Geothermal energy production by water circulation in natural and/or man-made fracture systems is referred to as enhanced or engineered geothermal systems (EGS). The permeable zones of an EGS must be created by stimulation, a process which involves fracture initiation and/or activation and propagation of discontinuities such as joints by pore pressure and stress perturbations. Economic design and operation of EGS can be achieved by reliable characterization of the stimulation results which relies mostly on analysis of MEQ and tracers. In this work we study the reservoir stimulation process on a laboratory scale to improve the current understanding and to help quantify the fracture geometry using AE cloud, spontaneous potential, and tracer analysis. To do so, we have developed a new poly-axial hydraulic fracturing test system which allows us to perform reservoir stimulation experiments on rock blocks with size up to 18’ x18” x 18” under pore pressure and representative in-situ stress regimes while simultaneously recording SP and AE during fracturing and circulation. The system can operate at relatively high temperatures (150oC). In this paper, we describe preliminary experiments conducted at room temperature. Results show excellent correlation between fracturing and the SP signal. Also, stimulation has been accompanied by AE events that are generally correlated with the stress state and fracture geometry.

Press the Back button in your browser, or search again.

Copyright 2016, Stanford Geothermal Program: Readers who download papers from this site should honor the copyright of the original authors and may not copy or distribute the work further without the permission of the original publisher.