habitat / high energy environment.

Table 4.5 Classification of Regional Habitats – Great Australian Bight

Marine Habitat / Seabed Feature Significance /
Sensitivity
Rationale
Unconsolidated subtidal sediments Low Widespread habitat / high energy environment.

Table 4.6 Classification of Regional Habitats – Otway Basin

Marine Habitat / Seabed Feature Significance /
Sensitivity
Rationale
Unconsolidated subtidal sediments Low Widespread habitat / high energy environment.

Table 4.7 Classification of Regional Habitats – Sydney

Marine Habitat / Seabed Feature Significance /
Sensitivity
Rationale
Unconsolidated subtidal sediments Low Widespread habitat / high energy environment.


5. Future Direction

Australia is in a position to develop consistent and responsible management decision processes to regulate the
discharge of non-water based drilling fluids on cuttings into the marine environment. These decisions must be
based on sound scientific understanding of the effects on the marine environment.

A significant number of research studies into the effects of marine discharge of drilling fluids on cuttings have
been undertaken, mainly overseas. There may be problems applying findings from overseas studies to
Framework for the Environmental Management of Drilling Fluids on Cuttings in Australia, March 1998 Page 12
Australian conditions, as the physical, biological and chemical properties of the various marine environments
are significantly different.

APPEA has identified the following projects as necessary steps towards assisting the development of more
consistent and effective regulations, and improved environmental management of drilling discharges.

(i) Compilation of Current Knowledge of the Potential Impacts of Marine Discharge of Drilling Fluids
on Cuttings in Australian Waters
Objective:
To summarise current knowledge of the potential direct, and indirect impacts of the
marine discharge of drilling fluids on cuttings in Australia.

Key Issues:- Toxicity
- Biodegradation
- Dispersion
- Bioaccumulation
- Leaching
- Form and biodegradation of cuttings piles
- Regional metocean data
Strategies:
(i) Central Register
To develop and maintain a comprehensive list of relevant research and
monitoring programs and their findings in Australia.
(ii) Literature Review
To summarise findings of Australian studies through a literature review of
published and unpublished studies. To liaise with operating companies and
government agencies to identify significant gaps in knowledge of impacts.
Responsibility:
(i) Central Register
APPEA to maintain.
(ii) Literature Review
APPEA to facilitate; funding to be agreed.
(ii) Register of Drilling Fluid Chemical, Biological and Physical Attributes
Objective:
To facilitate provision of information on chemical composition, biodegradation and
toxicity for individual used fluids in high, medium and low energy marine
environments and for water temperatures found in Australia.
Key Issue:
Access to chemical, biological and physical data.
Strategies:
(i) Provision of Information
To establish a central register of drilling fluid attributes. Detailed information
on chemical, biological and physical attributes should be relevant to Australia.
APPEA member companies would only support use of products, which on the
basis of this information, were deemed appropriate for use in particular
situations.
(ii) Central Register
To establish a central register of drilling fluids which contains chemical,
biological and physical data. This information will be available to regulatory
bodies, operating and service companies.
Responsibility:
(i) Provision of Information
Framework for the Environmental Management of Drilling Fluids on Cuttings in Australia, March 1998 Page 13
Drilling fluid suppliers and APPEA member companies.
(ii) Central Register
An independent organisation such as the International Association of Drilling
Contractors (IADC) or APPEA.
(iii) Australian Testing Protocols
Objective:
To ensure that testing protocols are relevant to Australian conditions.
Key Issues:
- Relevance to Australian species and environments
- Consistency of testing and analysis
- Comparison of research results
Strategy:
To adapt, develop where necessary, and validate testing protocols to determine the
level of toxicity, biodegradation and leaching attributable to the discharge of
drilling fluids on cuttings into high, medium and low energy marine environments
in water temperatures found in Australia. Assess the relevance and adequacy of
overseas protocols to Australian conditions and adapt or develop protocols as
standard practice. Require drilling fluid manufacturers to use these protocols to
test their products before use/sale in Australia.
Responsibility:
APPEA Environmental Affairs Committee or IADC.
(iv) Gaps in Knowledge
Objective:
To address gaps in knowledge of the environmental effects of the discharge of
drilling fluids on cuttings into the marine environment.
Key Issues:
- Toxicity
- Biodegradation
- Dispersion
- Bioaccumulation
- Leaching
- Form and biodegradation of cuttings piles
- Regional metocean data
Strategy:
1.To utilise conclusions from Australian field studies and results from (ii) to
identify what the potential impacts could be and identify the gaps in our
knowledge.
2.To further investigate the direct and indirect impacts associated with the marine
discharge of drilling fluids on cuttings in Australia through the implementation
of environmental research programs. The priority for research will be
determined by the outcomes of projects (i) and (ii). Work in collaboration with
research institutions (eg CSIRO, AIMS etc.).
Responsibility:
APPEA Environmental Affairs Committee in consultation with research
institutions and government agencies to develop and implement appropriate
research programs.
Framework for the Environmental Management of Drilling Fluids on Cuttings in Australia, March 1998 Page 14
(v) New Technologies and Products
Objective:
To develop improved technologies, practices and products for use by the Australian
petroleum industry.
Key Issues:
Cost effective fluids to drill complex, high temperature and pressure wells, while
minimising environmental impacts
Strategy:
(i) New Technologies
To develop new technologies for drilling and treatment of cuttings for
disposal into the marine environment.
(ii) New Products
To develop drilling fluids which are environmentally acceptable and provide
the required performance.
Responsibility:
(i) New Technologies
CSIRO, service companies and operating companies.
(ii) New Products
CSIRO, service companies and operating companies.
6. Conclusion
The Australian hydrocarbons industry recognises and promotes the need for responsible management of its
activities to minimise the potential impact of exploration and production operations on the environment. The
increased use of non-water based drilling fluids together with the industry's commitment to minimise the
environmental impact of offshore drilling has led to the development of these management guidelines and
acceptability criteria for the discharge of drilling cuttings containing non-water based drilling fluids.
The industry is committed to the implementation of best practice that are objectively based and scientifically
supported.
Drilling programs are undertaken in a variety of environments. Consequently, the management of non-water
based drilling waste should be assessed on a case by case basis to ensure that relevant restrictions are imposed
on the operator, whilst ensuring that the environmental effects are minimised. The potential impact of drilling
operations on the environment depends on the type of activity and the local environment in which it is
undertaken. The differences in exploration and development drilling (ie single versus multiple well sites) are
recognised and assessed accordingly. When evaluating the potential impact of any drilling proposal, the
physical, chemical and biological characteristics of the local environment should be considered. The case by
case assessment should consider the following principles:
(i) Preference should be given to the use of water based drilling fluids. It is recommended that operators
prepare a selection process to ensure consistency in the selection of drilling fluids.

