NETL-Sponsored Study Confirms Vast Energy Resource in Residual Oil Zones


A geologic core extracted from a West Texas well and analyzed by researchers sponsored by the National Energy Technology Laboratory (NETL) has confirmed that carbon dioxide enhanced oil recovery (CO2-EOR) can "push out" oil from largely untapped areas called residual oil zones (ROZs). This finding further demonstrates that these zones hold the potential to harvest billions of barrels of additional oil that could increase domestic supply, reduce imports, and increase U.S. energy security. Residual oil zones are areas of immobile oil within an oil-bearing reservoir that are found below the oil-water contact (the first observance of water). In these zones, natural water flooding has swept away much of the original oil, leaving the residual oil behind. Recovery of the oil in these zones is not economic using primary or secondary oil recovery; enhanced oil recovery techniques, such as CO2-EOR, are needed to successfully produce it. In the NETL-sponsored project, a research team led by the University of Texas-Permian Basin (UTPB) analyzed a geologic core taken during a pilot test from a well at the Goldsmith Landreth San Andres Unit in the Permian Basin, Ector County, Texas. The results provide unique insights into the potential oil displacement efficiency of the CO2-EOR process. The analysis confirmed significant reductions in ROZ oil saturation (oil left within the formation) in the upper section of the ROZ; nearly 40 percent of the post-CO2 flood samples measured below 15 percent residual oil saturation, compared to less than 2 percent of the pre-CO2 flood samples. The analysis also showed an increase in oil saturation in the lower section of the ROZ, indicating the formation of an oil bank as a result of CO2-EOR. The project builds on earlier UTPB findings that focused on understanding and modeling fluid flow within ROZs in the Artesia Fairway—a dolomitized trend in the San Andres formation containing oil-producing fields—in eastern New Mexico and west Texas. In those findings, UTPB researchers discovered that oil saturations in ROZs range from 20 percent to 40 percent. As part of the Energy Department's ROZ research, UTPB researchers are developing a state-of-the-art geologic model to compare past reservoir performance and current CO2-EOR flood performance using numerical simulation models. Their goal is to optimize the technical and economic performance of an ROZ CO2 flood and transfer the resultant knowledge to other operators. Data acquired from the core, in conjunction with an ongoing study to evaluate the effectiveness of CO2-EOR in an ROZ, clearly demonstrate the potential to move, and eventually recover, significant amounts of oil contained in the ROZ. The body of data accumulated over the 40-year history of CO2-EOR research is almost exclusively limited to areas called main pay zones, where oil is more easily recovered. Although nine industry CO2-EOR pilot projects are currently underway in ROZs in the Permian Basin, very little geologic, reservoir, or fluid characterization ROZ data is publicly available, nor are any comprehensive field studies of CO2 EOR projects in ROZs. Multiple studies supported by the Energy Department, continue to shed new light on ROZs for both EOR and carbon storage.



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