|Case Studies of the ROZ CO2 Flood and the Combined ROZ/MPZ CO2 Flood at the Goldsmith Landreth Unit, Ector County, Texas
||Last Reviewed 6/24/2013
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.
The University of Texas of the Permian Basin, Midland, Texas 79707-1423
Legado Resources, The Woodlands, Texas 77380-1921
Melzer Consulting, Midland, Texas 79701
Advanced Resources International, Arlington, Virginia 22203-1661
Although much of the field characteristics and oil recovery data accumulated over the 40-year history of carbon dioxide enhanced oil recovery (CO2-EOR) research and practice are available, the work exclusively represents studies of the main payzones and there are no publicly available geologic and reservoir characterization data on residual oil zones (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 intervals below existing fields that are productive of only water but have significant immobile oil saturation. In addition, there are areas within ROZs where no major fields are present. A number of ongoing industry pilot and demonstration projects are beginning to provide data on the feasibility of recovering as much as 30 percent of these resources. In the Permian Basin, CO2 flooding of ROZs has been in the demonstration 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 are 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.
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 (SADR), 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 CO2flood 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.
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 anaerobic processes 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 continuous, significant increase in the production from the expanding pilot. The reservoir engineering data from Legado Resources have 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 2011.
Core descriptions of five of the six available cores taken by Legado have been completed.
The research 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 (June 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 percent) 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
NETL – John Terneus (firstname.lastname@example.org or 304-285-4254)
UTPB – Robert Trentham (email@example.com or 432-552-2432)