Objetivo
To demonstrate the technical and economical feasibility of low cost, cold water stimulation methods to enhance the productivity of high enthalpy, low productive geothermal wells by improving the hydraulic connection between the reservoir fracture network and geothermal production wells.
To enhance the productivity of the low productive well BO-4 in the Bouillante geothermal field, Guadeloupe, from 15 t/h to 20-30 t/h steam. The annual electricity generation from well BO-4 after stimulation is expected to be in the range of 20-30 GWH.
The experiment was successfully carried out during Summer 1998. Cold sea water was injected into well BO-4 for 18 days. Several injection steps were conducted with increasing flow rates. Scale inhibitors were added to sea water in order to prevent anhydrite scaling. Monitoring during injection showed a continuous decline in pressure either at well head or at 600 m depth in the well. Injectivity of the well deduced from falloff pressure responses increased from 0.9 l/s per kg/cm² to about 1.4 l/s per kg/cm², or about 50%. It is considered that at least half of the injectivity increase is preserved in productivity. Such behaviour infers thermally induced fracturing as the near-bore reservoir formations were cooled down. Temperature profiles carried out during injection showed that the amplitude of cooling was about 100°C in the 550-750 m interval depth. It is likely that pre-existing permeable levels preferentially accepted injected cold water and underwent thermal contraction and stress-cracking. Their opening may have caused the observed pressure decline and improvement of the well injectivity.
Calculated well characteristic curves from pressure and temperature data obtained during dynamic profiles provide an estimation on the well performance before and after water injection. They indicate that the BO-4 estimated, maximum flow rate has increased from 80 t/h (22 kg/s) to 140 t/h (39 kg/s). Moreover, the calculated well characteristic curve of the Evaluation Production Test is confirmed up to 80 t/h by measured flow data. The improvement of the BO-4 production is regarded as a positive result of the cold water stimulation. Further long term production testing is however required to confirm the actual maximum output of the well and its sustainability with time.
As a result of the experiment, cold water injection is proved to be an efficient method to stimulate any new poor producer geothermal well and existing well affected by scaling. The demonstrated technology could be applied to a large scale in many geothermal reservoirs where low productive wells are existing. It is an easy-doing and low cost method especially suitable for geothermal fields situated in peripheral location (island) where large technical facilities are lacking. The use of sea water treated with adapted scale inhibitors also extends greatly the commercial potential of cold water stimulation of high enthalpy geothermal wells. Cost of a cold water injection varies according to the local context of the stimulated well. However, it is considered to be 8 to 10 times less than drilling of a new production well.
A problem frequently observed in the exploitation of high enthalpy geothermal reservoirs, is the poor hydraulic connection between the production wells and the geothermal reservoir. These circumstances restrict considerably the practical possibilities to extract the geothermal energy through the production wells, and the term "dry well" is used to describe the situation. In cases where some of the wells are productive and other dry, it is considered to be a sign of different connections between the wells and the reservoir fracture network. By using low cost stimulation methods to improve the hydraulic connection between the wells and the geothermal reservoir, it should be possible to improve the economical conditions for energy extraction from the reservoir, as fewer production wells need to be drilled. This problem is addressed in the proposed project.
The selected test site is the low productive well BO-4 in the bouillante geothermal field. It is 2500 m depth with a 248°C maximum recorded temp. Limited production test carried out after the drilling indicated a production rate of about 15t/h steam.
Before the stimulation, preparatory work will enable a careful design of the stimulation experiment. The stimulation will be carried out through wellhead injection flow rate and wellhead injection pressure will be monitored. Tracer test will be conducted in order to check any connection development between the stimulated well BO-4 and the neighbouring productive well BO-2. Seismic monitoring will be also carried out during the stimulation to evidence any induced microseismicity related to the cold water flow away from well BO-4.
After the stimulation, an evaluation production test will be carried out in order to measure the productivity benefit and to check the effects of cold water stimulation on the permeability of the reservoir fracture network. Energy balance of the experiment will be establish and the economy will be calculated.
Ámbito científico (EuroSciVoc)
CORDIS clasifica los proyectos con EuroSciVoc, una taxonomía plurilingüe de ámbitos científicos, mediante un proceso semiautomático basado en técnicas de procesamiento del lenguaje natural. Véas: El vocabulario científico europeo..
CORDIS clasifica los proyectos con EuroSciVoc, una taxonomía plurilingüe de ámbitos científicos, mediante un proceso semiautomático basado en técnicas de procesamiento del lenguaje natural. Véas: El vocabulario científico europeo..
- ingeniería y tecnología ingeniería eléctrica, ingeniería electrónica, ingeniería de la información industria electrotécnica ingeniería eléctrica generación de energía eléctrica
- ciencias sociales economía y empresa ciencia económica economía de la producción productividad
- ciencias naturales ciencias de la tierra y ciencias ambientales conexas geología sismología microseísmos
- ingeniería y tecnología ingeniería ambiental energía y combustibles energía renovable energía geotérmica
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