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Shales That Burn


The exploitation of shale oil and gas resources has expanded exponentially in recent years with the benefit of technological advances in drilling and completion practices, converting non-commercial low-permeability rocks into major producing reservoirs. The hydrocarbon-bearing character and source-rock potential of many of these shales has been known for decades, as millions of historical wells have drilled through them in the search for conventional reservoirs in stratigraphic proximity. Long before the drilling industry provided access to these shales under subsurface pressurized conditions, the outcrop versions of many of them had been studied and occasionally utilized along the basin margins, in some cases for a century or more. Reference to bituminous shale was common in geological studies from the 19th century. Although organic content was rarely analyzed in the pre-Drake era, shales with a high bituminous level were recognized from physical characteristics such as color and texture, and occasionally an associated oil or gas seep. The richest of the bituminous shales were identified by a unique property, the ability to burn and maintain a flame without any other fuel source. Geological and exploratory parties that encountered burning shales would commonly mention them in their reports because of their unusual properties, plus the hope that they could be indicative of proximity to coal deposits, a common objective for governmental surveys. By the time the 1859 Drake Well was drilled, inflammable shales ranging in age from Pennsylvanian to Ordovician had been documented in North America, with locations in at least 12 U. S. States and 4 Canadian Provinces. Based on this available information, if the modern shale plays had been described to a 19th century geologist, the choice of target formations such as the Marcellus and Utica would not have been a surprise.