Brad Artman undergraduate: Colorado School of Mines, Geophysical Engineer graduate: Stanford University, Ph.D. candidate work experience: –Western Atlas Logging Services, Junior Engineer –U.S. Geological Survey, Visiting Scientist –Shell Deepwater Development Inc., Petrophysicist & Exploration Geophysicist

passive seismic imaging at Valhall Brad Artman, Stanford Exploration Project – Advanced imaging team Monday, September 27

multiple modeling in the image-space Brad Artman, Stanford Exploration Project – Advanced Imaging Team Ken Matson, Advanced Imaging Team Monday, September 27

passive seismic imaging at Valhall Brad Artman, Stanford Exploration Project – Advanced imaging team Monday, September 27

passive seismology not event location structural imaging –reflection seismology: subsurface investigation from the time- delayed reflections of sound off of geologic variations. –passive imaging: with no application of controlled experimental sources, a relationship between a recorded transmission wavefield and reflection wavefields is required. requires: stationary seismometers, lots of disk space

crustal scale exploration

earthquake energy

capitalizing on ambient noise earthquake arrivals ocean waves wind vibrations coupled with foundations cultural activity –vehicle and boat traffic –drilling noise –nearby seismic acquisition

Valhall one of the North sea giant fields partners Amerada Hess, Shell and Total reservoir highly porous chalk first production1982 field life2028 field production 90,000 bpd/day expected ultimate recovery 1,050 mm stb oil produced to date ( ) 500 mm stb oil remaining reserves 540 mm stb oil high activity level – new wells & well work

Valhall Life of Field Seismic (LoFS) Permanent field wide seismic array installed at Valhall during 2003 –120 km seismic cables –2414 groups of 4C sensors –Covers 45sq km –3 seismic surveys acquired, 4 th to be acquired mid-September

operations state of the art airgun array carried by stand-by boat – 53,000 shots per survey ~1/2 cost of LoFS installations related to the source

passive seismology by correlation why image? –linearity of wavefield extrapolation application to Valhall LoFS why try passive seismic imaging? future plans

transmission wavefield time (s) depth (m) position(m)

ambient noise r1r2 t r1r2

ambient noise r1r2 t r1r2

ambient noise r1r2 t r1r2

ambient noise r1r2 t r1 r1 r1 r2 lag r1r2

ambient noise r1r2 t r1 r1 r1 r2 twt r1r2

ambient noise r1r2 t r1 r1 r1 r2 lag twt r1r2

position(m) time(s) lag(s) offset(m)

position(m) time(s) lag(s) offset(m) 300

position(m) time(s) lag(s) offset(m)

position(m) time(s) lag(s) offset(m) -300 n long traces n short traces 2

passive seismology by correlation why image? –linearity of wavefield extrapolation application to Valhall LoFS why try passive seismic imaging? future plans

why image? signal/noise enhancement one correlated shot gather migrated image

flow model T= Transmission wavefield D= Source wavefield (down-going) U= Receiver wavefield (up-going) R= Total reflection data R z+1 T z T z R z + U z D z U D +- T T +- correlation extrapolation

SR Migration flow model T= Transmission wavefield D= Source wavefield (down-going) U= Receiver wavefield (up-going) R= Total reflection data R z+1 T z T z R z + U z D z U D +- T T +- correlation extrapolation

CMP Migration flow model T= Transmission wavefield D= Source wavefield (down-going) U= Receiver wavefield (up-going) R= Total reflection data R z+1 T z T z R z + U z D z U D +- T T +- correlation extrapolation

Passive Migration flow model T= Transmission wavefield D= Source wavefield (down-going) U= Receiver wavefield (up-going) R= Total reflection data R z+1 T z T z R z + U z D z U D +- T T +- correlation extrapolation

Shot-profile datuming analogy R = U D R = R e R = U D e = U e (D e ) * * * * i Kz  z +i Kz(U)  z + i Kz(D)  z +i Kz(U)  z-i Kz(D)  z

imaging advantages poor data quality mandates imaging transformation from transmission to reflection wavefield can be accomplished along the way saves time –n instead of n 2 traces –removes IFFT of n 2 (long) traces –trace length difference ~cancels strict compute cost savings –file i/o provides big savings 1 shot of n traces vs. n shots of n traces multiple image-space summations

synthetic proof of concept reflection gather active migration

synthetic proof of concept correlated passive gather passive migration

passive seismology by correlation why image? –linearity of wavefield extrapolation application to Valhall LoFS why try passive seismic imaging? future plans

