Geochemical Reservoir Damage Due to Fluid-Mineral Interactions Induced by Drilling Fluid: an Inevitable Problem During Geothermal Drilling

Abstract

The target area for geothermal drilling is usually characterized by faulted as well as fractured structure, where the original cracks and fractures are beneficial to be functioned as flow channels during geothermal energy extraction. However, due to low formation pressure of geothermal reservoir, it is common for drilling fluid and its filtrate to invade into the surroundings of geothermal wells, and a series of fluid-mineral interactions along cracks and fractures will be induced under the promotion of high temperature. The results of fluid-mineral interactions are the characteristics evolution of cracks and fractures, which leads to permeability change inside rock, that is, geochemical reservoir damage. In this paper, a simulated fluid-mineral interaction experiment lasting 7 days was carried out between 1wt% KCl solution with a pH value of 10 referred to the drilling fluid used in geothermal wells and rock recovered from Gonghe Basin in Qinghai province. Further, electronic balance, XRD and XRF were conducted to identify the minerals and their mass as well as content changes. Based on the results above, the laws of geochemical reactions were analyzed. Finally, some design fundamentals of geothermal drilling fluid were proposed based on the laws of geochemical reactions, and hopefully will promote the development of geothermal drilling worldwide.