Proxy Equation Using Data Analysis for Benchmark Recovery Factor Estimation in Gas Cap Reservoir

Reservoir Performance Benchmarking (RPB) is a proprietary tool developed by PETRONAS for Malaysian Oil reservoirs which uses a combination of analytical equations and data driven approach to compute Reservoir Complexity Index and Benchmark Recovery Factor. Reservoir benchmarking tool considers water injection in an oil reservoir to evaluate potential recovery factor based on data analytics algorithm which has been calibrated to good performing oil reservoirs of Malaysia. However, for reservoirs with gas cap, the benchmark recovery factor has been observed to be overestimated. This necessitated requirement of a correction factor to be included in tool algorithm for benchmark recovery estimation in oil reservoirs with a gas cap. For reservoirs having current pressure below original bubble point, correction factor is being applied for opportunity validation to account for changes in fluid PVT properties (SPE-202459). For gas-cap reservoirs, an additional correction factor needs to be computed to account for reduction in recovery factor due to presence of gas-cap. This paper describes the methodology for computation of correction factor for gas-cap reservoirs which involves three key steps. Step-1 focuses on selection of key reservoir parameters which may impact oil recovery under water flood mechanism in gas cap reservoirs. Step-2 outlines generation of test experiments with a range of values of identified reservoir parameters that can be used as a sample database of results. Step-3 defines a proxy equation using reservoir parameters and obtaining a good match to actual test results for correlation validation. With these three steps, a correlation has been developed for estimation of correction factor. This paper illustrates the methodology of computing this correction factor through application of simple simulation models for test experiments and generation of proxy equations using data analysis tools of python and numerical simulation applications. The paper also outlines the impact of this correction to opportunity volumes identified through benchmarking tool in Malaysian reservoirs. Although the methodology has been developed for correction to benchmark recovery factor, it can also be applied to other oil reservoirs as well. In addition, this correlation also provides a quick assessment of recovery factor for water flood application in a gas cap reservoir.