Timing of Structural Growth at Northwest Stevens Field as Evidenced by Stevens Channel Geometries

BERKMAN, THOMAS A., ARCO Oil and Gas Company, Bakersfield, CA

Stacked upper Miocene Stevens sandstone bodies at Northwest Stevens (Tule Elk) are the product of two coalescing turbidite channels which reflect the influence of growing structure during deposition. One channel can be traced from the south through ARCO's 555 zone unit, the 26R and 2B pools at Elk Hills, and into Northwest Stevens. The 800-ft-thick "T" turbidite sands from this channel form offlapping geometries and structural/stratigraphic traps due to deposition across the rising northwest-plunging nose of the Northwest Stevens anticline. They are medium- to coarse-grained with abundant mudstone interbeds and are interpreted to represent a depositional channel fill which grades laterally to less permeable finer grained overbank deposits along the east side of Northwest Stevens.

The second coeval channel can be traced from McKittrick through Asphalto and the 24Z pool at Elk Hills into Northwest Stevens, where it forms a 1700-ft-thick sequence of 80 to 500-ft-thick sand packages at the 7R pool. Sand-shale ratios in these pebbly sandstones are nearly 9 to 1 with abundant conglomeratic interbeds. These channel sands display blocky electric log signatures, have lenticular geometries at the top of the sequence and offlapping geometries at the base, and document deposition in a structural low adjacent to the rising Northwest Stevens structure. The upper Miocene correlation point (UMPC) is sanded out at the 7R pool, indicating that turbidite sand deposition there persisted into lower Reef Ridge time.

Well correlations indicate only minor erosive deposition and amalgamation; thus, the sand bodies at Northwest Stevens are additive to the section.

AAPG Search and Discovery Article #91009©1991 AAPG-SEPM-SEG-SPWLA Pacific Section Annual Meeting, Bakersfield, California, March 6-8, 1991 (2009)