TWO DIFFERENT ROLES OF FRACTURES IN GEOTHERMAL DEVELOPMENT

Abstract

Heat, fractures and fluid are the fundamental elements of geothermal resources. From a different viewpoint, existence of natural hydrothermal convection to form convective geothermal resources, and fluid production from wells, are the important factors for geothermal development. The fractures play two different roles in geothermal development. One is contribution for the onset of the natural convection in geothermal systems, and the other is contribution as flow paths to connect wells to the reservoir for fluid production. Since the ascending velocity of natural convection in geothermal reservoirs is order of 10 9 m/s, fractures from very small to very large permeabilities contribute to the first role. However, in-flow velocity of singlephase liquid within fractures in the vicinity of the well face ranges from 10 -1 to 10 1 m/s for example. Thus, only fractures of very high permeability can contribute to the second role. We extend this discussion based on field data.