Turbidites of the Repetto Formation, Ventura Avenue Field, California

J. R. Schwalbach¹, J. W. Holloway², M. R. Glascock², and J. H. Harris^3
1Aera Energy LLC, Ventura, CA, [email protected]
²Aera Energy LLC, Bakersfield, CA, [email protected], [email protected]
³Numeric Solutions, Ventura, CA, [email protected]

A thick sequence of deepwater clastics filled the depositional trough of the Ventura-Santa Barbara Basin during the Pliocene. Rocks of Repettian age are represented by both thickly bedded, high-density turbidites and thin-bedded “classical” turbidites that reflect depositional processes and relate to reservoir quality. Cores and logs from the Ventura Avenue Field enable us to characterize these rocks and provide the framework to construct 3D geologic models.

The coarsest units are poorly sorted and contain pebble to granule-sized clasts. These occur at the base of some depositional packages, commonly have entrained shale rip-up clasts, and exhibit evidence of local erosion on well-log cross sections. Medium- to coarse-grained sands are a more common component of the stratigraphic section. These sands are homogeneous to graded and commonly very thickly bedded (10s of feet), with amalgamated sand-on-sand contacts that likely represent multiple or surging flows. Some of the medium-to-coarse sand beds have finer grained caps of Bouma Tb-e subdivisions, although the complete sequence is not always present. Finally, thin-bedded turbidites (medium sand and finer) commonly are interbedded with siltstones and hemipelagic shales. These facies packages commonly stack in a predicable manner, and the stratigraphic stacking helps to predict reservoir net-to-gross. We map the larger scale packages over broad areas of the field.

Conventional core data, thin sections, and mercury injection capillary data (MICP) indicate the best reservoir quality usually occurs in the finer grained (medium to very fine sand), better sorted intervals of the thin-bedded facies and in the finer grained caps of the thicker bedded units. Calibration with well logs indicates these facies can be difficult to characterize, particularly with older, conventional log suites. We can improve reservoir characterization by integrating log and core data with a robust facies model, enhancing our prediction of reservoir properties.

AAPG Search and Discovery Article #90088©2009 Pacific Section Meeting, Ventura, California, May 3-5, 2009