Joint Velocity Model and Microseismic Event Location Inversion Benefit the Measure, Monitor and Verify Value Chain

Abstract

In carbon capture and storage projects, and in unconventional plays, microseismic monitoring and optical fiber are critical components of the measure, monitor, and verify value chain. A velocity model is required to estimate source location (hypocenter), source parameters, and source mechanism of a detected microseismic event. Incorrect event locations are often the result of an inaccurate knowledge of the velocity model. We propose a new method to simultaneously invert for the hypocenter and the velocity model to provide a robust long-term microseismic monitoring workflow. Such problem has been studied in several areas of seismology over the last few decades. However, those studies focusing on large-scale earthquakes have remained of limited interest to reservoir-scale applications such as short-term and long-term microseismic monitoring and induced seismic monitoring. In such domains, the integration of sonic log-derived information into the joint inversion problem is critical as the scale is fundamentally different. Our algorithm respects the resolution of sonic measurement, while it calibrates the wavelength where microseismic data have sensitivity: the number of unknown parameters in the velocity model is decoupled from the number of layers included in the model. Therefore, we can solve for the velocity and event location inversion problem in a stable manner while respecting the resolution of the initial velocity model. In the present article, we introduce the science and technique behind the simultaneous inversion for the hypocenter and the velocity model and share case study applications based on a synthetic dataset and a real monitoring campaign.