Volume Based Curvature Analysis Illuminates Fracture Orientations, Fort Worth Basin, Texas
Charles H. Blumentritt1 and Bill Stinson2
1 Geo-Texture, Inc, Houston, TX
2 Carrizo Oil and Gas, Inc, Houston, TX
Analysis of the curvature of mathematic surfaces has been around since the time of Gauss (1820's) and has been applied to geologic surfaces for over 40 years. We compute a surface and the corresponding curvatures for every sample in a three dimensional (3-D) seismic survey and extract curvature values along interpreted surfaces and time slices to study the orientations of fractures and other geologic phenomena. We apply these techniques to a data set from the Fort Worth Basin and find that the lineaments identified on the curvature data volumes are consistent with the fracture orientations observed in FMI logs from two wells within the survey.
Historically, analysis of the so-called Gaussian curvature illustrates locations where the surface departs from a simple folded sheet, thus requiring warping or shattering of the surface. These areas, by necessity, are areas where the surface is most likely to be fractured. Fractures may also occur in areas where a surface is folded in a simple, cylindrical manner. Such folds appear as lineaments on horizon and time slice displays of maximum curvature, and its corollaries most positive curvature and most negative curvature. The orientations of these folds yields information about the orientations of the principal horizontal stresses.
In our case study, we observed lineaments in preferred orientations on the maximum curvature data and found that these preferred orientations correspond to the orientations of natural and drilling induced fractures interpreted from FMI logs from two vertical wells. We further observed a small rotation of the principal horizontal stress directions between the two wells and attribute this effect to the proximity of significant solution events to one of the wells.