3-D Finite Difference Modeling of Microseismic Source Mechanisms in the Wolfcamp Shale of the Permian Basin

Abstract

Summary Microseismic data acquired during hydraulic stimulations are a key tool in determining well spacing, stimulation parameters, frac barriers, and natural and hydraulic fracturing relationships. In addition to hypocenter locations of the fracturing mechanism, attributes associated with the microseismic event including magnitude and P-S amplitude ratios provide valuable insight into the stimulation. These attributes can be used as weights in the calculation of microseismic derived stimulated rock volumes to determine effective draining areas. High velocity layers associated with carbonate debris flows are known to distort the seismic wave field and may have an effect on associated microseismic derived attributes. In this study we use a 3D elastic finite difference algorithm to model double couple and open tensile source mechanisms at different levels in the Wolfcamp shale of West Texas to determine the sensitivity of microseismic attributes and location to the geology and array configuration. Magnitude, P-S ratio, and event location from a horizontal and vertical array are examined. 3D snapshot movies of the different mechanisms show the complexity of the developing wave field and the location of nodal planes which could interfere with the position or observation of microseismic events. The modeling showed that attributes derived from a vertical array are more robust than attributes from a horizontal array. Attributes from events that occurred near high velocity layers such as carbonate debris flows may be less accurate than events that occurred in more consistent lower velocity layers. Event location and microseismic event attributes recorded from a vertical array are more accurate than events recorded from a horizontal array.