Structural Geology, Seismic Imaging, and Genesis of Jonah Field
Hanson, William B., Victor Vega, Dennis Cox, and Terry J. Young
BP America Production Company, Houston, TX
Jonah Field is a large, complicated structural trap
located in the northwestern part of the Green River Basin. The structural components of the
trap
consist of a combination of
fault
zone deformation and broad, open folding. The two field-bounding faults, intersect up dip to form the overall wedge-shaped
trap
and the field is an aggregate of at least four
fault
compartments each comprised of a subtle, northeast-plunging faulted nose bounded on the west and south by sealing faults. The interior faults terminate at the south field bounding
fault
and production data indicates that these faults are at least partially sealing. All of the major faults are nearly vertical and extend to the basement although displacement appears to decrease with depth. The south field bounding
fault
is probably a left lateral wrench
fault
zone as discussed by Warner (1997); this
fault
zone locally displays extensional and possibly compressional structures and has a complex and protracted displacement history. The
fault
was active concurrently with Lance Formation deposition creating thicker Lance Formation locally on the north side of the
fault
(north-side down during Maastrictian time). Subsequently, post-Paleocene uplift of the thick Lance Formation package (north side displaced upward) may be responsible for the broad open folding. Detailed analysis of the west field-bounding
fault
suggests that it is a composite of two faults that have merged. This explains the apparent dip reversal along the length of these features and contrary to previous reports, is not a scissor
fault
.
Seismic imaging of Jonah Field is challenging because of complex fault
throws, and generally dim and discontinuous reflections within the producing interval. Advanced seismic techniques have been used to define the
trap
boundaries and to optimally locate development wells.