Cyclic Gas Injection EOR Pilot in Tight Viking Sand Pool

Abstract The primary goal of this project was to prove the feasibility of a Cyclic Gas Injection/Production (Huff & Puff) enhanced oil recovery (EOR) scheme and evaluate its economic viability in the Viking formation in Saskatchewan, Canada. Historically, the Viking formation has challenging waterflood economics due to limited injectivity into the tight sand reservoir and formation damage caused by movable and swelling clays. The objectives were to test horizontal well injectivity at desired pressures, assess the use of produced gas injection to repressurize the extremely depleted Viking reservoir, evaluate enhanced oil recovery with various inter-well spacings, and to optimize injection and production cycle lengths. This pilot was designed by utilizing analytical evaluation and numerical simulation. The Huff & Puff pilot consists of four 0.7 mile (1100 m) horizontal wells with two different inter-well spacings; 667 ft vs 1333 ft (200 m vs 400 m). The pilot consisted of two parallel horizontal well pairs, which were designed to alternate injection and production cycles. A detailed reservoir surveillance program was implemented to collect extensive data, including reservoir and wellhead pressures, gas composition analysis, production and injection rates of the pilot wells, and the production rates of surrounding wells to evaluate reservoir response and pilot performance. Whitecap has been operating this pilot project since its initiation in September 2021 with technical success. Six Huff & Puff cycles with varying durations, between one to three months on injection, have been completed without major operating issues. Per-well injectivity has reached higher than designed 750 Mscf/d (21 e3m3/d) at desired surface pressures. Through the course of six injection cycles, average reservoir pressure has increased from an initial 174-319 psi (1.2-2.2 MPa) to 623-885 psi (4.3-6.1 MPa). The incremental oil recovery factor for the pilot area is expected to be 1%, which is considerable for a reservoir with typical primary recovery factors expected to be only 6-8%. The gas injection has resulted in production increases in some offset wells, and a higher degree of gas breakthrough has been observed in the section with 667 ft (200 m) well spacing. The 3-month injection cycle has resulted in the largest incremental recovery and cycle time optimization efforts are ongoing. The pilot results are encouraging, indicating that a cyclic gas injection EOR scheme could have potential for further commercial expansion. The pilot has demonstrated Huff & Puff's potential economic viability as an EOR scheme for the tight Viking sand formation, which is one of the most prominent producing formations with low oil recovery factors in the Western Canadian Sedimentary Basin (WCSB). There is no such published pilot information available before. Detailed pilot design, production performance evaluation and learnings are presented in this paper.