Washington, D.C. — Billions of barrels of oil that could increase domestic supply, help reduce imports, and increase U.S. energy security may be potentially recoverable from residual oil zones, according to initial findings from a study supported by the U.S. Department of Energy’s Office of Fossil Energy (FE). The recently completed study, conducted by researchers at the University of Texas–Permian Basin (UTPB), is one of several FE-supported research projects providing insight that will help tap this valuable-but-overlooked resource.
Residual oil zones, called ROZs, are areas of immobile oil found below the oil-water contact of a reservoir. ROZs are similar to reservoirs in the mature stage of "waterflooding," in which water has been injected into a formation to sweep oil toward a production well. In the case of ROZs, the reservoir has essentially been waterflooded by nature and requires enhanced oil recovery (EOR) technologies, such as CO2 flooding, to produce the residual oil.
The UTPB study focused on understanding and modeling fluid flow within ROZs in the Artesia Fairway—a dolomitized trend in the San Andres formation containing oil-producing fields—of eastern New Mexico and west Texas. Utilizing geologic and production data, UTPB researchers determined that oil saturations within ROZs range from 20 percent to 40 percent, with an average of 32 percent, which is similar to that of mature, waterflooded reservoirs. The study also found that ROZs exist in all fields producing from the San Andres formation where it has been uplifted in the western part of the Permian Basin resulting in a tilted oil-water contact. The project’s final report should be available within 90 days from the Research Partnership to Secure Energy for America (RPSEA).
In another FE-sponsored research effort, UTPB is developing a state-of-the-art geologic and reservoir characterization model of the main pay zone and residual oil zone in the Goldsmith field, Ector County, Texas, where Legado Resources has initiated a CO2-EOR pilot project. A numerical simulator will then be used to match past reservoir performance and to examine the performance of the CO2 EOR flood under alternative flood design and operating practices. The goal of the research effort is to optimize the technical and economical performance of an ROZ CO2 flood and transfer the knowledge to other operators. This will be the first publicly available comprehensive case study of a ROZ flood.
A third study, awarded to UTPB in June 2012, will further delineate the presence and size of ROZ areas in the Permian Basin of Texas and New Mexico using geophysical well logs and well test data, core and fluid samples, and water chemistry data. Researchers will also determine if 3D seismic can be used for identifying the higher quality portions of the ROZ resource to assist small oil producers within the Permian Basin and other ROZ basins in the United States.
According to the 2012 worldwide EOR survey published in Oil & Gas Journal, U.S. CO2-EOR production is approximately 350,000 barrels of oil per day. There are currently nine industry ROZ CO2-EOR pilot projects in the Permian Basin of Texas, accounting for approximately 10,000 barrels of oil per day. Results and findings from FE-supported research should help to increase recovery from this domestic resource and create American jobs.