Influence of fracture pattern between Hot Sedimentary Aquifer (HSA) and Enhanced Geothermal Systems (EGS) on thermal production and permeability evolution

Abstract

Thermal energy extraction relies on the fluid circulation and heat transfer between fluids and rock matrix. The conductive fracture channel provides effective conduits for fluid circulation, while absorbing heat energy from adjacent blocks depending on heat transfer length. The vertical depth variation not only leads to the quality of heat reservoir, but also brings substantial influence on fracture pattern due to stress state and chronological tectonic evolution. Consequently, it is vital to explore the influence of fracture pattern on the model of thermal energy production and subsequent permeability evolution. The induced thermal stress plays an important role in the stress state and fractures and therefore permeability development. It is hypothesized that the two-stage evolution of permeability and porosity: shrinkage effect from thermal cooling is strong sufficient with the highest drawdown gradient, which leads to significant minimum horizontal stress reduction and permeability enhancement. The second stage when rock temperature completely drained allows permeability and porosity reduce to the initial magnitude, with the thermal stress diminishes. The shallow geothermal extraction with less consolidation induces less thermal stress to change rock permeability and porosity. Therefore, the thermal stress needs to be taken into account in evaluating the formation properties evolution and stress state.