Optional Field Course | 4–6 November
Petroleum Systems of the Cretaceous Platform, Onshore Gulf of Mexico
Field Course Leader: W. Lansing ‘Lans’ Taylor
As part of the 2016 EGI Corporate Affiliates Annual Meeting, we are pleased to offer a pre-conference two-day field trip to view ‘Petroleum Systems of the Cretaceous Platform, Onshore Gulf of Mexico.’
This field course provides access to high quality outcrops of key stratigraphic intervals for the Cretaceous-aged petroleum systems of the Texas Gulf Coast. Key concepts include: 1) comparison of conventional, karst, fractured, and unconventional reservoirs, 2) discussion of faulting process and how mechanical stratigraphy impacts the development of secondary porosity, and 3) the geologic setting of source rocks including impacts of tectonics vs eustacy and the role of volcanism.
These outcrops illustrate the characteristic geometry of post-rift thermal subsidence which produces a basin-ward dipping unconformity on-lapped by transgressive sediments. As such, the TX outcrops serve as analogs for other thermally subsiding petroleum basins such as the Cretaceous to Eocene section in the Llanos Basin of Colombia or the TAGI system in the Ghadames Basin of Algeria.
Estimates of the in-place resource in the Eagleford Formation range from 5 BBO to 28.7 BBO and from 50 TCF to as much as 315 TCF of gas (Gong, et al., SPE-167241-MS). Eagleford-sourced liquids are produced as gas condensate from the source rock as an unconventional reservoir, but gas also migrates up-section into the fractured Austin Chalk and down-section into the karsted Buda Formation. While the Eagleford has the largest in-place reserves, the Austin Chalk has the highest delivery with some historic gas wells flowing in excess of 100 Mmcf/day and producing more than 75 BCF/well.
The three formations are in pressure communication and are over-pressured compared to the encasing stratigraphy. The stratigraphic extent of overpressure is coincident with a strata-bounded polygonal fault system that appears to have formed through dewatering of the Eagleford formation near the end of the Cretaceous.
We will visit outcrops of the Buda, Eagleford, and Austin Chalk formations to compare secondary karst and natural fractures with porosity developed through maturation of organic matter. We will see soft-sediment deformation in the Eagleford and well-exposed faults in the Austin Chalk, both elements of a polygonal fault system. After visiting Natural Bridge Cavern, we end the day at McKinney Falls State Park with a discussion of volcanism and its role in producing organic-rich source facies.
On the second day, we will view the James Lime at Pedernales Falls State Park and Hamilton Pool illustrating differences between tectonic- and eustatic- controlled sedimentary systems. We will conclude the day at the Eocene Carrizo Sandstone, a prolific conventional reservoir.