Reactive Silica Transport in Hot Poroelastic Rock and its Effects on Fracture Aperture

Abstract

Induced and pre-existing fracture networks control the fluid flow in an Enhanced Geothermal Systems (EGS). The permeability of the network is affected by mechanical, thermal and chemical processes. Access to the thermal energy stored in the reservoir rocks strongly depends on the connection between the drilled boreholes and the natural fractures. As the water circulates through the reservoir it interacts with the rocks, often leading to mineral precipitation and dissolution reactions as well as large gradient in temperature and pressure. In this work we develop a semi-analytical solution for poro-thermoelastic reactive chemical transport and calculate the resulting fracture aperture changes. We focus on single component reactive fluid transport in a fracture and consider both solute reactivity along the fracture and its diffusion into the rock matrix using temperature dependant reaction kinetics. Poroelastic and thermoelastic effects of water injection are included by considering constant injection into an infinite fracture in hot, permeable rock with Darcy type leak-off into the rock-matrix. An examples problem is solved for the case of constant injection rate to investigate the individual and coupled effects on thermal, poroelastic and reactive silica transport on fracture aperture and pressure.