Horizontal Well Design to Optimize CO2 Sequestration and Oil Recovery in the Permian

Abstract

Abstract This paper presents a reservoir modeling study about positioning horizontal wells to optimize carbon sequestration and oil recovery simultaneously in the Wasson field, which is one of the largest reservoirs in the Permian Basin with 6 billion barrels of original oil in place. A significant portion of this field has been under CO2 injection for enhanced oil recovery for decades, so the CO2 gathering, processing, and distribution network in the area makes the Wasson area extremely cost-competitive as a CO2 storage site. Transitioning the source of CO2 injected in the Wasson area from natural to anthropogenic has the potential to sequester hundreds of millions of metric tons of carbon in the coming decades. Although the traditional development strategy has achieved attractive economic returns in the better-quality rock, novel well configurations are needed to be economically successful as development is expanded to areas with lower rock quality. We used a compositional, history-matched reservoir model to perform a sensitivity study of lateral section length, horizontal orientation, spacing, and vertical placement for both production and injection wells. We also studied the vertical placement of the wells with respect to the main oil column (MOC) and the residual oil zone (ROZ), a distinctive characteristic of the Permian Basin. In all the scenarios, the MOC is to be co-developed with the ROZ. Since our focus was on the lower-quality rock areas, we selected horizontal wells due to their success in the cost-effective development of tight reservoir rocks. The significant remaining greenfield potential in the Wasson area offers an opportunity for a complete revolution of the development strategy from vertical to horizontal wells. The most important finding of this study is that the vertical placement of the horizontal injector has a significant effect on oil recovery and lifecycle CO2 retention. Placing the injector close to the bottom of the ROZ and the producers in the MOC resulted in the highest carbon sequestration. The optimized case improved CO2 sequestration by 40% over the base case. The absence of significant vertical flow barriers in the area, along with our prior understanding of the reservoir heterogeneity and CO2 phase behavior, enabled us to optimize well placement to take advantage of gravity drainage. This configuration exposed a larger section of the reservoir volume to the injectant, resulting in a higher sweep efficiency. Our work provides relevant guidance on the design of future developments using horizontal wells to optimize carbon sequestration and incremental oil recovery simultaneously during CO2 EOR and carbon capture, use, and storage (CCUS) projects. These findings are likely to lead to technical and economic success, even in the poor rock quality areas in the Wasson reservoir, significantly increasing the sequestration and oil recovery potential of this field.