THOMPSON, TERRY W., Bechtel Petroleum, Tupman, CA, and GEORGE S. McJANNET, U.S. Department of Energy, Tupman, CA

ABSTRACT: Horizontal Well Development of Structurally-Controlled Turbidite Channel Sandstones, 26R Pool, Elk Hills Field, Kern County, California

The 26R pool is a complexly layered, deep marine turbidite reservoir equivalent to the late Miocene Elk Hills Shale Member of the Monterey Formation. Cumulative oil production from the 3-mi-long, northwest-trending pool is 188 million bbl. The pool is made up of five lenticular, stacked sand bodies, which reach a maximum total thickness of approximately 1800 ft.

The layers comprising the 26R pool are interpreted as channel-fill and levee deposits that were fed by the western-sourced, sand-rich 265R turbidite system. Incipient development of subsea structures in the late Miocene strongly influenced this turbidite system. The 26R system was deflected into the northwest-trending synclinal trough between the growing 29R and 31S structures. Relief of this structurally created channel was low when the earliest 26R sand bodies were deposited, leading to a wide channel complex bounded by broad, moderately permeable levee and overbank deposits. As deposition proceeded, structural relief of the constraining channel increased, resulting in narrower sand-body width and relatively abrupt channel terminations against low-permeability siliceous shale and ch rt. The variation in updip seal effectiveness between upper and lower sand bodies leads to a complicated relationship between the 26R sands and their lateral equivalents in the N/A shale pool. Reservoir management, including horizontal well placement, is influenced by this relationship.

Within the 26R reservoir, an expanding gas cap and descending gas-oil contact has resulted in a continually shrinking oil band. Undrained oil downdip and between existing vertical wells is commercially exploited with medium radius horizontal wells. Strong gravity drainage in steeply dipping beds into horizontal wellbores just above the stable, flat-lying oil-water contact provides a very effective drainage mechanism. This mechanism is enhanced by the low Kv/Kh ratio associated with the highly layered reservoir.

AAPG Search and Discovery Article #90992©1993 AAPG Pacific Section Meeting, Long Beach, California, May 5-7, 1993.