Valhall data

trace # Depth slice near 88m energy localized around rig moveout across traces suggests surface noise

Valhall data Reflector? mono-freq. boat noise rig activity

Valhall pipe cut normalization 4km 12km

Valhall pipe cut image 4km 12km

Valhall pipe cut image 4km 12km

Valhall active seismic 4km 12km

Valhall pipe cut image

passive seismology by correlation why image? –linearity of wavefield extrapolation application to Valhall LoFS why try passive seismic imaging? future plans

why try passive seismic imaging understand a completely undeveloped experiment capitalize on: –existing hardware –competitor’s sources –teleseismic & local noise extend imaging bandwidth to lower frequencies imaging forward scattered modes

passive seismology by correlation why image? –linearity of wavefield extrapolation application to Valhall LoFS why try passive seismic imaging? future plans

continued exploration of existing data –multi-component experiments –appropriate bandwidth parameterization –time/energy requirements –earthquake sources rig-site continuous correlation BP’s passive seismic imaging capabilities –file-handling infrastructure –native 3D imaging algorithms

Oyo-Geospace cable

multiple modeling in the image-space Brad Artman, Stanford Exploration Project – Advanced Imaging Team Ken Matson, Advanced Imaging Team Monday, September 27

Surface Related Multiple Elimination (SRME) –mechanics –classic shortfall –addressing the problem through imaging shot-record imaging multiple modeling at Maddog implications and status

* = = * = * Surface Related Multiple Extraction

r s SRME

r s ?

r s

r s ?

r s

r s ?

r s

E N *

E N *

Exact kinematic modeling Linearly increasing amplitude error w/ order of multiples Suffers when FULL acquisition not supplied co-located sources and receivers … in the image space Exact kinematic modeling- independent of velocity Same amplitude problems (requires adaptive subtraction) Wavefront healingWavefront healing SRME

z x wavefront healing

z x

z x

Surface Related Multiple Extraction (SRME) –mechanics –classic shortfall –addressing the problem through imaging shot-record imaging multiple modeling Maddog implications and status

flow model T= Transmission wavefield D= Source wavefield (down-going) U= Receiver wavefield (up-going) R= Total reflection data R z+1 T z T z R z + U z D z U D +- T T +- correlation extrapolation

flow model M= Multiple model U = Receiver wavefield (up-going) M z M o + U o U o U z U z +- convolution extrapolation * *

Z=0 shot-record migration

Z>0

shot-record migration

shot-record normalization Z>0

shot-record normalization

image-space multiple model Z>0

image-space multiple model

Surface Related Multiple Extraction (SRME) –mechanics –classic shortfall –addressing the problem through imaging shot-record imaging multiple modeling Maddog implications and status

shot-record migration

image-space multiple model

migration

migration after subtraction

subtraction after migration

migration after subtraction

migration

Surface Related Multiple Extraction (SRME) –mechanics –classic shortfall –addressing the problem through imaging shot-record imaging multiple modeling Maddog implications and status

image space multiple modeling exact kinematics –inexact dynamics requires adaptive subtraction –1-2 less dimensions makes subtraction less expensive velocity independent incremental expense (1.5x) to produce during shot- record migration –direct extension to Common Image Gathers –split-spread input data required less expensive than regularization + SRME + migration

status documented 2- and 3-D programs running suite of 2-D synthetic tests single shot 3-D synthetic test –comprehensive testing will require significant resources

acknowledgements Sverre Brandsberg-Dahl, Joe Dellinger, Valhall BU Richard Clarke, John Etgen, Advanced Imaging Team Phuong Vu, David Lewis, Keith Gray, Jerry Ehlers, Randy Selzer Ken Matson, Gerchard Pfau

migrated conventional multiples

migrated image

image-space multiple model

migrated conventional multiples

migrated image