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Puna Geothermal Venture Well Pairs – Production Impacts on Near Wellbore Reservoir Conditions
Nick PRINA, Drew SPAKE, John MURPHY, John AKERLEY, Paul SPIELMAN, Derek CARO, Adam JOHNSON, Simon WEBBISON
[Ormat, USA]
The Puna Geothermal Venture project hosts a high temperature reservoir with a complex permeability structure related to discrete basalt hosted fractures. Permeability has been observed to vary along known fractures at small offsets, making well targeting a more challenging exercise than in many other geothermal fields. Throughout the project history the challenge of finding permeability has twice resulted in the completion of production well pairs, encountering a small reservoir volume in the same fracture with vertical offset and limited lateral offset. Production from well pairs of this nature results in changes to the near-wellbore reservoir conditions, primarily liquid level, which can be used to optimize production conditions observed at the surface and related generation. This paper presents the datasets used to quantify production induced changes to reservoir conditions and discusses the physical processes driving the changes in the subsurface. The resulting changes in production conditions observed at the surface and their ultimate impact on generation are also discussed. The challenges related to producing well pairs in a high temperature, sea water influenced, fracture hosted geothermal reservoir are contemplated along with perceived long-term risks of such a production strategy.
Topic: Reservoir Engineering