Reservoir Compartmentalization Caused by Mass Transport Deposition, Northwest Stevens Pool, Elk Hills Naval Petroleum Reserves, California

Mark D. Milliken, David W. Shiflett, Harvey A. Deutsch, and George S. McJannet

The "A" sands of the Northwest Stevens Pool consist of six major subdivisions (A1-A6) and numerous sublayers. These sands are above the "N Point" stratigraphic marker, making them much younger than most other Stevens sands at Elk Hills. Cores show the A1-A3 sands to be possibly mass transport deposition, primarily debris flows, slumps, and sand injection bodies. The A4-A6 sands are characterized by normally graded sheet-like sand bodies typical of traditional outer fan turbidite lithofacies.

Most current production from the A1-A2 interval comes from well 373A-7R a recompleted waterflood well that came on line in 1992 at 1400 BOPD. Well 373A-7R is an anomaly in the A1-A2 zone, where average production from the other ten wells is 200 BOPD. Other evidence for compartmentalization in the A1-A2 interval includes sporadic oil-water contacts and drawdown pressures, difficult log correlations, and rapid thickness changes. In 1973, well 362-7R penetrated 220 ft of wet A1 sand. The well was redrilled updip and a successfully completed in the A1, where the oil-water contact is more than 130 ft lower than the original hole and faulting is not apparent. In 1992, horizontal well 323H-7R unexpectedly encountered an entirely wet A1 wedge zone. Reevaluation of the A1-A3 and other sands as mass transport origin is important for modeling initialization and production/development strategies.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California