Publications

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During the initial phase of this Department of Energy (DOE) Geothermal Technologies Office (GTO) SubTER project, we conducted a series of high-energy stimulations in shallow wells, the effects of which were evaluated with high resolution seismic imaging campaigns designed to characterize induced fractures. The high-energy stimulations use a novel explosive source that limits damage to the borehole, which was paramount for change detection seismic imaging and re-fracturing experiments. This work provided evidence that the high-energy stimulations were generating self-propping fractures and that these fracture locations could be imaged at inch scales using high-frequency seismic tomography. While the seismic testing certainly provided valuable feedback on fracture generation for the suite of explosives, it left many fracture properties (i.e. permeability) unresolved. We present here the methodology for the second phase of the project, where we are developing and demonstrating emerging seismic and electrical geophysical imaging technologies that have been designed to characterize 1) the 3D extent and distribution of fractures stimulated from the explosive source, 2) 3D fluid transport within the stimulated fracture network through use of a contrasting tracer, and 3) fracture attributes through advanced data analysis. Focus is being placed upon advancing these technologies toward near real-time acquisition and processing in order to help provide the feedback mechanism necessary to understand and control fracture stimulation and fluid flow.

During the initial phase of this SubTER project, we conducted a series of high resolution seismic imaging campaigns designed to characterize induced fractures. Fractures were emplaced using a novel explosive source that limits damage to the borehole. This work provided evidence that fracture locations could be imaged at inch scales using high-frequency seismic tomography but left many fracture properties (i.e. permeability) unresolved. We present here the methodology for the second phase of the project, where we will develop and demonstrate emerging seismic and electrical geophysical imaging technologies that characterize 1) the 3D extent and distribution of fractures stimulated from the explosive source, 2) 3D fluid transport within the stimulated fracture network through use of a contrasting tracer, and 3) fracture attributes through advanced data analysis. Focus will be placed upon advancing these technologies toward near real-time acquisition and processing in order to help provide the feedback mechanism necessary to understand and control fracture stimulation and fluid flow.

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Muons are subatomic particles capable of penetrating the earth's crust several kilometers. Muons have been used to image the Pyramid of Khafre of Giza, various volcanoes, and smaller targets like cargo. For objects like a volcano, the detector is placed at the volcano's base and muon fluxes for paths through the volcano are recorded for many days to weeks.

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Seismic attenuation is defined as the loss of the seismic wave amplitude as the wave propagates excluding losses strictly due to geometric spreading. Information gleaned from seismic waves can be utilized to solve for the attenuation properties of the earth. One method of solving for earth attenuation properties is called t*. This report will start by introducing the basic theory behind t* and delve into inverse theory as it pertains to how the algorithm called tstarTomog inverts for attenuation properties using t* observations. This report also describes how to use the tstarTomog package to go from observed data to a 3-D model of attenuation structure in the earth.

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