| Abstract |
After years of exploiting steam, geothermal wells may need stimulation to remain economically profitable. In some cases, hydraulic fracturing can be a suitable technique to improve steam production or to create new geothermal pay zones. Performing such a treatment in a geothermal volcanic environment presents several challenges. We investigated technical and geological issues that might affect the effectiveness and efficiency of stimulation, focusing on the feasibility of hydraulic fracturing in the Wayang Windu geothermal field (West Java, Indonesia). A major issue is given by the way in which the wells of this field are completed: a long perforated liner in an open hole section. When isolation of a short section of the perforated liner is not technically possible, or is economically too expensive, hydraulic fracturing might not be the proper stimulation technique. Moreover, executing a hydraulic fracture treatment on the long perforated intervals (500-1500 m) typical of the wells of the Wayang Windu field might jeopardize the integrity of the well. The focus of this work was to investigate whether hydraulic fracturing could be the proper stimulation technique to improve production of sub-commercial wells of the Wayang Windu geothermal field (West Java, Indonesia), as applying the right stimulation approach can push the production to the desired level. However, performing a fracture treatment in volcanic environments like these presents several challenges. We have investigated technical and geological issues affecting the effectiveness and efficiency of hydraulic fracturing. The impracticality of appropriately isolating a short section of the perforated liner appeared to be the biggest concern. In all studied scenarios, it was possible to propagate a hydraulic fracture, but only in a constrained area at the top of the perforated liner. The simulated fracture were also propagating vertically slightly above the top of the reservoir into the clay cap for a few tens of meters. We also demonstrated how the execution of a hydraulic fracture treatment on a long perforated interval (400-1500 m) can jeopardize the integrity of the well. This is related to the large differences in stresses along the open well path. If isolation of a short section of the perforated liner is not technically possible or economically too expensive, hydraulic fracturing might not be the correct stimulation technique. The high leakoff of the dense fracture system in combination with the large stress differences along the perforated section length make the Wayang Windu a bad candidate to perform a hydraulic fracture stimulation. The high injectivity that causes the high fracture leakoff can also be exploited to apply alternative stimulation approaches. For example, if the pressure and temperature fronts of high volumes of injected fluid can quickly penetrate deeply into the reservoir, thermal and acid stimulations can be a valuable alternative to hydraulic fracture stimulation. |