(ii) Discharge of non-water based drilling fluids into the marine environment should be carefully managed
and controlled, particularly in environmentally sensitive areas as defined in Section 4.

(iii) Continuous monitoring, review and improvement measures should be undertaken, and appropriate
technological improvements should be considered as they become available, and adopted where
practicable.

(iv) Discharge of base fluid shall be as low as reasonably practicable and consistent with Table 4.1.
Framework for the Environmental Management of Drilling Fluids on Cuttings in Australia, March 1998 Page 15
In environmentally sensitive locations where drilling programs require non-water based fluids, the
environmental risk may be higher (Table 4.1). In such locations APPEA recommends consideration of an
alternative method of disposal such as cuttings re-injection into an appropriate sub-surface formation or,
potentially, transporting waste to shore for treatment. Such alternative methods of disposal have been
implemented in a number of environmentally sensitive areas, demonstrating the industrys commitment to
minimising environmental harm. However, transporting cuttings ashore for treatment and disposal on land
brings its own suite of environmental risks and effects that must be carefully considered before making such a
decision.
The environments in which the exploration and production industry operates in Australia can be significantly
different to operations overseas. The Australian industry operates on a much smaller scale to major producing
nations. The environment is significantly different from that of the Northern Hemisphere with major
differences in marine characteristics and ocean dynamics. Historically, most research has been undertaken in
the Northern Hemisphere and the relevance of these outcomes to Australia needs careful evaluation.
Unconditional adoption of overseas regulations and practices may impose an unnecessary burden on the
Australian industry.
The Australian industry intends to fund further research and monitoring programs aimed at better
understanding of the specific Australian environment. Future research into the biodegradation, dispersion and
toxicity of drilling fluids in the Australian marine environment is essential so that guidelines and quantitative
acceptance criteria for the discharge of drilling fluids can be established. The implementation of such
guidelines would ensure that the environmental conditions are determined on a consistent basis for all State
and Commonwealth Waters.
Community perception of the industry, and ultimately government decisions, are important issues affecting the
oil and gas exploration and production industry. The industry is committed to meeting the challenges that lie
ahead, and would welcome any comment on the content and subject matter of this paper.
Framework for the Environmental Management of Drilling Fluids on Cuttings in Australia, March 1998 Page 16
7. References
ANZECC, 1996. Draft Sea Dumping Guidelines – for the disposal of dredged sediments. Australia
and New Zealand Environment and Conservation Council.
Candler JE, Hoskin S, Churan, M, Cui Wei Lai, Freeman,M, 1995. Seafloor Monitoring for
Synthetic Based Mud Discharged in the Western Gulf of Mexico. SPE Paper 29694.
Chegwidden, A, Fisher, S.J,Alexander, R and Kagi R.I, 1993. The Fate of Hydrocarbons Associated
with Drilling from the North Rankin "A" Gas and Condensate Platform, Western Australia. APPEA
Journal, 1993.
Daan, R, Booij, K, Mulder, M and van Weerlee,E.M, 1995. A Study on the Environmental Effects of
a Discharge of Drill Cuttings Contaminated with Ester Based Muds. Netherlands Institute of for Sea
Research NIOZ-RAPPORT 1995-2, Netherlands.
Davies, J.M, Addy,J.M, Blackman, R.A, Blanchards, Ferbrache,J.E, Moore,D.C, Sommerville,H.J,
Whitehead,A and Wilkinson, T, 1984. Environmental Effects of the Use of Oil-based Drilling Muds
in the North Sea. Marine Pollution Bulletin, 15 (10), 363-370.
Davies, J.M, Bedborough,D.R, Blackman, R.A.A, Addy, J.M, Appelbee,J.F, Grogan, W.C,
Parker,J.G and Whitehead,A, 1988. The Environmental Effect of Oil-based Mud Drilling in the
North Sea. In: Drilling Wastes. Proc. Int. Conf. 1988 (Eds: J.P. Rayjp, Englehert, F.R), pp.59-89.
Elsevier Science Publ.
Delvigne, G.A.L., 1996. Laboratory Investigations on the Fate and Physicochemical Properties of
Drill Cuttings After Discharge Into the Sea. Paper 3, E&P Forum Joint Study  The Physical and
Biological Effects of Processed Oily Drill Cuttings, E&P Forum Report Number 2.61/202.
Hinwood JB, Poots AE, Dennis LR, Carey JM, Houridis H, Bell R, Thomson JR, Boudreau P and
Ayling, AM "Australian Marine and Offshore Group Pty Ltd, 1994. The Environmental Implication
of Drilling activities." In: Swan JM, Neff JM and Young PC (Eds), Environmental Implications of
Offshore Oil and Gas Development in Australia - The Findings of an Independent Scientific Review,
Australian Petroleum Exploration Association, Sydney, pp 123-207.
NOAA, 1990. Potential for biological effects of sediment sorbed contaminants tested in the
national status and trends program. Technical Memorandum NOS OMA 52, National Oceanic and
Atmospheric Administration.
Poley,J.P and Wilkinson, T.G., 1983. Environmental Impact of Oil-based Mud Cuttings - a North
