CO2 WAG Huff-N-Puff for Waterflooded Conventional Reservoirs: Design and Field Learnings from Deployment in the Permian Basin of West Texas

Abstract

Abstract Single well Huff-N-Puff schemes have been attempted in waterflooded conventional reservoirs in the past, to limited success. The novelty of the method discussed in this paper is the inclusion of a water-injection cycle post CO2-injection "huff". Simulation models showed that this modification significantly increases the yield of incremental oil and increases retention of injected CO2 in the reservoir. A field experiment was designed and implemented in a San Andres field, using a specially designed CO2-gas lift bottom hole assembly that allowed injection and production with the same bottom-hole assembly. This design reduced the need for workover operations between production and injection cycles, as well as allowing injection and production logging of the reservoir zone to better understand the results of the process. We describe the design process for a cyclic CO2-alternating-water injection scheme for waterflooded conventional reservoirs from simulation to field execution. We also discuss operational learnings and resulting best practices for artificial lift, three-phase separation, and well testing that were developed for this recovery method. Results from the field pilot yielded peak incremental oil production rates over six times above the baseline water flood at the producer-well level. Additionally, the gas-lift assembly proved effective in allowing real-time wellbore monitoring, which greatly enhanced the understanding of the CO2-HnP in a single-well system.