A Comprehensive Simulation Study of Polymer Enhanced CO2 Injection in Light Oil Reservoirs

Abstract

Abstract Water-Alternating-Gas (WAG) injection has been widely implemented to improve volumetric sweep efficiency from gas injection alone. However, the WAG still suffers from gravity segregation, especially in thick and heterogeneous reservoirs with large well spacing. This study aims to investigate suitable Enhanced Oil Recovery (EOR) injection strategies for light oil reservoirs in Southeast Asia. The new injection techniques, such as Polymer-Alternating-Gas (PAG) and co-injection of CO2 with water/polymer, are also included. The study uses the real geological model in Thailand's oilfield and the INTERSECT software to fully integrate the physics modeling of fluid composition and polymer properties. The reservoir oil is characterized based on actual PVT data and has a viscosity of 0.3 cP at reservoir conditions. The injection strategies performed in this study are water, polymer, CO2, WAG, PAG, co-injection of CO2 and water, and co-injection of CO2 and polymer. The sensitivity of CO2 injection rate, WAG sequences, and polymer concentration on recovery efficiency are also investigated. Various EOR injection strategies are evaluated by using the history-matched model and compared with a waterflood case. The continuous CO2 injection at 4 MMscf/D yields an additional oil recovery factor of approximately 2.7%. The co-injection of CO2 with water and polymer can recover the oil additionally from waterflood by 3.0% and 2.9%, respectively. The benefit of co-injection methods is that the water/polymer co-injection helps maintain reservoir pressure after gas breakthrough at producers. Due to the reservoir dipping, the CO2 injection from updip location is promising because of the gravity-assisted effect. From the sensitivity analysis, the increase in CO2 injection rate from 4 to 8 MMscf/D results in propagation of gas farther from injection wells, leading to an additional RF gain of 0.6%. The different WAG injection sequences can be implemented at each WAG injector to fully utilize the gas compressor and maintain the constant volume of gas injection. This study examines the existing and new CO2-EOR injection techniques for multi-layered light oil reservoirs with dipping. The pre-selected injection strategies can be further investigated in the optimization study of oil recovery and CO2 storage.