Stimulating a High Enthalpy Well by Thermal Cracking

Abstract

Well BO-4 is situated in the geothermal area of Bouillante, Guadeloupe. The well was drilled in the 70ís to a depth of 2500 m. When electrical production started from a nearby power plant in 1988, it was not considered economical to connect the well due to low steam output. The actual stimulation took place between August 10 and 27 1998, with production tests before and after to evaluate the results of the stimulation. Up to 25 l/s of sea water, mixed with inhibitors to prevent anhydrite scaling, were injected into the well in periods of up to 72 h. The wellhead pressure and the downhole pressure at 600 m were monitored throughout the whole stimulation. The wellhead pressure decreased gradually during the injection and was close to zero for maximum injection at the end of the program. The pressure behavior at 600 m depth showed similar decrease which indicated thermally induced fracturing. After each injection period the pressure falloff was recorded at 600 m depth. The injectivity of the well increased by 50% and the skin effect decreased substantially. The production test after the injection period was not successful due to equipment failures. By simulating the dynamic pressure and temperature logs for the well flow a backpressure curve was obtained, that showed increase in productivity. The well produced about 40 ñ 60 t/h total flow at high wellhead pressure, during the production test, which corresponds to about 1 MWe. A year later a short production test confirmed the characteristic curve, which shows a 50% improvement. If the well can sustain this production it will be economical to connect it to the power plant.