Sea Perspective. IADC-SPE Drilling Conference, New Orleans, pp335-342.
Stagg, R.M. and McIntosh, A., 1996. The Effects of Drill Cuttings on the Dab (Limanda limanda).
Paper 7, E&P Forum Joint Study  The Physical and Biological Effects of Processed Oily Drill
Cuttings, E&P Forum Report No. 2.61/202
Tsvetrenko YB, Evans, LH, and Gorrie J., 1996. Toxicity bioassay with novaplus drilling fluid and
olefin base fluid using three Australian marine species. Prepared for West Australian Petroleum
Pty Ltd by Curtin University of Technology, Western Australia.
Framework for the Environmental Management of Drilling Fluids on Cuttings in Australia, March 1998 Page 17
APPENDIX A: CLASSIFICATION OF DRILLING FLUIDS
Definitions of non-water based drilling fluids have been contentious in recent years. Definitions have been
based on the origin of the base fluid rather than the environmental performance of the fluid. Until definitive
field environmental parameters are developed that indicate acceptable environmental impact, the definitions
will continue to be based on the manufacturing processes and chemical signatures of the fluid.
The following definitions are based on chemical composition and the manufacturing process of the fluid:
A1 Water Based Fluid
This is a general term covering all drilling fluid which have water as the continuous phase, whether or not oil
is present as a dispersed or emulsified phase. The water may be fresh, partially or fully saturated with various
salts, acids, alkalis, alcohols or polymers. The dominant component (after water) distinguishes one water
based fluid from another.
Examples of water based fluids are:
 Freshwater or seawater;
 Bentonitic clay mud;
 Various brines;
 Gypsum mud;
 Lime mud;
 Silicate mud;
 Lignosulphonate mud;
 Polyacrylate mud;
 Carboxymethyl cellulose mud;
 Xanthum gum mud; and
 Polysaccharide mud.
A2 Non-Water Based Fluid
This is a general term covering all drilling fluids that have an water insoluble substance as the continuous
phase. Water is usually present as the discontinuous emulsified phase and usually contains dissolved calcium
chloride and/or lime. The water insoluble substance may be artificially synthesised or extracted from naturally
occurring animal and mineral sources. The type of substance in the continuous phase distinguishes one non-
water based fluid from another.
i) Diesel Based Fluid
Non-water based fluid in which the continuous phase is diesel (petroleum distillate which is cracked into a
non-specific mixture of molecular groups of paraffins, olefins and aromatics).
ii) Low Toxicity Oil Based Fluid
Low tox oil based fluid is a non-water based fluid in which the continuous phase is refined petroleum distillate
containing less than 1%
w
/
w
total aromatic hydrocarbon.
iii) Enhanced Mineral Oil Based Fluid
Enhanced mineral oil based fluid is a non-water based fluid in which the continuous phase is a mixture of non-
toxic, saturated hydrocarbons, which have been purified from mineral oil into a discrete molecular range. Due
to the highly refined processing, enhanced mineral oil based fluid base fluids have trace quantities of total
aromatic hydrocarbon (below 0.1%
w
/
w
).
Currently, most enhanced mineral oil based fluids are paraffin-based fluids. However, new drilling fluids that
are not paraffin based may be developed in the future and may be classified as enhanced mineral oil based
fluid.
Framework for the Environmental Management of Drilling Fluids on Cuttings in Australia, March 1998 Page 18
iv) Synthetic Based Fluid
Synthetic based fluids are non-water based fluids in which the continuous phase is a material produced from
the reaction of specific, purified chemical feedstock, as opposed to fluids which have been derived solely
through physical separation processes including fractionation and distillation and/or minor chemical reactions
such as cracking and hydro-processing of crude oils. Due to the nature of the manufacturing process,
synthetic materials have negligible or very low total aromatic hydrocarbon content (below 0.001%
w
/
w
).
v) Ester Based Fluid
Ester based fluid is a synthetic based fluid in which the continuous phase is a mixture of unsaturated organic
compounds known as esters.
Esters are produced by an acid-catalysed esterification of vegetable fatty acids with various alcohols, but other
production methods may also be used. Esters have negligable aromatic hydrocarbon content (below 0.001%
w
/
w
). Esters are particularly biodegradable.
Framework for the Environmental Management of Drilling Fluids on Cuttings in Australia, March 1998 Page 19
APPENDIX B: TECHNICAL REQUIREMENTS FOR USING NON-WATER BASED DRILLING
FLUIDS
i) Safety
Health and safety risk to personnel is the primary consideration for operators when designing a drilling
program. Offshore individual risks include occupational risk, helicopter flying risk, and Major Accident
Event (MAE) risk (eg blowouts, ship collision & dropped objects). In all these categories, risk is directly
proportional to exposure. It can be demonstrated that for some wells such as highly deviated, extended reach
and highly active shales, non-water based fluid reduces drilling time, therefore, exposure and risk will diminish
accordingly.
