Seismic Data Acquisition COPYRIGHT. Introduction

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1 Introduction Seismic Data Acquisition Core Introduction In this module, the acquisition of Land Data and Marine Data are discussed in considerable detail These are the two end members of a continuum of data that exists from onshore to offshore, including data that is acquired in: The swamps near the shore The transition zone data (acquired in bays and inlets) Water depths that are too shallow for a seismic boat to operate and tow a recording streamer (for very shallow marine data) On a volume basis, the largest data base that an Oil Company has in their possession is marine data; this is both a function of the distribution of producing fields around the world and the fact that marine data is less expensive than land data The breadth of seismic method from marine through shallow water, transition zone and land using creative designs allow us to collect seismic data almost anywhere. 1

2 Introduction (Cont d.) Learning Objectives This module will cover the following Learning Objectives: Describe the marine configuration for a 3D survey including: Components used for data acquisition Arrays to attenuate noise Bin gathering as a CMP assemblage of reflections Describe the land configuration for a 3D survey including: Bin gathering for a land 3D survey Compare the costs of 2D and 3D surveys 2

3 Learning Objectives Seismic Data Acquisition Core Marine Data Acquisition This section will cover the following Learning Objectives: Describe the marine configuration for a 3D survey including: Components used for data acquisition Arrays to attenuate noise Bin gathering as a common midpoint (CMP) assemblage of reflections 3

4 Marine Configuration Marine Configuration Operations carried out 24 hours per day, 7 days per week Kept continuous by crews changing at sea Operations pause only for severe weather conditions or at survey completion 4

5 Marine Configuration The recording streamers extend for several kilometers behind the seismic vessel These and the gun arrays are at a depth of about 30 feet [8 to 10 meters] in the water and are therefore not visible From the surface we see the boat and the tow cables but the very extensive active portion of the system is hidden from view A marine acquisition system will be from 6 to 12 km [3.5 to 7 miles] in length and up to a kilometer [0.6 miles] in width The system is very complex, and takes days to deploy and pickup Economically, the less number of times you have to deploy and pickup, and the less time you take turning the entire configuration, the more cost effective the acquisition Marine Configuration Air gun array Air compressor system GPS receiver Active recording streamer Depth controller 5

6 Marine Configuration Both of these systems are towed in the Air water compressor at a depth of about 30 feet [9.1 m] to avoid the noise that system exists at the water surface For a conventional marine survey, the source is compressed air; the air guns are suspended from a chain harness that is attached to Air buoys gun array floating on the water surface Since the gun canisters are about 1500 cubic inches [38.1 m] GPS receiver and are pressured to about 2000 PSI [13790 kpa], the challenge here is to supply enough compressed air to the guns so that they can all be fired at about 8 second intervals Active One recording way to accomplish streamer this is called flip flop; the configuration has two identical gun arrays that fire individually every other time Depth controller 6

Single Air Gun Single Air Gun The trailing end, which is roughly 2/3 of the assembly, is a high pressure canister that provides the required volume of high pressure compressed air to fire the shot

7 Single Air Gun Single Air Gun The trailing end, which is roughly 2/3 of the assembly, is a high pressure canister that provides the required volume of high pressure compressed air to fire the shot These canisters vary in size to enable each member of the gun assembly to behave as a tuned array The air gun is not really a gun and does not fire. It is similar to a balloon being put underwater and burst, which causes air to be quickly released in the water 7

8 Streamer Reel and Depth Controller Streamer Reel Depth Controller Marine Configuration Pressure sensitive hydrophone Plastic spacer PVC cover Tow cable Cable fluid Marine Streamer Wrapped electrical wire and optical fiber A to D Converter 8

