Egs Geothermal Reservoir Potection and Permeability Enhancement Mechanism During Drilling

Under the situation of transition to non-fossil energy driven by “double carbon” (carbon emission peak in 2030 and carbon neutrality in 2060), the development of EGS of dry hot rock is getting more and more attention. However, due to the lack of initial fractures near borehole, poor connections between the originally existing fractures, and the high hydraulic-fracturing pressure of granite that is prone to induce earthquakes, the reservoir reconstruction has become a “neck” problem for the development of dry hot rocks worldwide. To overcome these challenges, this project innovatively proposed a new concept of advancing reservoir reconstruction to the upstream of EGS development process, that is, protect the existing fractures in the drilling process and creatively “drill” new fractures on the borehole wall to provide "guide fractures" for the subsequently hydraulic fracturing. This is a quite innovative idea and an extremely complicated system engineering, which requires the integration of multidisciplinary theories. Above is needed to characterize the dynamic evolution of the temperature and stress field around the well during drilling, to determine the fracture initiation-propagation-arrest mechanism, to understand the high-temperature control principles of drilling fluids, to reveal the interaction mechanisms between drilling fluid and fractures in geothermal reservoir under the coupling behaviors of “thermo-hydraulics-mechanics-chemistry”, to construct an adaptive drilling fluid with “constant pressure” to protect geothermal reservoir. Besides, investigating the “piston-bit-hard rock” coupling mechanism of percussive rock fragmentation and rock damage mechanism in high-temperature geothermal reservoir environment, reveals the controllable new fracture mechanism created by pneumatic percussion drilling on the wall of borehole in tight granite, and forms the design theory of high-temperature hard rock air DTH hammer and the technique of percussive rotary drilling beneficial to permeability enhancement. Those are expected to provide innovative theoretical and methodological support to promote the development of EGS technologies.