Optimization of a CO2 flood design Wesson Field - west Texas

Abstract

The Denver Unit of Wasson Field, located in Gaines and Yoakum Counties in west Texas, produces oil from the San Andres dolomite at a depth of 5,000 ft. Wasson Field is part of the Permian Basin and is one of the largest petroleum-producing basins in the United States. This research used a modeling approach to optimize the existing carbon dioxide (CO2) flood in section 48 of the Denver Unit by improving the oil sweep efficiency of miscible CO2 floods and enhancing the conformance control. A full compositional simulation model using a detailed geologic characterization was built to optimize the injection pattern of section 48 of Denver Unit. The model is a quarter of an inverted nine-spot and covers 20 acres in San Andres Formation of Wasson Field. The Peng-Robinson equation of state (EOS) was chosen to describe the phase behavior during the CO2 flooding. An existenting geologic description was used to construct the simulation grid. Simulation layers represent actual flow units and resemble the large variation of reservoir properties. A 34-year history match was performed to validate the model. Several sensitivity runs were made to improve the CO2 sweep efficiency and increase the oil recovery. During this study I found that the optimum CO2 injection rate for San Andres Formation in the section 48 of the Denver Unit is approximately 300 res bbl (762 Mscf/D) of carbon dioxide. Simulation results also indicate that a water-alternating-gas (WAG) ratio of 1:1 along with an ultimate CO2 slug of 100% hydrocarbon pore volume (HCPV) willallow an incremental oil recovery of 18%. The additional recovery increases to 34% if a polymer is injected as a conformance control agent during the course of the WAG process at a ratio of 1:1. According to the results, a pattern reconfiguration change from the typical Denver Unit inverted nine spot to staggered line drive would represent an incremental oil recovery of 26%.