Impacts of Rock-Brine Interactions on Petrophysical Properties of a Sandstone Reservoir, Utilizing Geochemical and Pore Network Modeling
Unfavorable consequences of geochemical reactions, such as calcite and silica scaling, in geothermal power plant surface facilities have been discussed in many recent studies. However, the impact of brine-rock interactions related to geothermal projects on reservoir properties has not been addressed fully. In this study, interactions between geothermal fluid and reservoir rocks in two fields located in Vermilion Parish, LA, and Chocolate Bayou, TX, are examined using geochemical modeling. The studied reservoir belongs to the Frio formation. In the geochemical models, the brine is cooled down to the estimated output temperature of a geothermal heat exchanger and re-equilibrated. Then, brine-rock interactions at reservoir temperature are simulated, and the changes of rock composition due to geochemical reactions are anticipated. Results show that the pore space volume change is negligible. Feldspar transformation to clay minerals, however, has been observed as a mineral conversion process which is expected to impact permeability. Pore Network Modeling has been utilized to investigate the impact of the geochemical interactions on the reservoir permeability. To build the pore network, micro-CT scan images were acquired from three core samples. The image segmentation was done considering the results of rock characterization studies. After completing the objective segmentation, the anticipated geochemical changes were incorporated into the micro-CT scan images using a computer code. Permeability of the resulted image was calculated and compared to the initial permeability calculations. The impact of the micro-porosity of newly formed clay minerals was estimated using an innovative method. Results indicate that the newly generated clay minerals due to the geochemical reactions may cause important damage, as high as 50 percent, to reservoir permeability.
Geochemical modeling, pore network modeling, geothermal reservoir, rock-brine interaction, Frio formation, clay morphology, clay micro-porosity, permeability alteration
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