Importantly, in this type of well, the use of non-water based fluid results in fewer drilling problems and
fewer incidences of hazardous remedial work such as working stuck pipe, fishing, tripping and pipe
handling on the rig floor. Reducing the requirement for these activities further reduces the risk to rig
crews.
ii) Wellbore Stability
Reactive claystones deteriorate quickly when exposed to water based mud due to the absorption of filtrate
water into the clay lattice structure causing swelling. In certain fields, the Cretaceous claystone may also
contain unrelieved tectonic stress, which becomes unstable when exposed to water as the stress is relieved
into the borehole, and cavings hamper the drilling process.
iii) Suspension of drilling due to weather
The wellbore stability characteristic of non-water based fluid is advantageous when drilling is suspended
due to bad weather. The North West Shelf and Timor Sea region are prone to cyclones during summer
months. The unpredictable nature of cyclones require the suspension of drilling operations when a
cyclone is approaching. Delays during the cyclone season (December through to March) may require a
hole to be left open for an extended period until the cyclone risk subsides. During these delays, sensitive
claystone intervals exposed to water based fluid will deteriorate, often resulting in extensive remedial
work.
Remedial work includes reaming and working pipe, mud conditioning (dilution of incorporated drill
solids) and possibly stuck pipe requiring fishing or re-drilling the open hole section. All these activities
pose additional exposure risks to personnel. Experience has shown that wellbore reconditioning is
minimal with non-water based fluid.
iv) Lubricity in Highly Deviated Wells
Highly deviated, extended reach and horizontal wells may require a non-water based fluid for lubricity (as
well as wellbore stability) during prolonged open hole sections.
Non-water based fluid can substantially reduce the friction factor compared to most water based fluid
(even after the addition of friction reducing materials). Minimising friction and being able to transfer
weight to the bit is a very important factor when planning deviated and extended reach wells. The
lubricity characteristics of water based fluid and non-water based fluid are illustrated in Table A1.
Table B1: Coefficient of Friction for Drilling Fluids
Fluid Type Coefficient of Friction
Non-Water Based Fluid 0.12  0.28
Water Based Fluid (unweighted) 0.35  0.50
Water Based Fluid (weighted) 0.25  0.35
Framework for the Environmental Management of Drilling Fluids on Cuttings in Australia, March 1998 Page 20
Extended reach wells require longer open hole duration because of their greater length, longer drilling
time, greater logging and steering requirements, and the greater demand for efficient hole cleaning. Non-
water based fluid are the only drilling fluids capable of maintaining satisfactory wellbore stability for
extended reach wells.
v) Productivity Improvement
Increased formation damage has been observed for highly permeable formations which readily imbibe
filtrate from water based fluid. Clay particles present in the sands will absorb the filtrate, disintegrate,
become mobile and flow with produced hydrocarbons toward the sand face. The clay particles
accumulate and block the permeability causing “skin” which can reduce productivity and dramatically
reduce the ultimate recovery of the reservoir.
Skin damage can also result in near wellbore effects such as condensate dropout in gas wells and early
wellbore gas breakout in undersaturated oil reservoirs. Non-water based fluid avoids formation damage
from water filtrate effects.
vi) High Temperature Stability
Non-water based fluids are stable at high temperatures above 200C, whereas most commonly used water
based fluid will deteriorate at much lower temperatures. It is much more difficult to maintain stable properties
and wellbore conditions using water based fluid in high temperature and pressure applications. In order to
find and exploit deeper reserves, operators in Australia must drill deeper, high temperature and pressure
wells.
vii) Low Mud Weight
Most non-water based fluids have a density between 0.75 and 0.82 SG. High base fluid/water ratios
allow for wells to be drilled with mud weights below 1.0 SG. This is not possible with water based
fluids. Even with constant dumping and diluting, mud densities are rarely below 1.05 SG for water based
fluid.
The ability to use low mud weight systems is especially pertinent for wells drilled in highly fractured
formations with low fracture strength, wells with lost circulation zones, or wells with low productivity.
The ability to introduce low mud weight systems may become more important as technology and
experience develops with under-balanced drilling operations where low mud weights are desirable.
viii) Improved Rate Of Penetration (ROP)
Non-water based fluid facilitates faster ROP by:
 keeping the bit cutting surfaces cleaner and minimising bit balling;
 maintaining gauge hole resulting in better stabilisation of the bottom hole assembly;
 providing improved lubricity and reduced torque and drag; and
 providing better shale control resulting in less time for reaming and cleaning the hole.

