Numerical Simulation of Fluid Flow in a Dual Porosity Geothermal System with a Thin Zone of High Horizontal Permeability
Ambusso, Willis J.
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A numerical simulator capable of mode ling fluid flow in layered dual porosity geothermal systems with high horizontal permeability has been developed. The simulator can match multiple-peaked tracer profiles from injection tests and reliably predict temperature and pressure changes caused by injection of brine in these systems. The simulator was tested and validated using data from Svartsengi geothermal field in Iceland, a non-layered geothermal field, and Olkaria geothermal field in Kenya, a layered geothermal reservoir. Simulated results show significant improvement over regular geothermal simulators and indicate that fluid flow within the horizontal layers with high permeability are best represented by fracture flow theory where fluid flow between the matrix-fracture network occurs in both directions rather than what is normally assumed that fluid flow is governed purely by dual porosity model where fluid flow occurs only from the matrix to the fracture. The study shows that fluid movement in horizontal fractures will dominate main fluid flow features in the reservoir and shall uniquely modify tracer profiles. These horizontal fractures will also lead to high returns of injected fluid at relatively low speeds in reservoirs with moderate permeability as has been noted in Olkaria. This simulator makes it possible to extract quantitative values of the hydrologic parameters of the respective layers. This should lead to better planned and managed brine injection programs.