Modeling Flow in a Jointed Geothermal Reservoir

Abstract

A coupled model of rock deformation, fluid flow, and heat transfer has been developed and used to simulate the Hot Dry Rock (HDR) geothermal reservoir at Fenton Hill, New Mexico. The goal of the model (GEOCRACK) is to address such questions as: the number and spacing of wells for optimal heat mining, the effects of low impedance flow paths (short-circuiting), the effects of operating the reservoir in different circulation modes (steady state or periodic pressurization), and the long term thermal performance of the reservoir. Simulations of the Fenton Hill HDR reservoir show the model correlates with actual flow rates under differing pressure conditions, replicates reservoir tracer behavior, and reproduces the transient reservoir behavior observed. The model also simulates the heat transfer behavior of an HDR reservoir and can therefore be employed to examine the long term behavior and energy availability from an HDR resource. The model predicts reservoir impedance to drop significantly due to the thermal contraction of rock and the adjacent joints opening as heat is mined from the reservoir.