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 simulations 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 carbon dioxide 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 ongoing 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 they affect 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 MPZ, the ROZ, and the interval below the ROZ, suggesting that the ROZ has undergone a different diagenetic history than the MPZ. Additionally, diagenetic “markers” were seen in core from ROZs in other fields that indicated the presence of native sulfur in voids near the base of the 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 within the ROZ from an unaltered interval to anhydrite replaced with leached skeletal grains. 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 baseline 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.

Core descriptions of five of the six available cores taken by Legado have been completed.

The team completed the history match of past oil, water, and gas production for the SADR Formation in the central portion (the ROZ CO₂ Pilot Flood Area) of the Goldsmith Field. The collected information (geologic, reservoir, and production performance) was input into the reservoir model to ensure the simulations are reflective of past history.

The team completed the initial reservoir simulation of the ROZ CO₂ flood using GEM. The results of this simulation are being used to compare the actual results being attained in Legado’s 4-pattern ROZ CO₂ flood at Goldsmith with the model input data and results (such as CO₂ injectivity, early time water, and oil and CO₂ production).

The various next generation production technologies were reviewed and evaluated for possible field application. A novel CO₂ gas lift has now been implemented and has demonstrated success in increasing production while decreasing costs.

Current Status (January 2013)
A meeting with project team members and Legado Resources was held in Houston in August 2012 to review progress and further plan the reservoir characterization, reservoir simulation, and production analysis activities. In addition to thoroughly reviewing the core descriptions, the team brainstormed the development of an oil/gas sampling procedure for obtaining ROZ information which has never been collected before now. The team decided during the meeting to change the way the initial saturation conditions in the model were set up as the different options available for initialization in the reservoir simulator GEM were not adequately representing the true conditions. In order to replicate lower initial oil saturation (40%) in the ROZ as compared to the initial oil saturation in the MPZ, water was assumed to be injected into the ROZ to simulate the natural waterflood (Mother Nature’s Waterflood) which has been modeled to have occurred over a span of 15 million years.

The Goldsmith ROZ field area characterization and geologic modeling are in progress. Although five of the six cores originally identified as available for study have been characterized, two additional wells have been cored by Legado and four cores originally taken by Amoco during the waterflood development in the 1960s have been located. These are considered to be important to the study, and will be characterized during the second year of the project. Oil recovered from core will be tested to provide additional data on the composition of oil in the ROZ. 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 gathered from the ROZ wells isolated from the MPZ are available and awaiting specialized laboratory testing and analysis.

Project Start: October 1, 2010
Project End: March 31, 2014

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)