A technical turning point-based framework to optimize CO₂ EOR-storage: Capacity dynamics of Brownfield Residual Oil Zones

Residual Oil Zones (ROZs) contains considerable oil at residual saturation underlying Main Pay Zones (MPZs), which renders its development challenging in conventional manner. Enhanced oil recovery (EOR), for example, CO₂ injection is therefore introduced. This technique unleashes the potentials of ROZs in terms of EOR and carbon storage. In field-scale simulation regard, although some researchers have investigated the effects of several operational variables such as well pattern, perforation interval, injection mode and injection strategy, on CO₂ EOR-storage performances, no published work attempts to reveal the EOR-storage capacity dynamics/variations of Brownfield ROZ reservoir upon its development. By addressing the questions: (1) when to start considering ROZ expansion beyond MPZ; (2) the timing when to perform ROZ expansion that could maximize the profit; (3) whether ROZ expansion always benefits the project; (4) what development strategy is more favorable given a certain CO₂ availability, this paper reveals the incentives of when to include ROZ into CO₂ EOR-storage project beyond MPZ in development strategy regard. Based on the envisioned technical turning point where ROZ outperforms MPZ assuming propensity to oil production, novel performance metrics—ROZ oil production critical point (ROZ-OPCP) and ROZ opportune oil production trade-off point (ROZ-OOPTP), are brought up to technically optimize the development strategy design of Brownfield ROZ reservoir, upon which a resultant designing framework is established. The concepts and framework are envisioned to facilitate development strategy configurations, narrow down the target range for optimization, reduce the cost of trial-and-error and therefore promote the Carbon Capture and Storage (CCS). Simulation study also provides following insights on CO₂ EOR-storage in Brownfield ROZ reservoir: (1) above ROZ-OPCP, the development of ROZ beyond MPZ is technically feasible under moderate and sufficient CO₂ supply case since positive surpluses in EOR-storage are observed. Project could benefit most from sequential and simultaneous MPZ-ROZ development under moderate and sufficient CO₂ supply case, respectively; (2) ROZ expansion without considerable CO₂ availability and opportune timing could technically and economically impair the project, and ROZ-OOPTP needs to be considered herein; (3) Designing CO₂ injection scenarios requires compromises. e.g., Higher injection rate in ROZ increases CO₂ storage and brings forward the peak EOR-storage performance, while the lower injection rate prolongs the desirable EOR-storage performance; (4) The envisioned technical turning point and the CO₂ EOR-storage capacity dynamics may strongly depend on original quality of ROZ and the current usage of MPZ, and less usage would lead to later occurrence of technical turning point.