Application of global outcrop belts to exploration and field extension in the deep-water Gulf of Mexico

Jonathan R. Rotzien
Basin Dynamics, LLC

ABSTRACT

Exploration and field extension wells drilled in the Gulf of Mexico continue to face key geologic risks including reservoir presence and reservoir deliverability.  In particular, the deep-water Paleogene Wilcox Group shows a broad spectrum of lithofacies, depositional architecture, and reservoir quality over a stratigraphic interval exceeding 6000 ft in the thickest parts of the trend.  Further, a number of industry-sponsored studies have argued that the depositional environment for this group ranges from traditional leveed channels, to sandstone-rich lobes that lack distributary channels and conform to the shape of the underlying topography, to sandstone-poor overbank deposits that likely represent deep-water background sedimentation.  Clearly, there is room to enhance the understanding of the sedimentology, stratigraphic architecture, and reservoir characterization of target intervals in this trend.  
One of the methods to better understand the uncertainty in Gulf of Mexico petroleum reservoirs is via the study of global outcrop analogues.  This presentation features segments of two of the most thoroughly studied and classic deep-water outcrop belts from the Carboniferous Shannon Group of western Ireland and the Paleogene Annot Sandstone of southeast France, to highlight the stratigraphic complexities and similarities of each system to the Gulf of Mexico.  The history of exploration into these turbidite-dominated outcrops began well over a half century ago and inspired the famous work that led to the identification of Bouma and Lowe division terminology.  Today, these systems remain relevant as reservoir analogues for petroleum provinces and will continue to be useful for years as the nature of industry challenges evolve.  
Despite decades of research, two important questions have not been solved using the deep-water outcrops in Ireland and France.  Using a core drilled through these outcrops, (1) can depositional environment be distinguished and lateral bed continuity be estimated using a process sedimentology approach, and (2) can deep-water sandstone margins be recognized and predicted?  These questions address reservoir extent and reservoir quality using common core data that would be acquired in a routine drilling program.  Characterization of high resolution stratigraphic data including grain size, sedimentary process, bed thickness, and bed length from previously unpublished sections in each system reveals the range of solutions to both questions as well as the applicability of the workflow in quantifying geologic risk and reducing uncertainty in modern deep-water drilling programs.  Additionally, these results provide useful insights for assessing performance of petroleum reservoirs in comparable siliciclastic strata, both within the Gulf of Mexico and more generally.

BIOGRAPHY

Dr. Jon Rotzien is President of Basin Dynamics, LLC in Houston, Texas.  His expertise is the sedimentology and stratigraphy of deep-water depositional systems, basin analysis, and source-to-sink sediment transfer.  Jon aims to solve key challenges in the exploration and production of petroleum, including reservoir presence and quality forecasting in frontier basins, and reservoir connectivity, distribution, and deliverability.  Prior to his present position at Basin Dynamics, he was an exploration and appraisal geoscientist at BP.  He received a Ph.D. in Geological and Environmental Sciences from Stanford University and a B.A. degree in Geology from Colorado College.  He has published peer-reviewed research papers and scientific conference proceedings pertaining to reservoir quality, reservoir characterization, petroleum geology, sequence stratigraphy, process sedimentology, basin analysis, and geophysics.

FIGURE CAPTIONS

Figure 1.  Depositional architecture and a variety of deep-water sandstone margins exposed in the Paleogene Annot Sandstone in southeast France.  A) Southern margin of Chalufy Mountain showing three overbank splays that onlap blue marl at the basin margin, B) northern margin of Chalufy Mountain showing a frontal splay complex overlain by a channel complex, C) study area for the Annot Sandstone in southeast France highlighted by the red box, D) sandstone-on-sandstone channel margin, part of a larger feeder channel complex above the town of Annot, and E) laterally continuous turbidite packages that onlap a steeply dipping basin margin (>10°) near the village of Braux.

Figure 2. Photographs of Pennsylvanian Ross Sandstone beds in the vicinity of Rinevilla, County Clare, Ireland, and sample measured sections of channelized (8 m interval above middle) and non-channelized (16 m interval above right) intervals. The main lithofacies include thick-bedded sandstone, medium- to thin-bedded sandstone and mudstone, and mudstone.  Some of the thick mudstone intervals show evidence of remobilization and deposition due to slumping or mass-transport processes.  The majority of the sandstone intervals exhibit diverse sedimentary structures, and include partial Bouma Ta-e sequences, as well as M and H divisions representing deposition via transitional flow.  This observation implies a significant reinterpretation of the flows that deposited these beds, because historic research suggests these beds were deposited strictly via direct suspension sedimentation and do not show evidence for traction sedimentation.  Red and white intervals on scale are 20 centimeters.