Effects of Convergent, Radial-Gliding “Corner” Geometry on Petroleum Charge, Port Isabel Passive-Margin Foldbelt, Northwestern Gulf of Mexico

Abstract

Previous workers have described the effects of downslope motion of salt and shale along relatively simple, straight passive margins versus more complex, passive margin “corners” like the Santos basin of Brazil and the Lions basin of the western Mediterranean Sea, where salt and shale evacuate and glide downslope from multiple directions to produce thicker and more chaotic thicks at a basal, accumulation point. The Port Isabel foldbelt (PIFB) of the northwestern Gulf of Mexico (GOM) is located at a right-angle corner defined by the intersection of the east-west-trending northwestern and north-south-trending western shelves of the GOM. We present a three-dimensional analysis of the complex salt deformation in this corner by combining high-resolution bathymetry with over 20,000 line km of seismic reflection data that ranges in vintage from 1980's to 2007 and in depth of penetration from 7 seconds to 25 seconds. Our mapping has revealed three structural zones: 1) Shelf and lower shelf normal faults of the Corsair fault system of coastal Texas that sole onto a two separate detachments within the convergent part of the Port Isabel passive margin fold belt on the slope and deeper basin; 2) Prominent salt evacuation surfaces of the upper slope area within the more elevated parts of the corner area; this area is also characterized by detached salt stocks with positive expression on the seafloor that we interpret as reflecting a higher degree of corner-related, radial convergent gliding; and 3) Lower slope, chaotic, salt-involved convergent structures including both landward and seaward-dipping reverse faults and large anticlines. Using this structural framework, we have constructed a 2D petroleum system model (PSM) for the entire PIFB that is based on three potential source rocks of Tithonian, lower Cretaceous and early Tertiary age. The PSM reveals that the Tithonian is mature with a high transformation ratio especially in the deeper part of the basin, the Cretaceous is peaked out, and the early Tertiary is in oil window. Only 7 wells have been drilled into the PIFB with 6 dry holes and one discovery. Dry holes may reflect migration pathways that are blocked by more complex, corner-related faults

AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017