FAULT OBSERVATIONS IN LOWER MIOCENE TO RECENT SEDIMENTS USING HIGH-RESOLUTION SHALLOW P-CABLE AND CONVENTIONAL OFFSHORE 3-D SEISMIC DATA IN THE SAN LUIS PASS, TEXAS

Offshore seismic studies along the Texas Gulf Coast have helped characterize normal faulting in the Clemente-Tomas fault system (CTFS) at considerable depth beneath the current continental shelf, but sufficient near-surface data resolving the characteristics these faults within the overburden sediments has been lacking due to the inherent resolution of conventional 3-D data and the low probability of borehole penetration through individual fault zones. Recent observations of the NE-SW trending, SE dipping listric growth faults and associated antithetic faults using both high resolution P-Cable 3-D (HR3D) and conventional 3-D seismic data collected over the San Luis Pass indicate that many Lower Miocene faults in the region offset shallow Middle Miocene and younger strata. High frequency (dominant frequency ≈ 150 Hz) HR3D surveys conducted in 2012 and 2013 allow for meter-scale vertical and horizontal resolution images (0-1500 ms TWT) of faults and strata, which are poorly represented in conventional seismic data with decameter scale vertical resolution and extent. Faults with hundreds of meters of offset at depth are found to have fault tips as close as 45 ms TWT (~ 35 m) below the sea floor, suggesting that the last episodes of displacement are recent or possibly ongoing. Faults are recognized to be both barriers and conduits for fluids within surrounding petroleum reservoirs, and the failure of wells drilled in and around the 72 km² HR3D survey area is linked to ineffective fault seal. Wells in close proximity to faults with measurable damage zone width and fluid plumes in the shallow subsurface tend to have low success rates. The data also indicates that large faults with tips close to the sea floor often displace Lower Pliocene top seals and may provide conduits for fluid migration, significantly reducing the amount of producible hydrocarbons within the reservoirs they intersect at deeper intervals. These observations support the utilization of high-resolution shallow seismic data, which can yield additional fault information for evaluating further petroleum development or proposed carbon sequestration projects in Lower Miocene reservoirs along the CTFS.