CO2 IOR Evaluation for the U.S. Rocky Mountain Assets

Abstract

CO2 flooding has become the fastest growing gas injection EOR method, contributing 4.8% of U.S. oil production. An integrated approach was undertaken to evaluate the CO2-EOR feasibility for Marathon's Rocky Mountain (RM) region assets. The RM assets of the Wind River and Big Horn basins were evaluated using detailed geological and compositional reservoir models imposed with multiple development scenarios. The fractured nature of the RM assets posed a challenge for reservoir modeling, which prompted combinations of approaches such as production ranking to facilitate fracture descriptions. Extensive laboratory CO2-oil PVT tests were also conducted to tune a representative equation-of-state fluid model to confidently quantify reservoir fluid behavior. CO2 injection scenarios for two oil fields were evaluated using compositional dual-porosity and dual-permeability reservoir models. Performance evaluation under multiple sensitivities, namely WAG ratio, fluid properties, injection pressures, and fracture characteristics were also investigated to quantify their impact on oil recovery factors. The simulation recovery results were non-dimensionalized to generate distinct type-curves, which were then applied to areas that have similar fracture and geological characteristics. The unique workflows generated during this study were verified and benchmarked by using them to history match the performance of an analogous RM field currently under CO2 injection. This paper describes the integrated approaches applied to maturing RM assets, which in addition to identifying significant IOR potential, have helped enhance the reservoir's characterizations, standardize subsurface workflows, aid facilities design, and scale-up performance data for optimal reservoir management. 1. Improved Oil Recovery In 1978, the United States Congress commissioned the Office of Technology (OTA)(1) to evaluate the state of the art in U.S. oil production. The OTA concluded that the 300 billion barrels of known U.S. oil were economically unproducible by conventional methods in practice at that time. The OTA report also evaluated a range of enhanced oil recovery (EOR) techniques and their potential for improving the prospects of extracting a sizeable fraction of this known resource base. These major political and administrative amendments triggered increased interest in EOR in late 70's and early 80's, most notably in California and the Permian Basin of West Texas. Now, 30 years later, there is again a strong interest in improving domestic oil production(2), which has been on a continuous decline of approximately 3% per year (Figure 1)(3), while the total 'unproducible oil' referred to in the OTA report(1) has increased to a whopping 400 billion barrels(4). The U.S. Geological survey reported(5) that the bulk of the conventional oil yet to be produced in the world resides in already discovered reservoirs, with the ever decreasing possibility of finding newer reserves. The most important conclusion of this report, from an oil self-reliance point of view, is that the EOR techniques have not been tried for most of these reservoirs. Therefore, the potential for EOR applications in the U.S. is very large with a target of approximately 400 billion barrels(6).

Enhanced Oil Recovery: An Update Review

“…Mexico (Muro et al [161] and the U.S. [147,163] are just few examples of countries evaluating CO 2 sources and EOR potential in mature fields and mature CO 2 floods [164]. However, this will be further discusses in the section of EOR gas methods in carbonate formations.…”

Estimation of The Wells Hydrodynamic Drag Level Based on Wells Geophysical Survey Data

“…Moreover, the methods should be based on the use of current field-geological information available. Some issues of solving this important problem of decisions substantiation based on current information from specific fields were considered in works [10][11][12][13]. However, the use of these results in other fields requires justification and adaptation.…”

Enhanced Oil Recovery Practices: Global Trend, Nigeria’s Present Status, Prospects and Challenges

“…Trinidad also has been operating CO 2 gas injection projects for more than three decades; CO 2 is sourced from an ammonia plant near the fields [26]. Few examples of countries evaluating CO 2 sources and EOR potential in mature fields are Mexico [26] and the U.S. [20,27].…”