Temperature Induced Dissolution or Precipitation In Geothermal Reservoirs and their Effects on Pressure Transient Analysis

Abstract

Under in situ conditions, geothermal reservoir fluids are in equilibrium with co-existing mineral phases or close to saturation. When cool water is re-injected into the hot reservoir or for long production periods the equilibrium between fluid and reactive minerals is disturbed. This may result in temperature induced dissolution or precipitation. Predicting the permeability changes caused by chemical reactions in such reservoirs over the entire period of operation one requires understanding of the complex interactions of the involved processes, namely flow, heat transfer, transport of dissolved species, and chemical reactions. A chemical reaction model coupled with a relationship between porosity and permeability was used to simulate pressure transient tests conducted in such reservoirs. Several different cases were generated by changing deposition and dissolution rates. The pressure transient analyses showed marked differences in early time region in the form of changing wellbore storage.