ADVANCED OIL RECOVERY TECHNOLOGIES FOR IMPROVED RECOVERY FROM SLOPE BASIN CLASTIC RESERVOIRS, NASH DRAW BRUSHY CANYON POOL, EDDY COUNTY, NM

The Nash Draw Brushy Canyon Pool in Eddy County New Mexico was a cost-shared field demonstration project in the U.S. Department of Energy Class III Program. A major goal of the Class III Program was to stimulate the use of advanced technologies to increase ultimate recovery from slope-basin clastic reservoirs. Advanced characterization techniques were used at the Nash Draw Pool (NDP) project to develop reservoir management strategies for optimizing oil recovery from this Delaware reservoir. The objective of the project was to demonstrate that a development program, which was based on advanced reservoir management methods, could significantly improve oil recovery at the NDP. Initial goals were (1) to demonstrate that an advanced development drilling and pressure maintenance program can significantly improve oil recovery compared to existing technology applications and (2) to transfer these advanced methodologies to other oil and gas producers. Analysis, interpretation, and integration of recently acquired geological, geophysical, and engineering data revealed that the initial reservoir characterization was too simplistic to capture the critical features of this complex formation. Contrary to the initial characterization, a new reservoir description evolved that provided sufficient detail regarding the complexity of the Brushy Canyon interval at Nash Draw. This new reservoir description was used as a risk reduction tool to identify ?sweet spots? for a development drilling program as well as to evaluate pressure maintenance strategies. The reservoir characterization, geological modeling, 3-D seismic interpretation, and simulation studies have provided a detailed model of the Brushy Canyon zones. This model was used to predict the success of different reservoir management scenarios and to aid in determining the most favorable combination of targeted drilling, pressure maintenance, well stimulation, and well spacing to improve recovery from this reservoir. An Advanced Log Analysis technique developed from the NDP project has proven useful in defining additional productive zones and refining completion techniques. This program proved to be especially helpful in locating and evaluating potential recompletion intervals, which has resulted in low development costs with only small incremental increases in lifting costs. To develop additional reserves at lower costs, zones behind pipe in existing wells were evaluated using techniques developed for the Brushy Canyon interval. These techniques were used to complete uphole zones in thirteen of the NDP wells. A total of 14 recompletions were done: four during 1999, four during 2000, two during 2001, and four during 2002-2003. These workovers added reserves of 332,304 barrels of oil (BO) and 640,363 MCFG (thousand cubic feet of gas) at an overall weighted average development cost of $1.87 per BOE (barrel of oil equivalent). A pressure maintenance pilot project in a developed area of the field was not conducted because the pilot area was pressure depleted, and the reservoir in that area was found to be  compartmentalized and discontinuous. Economic analyses and simulation studies indicated that immiscible injection of lean hydrocarbon gas for pressure maintenance was not warranted at the NDP and would need to be considered for implementation in similar fields very soon after production has started. Simulation studies suggested that the injection of miscible carbon dioxide (CO2) could recover significant quantities of oil at the NDP, but a source of low-cost CO2 was not available in the area. Results from the project indicated that further development will be under playa lakes and potash areas that were beyond the regions covered by well control and are not accessible with vertical wells. These areas, covered by 3-D seismic surveys that were obtained as part of the project, were accessed with combinations of deviated/horizontal wells. Three directional/horizontal wells have been drilled and completed to develop reserves under surface-restricted areas and potash mines. The third well has not been on production long enough for an accurate assessment but initial results from it are encouraging. Cumulative production from the first two wells through August 31, 2005 was 235,039 BO, 816,592 MCFG and 310,333 barrels of water (BW). Total estimated reserves from all three of the horizontal wells are 878,135 BO and 3.87 BCFG. The ratio of net revenue to cost for the first two wells is approximately 2.9 to 1 for an oil price of $30 per barrel that existed when the wells were drilled. Based on recent pricing trends, a detailed reserve study for the project was performed that assumed an oil price of $40 per barrel and a gas price of $7 per MCFG. These results show that this project has acceptable economics and similar projects can be economically developed as long as oil and gas prices remain over $30 per BOE. The nine wells that were part of the DOE Class III project have produced 526,947 BO and 3.04 BCFG. Ultimate recovery from the nine project wells is projected to be 1.3 million barrels of oil and 6.73 BCF natural gas. Using a 6 to 1 ratio gas to oil, this equates to 2.35 million BOE. The before tax return on investment for the project is slightly in excess of three to one, and taxes and royalties from the project will generate almost three times the DOE contribution to the project.

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