Determining Reservoir Quality, Distribution, and Continuity in Complex Lacustrine Margin Sandstones, Red Wash Field (Main Area), Uintah County, Utah

D. M. Thompson

Rocks deposited in lacustrine margin environments are important oil producers, but can pose unique problems in field development. An example is Red Wash field, located in the Uinta basin of northeast Utah. Red Wash produces from over 80 separate reservoir zones in the Eocene lower Green River Formation. The reservoirs are 2-20 ft thick and each has a unique areal distribution and fluid content. Since discovery in 1951, the field has produced 76 million bbl of oil and 270 billion ft³ of gas from 260 wells. A low recovery factor after 26 years of waterflood is due to complex stratigraphy and inadequate definition of each reservoir. A core study was initiated to address these problems.

Study of 2,000 ft of core from 10 wells led to the development of a detailed depositional model. Reservoir-quality parameters were defined by comparing cores with production test data. Because depositional environments controlled reservoir quality and geometry, criteria were established so that logs could be used to identify environments. Net effective reservoir, porosity, and permeability maps were then constructed using interpreted depositional geometries. All maps were integrated with original and current fluid contents. Oil chromatography was used to help determine details of reservoir continuity by comparing peak height ratios of oil extracted from core. Since each reservoir had a distinct chromatographic signature, it was possible to distinguish isolated from interconnected reservoirs.

This study resulted in information that helps evaluate well recompletions, existing waterflood patterns, original oil in place, and the field's EOR potential.

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