Recovery Act funding recipient profile IV: MIT using $2 million in grants to advance EGS

Killian Court at MIT

In Massachusetts, three separate research projects are aimed advancing enhanced geothermal systems – and two have been in play since 2008. With the addition of a $549,148 grant to civil and environmental engineering professor Herbert Einstein from the most recent round of funding in late summer, MIT researchers now have over $2 with which to advance the technology.

The three projects cover the gamut of EGS advancement requirements: geothermal analysis (decision analysis tools – Einstein’s work); fracture characterization, led by geophysics professor M. Nafi Toksoz; and imaging fluid flow, by seismologist Michael Fehler.

In his work titled “Develop a decision analysis procedure consisting of an integrated set of computerized tools (modules), with which an Enhanced Geothermal System (EGS) development can be assessed.” Einstein is developing a decision analysis procedure that will aid assessing the cost and time required for development of an EGS on the basis of risk. The emphasis is placed on the subsurface where there are the greatest uncertainties.

The ultimate goal is to create a simple circulation/heat transfer model using subsurface cost/time model that can be translated into a virtual exploration tool, which will help locate drilling sites.

Toksoz, along with Michael Fehler and Haijian Zhang received a grant of over $1 M in October of 2008 for a project titled “Detection and Characterization of Fractures for the Development of EGS.” The intent is to create a rock physics model combining geophysical methods for reservoir and fracture characterization using advanced laboratory measurements made on reservoir rocks under in situ conditions of temperature (up to 300°C) and pressure.

The investigators will be using data from the Cove Fort –Sulphurdale Geothermal field, which is an active geothermal energy field operated by ENEL North America (ENA). The resulting rock physics model will be combined with field observations into a comprehensive model of the fracture system, its flow properties, and new fracture development under realistic conditions within the reservoir. Characterization will include measurements of the bulk reservoir properties from P and S wave velocities, electrical resistivity, and seismic attenuation. Teleseismic, regional, and local seismic data will be analyzed to determine the bulk reservoir properties that will provide the foundation for fracture characterization studies. Direct fracture detection and characterization measurements will be made from new microseismic data collected in the field.

There remain additional complex observations to be made, but ultimately, laboratory and field results will be combined into a comprehensive model of in situ fracture locations, orientations, flow properties, and fracture development during reservoir development. The model will be tested with flow data from the existing reservoir and will be provided to ENA for use in designing a development plan for the higher-temperature resource that is believed to be located beneath the shallower, lower temperature reservoir.

Finally, Fehler, along with Alison E. Malcolm were awarded another $0.5 M for a proposal titled “Monitoring and Modeling Fluid Flow in a Developing EGS Reservoir.” The intent with this work is to combine detailed high-resolution analysis of microseismicity accompanying the stimulation of an EGS reservoir with a state-of-the-art geomechanical model of the reservoir to investigate the relationship between the seismicity and flow characteristics.

His work will be done using on a dataset from the Gunung Salak geothermal field that is being collected by Chevron. The site currently has cold water being injected into a borehole adjacent to the geothermal power development, creating an enhanced geothermal system in hot, low permeability rock.

Available data include open-hole log data from the injection borehole, pressure-temperature-spinner logs, fluid injection data (pressure and injection rate), and core samples and microseismic data from several monitoring stations. The microseismic data will be analyzed using a suite of contemporary techniques, and a description of the spatially-variable fracture permeability will be developed.

This description, and how it changes with time, will be used to predict the injection pressures and flow rates using the coupled thermal-hydraulic-geomechanical model. It is hoped that comparing the computed injection parameters with the observed parameters, as well as their change with time, will allow the narrowing of the range of descriptions that are plausible.

Taken together, the three sets of ongoing work, if successful, will go a long way in aiding EGS advancement by creating methods of determining the potential for success in advance. This would remove a good deal of the up-front cost risk. Another description of the three sets of ongoing work can be found here, from the MIT media folks.