Hot dry rock fracture propagation and reservoir characterization
North America's largest hydraulic fracturing opeations have been conducted at Fenton hill, New mexico to creae hot dry rock geothermal reservoirs. Microearthquakes induced by these fracturing operations were measured with geophones. The large volume of rock over which the microearthquakes were distributed indicates a mechanism of hydraulic stimulation which is at odds with conventional fracturing theory, which predicts failure along a plane which is perpendicular to the least compressive earth stress. Shear slippage along pre-existing joints in the rock is more easily induced than conventional tensile failure, particularly when the difference between minimum and maximum earth stresses is large and the pre-existing joints are oriented at angles between 30 and 60)degree) to the principal earth stresses, and a low viscosity fluid like water is injected. Shear slippage results in local redistribution of stresses, which allows a branching, or dendritic, stimulation pattern to evolve, in agreement with the patterns of microearthquake locations. Field testing of HDR reservoirs at the Fenton Hill site shows that significant reservoir growth occurred as energy was extracted. Tracer, microseismic, and geochemical measurements provided the primary quantitative evidence for the increases in accessible reservoir volume and fractured rock surface area. These temporal increases indicate that augmentation of reservoir heat production capacity in hot dry rock system occurred. For future reservoir testing, Los Alamos is developing tracer techniques using reactive chemicals to track thermal fronts. Recent studies have focused on the kinetics of hydrolysis of derivatives of bromobenzene, which can be used in reservoirs as hot as 275)degree)C.
- Research Organization:
- Los Alamos National Lab., NM (USA); Massachusetts Inst. of Tech., Cambridge (USA); Mechanical Design Services, Los Alamos, NM (USA)
- DOE Contract Number:
- W-7405-ENG-36
- OSTI ID:
- 5322647
- Report Number(s):
- LA-UR-88-1358; CONF-880477-2; ON: DE88009116
- Resource Relation:
- Conference: DOE geothermal program review, San Francisco, CA, USA, 19 Apr 1988
- Country of Publication:
- United States
- Language:
- English
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