Two Mechanisms of Production of Superheated Steam from Geothermal Wells

Abstract

There are two mechanisms for the production of superheated steam from geothermal wells. The first one is that the steam generated by the boiling of immobile liquid trapped within micro fractures in rock matrix of geothermal reservoirs flows through fractures of high permeability and eventually flows into wellbores as superheated steam (Mechanism 1). The second one is that two-phase fluid flashes and dries-out during the flow within in-flow zones around wellbores. The superheated steam then eventually flows into wellbores (Mechanism 2). Mechanism 1 is from a microscopic viewpoint, while Mechanism 2 is from a macroscopic viewpoint. The largest difference between the two is the presence or absence of a flow of two-phase mixture. Mechanism 1 is involved in the generation of HCl gas in superheated steam. The mechanisms have been described by Truesdell and White (1973) and Grant (1979). However, based on advances in our understanding in recent years, we need to add explanations to these models in terms of relative permeability. Also, the interrelationships and the differences in thermodynamic processes between these two mechanisms have never been described. In this paper, they are discussed from a viewpoint of geothermal reservoir engineering.