Method and Application of Stress Inversion based on Strike, Dip, and Rake Data from Microseismic Focal Mechanisms and Fracture Network

Abstract

The hydraulic fracturing of horizontal wells is a key stimulation technology for unconventional tight oil/gas reservoirs. Good knowledge of the near-well stress field of a horizontal well can be helpful for the hydraulic fracture design optimization of new wells and refrac design optimization of fractured wells. Azimuth and dip data derived from either focal mechanisms of hydraulic fracturing-induced microseismic events or fracture attributes of hydraulic fracture networks can be used for new-well stress field inversion. In this work, we present a novel stress inversion method integrating azimuth, dip, and rake data from the focal mechanisms of hydraulically induced microseismic events and fracture attributes of hydraulic fracture networks. For those stages having sufficient reliable microseismic focal mechanisms, strike, dip, and rake data derived from microseismic focal mechanisms are taken as input data for stress inversion. Meanwhile, for those stages that have no microseismic events or insufficient reliable microseismic focal mechanisms, azimuth and dip data derived from fracture attributes of prebuilt hydraulic fracture network are used for stress inversion, along with azimuth, dip, and rake data derived from other stages with sufficient reliable microseismic focal mechanisms. Thus, the near-well stress field of each stage can be inverted, regardless of whether or not it has hydraulically induced microseismic events. The new method has been applied in the field surface microseismic dataset during hydraulic fracture stimulation. The results reveal that the inverted near-well stress fields are consistent with the stress orientation derived from shear-wave splitting analysis for sonic logs. This finding demonstrates that the stress inversion method based on strike, dip, and rake data derived from microseismic focal mechanisms and fracture networks can correctly obtain the azimuths of maximum and minimum horizontal stress.