Print this pageExperimental Study on CO[2] Core-Flooding Using Dolomite- and Anhydrite-Cemented Tensleep Sandstone from the Bighorn Basin, Wyoming
SHIRAKI, RYOJI and THOMAS L. DUNN
Three core flooding experiments were carried out to understand the effect of water-rock interactions on scale formation during CO[2] treatments in Tensleep sandstone reservoirs in Wyoming. The experiments were run at 80 degrees C and 166 bars total pressure in systems CaSO[4]-MgSO[4]-NaCl brine (9.69g/l TDS) - cores (Run 1), 0.25 mol/l NaCl solution-cores (Run 2), and 0.25 mol/l NaCl solution-crude oil-cores (Run 3).
Three major reactions during flooding were dissolution of dolomite, alteration of K-feldspar to form kaolinite, and precipitation of anhydrite (Run 1) or dissolution of anhydrite (Runs 2 and 3). All sample solutions remained under-saturated with dolomite in all runs. In Runs 1 and 2, solutions were saturated with both anhydrite and barite throughout the runs. In Run 3, however, sulfate ion released by anhydrite dissolution was reduced by crude oil and allowed a higher concentration of Ba than in the other two runs, whereas the solution did not obtain saturation with barite. Permeability of cores used in Runs 1 and 2 decreased after the runs and SEM observation of cores suggests that the decrease in permeability is mainly due to crystallization of kaolinite in the pore spaces.
Simulations based on the experimental results showed that dissolution of cement minerals should take place very near the injection wells and that the potential of carbonate scale formation will depend on the extent of dissolution of dolomite and anhydrite in the region. Simulations suggests that reducing P[CO2] lowers the potential of carbonate scale formation. Chemical composition of brines for injection does not affect the potential significantly.