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The EGS Collab Project: Stimulation Investigations for Geothermal Modeling Analysis and Validation

DOE-EERE-GTO-Geothermal Energy Office

 

The EGS Collab Project is addressing fundamental challenges in understanding the relationship between permeability creation, induced seismicity, and heat production in crystalline rocks under relevant stress (and temperature) conditions for Enhanced Geothermal Systems (EGS). The project focus is to test and verify computational models that can be used in EGS or the Frontier Observatory for Research in Geothermal Energy (FORGE) EGS field laboratory. The EGS Collab team is comprised of eight national laboratories, six universities, and industrial partners who are working to improve geothermal technologies.

To allow comparison between field data and model results, we are performing intermediate-scale field tests and conducting well-controlled in-situ experiments focused on rock fracture behavior and permeability enhancement. Our field experiments are extensively monitored using continuous active source seismic monitoring (CASSM), distributed temperature (DTS) and strain (DSS), acoustic emissions (AE), passive seismic, and electrical resistance tomography (ERT) in a well-characterized test bed. In addition, we are using Step-Rate Injection Method for Fracture In-Situ Properties (SIMFIP) tools in our active boreholes to directly measure fracture opening and shear.

EGS extracts energy from untapped and imperfect hot rock, which is accessible, particularly across the western US. EGS research aims to refine energy extraction technologies until they are efficient, affordable and ready to power 100 million American homes. To get there, multiple field experiments focusing on understanding and modeling rock fractures and heat transfer in the fractured system are needed.

We have a number of experiments in progress. In Experiments 1 and 2, we stimulate and characterize a number of intensely monitored stimulations. In Experiment 1, we are stimulating and performing flow tests in ~1500 m deep (4850 feet) phyllite at the Sanford Underground Research Laboratory in Lead, SD. We are quantifying permeability enhancement, characteristics of the stimulated rock, determining the nature of stimulation in crystalline rock under reservoir-like stress conditions and generating high-quality, high-resolution, diverse data sets for model validation. In addition, we are testing and developing monitoring techniques under controlled conditions to allow selection of technologies appropriate for deeper full-scale EGS sites. Experiment 2 is expected to investigate shear stimulation, and it will be performed under different stress/fracture conditions than Experiment 1. Having multiple tests conducted under different conditions is important because it provides appropriate data for model comparison and leads to a better understanding of different stimulation mechanisms and their efficacy in creating reservoir permeability.

Schematic of SURF depicting a small fraction of the underground facilities including the Yates (left) and Ross (right) shafts, the 4850 level, the location of the kISMET experiment, and Experiment 1.

Ortho-view schematic of boreholes for Experiment 1. The green line represents the stimulation well, the red line represents the production well, and yellow lines represent monitoring wells. Blue disks are notch locations. The orientation of stimulation and production boreholes is approximately parallel to Shmin.

Experiment 1 along the West Drift on the 4850 level of SURF.

SIMFIP tool used to measure displacement across a fracture during stimulation and flow.

This material was based upon work supported by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy (EERE), Office of Technology Development, Geothermal Technologies Program, under Award Number DE-AC02-05CH11231 with LBNL and other subcontracts. The research supporting this work took place in whole or in part at the Sanford Underground Research Facility in Lead, South Dakota. The assistance of the Sanford Underground Research Facility and its personnel in providing physical access and general logistical and technical support is gratefully acknowledged.

The EGS Collab Team visits the Sanford Underground Research Facility at Homestake Mine in South Dakota. Source: Mark White, Pacific Northwest National Laboratory.

Credit: Sanford Underground Research Facility, ©South Dakota Science and Technology Authority

 

Read more about the video below: EGS Collab: A Path to FORGE, LBNL, June 2018