The paper demonstrates a robust and efficient screening workflow and methodology that identifies reservoir candidates for improved oil recovery/enhanced oil recovery (IOR/EOR) methods. This workflow integrates rigorous analysis of production/injection data with understanding of reservoir geology and petrophysics. Firstly, based on screening criteria including reservoir properties and volumetric estimates, the reservoirs were studied and ranked. The screening study was supported by incorporating the evaluation of geological framework, facies distribution, and flow barrier. Secondly, the reservoir drive mechanism was investigated through MBAL study. Thirdly, various production performance plots were generated to evaluate waterflood performance. The diagnostic plots included hydrocarbon production rate, water injection rate, gas oil ratio (GOR), number of active oil producers versus time; and water oil ratio, hydrocarbon production rate, water injection rate versus cumulative oil. The ABC (after before compare) plot was also analysed to identify the regions for IOR/EOR opportunity. Simple gas/chemical EOR feasibility studies were also performed based on reservoir static and dynamic data available.
Fifty (50) mature oil reservoirs were ranked and the high potential reservoirs for IOR/EOR were identified. Considering gas EOR opportunity, the key parameter under study was the minimum miscibility pressure (MMP), mobility ratio, GOR and reservoir pressure. Diagnostic plots were generated to assist in the analysis of waterflood response. A plot of water oil ratio with cumulative oil led to a conclusion to maintain the WOR to follow a specific trend. The time needed to re-pressurize a reservoir was considered in addition to evaluating geological heterogeneities and sand continuity to determine if certain IOR methods will be effective and economic. Through this workflow, additional IOR/EOR opportunities were identified to increase production and/or extend the reservoir life. The reservoir analysis has indicated the reservoirs under study have a high side opportunity of adding over 5.4 MMKLS of recovery through effective reservoir management.
The waterflood performance review and IOR/EOR screening workflow incorporates geological aspects along with static, dynamic, and operational parameters, which is appropriate for a large number of reservoirs underconsideration. These insights, evolved from practical field experiences, are beneficial for revitalizing mature water floods, and more importantly the design and implementation of suitable EOR pilots.