STRESS-CONTROL OF SEISMICITY PATTERNS OBSERVED DURING HYDRAULIC FRACTURING EXPERIMENTS AT THE FENTON HILL HOT DRY ROCK GEOTHERMAL-ENERGY SITE, NEW-MEXICO

A new scheme for determining orientations and locations of planes along which the micro-earthquakes occurred was recently developed. The basic assumption of the method, called the three-point method, is that many of the events fall along well-defined planes; these planes are often difficult to identify visually in the data because planes of many orientations are present. The method has been applied to four hydraulic fracturing experiments conducted at Fenton Hill as part of a hot dry rock geothermal energy project. While multiple planes are found for each experiment, one plane is common to all experiments. The ratio of shear to normal stress along planes of all orientations is calculated using a best estimate of the current stress state at Fenton Hill. The plane common to all experiments has the highest ratio of shear to normal stress acting along it, so it is the plane most likely to slip. Additional aspects of the subject are discussed.