Alkaline/Surfactant/Polymer (ASP) Flooding: Laboratory Evaluations, Simulation Studies and Pilot Planning for a Matured Carbonate Reservoir in Bahrain

Abstract

Abstract The Mauddud reservoir discovered in 1932 in Bahrain is now in a mature stage of development. A detailed feasibility study is carried out for identifying the most appropriate enhanced oil recovery (EOR) process for Mauddud reservoir and defining a strategy for further evaluation and implementation of the most promising EOR options. Detailed laboratory studies have identified alkaline-surfactant-polymer (ASP) process as the most technically attractive EOR process to increase the ultimate recovery from Mauddud reservoir by significantly improving the volumetric sweep and displacement efficiency. This paper aims to present detailed design of laboratory experiments and results en route to sector modeling studies in three (3) selected large areas. A 3.6 acres area is selected in Mauddud waterflooded reservoir for piloting. Detailed cost estimate is carried out using laboratory design data and simulation results. Extensive laboratory design and testing such as polymer rheology, thermal stability tests, polymer injectivity, viscosity, adsorption, ASP phase behavior and coreflood tests are performed. 1-D coreflood simulation model was conducted using University of Texas Chemical Compositional Simulator (UTCHEM). Polymer rheology and surfactant phase behavior laboratory test data were matched to generate input parameters for the ASP injection simulation forecast. Representative sector and pattern simulation models were developed to estimate the EOR production potential from the Mauddud reservoir. The sector model developed was calibrated to the historical production, injection, and pressure data. The history matched sector model was used to select and develop pattern simulation models that were used to estimated EOR production potential. Based on the evaluation of laboratory results, polymers are identified to give adequate viscosifying power and thermal stability. ASP formulations are identified for designing coreflood. Coreflood tests provided the process recovery data on residual oil saturation, chemical retention facilitating optimum slug design resulting in maximum oil recovery with minimum amount of chemical mass. The chemical formulation selected showed good phase behavior at different oil/water ratios, equilibrated quickly, good aqueous solubility, and generated ultra-low interfacial tension (IFT). The surfactant formulation showed great promise in the coreflood tests. The ASP coreflood tests recovered 63 to 70% of the waterflood residual oil and left a residual oil saturation after chemical flood (Sorc) of 9%. ASP pattern simulations showed incremental oil recovery factors between 26.7 and 31.9 percent of the original oil-in-place (OOIP). The laboratory and sector simulation results are crucial to explore the feasibility of EOR project and will serve as inputs to detailed economic evaluation as well as pilot design and facilities planning.