Lesson Overview: Marine Seismic Exploration

heehawultraMécanique

22 févr. 2014 (il y a 7 années et 6 mois)

231 vue(s)

1

Lesson Overview:
Marine Seismic Exploration

2

Learning Objectives

3


Introduction to
Geology & Geophysics


in
Deep Water

Without discoveries, there would be no offshore oil and gas
industry
.


In

this lesson, we will
briefly review:




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4

Success in Deepwater Seismic Technology



The
technology
for
marine seismic exploration in
deep water
differs
little from
that
used in shallower depths.




The much
higher cost of deepwater exploratory wells
could
have
have precluded
exploration.




However, major
improvements in seismic technology
resulted
in
a higher success rate.




Deepwater
exploration continues despite the very high
costs.




The dramatic increase in the success rate has led to fewer
dry
holes.

5

Formation of
Petroleum Reservoirs

Oil and gas
reservoirs are formed from microorganisms
, plankton, that live
and die in
the oceans
.
Their settling
to the seafloor together with silt and
sand
is
called
sedimentation.


GR
-
98

6

Formation of Petroleum Reservoirs, cont.

Over time and in the presence of heat and pressure, the micro
-
organisms
become hydrocarbons, usually in fine
-
grained rock called
shale
.

Migration and Traps

7

Oil and gas migrate away through the permeable rock, unless there is a trap
(impermeable rock
or
salt) to prevent its escape leading
to formation of a
reservoir.

GR
-
100

Finding the
Traps

8

Seismic
exploration maps
the rock strata in sufficient detail to define
structures that may be hydrocarbon traps.

WV
-
21

Finding the Traps, cont.

9

With data from millions of shots, the computer can map the boundaries,
i.e., the surfaces between the layers of rock.

GR
-
101

Finding the Traps, cont.

10

Geologists must then use other data, such as samples from offset
wells, to determine if a structure might contain hydrocarbons.


GR
-
102

11

Exercise

1.
How has seismic exploration affected the success
of deepwater wells?

2.
What natural occurrences can trap hydrocarbons?

3.
How do geophysicists find hydrocarbons under the
sea?

4.
How do micro
-
organisms become hydrocarbons?


Marine
Seismic Vessels
and
Streamers

12

The newest seismic
vessels
can tow up to 32 streamers, each several
kilometers long
with
hydrophones every meter or so.

GR
-
93

Marine Seismic Vessels and Streamers, cont.

13

GR
-
176

Multi
-
streamer vessel

Marine Seismic Vessels and Streamers, cont.

14

GR
-
175

Precise streamer spacing
is critical to the accuracy
of the seismic data.

Marine Seismic Vessels and Streamers, cont.

15

GR
-
94 Controlled Tailbuoy

For controlling their position, the streamers have steerable
tail buoys with Differential Global Positioning System
(DGPS).

Marine Seismic Vessels and Streamers, cont.

16

GR
-
174 Sercel Nautilus Seismic
Streamer Leveling and Steering

This device
both steers and
levels the
streamer.

Modern Seismic Vessels

17

GR
-
95

M
any geophysicists and
geologists use large
computers
to gather and
analyze data onboard the
seismic vessel.


This one:



Cruises at 13.5 knots



Can sleep 50 geologists

Modern Seismic Vessels, cont.

18

GR
-
97
Ramform Sovereign
Seismic
Vessel Petroleum Geo
-
Services
(PGS)

3D concept for a modern seismic vessel

4D Seismic:
The Fourth Dimension is Time


19

GR
-
177 Sercel
Optowave™ 4D
Seabed Reservoir
Monitoring

Hydrophones for permanent installation in the seabed

Permanent seismic installations monitor the reservoir during
the production period to maximize hydrocarbon extraction

20

Exercise

1.
What some innovations in seismic vessel design?

2.
What is important in streamer design?

3.
Describe two tools that help position the vessel.

4.
What are hydrophones?