Effective anisotropic velocity model from surface monitoring of microseismic events |
| |
| Authors: | Yang Zhang Leo Eisner William Barker Michael C Mueller Kevin L Smith |
| |
| Institution: | 1. Department of Geological Sciences, University of Michigan, , Ann Arbor, MI, 48109 USA;2. Institute of Rock structure and Mechanics, Academy of Sciences of the Czech Republic, , Prague, Czech Republic;3. Microseismic Inc., , Houston, TX, 77042 USA;4. Encana Corporation 1800, , Calgary, Canada |
| |
| Abstract: | We develop a methodology to obtain a consistent velocity model from calibration shots or microseismicity observed on a buried array. Using a layered 1D isotropic model derived from checkshots as an initial velocity model, we invert P‐wave arrival times to obtain effective anisotropic parameters with a vertical axis of symmetry (VTI). The nonlinear inversion uses iteration between linearized inversion for anisotropic parameters and origin times or depths, which is specific to microseismic monitoring. We apply this technique to multiple microseismic events from several treatments within a buried array. The joint inversion of selected events shows a largely reduced RMS error indicating that we can obtain robust estimates of anisotropic parameters, however we do not show improved source locations. For joint inversion of multiple microseismic events we obtained Thomsen anisotropic parameters ε of 0.15 and δ of 0.05, which are consistent with values observed in active seismic surveys. These values allow us to locate microseismic events from multiple hydraulic fracture treatments separated across thousands of metres with a single velocity model. As a result, we invert the effective anisotropy for the buried array region and are able to provide a more consistent microseismicity mapping for past and future hydraulic fracture stimulations. |
| |
| Keywords: | Anisotropy Microseismicity Inversion |
|
|
