Author: Publisher:
ISBN:
Category :
Languages : en
Pages : 10
Book Description
Vapor-dominated geothermal reservoirs such as Larderello, Italy, and The Geysers, California, are fundamentally water-short systems. This is apparent from the relatively low pressures in the natural state, typically about 35 bars at 1000 m depth, which is much below hydrostatic pressures. It is also apparent from the high heat content of the produced fluids, typically superheated steam. Large-scale production from these systems has caused reservoir pressures and well flow rates to decline, leading to an underutilization of installed electrical generating capacity. Clearly, these reservoirs are beginning to run out of fluid, while heat reserves in place are still enormous. (At Larderello, there is a long-term trend of increasing formation temperatures in the upper productive zones of the reservoir; Sestini, 1970). Reinjection of colder waste waters, or injection of waters from a source other than the geothermal reservoir, is the primary means by which dwindling fluid reserves can be replenished. A considerable body of field experience with injection has been accumulated at Larderello and The Geysers; the results have been mixed. There are well documented cases where injection has increased flow rates of nearby wells. Return of injected fluid as steam from production wells has been observed directly through chemical and isotopic changes of produced fluids (Giovannoni et al., 1981; Nuti et al., 1981). In other cases injection has caused thermal interference and has degraded the temperature and pressure of production wells. Water injection into depleted vapor zones gives rise to complex two-phase fluid flow and heat transfer processes with phase change. These are further complicated by the fractured-porous nature of the reservoir rocks. An optimization of injection design and operating practice is desirable; this requires realistic and robust mathematical modeling capabilities.
Author: 
Author: 
Author: 
Author: 
Author: 
Author: 
Author: Geothermal Resources Council
Author: M. P. Hochstein
Author: Enrico Barbier