ix) Coring
Formation cores provide information critical to evaluating future development decisions. In addition to
the more traditional approach of using core for stratigraphical information, cores may also be used (in
concert with reservoir fluid properties) for input to reservoir productive capacity estimation as an
alternative to production testing. Removing the requirement to production test can add tremendous value
to investment opportunities, as well as considerably lower exposure to hazardous activities.

Coring with non-water based fluid offers a number of advantages over water based fluid:
 improved lubricity facilitates smoother entry of the core into the barrel with less risk of
jamming;
 the inhibiting effect of non-water based fluid reduces the probability of cores swelling;
 less risk of mobile fines blocking pore throats during analysis; and
 less filtrate invasion resulting in better estimates of connate water saturation.
Framework for the Environmental Management of Drilling Fluids on Cuttings in Australia, March 1998 Page 21



x) Well Design
Use of non-water based fluid leads to an optimum well design due to the fluid’s capability to stabilise
claystone intervals using lower mud weights. Hence, non-water based fluid allows slimmer holes to be
drilled.

Non-water based fluid enable normally pressured zones underlying geo-pressured intervals to be drilled
overbalanced with a greatly reduced probability of differential sticking.

Completion liner, casing, cementation and perforation operations are more effective when using non-water
based fluid due to the better gauge hole, therefore, better inflow performance and reservoir management.