9 Marine Hydrophone Crystal Sercel solid streamer Pressure sensitive hydrophone 9

10 Marine Configuration Active recording streamer Gun arrays Paravane tow section 10

11 On Bottom Cable (OBC) Contractor Versions of OBC Detectors The Ocean Bottom Cable (OBC) are a very specialized type of seismic Predominantly used in production operations Can be left on the sea floor for years Can be used to monitor the reservoir changes over time The 4C are two primary or compressional vertical motion recorders and two horizontal-component 3C MEMS recorders receivers and a pressure detector These horizontals are used to measure shear wave and map fractures and fluid movement Gimbal 4C mounted receiver 4C receiver in the OBC cable records the four components of motion On Bottom Cable (OBC) Gimbal mounted 4C receiver in the OBC cable 3C Optical OBC unit Contractor Versions of OBC Detectors 3C MEMS receivers and a pressure detector 4C receiver records the four components of motion 3C Optical OBC unit 11

12 On Bottom Cable (OBC) Contractor Versions of OBC Detectors Gimbal 4C mounted receiver 4C receiver in the OBC cable records the four components of motion 3C MEMS receivers and a pressure detector 3C Optical OBC unit 12

13 Arrays to Attenuate Noise Horizontally propagating noise See Nature of Seismic Image Core about spherical outward propagating energy. Arrays to Attenuate Noise Air gun array Single source 13

14 Marine Bin Gathering Source array Receiver arrays Marine Bin Gathering Midpoints 25 X 25 meter bins Midway points for multiple shot locations Source array 25 X 25 meter bins Midway points for multiple shot locations 14

15 Midway Points for Multiple Shot Locations Animation Marine Bin Gathering Midpoints Source array Receiver arrays 25 X 25 meter bins Midway points for multiple shot locations 15

16 Marine Bin Gathering Source array Receiver arrays Marine Bin Gathering Midpoints 25 X 25 meter bins Midway points for multiple shot locations 25 X 25 meter bins Midway points for multiple shot locations 16

17 Marine Bin Gathering Marine Bin Gathering 25 X 25 meter bins Midway points for multiple shot locations 25 X 25 meter bins Midway points for multiple shot locations 17

18 Marine Bin Gathering Marine Bin Gathering 25 X 25 meter bins Midway points for multiple shot locations 25 X 25 meter bins Midway points for multiple shot locations 18

19 Marine Bin Gathering Marine Bin Gathering 25 X 25 meter bins Midway points for multiple shot locations 25 X 25 meter bins Midway points for multiple shot locations 19

20 Marine Bin Gathering Marine Bin Gathering 25 X 25 meter bins Midway points for multiple shot locations 25 X 25 meter bins Midway points for multiple shot locations 20

21 Marine Bin Gathering Marine Bin Gathering 25 X 25 meter bins Midway points for multiple shot locations 25 X 25 meter bins Midway points for multiple shot locations 21

22 Marine Bin Gathering 25 X 25 meter bins Midway points for multiple shot locations 22

23 Marine Data Acquisition (Bin Gathering) Animation Marine 3D Acquisition 23

24 Marine 3D Acquisition Marine 3D Acquisition Mid-Points Inline Mid-Points Crossline Stacked Trace 24

25 Other Advanced Methods of Seismic Acquisition Animation Undershooting a Platform Gun Vessel Platform Obstruction Recording Vessel Midpoints 25

26 Multi-Azimuth Seismic Acquisition Animation Multi-Azimuth Survey MAZ Multiple Azimuth towed streamer 26

27 Multi-Azimuth Survey Multi-Azimuth Survey MAZ Multiple Azimuth towed streamer MAZ Multiple Azimuth towed streamer 27

28 Multi-Azimuth Survey Multi-Azimuth Survey Fig. 2. Prestack depth migration (PSDM) comparison of (left) one azimuth from a conventional NAZ survey versus (right) three azimuth cubes processed to output one MAZ cube. (Courtesy PGS) 28

