Fault Patterns and Connectivity along Extensional Oblique and Lateral Ramps: Insights from Experimental Models

Bose, Shamik¹, Shankar Mitra¹ (1) University of Oklahoma, Norman, OK

Listric faults in passive margins such as Gulf of Mexico and Niger Delta are commonly characterized by oblique and lateral ramps caused by pre-existing structural or stratigraphic discontinuities. Clay experiments have been used to model geometry and connectivity of secondary faults formed along lateral and oblique ramps. Two configurations were used for the experiments, (1) a lateral ramp, with 90° offset of the frontal ramp, and (2) an oblique ramp, with 30° offset. The ramp configurations were created by offsets at the frontal edge of fixed footwall base plate. During extension, a set of synthetic and antithetic faults were formed, tied to the fixed footwall and moving hanging wall, respectively. The synthetic faults coalesced to form a single master fault, whereas antithetic faults formed a fault zone, made up of evenly-spaced, discrete fault segments. Characteristics such as fault orientation, density distribution, and shape, size and distribution of connected fault clusters varied with ramp offset angles, structural position and total extension. The secondary faults along oblique and lateral ramps were typically oriented at one third the angle of the basal offset. With increasing total extension, the maximum cluster size of connected faults increased dramatically in the oblique and lateral segments, due to intersection of fault sets of different orientations. Observations from the experiments provide important insights on geometry, shape and complexity of fault patterns, resulting compartmentalization of reservoirs adjacent to major faults, and influence of connected fault clusters on fluid flow and migration.