Effect of Fracture Compressibility on Fluid-in-Place Calculation of Chingshui Geothermal Reservoir, Taiwan

Abstract

Naturally existing tritium in groundwater was applied as a tracer for dating the age of Chingshui geothermal water. The residence time (or, age) was determined at 15.2 years using the plug-flow model with tritium data. The rate of natural recharge for Chingshui geothermal reservoir can be estimated from the production history from 1981 to 1993. Fluid-in-place can then be calculated from the residence time (or, age) and recharge rate. Alternatively, fluid-in-place can be calculated using the porosity-thickness product obtained from well interference tests. This paper shows that ignoring the effect of fracture compressibility can lead to overestimating the porosity-thickness product and fluid-in-place of Chingshui geothermal reservoir, a stress-sensitive naturally fractured reservoir.