Rock-Fluid Characterization for Miscible CO2 Injection: Residual Oil Zone, Seminole Field, Permian Basin

Abstract

Low to moderate remaining oil saturation exists in deeper zones of several Permian Basin oil reservoirs. The Residual Oil Zone (ROZ) in the Seminole San Andres Unit (SSAU) is found below its traditional producing oil-water contact and contains significant (20-40%) immobile oil. ROZ production is not technically or economically feasible through primary or secondary oil recovery mechanisms. However, miscible flooding with carbon dioxide, CO 2 , has emerged as a viable enhanced oil recovery mechanism with a high potential to mobilize significant portions of this resource. Reliable rock and fluid characterizations are critical to evaluate the CO 2 flood potential and an optimum design of CO 2 flood strategy.The critical rock-fluid parameters and processes influencing the feasibility of producing the remaining oil in the ROZ are:Reliable estimates of Remaining Oil Saturation (ROS) -obtained from pressure core, sponge cores and laboratory waterflood tests at reservoir conditions Characterization of formation anisotropy and scale-dependency of permeability through whole core analysis and potential formation damage during CO 2 flood Residual oil saturation to miscible CO 2 flood (Sorm)-obtained from miscible CO 2 flood tests at reservoir conditions using live oil and field observation Reservoir oil/ CO 2 PVT properties -obtained by basic oil PVT tests, oil swelling and multi contact tests Minimum miscibility pressure to CO 2 -obtained through slim tube and coreflood laboratory CO 2 flow tests Equation of state compositional fluid characterization to capture key mechanisms of CO 2 miscible flooding Compositional CO 2 flood simulation using geocellular models and the above rock and fluid data and models Significant variation in remaining oil saturation of 20-40% were observed field-wide in ROZ, but through data integration, it was shown that the most probable average value of the remaining oil saturation is 28-32%. The residual oil saturation to waterflood from centrifuge imbibition capillary pressure tests were shown to be in the range of 20-28% with an average of 25%. Residual oil saturation to miscible CO 2 flood was measured in 6.0" to 12.0" long core composite found to be moderately low, ~12%. Coreflood tests showed no formation damage due to CO 2 injection after water flooding but significant porosity and permeability enhancement during WAG process. Laboratory measurements showed that the MMP of ROZ oil with CO 2 is below the current reservoir pressure and the oil swelling is nearly 75%. This result indicates that miscibility development is achievable under current operational conditions. However, there is a possibility of a second liquid phase, rich in CO 2 appearing over a small pressure window, that may complement the miscible recovery process through liquid-liquid extraction. Compositional simulation with reliable rock and fluid data input was used in the design and implementation of the CO 2 flood in Seminole ROZ.Significant improvement in data quality and reduction in rock and fluid data uncertainty for miscibl...

Residual Oil Saturation Determination for EOR Projects in a Mature West Texas Carbonate Field

“…Unlike a conventional oil reservoir in which the higher oil saturations would be located close to the POWC, there is no such trend in the ROZ data, and the higher oil saturations can be found in the middle and bottom of the ROZ also. A similar distribution in ROZ oil saturations has been noticed in other West Texas fields also but the average saturations were higher (Honarpour 2010).…”

“…ROZ's in other West Texas fields have been shown to have areas with thick transition zones with high oil saturations and other areas with lower oil saturations (Hsu et al 1997). A recent paper (Honarpour et al 2010) showed that oil saturations in the ROZ can range between 20-40% with an average around 28-32%. It is critical to assess the ROZ oil saturation because low saturations will make the project uneconomic while higher oil saturations will lead to a successful project.…”

Technical Challenges in the Conversion of CO2-EOR Projects to CO2 Storage Projects

“…The following is a summary of some CO 2 -EOR pilots and projects targeting the ROZ paleo oil in Permian Basin, west Texas , Honarpour et al 2010Koperna et al 2006):…”

A data analysis of immiscible carbon dioxide injection applications for enhanced oil recovery based on an updated database

“…Several empirical correlation have been developed along the year to predict CO 2 solubility in crude oil and oil swelling [22][23][24]. CO 2 -Oil interaction using reservoir simulation and computer modelling have been studied using basic black oil reservoir models, and also complex models that can distinguish the different phases and the interfacial tension [25][26][27]. Recently, a more complex computer modelling technique referred to as Gene Expression Programming was used to develop a novel correlation used to determine CO 2 swelling in oil as a function of oil MW, oil specific gravity, reservoir temperature, bubble point pressure, and saturation pressure [28].…”