Microholes for Improved Heat Extraction from EGS Reservoirs: Numerical Evaluation

Abstract

The use of microholes is a potential approach to enhance fluid flow and heat exchange within an engineered geothermal system (EGS). Multiple microholes, created using coiled tubing drilling technology, are drilled as sidetracks off of injection or production wells. Because microholes can be spread widely, thus intersecting a larger portion of the fracture network, the use of microholes increases the rock volume that is accessed by the circulating working fluid, therefore extracting more heat from the geothermal reservoir. The objective of this study is to evaluate EGS performance of microhole configurations using numerical simulations. This is performed by comparing the amount of heat that is extracted over a period of time using a conventional EGS design and one based on microholes. We examined multiple scenarios using numerical simulations with explicitly discretized microholes. Different scenarios have been considered and comparisons of energy production were made to contrast the conventional and microhole designs, providing preliminary insights into the potential of microholes to improve the efficiency and robustness of heat extraction from an EGS. This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Technology Development, Geothermal Technologies Program, of the U.S. Department of Energy through award DE-EE0002783 to Impact Technologies LLC and via Contract No. DOE-EGS-LBNL-2010 between LBNL and Impact Technologies LLC.