Microseismic Monitoring of Hydraulic Fractures in Prudhoe Bay

Abstract

Abstract Production stimulation is commonly performed on reservoirs by hydraulically fracturing the formation. Fracture geometry is controlled by the regional stress field, strength and contrast in local rock stress and fracture fluid properties. Computer models predict the length and height of the fracture as a function of injection volume, pressure and rate, and, fluid and rock properties. Until recently, these computations were unable to be verified except for the fracture half length with pressure transient analysis and through log interpretation in close proximity to the well. Direct confirmation of fracture geometry has been shown possible with availability of downhole geophysical monitoring of the seismicity associated with the fracture production. This paper presents results of a test to directly measure the height, length, and azimuth of a fracture generated in the Prudhoe Bay Field, Alaska. Two triaxial geophone tools were deployed during August 1993 to monitor for microseismicity associated with a hydraulic fracture. One tool was deployed in an offsite monitoring well, and the second tool was deployed in the rathole of the fractured well. The objectives of the test were (1) to determine if seismicity existed and if it could be detected from within the fractured well and from the distant offsite monitoring well, (2) to evaluate techniques used to locate the fracture, and (3) provide guidance for the development of seismic recording systems used in fracture monitoring.