DE-FE0005889

Goal
The goal of this project is to optimize the technical and economical performance of a residual oil zone (ROZ) carbon dioxide (CO₂) flood and transfer the knowledge to other operators. The objectives are to (1) characterize the main pay zone (MPZ) and ROZ within the ROZ pilot area; (2) conduct laboratory analyses and reservoir simulation to evaluate the performance of the ROZ pilot flood; and 3) provide recommendations for an optimum field wide expansion of the CO₂ flood in the ROZ and MPZ at the Goldsmith Field.

Performers
The University of Texas of the Permian Basin, Midland, Texas 79707-1423
Legado Resources, The Woodlands, Texas 77380-1921
Meltzer Consulting, Midland, Texas 79707-1423
Advanced Research International, Arlington, Virginia 22203-1661

Background
Although much of the data accumulated over the 40-year history of CO₂ enhanced oil recovery (CO₂ EOR) research are available, there are no publically available geologic and reservoir characterization data on ROZs nor any comprehensive field studies of CO₂ EOR projects in ROZs. This study will document the application of state-of-the-art geologic and reservoir characterization, laboratory work, and field testing to the ROZ in the Goldsmith Field, Ector County, Texas where Legado Resources has initiated a ROZ CO₂ EOR pilot project as well as an MPZ CO₂ flood in parts of the ROZ pilot area.

Past research has identified the potential for major ROZ resources in areas where no major fields are currently productive. A number of on-going industry pilot and demonstration projects are beginning to provide data on the feasibility of recovering a portion of this resource. In the Permian Basin, CO₂ flooding of ROZs has been in the testing phase for several years; however, there are no published reports on the performance of these CO₂ floods. Work by Advanced Resources International (ARI) has estimated that 11.9 billion barrels of oil is technically recoverable from the 30.7 billion barrels of ROZ oil-in-place in five Permian Basin oil plays. Other ongoing work suggests this number dramatically underestimates the resource when considering areas between producing fields.

Impact
This project involves the application and testing of a variety of advanced methods for increasing the recovery of oil from the ROZ of the San Andres Formation, Goldsmith Oil Field in the Permian Basin. Specifically, the impacts and benefits include:

• Optimization of CO₂ flood design using high-resolution reservoir characterization and full-scale compositional reservoir modeling plus laboratory- and bench-scale core studies of the San Andres ROZ. The optimized CO₂ flood design will lead to higher oil recovery efficiencies and improved economics for developing the ROZ.
• Incorporation of real-time data acquisition and diagnostic tools to monitor CO₂ flood performance (using conformance surveys and chemical tracers to establish CO₂ flow paths and sweep efficiency). The real-time data will be linked with a full-scale reservoir simulator to control and modify the CO₂ flood on a continuing basis with the purpose of achieving improved reservoir conformance, and with it, more optimum use of injected CO₂ for oil recovery.
• Analyses of the flow unit properties, depositional facies, mineralogy, diagenetic dolomitization, and reservoir fluids will form a more complete understanding of the impact of late stage diagenesis and flushing on the ROZ, and how it affects CO₂ sweep efficiency. This first-of-its-kind detailed geologic and engineering reservoir characterization will provide a standard for future ROZ CO₂ flood data acquisition and design. It will also provide industry with a geologic/engineering based reservoir characterization and field testing process that will increase the potential for future successful CO₂ floods in the ROZ.

The larger benefits of this project are that it will build a publicly available scientific base of information on the nature of ROZs and provide optimized CO₂ flooding designs for this highly promising oil resource. This information is not currently available, and access to the information would greatly accelerate the timely and efficient recovery of oil from the residual oil zones of the Permian Basin and other ROZ-rich basins in the U.S.

Accomplishments
Reservoir core description has led to the identification and documentation of differences between the depositional facies and diagenetic overprint in the Main Pay, ROZ, and interval below the ROZ, suggesting that the ROZ has undergone a different diagenetic history than the Main Pay. Additionally, diagenetic “markers” seen in core from ROZ’s in other fields including the presence of native sulfur in voids near the base of ROZ, a transition from partially dolomitized limestone below the base of the ROZ to partial to pervasive dolomitization above the base of the ROZ, and a sequence of unaltered to anhydrite replaced to leached skeletal grains in the ROZ is seen. These changes are believed to be associated with “Mother Nature’s Waterflood” of the ROZ.

Oil and water samples from the pilot CO₂ flood have been collected and are being analyzed. Additional samples will be taken to help establish a base line for the fluids in a ROZ CO₂ flood. The team continues to monitor the progress of the CO₂ flood in Goldsmith Field. There has been a continued, significant increase in the production from the expanding pilot. The reservoir engineering data from Legado Resources has been transferred to the research team, and the Engineering Reservoir Characterization is in progress.

The team participated in a ROZ roundtable in October 2011 with representatives from 10 companies interested in or participating in ROZ CO₂ floods in the Permian Basin. The team presented a summary of the ROZ research being conducted under this project. A preliminary review of the core evaluation was presented at the West Texas Geological Society Fall Symposium in Midland in September.

Current Status (January 2012)
The project team continues core description of the ROZ. The cores from the GLSAU #190 and GLSAU #204R wells are being studied for similarities and differences in the depositional facies and diagenetic overprint among the Main Pay, Residual Oil Zone (ROZ), and Water Zone beneath the ROZ. Detailed core description for the #190 is near completion and description of the #204R has begun. Legado Resources indicated that additional older (1960’s vintage) cores have been located and would soon be made available.

The project team is investigating the use of a downhole sensor technique that is capable of diagnosing the presence of a variety of molecular components in the near wellbore fluids. The sensors are currently proprietary but are very small and can be conveyed on tubing strings in producing wells. With the goal of identifying MPZ vs. ROZ oil and water production, the technique may prove of extreme value. Innovative methods will have to be employed to transmit the data streams to the surface.

Legado Resources has made available to the project two separate wells perforated in only the ROZ interval. They recently put both wells on production test. Samples were gathered using some applications of conventional technologies (well site test separators, both pressurized and flash samplers) on the ROZ wells isolated from the MPZ. The samples are in hand and awaiting delivery to laboratories for specialized testing.

Project Start: October 1, 2010
Project End: February 24, 2013

DOE Contribution: $1,198,547
Performer Contribution: $654,563

Contact Information:
NETL – John Terneus (john.terneus@netl.doe.gov or 304-285-4254)
UTPB – Robert Trentham (trentham_r@utpb.edu or 432-552-2432)