xi) Formation Evaluation Data Acquisition

WBM and non-water based fluid have various advantages and disadvantages associated with them in
relation to logging and formation evaluation. The advantages of non-water based fluid for logging include:
 increased filter cake quality and lubricity of non-water based fluid minimising the likelihood
of tool failure and logging tools sticking;
 maintaining gauge of the open hole, and tool response is not affected by wellbore rugosity;
and
 minimisation of filtrate invasion, resulting in a better estimate of the connate water saturation.
The main disadvantages of non-water based fluid on formation evaluation include limitations for certain
wireline logs, the ability to identify natural hydrocarbons during drilling and the geochemistry of the
formation (reservoir fluid sampling is complicated by the similarity between the non-water based fluid
filtrate and native reservoir fluids).
a) Wireline Logging
Wireline logs for sections drilled with non-water based fluid are more in-gauge and have a better hole
condition. The improved hole condition is based on the inhibition of water sensitive clays, increased
lubricity and smaller filtrate invasion profile.
However, newly developed reservoir characterisation logging tools are able to avoid the requirement for
extensive coring operations. Poor image logs require an extensive coring program to calibrate against
wireline log responses.
However, certain logging tools can only be run in
water based fluid
. An important log for reservoir
characterisation is the micro-resistivity log. The micro-resistivity log represents the highest resolution-
imaging tool. Unfortunately, log quality is very poor when run in non-water based fluid wells. An
ultrasonic imaging log is available for use with non-water
based fluid
and fair images have been
obtained, but do not have the vertical resolution and clarity of micro-resistivity log data used in
water
based fluid
.
b) Hydrocarbon Indications During Drilling
Fluorescence techniques are employed by mud loggers to determine the presence of natural
hydrocarbons. The technique is less effective when using non-water based drilling fluids. Determination
of reservoir hydrocarbons can also be determined using measurement while drilling (MWD) tools or
wireline logs at the completion of the well.
When drilling through stratigraphic intervals where hydrocarbons are not expected, MWD tools may not
be run. There is then a risk that a hydrocarbon show will not be identified when using non-water based
fluid. This risk is more evident for exploration drilling where unknown hydrocarbons may exist.
Framework for the Environmental Management of Drilling Fluids on Cuttings in Australia, March 1998 Page 22
Gas wetness data indicates the likely hydrocarbon type encountered while drilling with oil based mud
(light oil, heavy oil, dry gas, wet gas), in non-water based fluids the type of hydrocarbon may not be
apparent until modular dynamic tester samples are analysed at the end of the logging program. The
advanced notice from mud gas shows using
water based fluid
systems enables better planning for testing
and production operations.
c) Geochemistry
Non-water based fluid has a very acute impact on geochemical analysis. Quantitative screening of source
rocks is not possible on wells drilled with non-water based fluid. Non-water based fluid contain their
own indigenous biomarkers or a set of biomarkers they inherited while drilling a previous well. These
contaminants often make it impossible to distinguish any natural biomarkers from the contaminants.
Framework for the Environmental Management of Drilling Fluids on Cuttings in Australia, March 1998 Page 23
APPENDIX C: FIELD STUDIES
C1 Findings from Australian Studies
i) Fortescue, Bass Strait
A seabed monitoring program was undertaken around the Fortescue platform in Bass Strait. The program
involved sampling from August 1995 to August 1997 at sites along a transect in line with the predominant
ocean current and at control sites before, during and after the period in which ester synthetic based fluid on
cuttings were discharged from sections of seven development wells. The seabed sediments were measured for
esters, barium, biological change, and grain size. Results show clearly the increase in ester concentration in
sediments, then rapid decrease after completion of cuttings discharge, and limited effect footprint
predominantly within 100m of the platform discharge point. The impact on the sediment biology was found to
be short and limited in area with recovery evident within the study period. Mechanisms for recovery of the
minimal zone of effect are thought to be a combination of the biodegradation of the ester synthetic based fluid
used and the physical seabed dispersion process evident in eastern Bass Strait.
ii) Minerva-2A , Otway Basin
Minerva-2A was drilled in the Otway Basin, offshore Victoria, in September 1993. The well was spudded
close to the coastline and BHP Petroleum was required to monitor any discharges and their associated toxicity.
In addition to the baseline survey, conducted just prior to the spudding of the well, 3 post-drilling surveys were
undertaken; one at 2 weeks, one at 4 months and one at 12 months.
The ROV component of the survey revealed that sediment size distribution had changed significantly at the
wellsite. However, after 4 months, the distribution had returned to normal.
Chemical analysis of the sediments revealed that levels of some heavy metals and radionuclide were elevated.
However, these elevations were within 400m of the drill site and lasted for only 4 months. Levels were always
well below that which would cause ecological effects as recognised by NOAA (1990) and ANZECC (1996).
Only barium was found to have an increased bioavailability and this was observed to have returned to normal
levels within 4 months. Levels were always below that predicted to be capable of having an adverse effect on
fauna.
A reduction in species diversity and abundance was noted within 200m of the well site and this is typical of
drilling operations. Community changes were still evident at the drill site even after 12 months. Between 100m
and 200m of the well site, faunal changes were observed to have returned to normal after 4 months. Any
faunal impacts noted were interpreted as resulting from short-term changes in particle size or smothering, as
opposed to release of contaminants.
iii) Buffalo-1, Timor Sea
Buffalo-1 was drilled in the Timor Sea in August 1996. The well was spudded on a large seamount called Big
Bank. Due to the increased environmental sensitivity of this area in comparison to the deeper surrounding
waters, and because drilling was conducted using SBM, both pre and post-drilling environmental surveys were
undertaken to assess any impact. Pre-drill surveys were conducted throughout January and February 1996,
and the post-drill survey was undertaken in January 1997.
The post-drilling ROV and sediment analysis survey revealed that the drilling program had caused minimal
physical disturbance. Cuttings were observed 100m SE of the drill site but were not evident 100m to the NW,
