Optimization of Infill Development in a Highly Heterogeneous Giant Offshore Carbonate Reservoir

摘要

The subject field is a highly heterogeneous giant offshore reservoir. Current field development is predicated upon line drive water injection with 1 km spacing; however, it is anticipated that some oil will be bypassed due to geologic heterogeneity. In order to address the bypassed oil and improve recovery, a simulation study evaluating infill well potential for the target reservoir and an optimization of the full field development plan with infills was carried out. This reservoir consists of two geologically similar areas which are a "Homogeneous" area and a "Heterogeneous" area. High permeability streaks (HKS) having ten times higher permeability than the matrix permeability are dominant in the Heterogeneous area while HKS are significantly less prevalent in the Homogeneous area. Two sector models which represent the Heterogeneous and the Homogeneous areas were generated and sensitivity simulations were carried out to evaluate the vertical and lateral placement of infills. Based on sector model findings, full field simulations were carried out to generate an optimized full field development plan with infills. As a result of sector model simulation for the Heterogeneous area, infill wells showed higher recovery relative to the "No Infill" base case. Vertical and lateral well placement on infill location had little impact on the oil recovery. This is because the HKS in the upper layers were water-saturated by historical water injection from the base 1 km development; hence, water breakthrough at infill wells occurred from HKS within a short period of time wherever infills were drilled. For the Homogeneous area, infill wells showed slightly higher recovery but no oil plateau extension and high water production relative to the "No Infill" base case. Based on these findings it was concluded that (i) infills were required for Heterogeneous area and (ii) infill are not recommended for the Homogeneous area. For the full field evaluation, three different infill scenarios (i.e. 500m spacing infill implementation, 375m spacing infill implementation and no-infill implementation) were evaluated. The optimal infill development scheme for each pattern was chosen by comparing the production performance of each pattern of these three simulations. As a result, in the optimized infill case, infill wells were required primarily in the Heterogeneous area and were not required for the Homogeneous area. Through this analysis, the impact of geological heterogeneity on the performance of infill wells and incremental oil recovery was assessed and the full field development plan was significantly improved. Based on these findings the resulting full-field development plan (i) minimizes the number of infill wells required, (ii) optimizes incremental oil production by addressing the bypassed oil.