Impact of Water Softening on Chemical Enhanced Oil Recovery Project Economics

Abstract

Abstract Chemical enhanced oil recovery (EOR) provides the means to increase oil production through manipulation of the chemical and fluid properties within a given reservoir. The number of chemical EOR projects being developed, pilot tested, and commercially implemented is on the rise as a function of the relative decrease in chemical costs, advancements in chemical performance, more precise subsurface modeling, and recent stable oil pricing. The amount of calcium and magnesium (hardness) in the injection water plays a critical role in determining the type and dosage of alkali, surfactant, co-solvents and/or polymer (ASCP) used in a chemical EOR flood. The hardness dictates whether alkali can be used and affects the surfactant adsorption, achievable viscosity at specific polymer dosages, polymer stability, polymer choice as a function of thermal stability, as well as emulsion stability in the produced water. The ability to remove hardness and thereby use soft injection water with chemical EOR is a game changer, in that it can enable chemical floods that are otherwise uneconomic, infeasible or that are considered too risky. Soft water, invariably, comes at a cost related to treating the source water to remove calcium and magnesium. Source water for a chemical EOR flood is dictated by availability and environmental constraints and is usually limited to produced water, seawater or brine from deep aquifers. Occasionally, a surface water source is available. This paper reports on representative chemical EOR project case studies in seawater, brackish water and produced water applications at various sites and capacities. The cost of water softening is weighed against the reservoir and production benefits, culminating in a side-by-side economic analysis for each case study based on cost per incremental barrel of oil. The results can be used to guide the development of new chemical EOR projects in determining facility needs as a function of economics.