Fracture Evaluation by VEP Electrical Resistivity Method

点击翻译按钮获取中文摘要

For Hot Dry Rock (HDR) geothermal energy development, it is necessary to establish technologies for creating artificial fractures between injection and production wells as geothermal reservoirs and for evaluating their distribution and flow capacity on the site.In this study, Vertical Electric Profiling (VEP) method using a casing pipe as a current electrode has been conducted for monitoring fluid-flow behaviors during massive hydraulic fracturing operations'on HDR project at Akinomiya by Central Research Institute of Electric Power Industry in Japan. The injected fluid-flow could be continuously detected and monitored with multiple non-polarizing electrodes on the ground surface surrounding the hydraulic fracturing well by the digital recording system controlled by a Personal Computer on the site.The distribution of fractues estimated from the detected flow paths showed good agreements with the geometry of fractures obtained by Borehole Television (BHTV) and Acoustic Emission (AE) survey data.Hole-to-hole (crosshole) survey was also conducted during fracturing operations for locating the major flow paths more accurately with depth.The VEP (hole-to-surface) survey provides lateral distribution of major fractures created by hydraulic fracturing operations, while the crosshole (hole-to-hole) survey gives information about the depths of flow paths connected between injection and production wells on the site.Therefore, we could obtain the fluid-flow paths with time variations and major fractures in three-dimensions by the joint use of hole-to-surface (VEP) and hole-to-hole (geotomography) electrical resistivity surveys with computer cotrolled data acquisition system on the site.