Cross double‐difference inversion for simultaneous velocity model update and microseismic event location

Abstract

Microseismic monitoring is an approach for mapping hydraulic fracturing. Detecting the accurate locations of microseismic events relies on an accurate velocity model. The one‐dimensional layered velocity model is generally obtained by model calibration from inverting perforation data. However, perforation shots may only illuminate the layers between the perforation shots and the recording receivers with limited raypath coverage in a downhole monitoring problem. Some of the microseismic events may occur outside of the depth range of these layers. To derive an accurate velocity model covering all of the microseismic events and locating events at the same time, we apply the cross double‐difference method for the simultaneous inversion of a velocity model and event locations using both perforation shots and microseismic data. The cross double‐difference method could provide accurate locations in both the relative and absolute sense, utilizing cross traveltime differences between P and S phases over different events. At the downhole monitoring scale, the number of cross traveltime differences is sufficiently large to constrain events locations and velocity model as well. In this study, we assume that the layer thickness is known, and velocities of P‐ and S‐wave are inverted. Different simultaneous inversion methods based on the Geiger's, double‐difference, and cross double‐difference algorithms have been compared with the same input data. Synthetic and field data experiments suggest that combining both perforation shots and microseismic data for the simultaneous cross double‐difference inversion of the velocity model and event locations is available for overcoming the trade‐offs in solutions and producing reliable results.

Localization for surface microseismic monitoring based on arrival time correction and VFOM

“…Categorized according to the type of observation information utilized, current methods generally fall into two groups: travel time-based and waveformbased approaches. In the conventional positioning method, the objective is to achieve the optimal alignment between the theoretical framework and the observed (relative) arrival time of P/S waves, employing functions such as double difference [13], cross double difference [14]. Consequently, the precision of time picking significantly influences the accuracy of localization.…”

Microseismic Source Location Estimation Using Reverse Double-Difference Time Imaging

“…Guo et al [17] proposed a double-pair double-difference location method, using the advantages of the two double-difference methods to estimate a higher-precision earthquake location. Tian [18] proposed a cross double-difference location method using the travel time difference of the P wave and S wave of the event pair. This method adds absolute location information to the traditional double-difference location method and inverts the relative location and absolute location at the same time.…”