Gas-Producing Submarine-Fan Channel-Levee Complexes in Forbes Formation, Arbuckle Field, Central Sacramento Basin, California

Douglas P. Imperato, Tor H. Nilsen

The Campanian Forbes Formation was deposited as a south-prograding basin-plain, deep-sea fan and slope turbidite system in the Late Cretaceous Great Valley forearc basin of California. Gas production from the Arbuckle field is from the middle deep-sea fan deposits of the Forbes Formation at depths of 5,500-7,000 ft. The field is located approximately 7 mi east of the western erosional margin of the Sacramento basin, where the Forbes Formation crops out and dips steeply to the east. The field has a proven acreage of 3,450 and contains 25 producing wells. A north-trending anticline, which is present on the regional easterly dip, provides 150-200 ft of closure in the southern part of the field.

Detailed maps and cross sections of the gas-producing intervals of the Forbes Formation in the Arbuckle field have been constructed from correlation of 77 well logs and detailed examination of the nearby outcrops. Well-log correlations and sedimentary facies identified in outcrop indicate that the gas-producing intervals are chiefly channel-levee complexes in a mud-rich deep-sea fan system. These channel-level complexes trend southward, are slightly sinuous, and are as much as 1 mi wide.

A comparison of structure-contour maps with net-sandstone maps and gas production data indicates that not all gas production is structurally controlled. Channel-axis sandstone that is as thick as 250 ft generally produces gas only within structural closure, whereas thinner, more shale-rich, channel-margin and levee deposits produce gas from updip stratigraphic pinch-outs into interchannel shale.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.