--> ABSTRACT: Integration of 3D Imaging Techniques with Structural Analysis Tools for Trap Definition in Offshore California, by M. F. McGroder, Y. C. Kim, T. A. Hauge; #91020 (1995).

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Integration of 3D Imaging Techniques with Structural Analysis Tools for Trap Definition in Offshore California

M. F. McGroder, Y. C. Kim, T. A. Hauge

Structural traps in the Santa Ynez unit in the northwestern Santa Barbara channel present challenging imaging and structural interpretation problems. The structures are faulted compressional anticlines that appear to have been actively growing for the last 4 Ma. Geophysical problems with 3D data from this area include poorly focussed events and probable mispositioning due to a sloping water bottom and a shallow fold situated above the Miocene reservoir. Aspects of the structural geology that impede a straightforward interpretation of the cube include the presence of older, high-angle faults within the actively growing anticline, the possibility of strike-slip or oblique slip on the high-angle faults, and the likelihood that multiple low-angle detachment horizons exist wit in and beneath the structure.

Our geophysical strategy for imaging the structures relies on pre-stack 3D time migration to provide improved focussing of seismic events. Our structural interpretation is performed on this cube. To address positioning problems caused by the time migration, we use raytracing to perform time-depth conversion by 3D horizon demigration using time migration velocities followed by map migration using interval velocities derived from wells. This time-depth procedure has allowed us to define an area in the northern part of the survey where the field-bounding high-angle fault is mispositioned by several hundred feet in the north-south direction.

For structural interpretation, we use horizontal time slices, dip maps and azimuth maps of several autopicked layers within the cube to identify discrete structural dip domains within the survey area. We compare the distribution of dips to those predicted by forward modeling the complex structures using a 2D structural modeling program. This approach has yielded an improved understanding of structural timing and kinematics of fold growth, an increase in confidence in the quantity and locations of detachments, and a means of quantifying the magnitude of slip on the individual low-angle faults within and beneath the field.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995