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AAPG Bulletin, V.
A new process-based methodology for analysis of shale smear along normal faults in the Niger Delta
1Shale Smear Project, Department of Geological and Environmental Sciences, Stanford University, Stanford, California, 94305-2115; present address: Chevron Nigeria Limited, Lagos, Nigeria
2Shale Smear Project, Department of Geological and Environmental Sciences, Stanford University, Building 320, 450 Serra Mall, Stanford, California, 94305-2115; email: aydinpangea.stanford.edu
3Chevron Overseas Petroleum Incorporation, San Ramon, California, 94583
Bashir Koledoye received his B.S. degree in geology and M.S. degree in mineral exploration (geophysics option) from the University of Ibadan. He also received an M.S. degree in geology from Stanford University. He has worked for Chevron Nigeria for 9 years, including short assignments with Chevron Petroleum Technology Company in both La Habra, California, and Houston, Texas. He worked on several exploration and development portfolios. His interests include sealing capacity of faults, geological models, and field-development studies.
Atilla Aydin received his B.S. degree in geology from Istanbul Technical University, Turkey, and both his M.S. degree and Ph.D. in geology from Stanford University, California. After 13 years of teaching at Istanbul Technical University and Purdue University, he moved to Stanford University as a research professor of structural geology and geomechanics. He is the codirector of the Rock Fracture Project and the director of the Shale Smear Project at Stanford. His research interest includes fracturing and faulting of rocks and fluid flow through fractures and faults with a primary application to hydrocarbon entrapment, migration, and recovery.
Eric May received his B.A. degree in geology from the College of Wooster in 1983 and his M.S. degree in geology from the University of Cincinnati in 1990. He has worked for Chevron Texaco in a variety of international and domestic earth science positions since joining the company in 1987, and is currently working deep-water Nigerian exploration for Chevron Texaco's affiliate in Lagos, Nigeria.
Chevron Nigeria Limited and the Nigeria National Petroleum Corporation Joint Venture sponsored this study. We would like to thank Mark Koelmel and Gil Ankenbauer for their encouragement and support. Scott Sollee and John Hohenberger provided the management support for the availability of data and other resources. P.C. Okoro, Michelle Ike, and other members of the South Offshore group were very helpful with transferring of data and in the critical discussions on the geological and engineering status of the field. Dave Kissinger helped to solve the numerous problems with transferring, loading, and maintaining the seismic database in both Stanford and San Ramon. Loren Stewart helped with getting well-log and other data from the San Ramon Records. Jerome Glass helped set up the Stratworks software and gave very useful criticisms on the quantitative shale-smear analysis. Gene Luziotti assisted in the construction of several synthetic seismograms. We would like to thank the Shale Smear Project of Stanford University for supporting the field geology aspect of this study and Amgad Younes for sharing his field observations with us. In addition, we thank the graduate and postdoctoral students in the Rock Fracture group at Stanford for their technical help and valuable suggestions. We thank R. Humphrey, R. Davies, and J. Handschy for their reviews of the earlier version of the manuscript.
Three-dimensional (3-D) seismic and well-log data from the producing Okan field in the Niger Delta and a working conceptual model derived from field observations and theoretical considerations were used to map the 3-D geometry of a representative normal fault with shale smear. Seismic data show clear fault segmentation in the dip direction with extensional relays inferred to be occupied by smeared shales. Log data help to identify lithologic horizons throughout the field, and in some cases, where a wellbore crossed the fault, to quantitatively determine the amount of smeared shale within the fault zone. Conceptual models provide means to interpret crucial details of the fault geometry and the distribution of shaly fault rock beyond the conventional resolution of a 3-D seismic data set.
Combining the seismic data, well-log data, and conceptual model, we developed a procedure to determine the fault geometry and to assess the nature of the smeared shales and their evolving configurations as a function of fault throw, the thickness of corresponding shale units, and the thickness of the sand units between the shales. The product is a new and improved technique to visualize fault architecture and to interpret fault rock, both of which lead to constructing a structurally realistic juxtaposition diagram and a physically sound shale-smear analysis in a reservoir.
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