ABSTRACT: Significance of Compensation Cycles for Improved Reservoir Management in Thin-Bedded Turbidites

SLATT, ROGER M., PHILIP LOWRY, DOUGLAS W. JORDAN, and MARK H. SCHEIHING, ARCO Oil & Gas Co., Plano, TX

Turbidite sequences are often arranged vertically and laterally into compensation cycles. These cycles form in response to repeated switching of depositional axes as newly deposited beds create adjacent bathymetric lows into which successive beds are deposited.

Correlation of over 1000 well logs from the Miocene-Pliocene section of Long Beach Unit in the giant Wilmington Oil field (California) indicates that thick (30-65 m) sand-rich stratigraphic intervals are arranged into a series of compensation cycles. In the mud-rich part of the 300 m thick Ranger Zone, 7-20 m thick intervals can be correlated over interwell distances (170-230 m). Within these intervals, individual sand and mud beds have been assumed to be relatively planoform.

Recent examination of turbidite outcrops from Arkansas (Pennsylvanian Jackfork Group) reveals that similar thin-bedded intervals often exhibit the same compensation style of deposition as the larger scale sandbodies. The compensation cycles in the thin-bedded sequences occur both at and below the scale of interwell spacing.

Because thin-bedded intervals in the Long Beach Unit are selectively targeted as part of a waterflood redevelopment, an understanding of lateral continuity and connectivity of individual beds at the interwell scale becomes critical. Thickness and length measurements of individual beds from the Arkansas outcrops have provided a database for estimating lateral continuity of the thin-bedded turbidites for improved reservoir management.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)