Polymer Flooding in a Major Carbonate Reservoir Using High-Salinity Water: Promising Pilot Results and Techno Economic Evaluation for the Umm Gudair Minagish Oolite Reservoir in West Kuwait

Abstract

A significant portion of the world's oil reserves are trapped in carbonate reservoirs, many of which are located in the Middle East. Polymer EOR in the carbonate reservoirs tends to be challenging due to limited injectivity and reservoir heterogeneity. This paper presents field results of a successful polymer EOR pilot in the Umm Gudair Minagish Oolite (UGMO) reservoir using treated effluent water at a salinity of up to 257,000 ppm and a reservoir temperature of 72°C. A suitable polymer was identified for UGMO polymer EOR based on extensive laboratory evaluation. Work was then geared towards the implementation of a pilot, mainly to de-risk polymer injectivity using an injector and an offsetting producer located nearly ~87m away. Before starting the pilot operations, a representative sector reservoir model was extracted, history-matched and calibrated using available data to design the envisaged pilot. Thereafter, pilot operations were carried out to generate reliable data using a fit-for-purpose surveillance program and surface facility. The acquired field data were then used to calibrate a high-resolution reservoir simulation model that was used for techno-economic optimization. Based on actual field data, it was observed that polymer injectivity far exceeded original simulation-based expectations. Field operations indicated limited polymer dissolution time, in the range of 1 to 2 hours, despite the extremely high-salinity effluent water that was used. Injected polymer concentration was progressively increased, reaching 2,500 ppm and a surface viscosity of 17 cP, at an injection rate of 3,500 BPD, while staying below the pre-defined maximum allowable injection pressure. Polymer breakthrough was detected at the nearest producer after approximately 3 months of polymer injection, thus indicating favourable sweep efficiency. Resistance factors were found to be more responsive to variations in injection rates as opposed to polymer concentrations as evident from downhole pressure data. Calculated in-situ viscosities were within the expected range and the injected polymer solution demonstrated non-Newtonian pseudo-plastic behavior in line with previously acquired lab data. Based on downhole pressure data, polymer injection was maintained under matrix conditions with no evidence of induced fractures. High-resolution reservoir simulation results indicate promising techno-economic results in terms of oil recovery and cost, thus indicated the feasibility of achieving a Unit-Technical-Cost (UTC) of approximately $20.5/incremental barrel of oil over a waterflood infill case. This paper sheds light on the feasibility of polymer-flooding for a deep carbonate reservoir, using extremely high-salinity effluent water, at a reservoir temperature of 72°C. Techno-economic evaluation of field results is promising. Work is in progress to pave the way for UGMO phased commercial polymer-flooding development on a fast-track basis.