NE or SW.
Framework for the Environmental Management of Drilling Fluids on Cuttings in Australia, March 1998 Page 24
Chemical analysis of the sediments revealed that there were detectable concentrations of the synthetic based
fluid, Novaplus, which was used during drilling, up to 1000m from the well. High concentrations were limited
to within 100m of the well site (51,000ug/kg). These concentrations had, however, been reduced by two orders
of magnitude within a further 100m.
Although concentrations of Novaplus and barium were higher than the background levels determined from the
pre-drilling survey, no other contaminants exceeded background levels. Barium is a naturally occurring clay
mineral and is not toxic. According to bioassays conducted by Tsvetrenko et al., (1986), using OECD
procedures, Novaplus has very low toxicity. This low toxicity, in conjunction with the greatly reduced
concentration with respect to distance from the well site, would suggest ecotoxic impact from drilling fluids is
extremely unlikely.
iv) Wanaea-3/6, North West Shelf
A long term seabed study into the effects of the discharges of drill cuttings contaminated with the low toxicity
oil based mud Shellsol DMA is being undertaken by Woodside Offshore Petroleum in the Wanaea oil field on
the North West Shelf.
A baseline environmental survey was conducted in the vicinity of the Wanaea 3 well in October 1993, prior to
the drilling of the offset well Wanaea 6. A program of follow up work was agreed involving the collection of
additional data approximately 12 and 36 months following the cessation of drilling. The broad objectives of
the study were to assess the persistence of hydrocarbons derived from the drilling discharges and to assess the
recovery of the benthic fauna over time.
Wanaea 6 was drilled in November/ December 1994. The first follow up survey, restricted to physical and
chemical sediment characteristics only, as conducted in November 1995, approximately 11 months following
the cessation of drilling and demonstrated relatively low residual hydrocarbon concentrations (<200ppm),
reducing to less than 1ppm within 200m of the cutting discharge point. Some additional sampling, including
coring, was conducted at a point directly under the Wanaea 6 cuttings discharge point in April 1996, and
confirmed the above findings. Barium was found to be elevated 400m from the wellhead.
The final survey is planned for 1997 and will assess the biological component as well as the physical and
chemical characteristics.
v) North Rankin A Platform, North West Shelf
Drilling from Woodsides North Rankin A Platform, located in 125m water depth, on the North West Shelf
commenced in August 1983 and was completed in August 1991. In total 23 wells have been drilled from the
platform, including 11 wells with low toxicity oil based drilling fluid. The maximum hydrocarbon
concentration recorded, recorded beside the platform, was 75,000 ppm. Concentrations decreased rapidly
away from the platform (40 ppm at 800m and 2 ppm at 2,000m) in the direction of the prevailing current.
Trace levels of hydrocarbons were detected at least as far as 3km in the direction of the prevailing current
(Chegwidden et al.1993).
Ongoing sampling 800m NW of North Rankin 'A' has indicated a consistent downward trend in hydrocarbon
concentrations (37ppm in 1991, 15ppm in 1992 and 9ppm in 1993) suggesting that away from the cuttings
pile, degradation of residual hydrocarbons was occurring successfully with an annual half life of
approximately 1 year.
Within the North Rankin 'A' cuttings pile itself hydrocarbons degradation is occurring much more slowly and
hydrocarbons levels are well preserved 5cm into the pile.
Framework for the Environmental Management of Drilling Fluids on Cuttings in Australia, March 1998 Page 25
vi) Lynx 1a, North West Shelf
Lynx 1a was drilled by Woodside in 79m of water on the North West Shelf in October 1996 using the
enhanced mineral oil XP-07 - a linear paraffin with negligible aromatics. A seabed monitoring program was
designed to assess the persistence of hydrocarbon contamination in the immediate vicinity of the cuttings
discharge point and to this end a series of sampling stations were established immediately below the point of
cuttings discharge and centrically on the 50m and 100m radii. Sampling stations were also established at
200m in the direction of the prevailing current. Samples were obtained by ROV with a purpose built grab
sampler and position fixing by DGPS linked to the ROV by an acoustic tracking system (ATS). Upon
cessation of drilling a cuttings mound was present, approximately 1.5-2.0m high and 10-15m in diameter and
that high levels of hydrocarbons (up to 40400 ppm) were present within and adjacent to the cuttings pile.
Cores taken from the grab sample showed that the highest concentrations of hydrocarbons were obtained in the
upper 5cm of the grab (nominal 15cm cutting depth) with sediments from 10-15cm depths being typically 2-3
orders of magnitude lower.
A follow up survey was undertaken in August 1997, approximately 10 months after the cessation of drilling.
Whilst physical and chemical analysis is continuing, a number of site observations have been made including:
i) the cuttings pile no longer exists;
ii) the cuttings are still visible within sediment samples; and
iii) faunal elements, including echinoderms (ophuroids and holothurians), polychaetes and
crustaceans are present in the sediments obtained from the discharge point.
vii) Mydas 1 and Hawksbill 1, North West Shelf
Mydas 1 and Hawksbill 1 were drilled on the North West Shelf in late 1993 and early 1994. A detailed
monitoring program was initiated prior to commencement of drilling.
Sampling was designed to detect statistically significant changes in the benthic environment associated with
the drilling program. Spatial scales were chosen on the basis of earlier qualitative work carried out on two
other exploration wells in the region, Logger head 1 and Leatherback 1. At each well, one impact location and
two control locations were established, and within each location seven sites were established along two
transects  one in the direction of the current, the other perpendicular. At each site four replicate grabs were
taken within two plots.
Sampling has been carried out four times at each well, one pre-drilling, and three post drilling. The attributes
being measured are:
Biological: Animal abundance, diversity, composition, biomass.
Physical: Sediment and particle size.
Chemical: Heavy metals, hydrocarbons (including PAH).
General findings of the survey were:
- exploration drilling did impact seabed fauna, but the impacts were limited in extent and duration;
- the extent of contamination was approximately 100m from the well head in the direction of the
currents;
- the biomass and densities of some of the common and numerous taxa had decreased by 1-2
months after drilling and were limited to 100m of the well; and
- in most cases, biomases and densities of these taxa had recovered 6-8 months after drilling.

