Comparison of North American and European Shale Gas and Oil Resource Systems
Zumberge, John E.; Curtis, John B.; Brown, Stephen W.
The first natural gas well in North America was drilled into a Devonian shale formation near Fredonia, New York, USA in 1821. Shale gas production comprised only a small percentage of US production for the next 180 years, at which time a combination of technologies - primarily horizontal drilling improvements and development of multi-stage hydraulic fracturing for such wellbores - allowed what was predominantly gas-in-place to become economic production. Shale gas accounted for 23% of US gas production and 35% of technically recoverable resource in 2011.
A model for shale-gas and shale-oil producibility requires sufficient shale thickness, organic content (ideally hydrogen-rich), and an adequate level of thermal maturity to generate economic gas or oil volumes. Additionally, the mineral composition of the rock matrix (ideally silica-rich and clay-poor) must impart sufficient brittleness to enhance the effectiveness of stimulation treatments. Increased pore pressure (e.g., almost twice hydrostatic in the Jurassic Haynesville Formation of east Texas and north Louisiana, USA) will also enhance the nano- to micro-Darcy matrix permeability.
To begin any shale gas or oil resource evaluation, detailed information about hydrocarbon generation through time is required. This information has historically been derived through source rock analysis. However, another method using information on reservoired oils, depositional settings and thermal history is equally effective.
This study utilized a large oil database covering North America and all but Eastern Europe to compare and contrast the potential of shale gas and shale oil resource plays in each of the regions. The technique effectively identified basins with deepwater marine source rocks (type II kerogen) and measured the level of thermal conversion. The oil geochemistry and ancillary geological data analysis correctly identified known North American basins with shale gas/oil production or potential. The oil and gas play fairways were mapped for the North American basins, and prospective European basins were identified. Comparisons to North American plays indicated relative resource potentials to the sub-basin scale. As samples of reservoired oils are commonly more available (and at times more stratigraphically representative) than source rock information from outcrop, cores or cuttings, this approach can provide a deeper geochemical understanding of shale resource systems.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013