Tool and Velocity Model Calibration for Downhole-Based Hydraulic Fracture Monitoring of Induced Microseismicity

摘要

With downhole-based microseismic monitoring jobs, obtaining accurately mapped hypocentral locations and associated source parameters depends on the correctness of the calibration process. Commonly downhole-based passive microseismic monitoring requires one or more arrays of 3C sensors to be lowered to appropriate depth(s) in one or more monitoring wellbores using wireline cables. During this process, each shuttle housing a three-component sensor might rotate (Le Calvez et al., 2005, Bulant et al., 2006). For this reason, tool orientation using one or more sources at known locations is critical to properly locate detected microseismic events. Similarly, once the tool string has been oriented, the initial log-derived isotropic velocity model must be calibrated for anisotropy. Though a fully 3D velocity model describing the relevant geology and rock physics is preferable, the velocity model used for microseismic monitoring is most often ID or, at best, 2D (i.e., ID with dip and azimuth).