Carbon Dioxide Well Stimulation: Part 1-A Parametric Study

Cyclic Ctheta/sub 2/ stimulation of a production well, especially in viscous oil reservoirs, is developing as a method of rapidly producing tertiary oil and obtaining valuable data. History matching provides confirmation of Ctheta/sub 2//crude interactions measured in the laboratory resulting in increased accuracy of Ctheta/sub 2/ flood predictions. Profitability of the process is enhanced by proper control of key operating parameters. The most important are Ctheta/sub 2/ injected per cycle, number of cycles, and backpressure during production. Reservoir parameters dictate the selection of commercial applications. The dominant factors are oil viscosity, oil swelling and viscosity reduction resulting from Ctheta/sub 2/ dissolving in the crude, trapped gas saturations, fluid saturation, permeability, and wettability. In the absence of published field data, this study utilized a numerical simulator to predict incremental oil recovery as a function of these operating and reservoir parameters. Multiple regression analysis was used to relate the efficacy (STB incremental oil/Mcf Ctheta/sub 2/ injected) of the Ctheta/sub 2/ cyclic stimulation process to six parameters. Under ideal conditions, one extra barrel of stock-tank oil is produced for each thousand cubic feet of Ctheta/sub 2/ injected. Efficacy decreases with both number of cycles and volume injected.