The sediment samples at sites within 100m of the wells along the direction of the currents showed traces of
hydrocarbons and heavy metals. However, background levels were attained 6-8 months after drilling.


C2 Overseas Findings

Framework for the Environmental Management of Drilling Fluids on Cuttings in Australia, March 1998 Page 26
A field survey on the impact of synthetic based fluids was undertaken by Baroid for a well (K14-13) drilled
with an ester synthetic based fluid in the Dutch sector of the North Sea (Daan et al. 1995). Sampling included
a baseline survey and post drilling sampling after 1, 4 and 11 months. Within 200m of the discharge,
concentrations of ester were present up to four months after drilling (maximum 4,700mg/kg) with the benthic
fauna impoverished and traces of esters detectable up to 3km away. After 11 months esters within 200m of
the discharge point were detected at a concentration of 84mg/kg with some species beginning recolonisation.
Sediments within this area were generally anoxic as is the case generally with biodegradation in sediments.
Effects were even less at distances beyond 200m from the discharge. Some evidence of anoxic conditions was
found after four months at a distance of 500m but this was to a lesser extent than found closer to the
discharge. Ester concentrations were below the detection level in this area 11 months after discharge and
recovery of the natural macrobenthic community has set in. There was no evidence of persistence effects at
distances of 500m and 1,000m after 11 months and a mean half-life for ester degradation was estimated at 133
days.

Baroid observed similar effects for a well drilled with an ester synthetic based fluid in the Norwegian sector of
the central North Sea. The seabed survey was carried out 2 days after the cessation of drilling and comprised
12 sampling stations. The following findings were obtained:

 At the sampling station closest to the well site, the sediment was completely different, showing obvious
signs of severe perturbation from drill cuttings and mud solids. The analysis of sediment ester
concentration showed high values in the area surrounding the well site.
 The benthic infaunal analysis highlighted a clearly detectable zone of effect to a distance of 100m from the
well site. The faunal communities within this zone were characterised by very low species diversity, low
species abundance and high numbers of the polychaete worm Capitella capitata, which is characteristic of
soft marine sediments disturbed by organic enrichment.
 At more distant sampling stations the macrobenthic communities were comparable to control sites.
 One year after the cessation of drilling the cuttings pile and the zone of effect had significantly reduced.
Traces of cuttings and mud solids were still present on the seabed in isolated patches, however, in most
samples the ester concentration of the sediment were below detection limit and substantial signs of faunal
recovery were evident.

Survey results for a well drilled with an ether synthetic based fluid in the Norwegian sector found
concentrations of ether 200m from the discharge. Degradation rates were less than those found for ester
synthetic based fluids but reductions in concentrations were evident two years after discharge.

There have been other surveys off Norway as part of regular monitoring programs that have been summarised
as part of annual environmental reports issued by the pollution control authority. The results suggest that
synthetic based fluids can be detected in some circumstances up to 2km from the discharge. The UK
government has also established a program to survey synthetic based fluid well sites. The first post drilling
survey results are expected to be available late 1997/early 1998.

Chandler et al. (1995) reported the following findings of a seabed study for the use of polyalphaolefin (PAO)
in the Gulf of Mexico:

 Higher amounts of PAO drill cuttings within 200m of the discharge point than water based fluid.
 Shortly after discharge all of the PAO drill cuttings were in the top 2cm of the sediment within 200m of
the discharge point, with concentration reducing to 7% after 2 years.
 Three sampling sites within 50m of the discharge point indicated that the benthic community was
adversely affected.
 Recovery of the benthic community showed improvement over oil based fluid sites and the zone of
transition of lesser biological effects was much smaller than that described in the PARCOM 1988
findings.
 Macrobenthic structure similar to background can occur in the presence of PAO up to 1,000 mg/kg and
before complete degradation occurs.
Framework for the Environmental Management of Drilling Fluids on Cuttings in Australia, March 1998 Page 27
Davies, et al. (1988) reported the findings from a survey in the southern Sector of the North Sea field Vulcan,
from which 8 wells were drilled with a low toxicity drilling fluid. Surveys conducted at the cessation of
drilling in 1987 found marked hydrocarbon concentrations at the 200m mark, low levels of contamination at
500m (<10ppm) and extremely low levels from 800-1200m and possibly at the 2,500m site. At 5,000m levels
were at background. Although a high hydrocarbon content was detected at the 200m site, the depression of the
diversity index was not marked.
Davies et al, (1988) also reported findings from two separate single well drilling sites (16/28H & 16/28I) in
the UK sector which utilised low toxicity drilling fluids. Post drilling findings were that minor contamination
extended out to 800m and 500m and that high levels of contamination (up to 100x) were restricted to 250m
and 100m from 16/28H and 16/28I respectively. A post drilling study outcome (6 years after drilling
cessation) from a single well site using low toxicity oil based mud was also reported by Davies et al., (1988)
which found that the zone of biological effect was restricted to less than 200m, with detectable hydrocarbon
contamination to 750m.