Modeling of the Thermomechanical Effect of Cold-Water Injection on Geothermal Well Injectivity

The injectivity during the completion test is acquired to calculate the demand for injection wells. Rock formation factors like porosity and permeability remain constant when calculating the injection capacity. Meanwhile, temperature variations caused by injection might cause the rock matrix to shrink or expand, thereby changing the injectivity value of the well due to changes in the permeability of rock formations surrounding the well. This impact on the calculation of the injection capacity during the completion test could be overestimated compared to the operation because the temperature of the rock formation during the completion test is much lower than the operating temperature. This study aims to generate a numerical model that considers the effect of rock thermomechanics on the injectivity of geothermal wells. Synthetic model was built using coupling method between Visual Basic for Application (VBA) Microsoft Excel and Petrasim software which is a TOUGH2 pre- and post-processor. The numerical model has been successfully developed and can represent changes in injectivity due to the injection of cold water. Overestimated injectivity values in a field with a restricted number of injection wells could result in insufficient injection capacity during the operating period and curtail the power generation. The findings of this study should serve to correct injectivity values during well testing with cold water injection to determine a better injection capacity, ensuring production continuity.