29 Wide Azimuth Seismic Acquisition Animation Wide Azimuth Survey WATZ Wide Azimuth towed streamer 29

30 Wide Azimuth Survey Wide Azimuth Survey WATZ Wide Azimuth towed streamer WATZ Wide Azimuth towed streamer 30

31 Wide Azimuth Survey Wide Azimuth Survey WATZ Wide Azimuth towed streamer Single Azimuth Wide Azimuth 31

32 For More Information Multi-azimuth and wide azimuth seismic: Shallow to deep water, exploration to production by Brian Barley BP Exploration, Cairo, Egypt and Tim Summers, BP Exploration, published in The Leading Edge, April

33 Marine Bin Gathering Schematic illustration of a vessel towing an array of 8 streamers and two source arrays 33

34 New Marine Methods Conventional PGS Geostreamer MEMS Geophone CGGV Broadseis Western Discover Air gun array Air gun array Air gun array Air gun array New Marine Methods 34

35 Benefit of Wavefield Separation Pressure Particle Velocity Up-Going Pressure GeoStreamer Examples Conventional GeoStreamer 35

36 CGGV Broadseis BroadSeis Examples Conventional BroadSeis Frequency, HZ BroadSeis 36

37 Western Discover Discover Examples Conventional Discover 37

38 Western IsoMetrix Recording Multi-directional Data to Reconstruct Wavefield (Qmarine) 38

39 Learning Objectives This section covered the following Learning Objectives: Describe the marine configuration for a 3D survey including: Components used for data acquisition Arrays to attenuate noise Bin gathering as a CMP assemblage of reflections 39

40 Learning Objectives Seismic Data Acquisition Core Land Data Acquisition This section will cover the following Learning Objectives: Describe the land configuration for a 3D survey including: Bin gathering for a land 3D survey Compare the costs of 2D and 3D surveys 40

41 Introduction Land operations are extremely varied and almost every survey is unique. Land surveys are done 24 hours a day and 7 days a week unless otherwise defined by the local conditions and requirements of the client. Land operations are planned to have the least amount of impact on the environment and land use requirements. Land data can be acquired in orthogonal (most desirable), parallel, and can collect both horizontal and vertical particle motion data. The survey is designed to best sample the subsurface in a cost and environmental manageable basis. Components of Land Acquisition Configuration The digital recording system is connected to the truck. Vibroseis units Recording truck Junction boxes Geophone arrays 41

Components of Land Acquisition Configuration The digital recording system is connected to the truck.

many years and have quickly become the standard in regular operations.

42 Components of Land Acquisition Configuration The digital recording system is connected to the truck. Recording truck These wired systems have been replaced by wireless system in very remote and difficult areas for many years and have quickly become the standard in regular operations. Vibroseis units Wireless systems are expensive but allow quicker deployment and more flexible shooting configurations. Junction Digital geophones have been used in boxes multicomponent acquisition for many years, and Geophone they are arrays also replacing analogue geophones in normal operation. Geophones Bottom Protective casing Geophone Moving coil geophone components Top 10 meter string of geophones 42

geophones need to be multi-direction 2 horizontal, 90 degrees orthogonal to each other O

43 Seismic Data Acquisition Core Geophones Bottom 3C (3 Component), or Multi Component Acquisition Protective casing Geophone The source (Vibroseis) is the sametop but the geophones need to be multi-direction 2 horizontal, 90 degrees orthogonal to each other O PY R IG H T 1 vertical C Geophones Moving coil geophone components 10 meter string of geophones 43

44 Moving Coil Geophone Components Flexible two wire cable Plastic casing Metal casing Vibroseis Unit Seismic Sources Ground spike Suspension spring Suspended coil Strong magnet Anything that will disrupt the surface to generate a wavefield to transmit down in the earth and be reflected back Dynamite or explosive sources Very effective at creating wavefields Portable, but destructive, and not repeatable Weight drops and land air guns Less destructive, more repeatable, and able to be modeled Large, and not very portable All these methods are an impulse (instantaneous) source, dependent on the land surface 44

