Optimum sensor configuration of surface arrays for retrieving accurate source mechanisms of microseismic events

Abstract

Hydraulic fracturing and induced networks are significant for effective production of oil and gas from unconventional resources. The knowledge of fracturing source mechanisms is helpful for optimizing hydraulic fracturing treatments to maximize production. For source monitoring, the moment tensor inversion is commonly used and the source mechanisms are interpreted by the radiation patterns of microseismic waves. The accuracy of source interpretation is significantly influenced by sensor configurations, which still need further researches. In this study, the mechanism of sensor arrangements to suppress noise effect is analyzed and clarified mathematically, then an optimization method of searching for proper sensor configurations is proposed. For superior sensor configurations, errors caused by noise can be allocated evenly to the 6 moment tensor components and the source interpretation based on the moment tensor decomposition is till accurate, but errors can not be completely eliminated by optimizing sensor configurations. Generally, high-precision inversion results can be calculated by the sensor configuration that one sensor is at the center and the others are around at the same angular intervals. Compared with tradition sensor configurations, this new one can achieve similar inversion accuracy by less than a third of the sensors. Sensor numbers are not the more the better and dependent on the sizes of the regions of sensor arrangement. The conclusions arrived in this study are helpful for evaluating and designing sensor configurations for hydraulic fracturing monitoring.