Leon Dzou¹, Stephen Petmecky¹, Andrew Pepper¹
(1) BP Amoco Upstream Technology Group, Houston, TX

Abstract: East Texas Basin petroleum systems revisited: is long distance migration to the giant East Texas Field really necessary?

The East Texas Basin is a prolific petroleum province with production from many trap types and reservoirs (Upper Jurassic through Upper Cretaceous). Geochemical data indicate three major chiefly oil-prone source rocks: Oxfordian Smackover carbonates, Aptian Pearsall clastics and Turonian Eagle Ford clastics; an additional clastic source rock, the Tithonian Bossier Shale, appears to be gas-prone here. While vertical migration clearly can be demonstrated in the basin, geochemical data show that the Eagle Ford is the source of the 7.5 billion barrels of oil in place in underlying Woodbine reservoirs in the East Texas Field. Previous studies of petroleum migration suggested that East Texas Field oil was generated beyond the southern confines of the East Texas basin, implying a migration distance of 100 km or more. We re-evaluated the thermal and petroleum expulsion history of the area using a combination of 1-D (GENEX) and 2-D (TEMISPACK) thermal models; these are calibrated using available temperature data in addition to proprietary global models of both vitrinite reflectance and thermal stress-dependent biomarker ratios. Our study shows that inclusion of multiple thermal stress indicators (rather than relying solely on over-simplified models of vitrinite reflectance) can yield significantly different results. While it is not possible to rule out a long distance contribution from the Gulf Basin, we show that, prior to regional uplift and erosion in the Neogene, Eagle Ford source rocks in the East Texas Basin to the west of the East Texas Field were mature for expulsion and probably delivered significant volumes of petroleum into the underlying Woodbine sand carrier-reservoir system. This provided an efficient, focussed drainage pathway into the updip truncation trap which forms the East Texas Field on the western flank of the Sabine Arch.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana