Surface Array Moment Tensor Microseismic Imaging

Abstract

Moment Tensor Microseismic Imaging (MTMI) is a novel and robust technique for locating point sources with a higher accuracy than conventional diffraction stack methods, and allows for either single or multicomponent data. The effect of the source radiation pattern is negated by projecting data onto moment tensor (MT) components prior to stacking, and a source intensity (SI) stack function is computed as the sum of the squares of the MT components. In addition to the accurate locations, MTMI has the advantage of using non-linear imaging statistics, such as semblance, to provide source characterisation even at low signal to noise ratios (i.e. << 1). In this study, single component data recorded at a surface receiver network during hydraulic fracturing are processed and analysed using MTMI. Two distinct clusters of point sources are identified in the results. These clusters exhibit grouping in position, amplitude and time. For each cluster, a representative event is taken and further examined. Through comparison with synthetic sources, it is shown how the MTMI component stack functions can be used to categorise event/source mechanisms and aid fracture interpretation.