| Abstract |
Hot Dry Rock (HDR) is a kind of high temperature rock, with low porosity and permeability, which is mostly composed of metamorphic rock or granite. Enhanced Geothermal System (EGS) is an effective method for exploiting HDR geothermal resources, which stimulates the rock matrix artificially for improving the production performance. Efforts have been made to create fracture networks and open the existed fractures to improve performance of EGS. As a consequence, chemical stimulation, in addition to hydraulic/thermal fracturing, has been proposed and employed as an important method for the reservoir stimulation. In 2017, huge potential of HDR resources was found by drilling in Gonghe Basin of Qinghai Province, Northwest China. The temperature reached 236oC at the depth of 3706m. Consequently, the first EGS demonstration project of China will be developed in the basin. The lithology of drilling core samples in Gonghe Basin is mainly feldspar and quartz minerals. Alkaline chemical stimulation may be the best choice for improving permeability of HDR. However, complex chemical composition of lithology in the actual stratum resulted in the formation of secondary minerals. This study explored the interaction mechanism of alkaline agents on feldspar and quartz minerals. Based on laboratory experiments, the effective components of alkaline agents are proposed to promote dissociation of specified minerals and avoid serious formation of secondary minerals. Laboratory experiments results show that solution ratio is more than 20%. The components of scale inhibitors and masking agents can effectively extend the reaction time and increase penetration distance by reducing the formation of secondary minerals. The results of this study can provide theoretical support for the construction of EGS demonstration projects in the Gonghe Basin, and provide a corresponding scientific basis for the development of similar types of HDR in the future. |