Microseismics / Stress

Microseismic events, basically very small earthquakes, accompany the production of hydrocarbons from some fields. They can also occur with the injection of fluids under pressure into subsurface rocks that is carried out to improve the permeability of hydrocarbon and geothermal energy reservoirs. Characterizing the microseismic events associated with human activities in the Earth’s subsurface provides information about the changes in the reservoirs and hence provides information about how to improve reservoir performance.

ERL undertakes several activities focused on improving our understanding of microseismic events. Some of these activities are focused on the application of earthquake seismology for locating the events and determining their focal mechanisms using approaches like full waveform moment tensor inversion. Along with location studies comes the use of traveltime tomography to determine velocity structure of the reservoir and to refine the location of the events. For geothermal exploration and reservoir characterization, we are collaborating with investigators at Lawrence Berkeley National Laboratory, in Iceland, and in Sweden to develop a method to simultaneously determine seismic and electromagnetic structure within a reservoir. The seismic data used for this inversion will come from natural and induced seismic events. Electromagentic data may come from active field measurements using manmade sources or from passive measurements where the electromagnetic source is the background electromagnetic field incident on the Earth from space. The use of a joint inversion approach will allow us to take advantage of the strengths of each type of data to better constrain the model. In addition, since reservoir changes are reflected differently in seismic and electromagnetic responses, we will obtain a more comprehensive characterization of reservoir processes by combining seismic and electromagnetic data.

A thorough understanding of the causes of the microseismic events and how they reflect reservoir evolution requires developing geomechanical models of the reservoir that include faults, the flow of fluids within the fracture structure, and the changes in the fracture structure in response to changes in fluid pressure and volume that accompany injection or production of fluids. We use space geodesy, including Interferometric Synthetic Aperture Radar (InSAR) and GPS measurements, to provide information about ground deformation that constrain the spatial distribution and size of volumetric changes within a reservoir and about slip along the larger faults within the reservoir.

Researchers with expertise in seismology, geomechanics, reservoir processes, and geodesy are studying microseismicity in energy reservoirs. Due to the breadth of expertise of the staff within the Earth Resources Laboratory that is being used to study microseismicity, we are in a strong position to greatly improve our understanding of these events.