Abstract
Recently it has become important to develop a deep, high temperature and low permeable ge-othermal reservoir in the Kakkonda geothermal field. Thus, it is important to develop new techniques for the efficient well stimulation. This paper describes an example in which we succeeded to increase the production of a geother-mal well by hydraulic fracturing using AE (Acoustic Emission) measurement and temperature logging. The depth of the stimulated well is 2126m, to produce steam from high temperature reservoir. In this field, temperature of the reservoir deeper than 1500m is higher than 300°C. Therefore, casing covers the well from the surface to 1700m depth, to avoid low temperature fluid. From 1700m to the bottom, this well is an openhole. The well encountered four fractures that induced lost circulation during drilling in the high tem-perature reservoir. However this lost circulation gradually ceased. Temperature logging after the drilling did not show temperature anomaly between 1700m and the bottom. Therefore, permeability of the well was estimated to be low. To increase the permeability of the well, hydraulic fracturing was carried out using water for five days. Pressure brake-down occurred on the 2nd day of the fracturing, and AE was observed. On the 3rd day of the fracturing, temperature logging indicated that the injection point created by the fracturing was at the depth of 1798m. Then, we tried to increase permeability of the fracture by increasing the pumping rate. On the 5th day of the fracturing, as AE's activity and wellhead pres-sure became low, then we stopped pumping and finished the hydraulic fracturing job Finally, we could get a steam amount of 50t/h from the well. This course of fracture treatment suggests that the AE measurement and the temperature logging are useful to control and optimize the hydraulic fracturing. These techniques also give us information for exploration of fractures because they disclose fracture distribution around wells.
