DOE sees vast energy resource in residual oil zones

By OGJ editors

Billions of barrels of oil that could increase domestic supply, help reduce imports, and improve US energy security may be potentially recoverable from residual oil zones, according to initial findings from a study supported by the US Department of Energy’s Office of Fossil Energy.

The recently completed study, conducted by researchers at the University of Texas-Permian Basin, is one of several DOE-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.

DOE estimated in 2006 that ROZs could contain 100 billion bbl of the 1.124 trillion bbl of technically recoverable oil in place in US reservoirs (OGJ, Mar. 13, 2006, p. 30).

The UTPB study focused on understanding and modeling fluid flow in ROZs in the Artesia Fairway, a dolomitized trend in the San Andres formation containing oil-producing fields in eastern New Mexico and West Texas. Utilizing geologic and production data, UTPB researchers determined that oil saturations within ROZs range from 20% to 40% with an average of 32%, 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 DOE-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 Goldsmith field, Ector County, Tex.

At Goldsmith, Legado Resources has initiated a CO2 EOR pilot project (OGJ, July 2, 2012, p. 72). A numerical simulator will then be used to match past reservoir performance and to examine the performance of the CO2 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.

In a third study awarded in June 2012, UTPB 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 to identify the higher-quality portions of the ROZ resource to assist small oil producers within the Permian basin and other US ROZ basins.

According to OGJ’s 2012 worldwide EOR survey, US CO2-EOR production is 350,000 b/d of oil (OGJ, Apr. 2, 2012, p. 57). Nine industry ROZ CO2-EOR pilot projects in the Permian basin of Texas account for 10,000 b/d of oil. Results and findings from DOE-supported research should help to increase recovery from this domestic resource and create American jobs, the Office of Fossil Energy said.

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