Lithologic Diversity and Environmental Restrictions are a Challenge to Reservoir Development of the Upper Miocene Deep Water Sandstones of the Union Pacific and Ford Zones in the Wilmington Oil Field, Los Angeles County, California

BERMAN, B. H., Thums Long Beach Company, Long Beach, CA, and K. D. JUNG, California State University, Long Beach, CA

The Union Pacific and Ford zones of the Long Beach Unit portion of the Wilmington oil field consist of more than 1900 ft (600 m) of interbedded sediments in an asymmetrical faulted anticline divided into five fault blocks.

The depositional environment of the sediments was a restricted borderland basin. The Union Pacific and Ford sediments contain 15 depositional sequences within a retrogradational turbidite suite. Cross section analysis shows a 70% continuity of individual sands throughout the study area. Major sands show an overall thickening from west to east. The sands have been diagenetically altered resulting in increased silt and clay fractions. The clay content ranges from 0.5 to 5.0 wt.%.

Seventeen percent of the original oil in place has been produced predominantly from the major sand units in the lower Ford zone which possess the most favorable reservoir characteristics. This zone has watered out and has been abandoned. Reservoir development is now concentrated in two distinct overlying zones. The lower interval has major sand units and is being successfully waterflooded. The upper interval consists of 1300 ft (400 m) of thinly interbedded sands and shales with a sandstone/shale ratio of 0.43. This zone cannot be evaluated with conventional logs. Core descriptions show twice the sand count compared to sand counts from wireline logs. Resistivity logs indicate wells would produce with high water cuts (high water saturation) while wells actually produce at lower water c ts. The sands are poorly consolidated so core analyses do not reflect in situ conditions. They have a high productivity damage potential because of high clay content and fines movement. The entire zone is not depleted because of formation damage incurred.

The volumetrics and reservoir quality of the upper zone are being re-evaluated using new logging techniques and new interpretation methods designed for thin bed analysis. In addition, shear wave sonic data and wireline formation pressure data has been obtained to evaluate hydraulic fracture potential and the subdivision of sands into high and low permeability flow units. Environmental restrictions require kill fluids and drilling muds other than an oil base system. These kill fluids and drilling muds have the potential for damaging the formations. Successful development of the upper section of the Union Pacific and Ford Zone can only succeed by paying close attention to and respecting the heterogeneity of the lithology. This requires new methods of formation evaluation, well completio , and production practices.

AAPG Search and Discovery Article #91009©1991 AAPG-SEPM-SEG-SPWLA Pacific Section Annual Meeting, Bakersfield, California, March 6-8, 1991 (2009)