Bureau of Economic Geology, The University of Texas at Austin (www.beg.utexas.edu).
AAPG Annual Convention, Houston, Texas, April 9–12, 2006
Nucleation and Evolution of the Early Stage in the Development of Growth Faults Using 3D Seismic Interpretation
Growth faults can have a significant impact on reservoir geometry, shale layer extent and hydrocarbon migration. Small growth faults however, cannot easily be distinguished from blind faults which are the result of propagation entirely within the subsurface domain, with no free surface interaction. This has considerable implications for fault dating activity, reservoir prediction and seal integrity, and therefore a better understanding of the kinematics of fault growth is required.
In order to address this problem, geometrical and displacement analyses have been undertaken using 3D seismic data from the Levant Basin, offshore Israel. The dataset shows a diversity of structures and sedimentation of a passive continental margin related to gravity tectonic. A simple geometrical approach based on throw-versus-depth plots was used to reconstruct the nucleation, segmentation and propagation history of medium scale coast-parallel growth faults located on the shelf break. These faults offset clay-rich Pliocene and Pleistocene sediments overlying a thick layer of Messinian evaporites. We show that the timing of growth faulting is linked to the long term kinematic evolution of a major salt-withdrawal graben. A detailed analysis of the displacement, fault drag and tip line geometry reveals the parts of segmentation that are related to lateral linkage or bifurcation of the fault plane. It also shows that these faults nucleated close to the surface with blind tips propagating downwards at high gradients.
These results have wide implications for the early propagation history of growth faults, and show that significant wallrock strains can develop prior to the synsedimentary stage.