Distributed parameter modeling of a producing vapor‐dominated geothermal reservoir: Serrazzano, Italy

Abstract

The simulator SHAFT79 of Lawrence Berkeley Laboratory has been applied to a field‐wide distributed parameter simulation of the vapor‐dominated geothermal reservoir at Serrazzano, Italy. Using a three‐dimensional geologically accurate mesh and detailed flow rate data from 19 producing wells, a period of 15.5 years (from 1959 to 1975) has been simulated. The reservoir model used is based on field measurements of temperatures and pressures, laboratory data for core samples, and available geological and hydrological information. The main parameters determined (adjusted) during development of the simulation are permeabilities and much of the initial conditions. Simulated patterns of pressure decline show semiquantitative agreement with field observations. Field pressures decline overall somewhat more rapidly than predicted in the simulation. It is concluded that (1) the interface between overlying steam cap and deeper boiling aquifer remains stationary during exploitation and (2) the aquifer boils approximately uniformly throughout in response to production. Furthermore, the simulation suggests that some steam flowing to the main well field originates from deep fractures rather than from boiling in the two‐phase zones modeled. Effects of cold recharge, incomplete thermal equilibration between rock and fluid, and different assumptions regarding the depth of the steam/two‐phase interface are investigated. The reservoir model is used to extrapolate (forecast) production rates on a well‐by‐well basis through 1990. Injection of spent condensate is briefly examined, and negligible impact on field performance is predicted. Simulation methodology and ambiguity of parameter determination are discussed.