AAPG Annual Convention and Exhibition

Datapages, Inc.Print this page

Eagle Ford Petroleum System as an Exploration Analog

Abstract

Eagle Ford is a complex petroleum system of a prolific source rock related to multiple conventional and unconventional plays through juxtaposition or faults, in addition to being a source rock play. This study reviews the relationship and dynamics that resulted in these accumulations and the potential for it being an exploration analog in other basins. Eagle Ford is recognized as an excellent source rock for conventional accumulations, based on its geochemical properties, maturation history and oil-source correlations, in East Texas basin where it is vertically homogenous, clay-rich with limited to no carbonates. Direct juxtaposition with the enclosed Woodbine sand, enabled primary migration. Primary migration also takes place the overlying Austin Chalk, where low permeability limits secondary migration, resulting in a pervasive regional accumulation. Eagle Ford resource play appears to have resulted due to stratification of kerogen-rich and diagenetically altered tight limestone layers, that act as internal seals. The regional extent of the play is related to the extension of this architecture across the entire central and south Texas area. The only paths for migration for the hydrocarbons trapped in this overpressured system were fault systems, flanking Karnes Graben, Edwards- Sligo shelf margin and salt rollers & diapirs, connecting the source rock to shallower reservoirs. Numerous tight reservoirs form regionally continuous plays along these fault zones including Austin Chalk, Buda, Pecan Gap and Olmos. In Austin Chalk, the fault zones are loci of fracture swarms where increased permeability elevates the play above economic threshold. The same may apply to Buda and Pecan Gap. Olmos play distribution is determined by the sand geometry and its intersection with fault conduits that connect to Eagle Ford. Coincidence of fluid zones and fluid contacts of these reservoirs, is a strong evidence of the genetic correlation between these plays and source rock. Understanding source-reservoir relationships in the Eagle Ford petroleum system can help in applying the migration-accumulation mechanism to exploration of other mixed conventional-unconventional petroleum systems. Further, analysis of rock properties including TOC & organic porosity and fluid properties, including overpressures, in a geological context can assist in building geologically constrained sweet spot models for field development.