Thermal Drawdown-Induced Flow Channeling in a Single Fracture in EGS

Abstract
The evolution of flow pattern along a single fracture and its effects on heat production is a fundamental problem in the assessments of engineered geothermal systems (EGS). The channelized flow pattern associated with ubiquitous heterogeneity in fracture aperture distribution causes non-uniform temperature decrease in the rock body, which makes the flow increasingly concentrated into some preferential paths through the action of thermal stress. This mechanism may cause rapid heat production deterioration of EGS reservoirs.
In this study, we investigated the effects of aperture heterogeneity on flow pattern evolution in a single fracture in a low-permeability crystalline formation. We developed a numerical model on the platform of GEOS to simulate the coupled thermo-hydro-mechanical processes in a penny-shaped fracture accessed via an injection well and a production well. We find that aperture heterogeneity generally exacerbates flow channeling and reservoir performance generally decreases with longer correlation length of aperture field. The expected production life is highly variable (5 years to beyond 30 years) when the aperture correlation length is longer than 1/5 of the well distance, whereas a heterogeneous fracture behaves similar to a homogeneous one when the correlation length is much shorter than the well distance. Besides, the mean production life decreases with greater aperture standard deviation only when the correlation length is relatively long. Although flow channeling is inevitable, initial aperture fields and well locations that enable tortuous preferential paths tend to prolong heat production lives.
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Additional Info

DOE Project Name: Validation of EGS Feasibility and Explosive Fracturing Techniques
DOE Project Number: FY15 AOP 1.3.2.4
DOE Project Lead: Elisabet Metcalfe
Last Updated: over a year ago
Nov
2015
Data from November, 2015
Submitted Nov 25, 2015

Lawrence Livermore National Laboratory

Contact

925.422.3941

Authors

Bin Guo
Lawrence Livermore National Laboratory
Pengcheng Fu
Lawrence Livermore National Laboratory
Yue Hao
Lawrence Livermore National Laboratory
Catherine A. Peters
Princeton University
Charles R. Carrigan
Lawrence Livermore National Laboratory

Keywords

geothermal, thermal drawdown, single fracture system, thermomechanical coupling, flow channeling, reservoir simulation, EGS, engineered geothermal systems, geothermics, heat production, single fracture, thermomechanical

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