Application of Sequence Stratigraphic Modeling to Integrated Reservoir Management at Aneth Unit, Greater Aneth Field, Utah

Larry J. Amateis

The Greater Aneth Field was discovered in 1956 using a combination of surface geology and seismic. Aneth Unit has been waterflooded since 1962. It has produced 134 million barrels of an estimated 535 million barrels of oil in place.

Engineering studies of the reservoir had shown that existing geological models of the reservoir did not adequately address the heterogeneity of the reservoir. Understanding the heterogeneity required a new geological model.

Stratigraphic cross-sections and examination of a limited number of cores were used to zone the reservoir. The zonation depended on recognition of a sequence boundary dividing the Pennsylvanian Desert Creek into two separate reservoirs: an upper ooid grainstone unit and a lower algal mound unit. Additional surfaces separate higher energy facies from the algal mound in the lower reservoir. Numerous events in the upper reservoir complicate flow-unit continuity.

A three-dimensional geological model including porosity and permeability distribution, dolomitization, and the stratigraphic zonation was created from normalized cad hole neutron logs, compensated neutron-density logs, and data from approximately 84 cores. The three-dimensional model indicated the need for additional cores to be studied in detail. The new model helped explain anomalous production in many areas of the reservoir.

The geological model combined with reservoir engineering analysis contributed to identifying workover locations, horizontal well locations, and may lead to CO₂ flooding of the reservoir.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995