Carbon capture and sequestration (CCS) is one of “Five Grand Challenges” of E&P industry to develop sustainable use of hydrocarbons. Success of CCS projects depend greatly on selecting adequate target reservoirs for storage. Numerical simulation is time consuming, expensive, and requires detailed input data, yet it remains the accepted method to forecast CO2 storage in depleted oil and gas reservoirs. This investigation presents an analytical method, based on thermodynamic state functions, to estimate ultimate CO2 storage capacity in such reservoirs. The proposed method makes fast and accurate estimates, while considering contaminants such as nitrogen and carbon monoxide contained in the injection stream. Results are used to select target reservoirs, estimate amount of CO2 to be stored, design injection schemes and surface facilities, and evaluate the injection process. Performance of the new method was compared against compositional reservoir simulation for a wide range of reservoir depletion pressure, target pressure, temperature, water saturation, fluid compositions, and reservoir size. Excellent agreement was observed between analytical and numerical models, with only 1.3% molar basis average difference. Average oil, gas, and water saturations were also matched. Analytical method performed orders of magnitude faster than numerical simulation, with an average time per run of 5 seconds.


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