Modeling recharge and convective downward migration of fractures in low-temperature geothermal systems
Abstract
Fractures and faults play a key role in the meteoric recharge of geothermal systems, allowing cold water to enter from local sources. As dense, cold water enters the system, it flows downwards and reduces the temperature of the nearby country rock. Thermo-mechanical forces introduced by this thermal perturbation result in contraction of the host, reducing stress and enhancing the aperture and permeability of the fractures. Under certain conditions, these thermal strains may lead to mechanical failure of the host, opening new fractures and allowing further flow of cold water in a process referred to as convective downward migration (CDM) of the fracture. The CDP concept is often cited, but has yet to be modeled with modern tools.
Using the Complex Systems Modeling Platform, CSMP++, we perform numerical simulations of natural convection of water in a fractured host. Rock and fracture parameters are loosely based on those of the Reykjanes low-temperature geothermal system in Iceland, where convection is thought to play a key role in heat transport. We describe a novel behavior of cold-water influx into a geothermal system and present supporting evidence for CDM under certain thermal and mechanical conditions. By varying rock properties and initial conditions, we develop first-order approximations for the degree of flow channeling and fracture migration depth possible in such systems.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.H31C..04P
- Keywords:
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- 1822 Geomechanics;
- HYDROLOGYDE: 1847 Modeling;
- HYDROLOGYDE: 1869 Stochastic hydrology;
- HYDROLOGYDE: 1873 Uncertainty assessment;
- HYDROLOGY