Assessment of Miscible EOR in a Giant Offshore Carbonate Reservoir

Abstract In this paper we present a comprehensive assessment of the EOR potential in a giant off shore carbonate reservoir including a novel screening methodology to assess reservoir, fluid and miscible characteristics across various reservoir and geologic units. We employed a multi-disciplinary approach to identify potential pilot locations within the leading geologic and reservoir units and assessed the miscible EOR uplift through both an analytical assessment of potential to screen for the broad uplift within the targeted geologic areas and developed compositional simulation models for the pilot areas utilizing a history matched simulation model to estimate the uplift for the specific pilots. In this paper we utilize a quantitative estimate of incremental EOR potential utilizing an analytical estimate of sweep efficiency which is based on the viscous to gravity ratio (VGR) coupled with SCAL measurements of the remaining oil saturations to estimate the uplift from miscible EOR based on core flood results using hydrocarbon separator gas, CO2 and enriched hydrocarbon separator gas. To identify pilot areas within the leading geologic areas, a multi-disciplinary Task Force spanning Field Development, Projects, Drilling, Well Operations and Facilities was formed. Key assessment criteria include pilots are geologically representative of the broader geologic area, pilots are aligned with field development plans, pilots are sourced from drilling and production centers (in this case artificial islands) with appropriate facilities (including corrosion resistant alloys if required), pilots are optimally located considering drillability and anti-collision, and pilot areas are of higher maturity such that field implementation can be expedited. Identified pilot areas were then assessed for miscible EOR uplift utilizing a history matched compositional simulations with a tuned Equation of State (EOS). Sector models for the pilot areas were created to investigate the uplift in incremental recovery under various WAG ratios, gas injection schemes, injection gas timing and PV injected. In summary, a unified methodology was created to access miscible EOR potential, rank various reservoir and geologic areas, specific pilot areas were identified, and miscible EOR potential was quantified for the identified pilot areas using compositional simulations based on a tuned EOS and history matched simulation model.