Quantitative Analysis of Relay Ramp Evolution and Breaching: Implications for Structural Interpretation of Linked Fault Arrays

Trudgill, Bruce¹ (1) Colorado School of Mines, Golden, CO

The segmentation of normal fault systems is now well established from both field and seismic interpretation analyses. Relay ramps are ephemeral features that develop during the evolution and growth of fault systems by linkage of overlapping segments. The controls on relay ramp development have been discussed in a general sense, e.g., preexisting structures, lithology, ramp width, fault overlap lengths etc., but a better understanding of the variables that control ramp breaching is needed before any quantitative predictions can be made as to whether or when a ramp in the subsurface has breached. This study examines the controls on fault segmentation and growth across a wide range of scales from small-scale field examples to large-scale normal fault systems imaged on 3D seismic data and superbly exposed in the field in southeast Utah.

The results of this study have important practical implications for the structural interpretation of subsurface data (trapping mechanisms, fault seal etc.), and understanding the growth of normal faults through time (extensional basin evolution).

Some key questions addressed by this study include: (1) How (and why) do controls on relay ramp breaching vary between field, sandbox models and subsurface examples? (2) Why do sandbox model examples show a preference for frontal breaching (55%), while field examples show a strong preference for rearward breaching (~90%)? (3) What controls the dip of relay ramps and how do dips vary with overlap/spacing variations? (4) How do these variables influence trapping mechanisms for oil and gas?