Autotracking of faults on 3D seismic data

Abstract

Manual fault mapping in 3D seismic interpretation is labor-intensive and time-consuming. Complex fault geometries and the distortion of the seismic signal close to faults complicate full automation of the fault-mapping process. We present a semiautomatic fault-tracking method for 3D seismic data that consists of fault highlighting followed by model-based fault tracking. Fault highlighting uses log-Gabor filters for emphasizing oriented amplitude discontinuities at faults in the presence of noise. Subsequent fault tracking fits an active contour to the highlighted fault voxels. The active contour searches for a connected, smooth curve which fits the data and disambiguates misleading or missing information. The fault tracker requires the interpreter to place the active contour close to a fault on one initial seismic inline (2D pick). The active contour deforms to the closest amplitude dis-continuity highlighted. This tracking result is then projected forward to the next inline, providing an initial fault pick on this section that is again optimized by the active contour. Tracking results on a series of successive seismic sections, finally, constitute a 3D fault surface. User interaction is solely required for an approximate fault pick on the first inline, and in cases where the fault line is lost due to insufficient signal. Use of the autotracker prototype provides a fast solution for the mapping of complete 3D fault surfaces of constant dip, and for the automated tracking of fault portions within distinct dip domains, if fault surfaces are curved (i.e., listric). The method was applied to a series of high-quality reflectivity sections extracted from a 3D seismic volume from shallow-offshore Nigeria, with the tracking results (generated within seconds) comparing well with manually interpreted fault surfaces.