A gas component (CO2) is added to fracturing fluids in tight gas wells of South Texas in order to energize, or stimulate the invaded zone for improved flowback. It was observed that traditional fracturing fluids were being trapped because of the lack of drawdown pressure caused by depletion of the reservoir. This study uses a recently developed energized fracture model to predict fracture behavior. It is shown that this model can be used instead of costly trial and error methods in the field to help improve upon the design of the treatments. This study investigates the effects of drawdown pressure, inlet gas composition (or quality), inlet temperature, flowrate, base viscosity, and reservoir pressure on three previous fracture designs. The effect of energizing only specific stages of the fracture treatment is also demonstrated.

Our results show that if the drawdown pressure is much larger than the capillary forces holding water in the invaded zone, energizing the fluid may not be necessary. In wells with low drawdown pressure, adding CO2 to energize the fracturing fluid may be able to completely remove damage by increasing the gas saturation in the invaded zone. Specifically for the wells that were modeled, we determined that 30 quality CO2 would be sufficient to stimulate the invaded zone. When the reservoir pressure was as low as 800 psi, even less CO2 was necessary because of additional expansion of the gas during production. Pumping of a gas with high quality (> 52%) will result in foaming of the fluid that will increase the fracture fluid viscosity. This may be undesirable in tight formations where fracture length is favored over conductivity. Pumping volumes should be corrected in order to account for the expansion of gas when there is a large difference between inlet and reservoir temperature. Changing the inlet temperature of the fluid does not greatly affect the performance of the fractured wells in this area. No compositional or phase behavior issues arose when altering the flowrate or the base fluid viscosity. Finally, it is recommended that every stage of the treatment be energized. However, in some instances it may be possible to stimulate the invaded zone by energizing only certain stages of the treatment.

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