Seismic Data Acquisition Core Vibroseis Unit O PY R IG H T Vibroseis Vibroseis Unit Seismic Sources Vibroseis Anything that

sources The electronic signal used to drive the hydraulic vibration system sweeps through Weight drops and land air guns of

very portable the earth and thereby controlling the resolution All these methods are an impulse (instantaneous) source, of

45 Seismic Data Acquisition Core Vibroseis Unit O PY R IG H T Vibroseis Vibroseis Unit Seismic Sources Vibroseis Anything that will disrupt the surface to generate a wavefield to transmit down in the earth and be reflected back C Dynamite or explosive sources The electronic signal used to drive the hydraulic vibration system sweeps through Weight drops and land air guns of frequencies to Less destructive, more repeatable, and able to aberange modeled control the signal put into Large, and not very portable the earth and thereby controlling the resolution All these methods are an impulse (instantaneous) source, of the recorded data. dependent on the land surface Very effective at creating wavefields Portable, but destructive, and not repeatable 45

46 A Vibroseis Array Electronic feedback system ensures that all vibrators are locked on to the same drive signal. They must vibrate in unison. A Vibroseis Array The array design criterion here is the same as the array for the marine sources Since vibrator array is portable, one source location can be occupied for several sweeps, which are summed to provide the required energy for adequate energy penetration Recent research in acquisition has been to concentrate on broader bandwidth Vibroseis allows us to configure the acquisition methods to do that Several new methods have been developed to exploit the phase matching we just discussed to separate out vibrators and record higher frequency data Other methods allow acquisition faster by digitally monitoring individual vibroseis and separating them out digitally from the recorded signal 46

Seismic Data Acquisition Core Land 3C Recording Three

interest in recording all three components of ground

vertical sensor and two horizontal sensors.

47 Seismic Data Acquisition Core Land 3C Recording Three component geophone O PY R IG H T There is increased interest in recording all three components of ground motion with three geophones which are oriented as one vertical sensor and two horizontal sensors. This is referred to as 3 component or 3C data. C Land Configuration 2 cm. VectorSeis sensor by I/O Inc. MEMS Micro Electro Mechanical System Sercel 3 Component Digital Geophone 47

48 Land Bin Gathering Land Bin Gathering Subsurface coverage from one source location Subsurface coverage from three source locations 48

49 Undershooting a Land Obstacle (Stream, Cliff, Town) Stream Obstruction Recording Truck Midpoints 49

50 Cost of Seismic Data Acquisition Costs of Seismic Data (Acquisition and Processing) 3D / for a 3 X 3 mile block in Millions of $: Land West Texas open area 0.40 Land coastal woods to wetlands 0.58 Land transitional zone - marsh 0.80 Jungle 2.00 Marine 0.25 Sold to several companies Speculative data 25% of proprietary Acquired solely for a single company 50

51 Learning Objectives This section covered the following Learning Objectives: Describe the land configuration for a 3D survey including: Bin gathering for a land 3D survey Compare the costs of 2D and 3D surveys PetroAcademy TM Basic Geophysics Core Nature of Seismic Image Core Geological Association with Seismic Reflections Core Seismic Data Acquisition Core Wavelet in the Seismic Data and Limits on Resolution Core Seismic Velocities Core Overview of Seismic Data Processing Core Seismic Migration Core Seismic Mapping Fundamentals Direct Hydrocarbon Indicators Core Amplitude vs. Offset Core Seismic Inversion Core Attributes Core Seismic Unconventional Reservoir Core 51

L 5 Seismic Method. Courtesy of ExxonMobil. Mitchum et al., 1977b

L 5 Seismic Method. Courtesy of ExxonMobil. Mitchum et al., 1977b Courtesy of ExxonMobil L 5 Seismic Method AAPG 1977 reprinted with permission of the AAPG whose permission is required for further use. Mitchum et al., 1977b Basic Exploration Workflow Identify Opportunities