--> ABSTRACT: The Correlation between Natural Fracturing and Gas Shales, by Engelder, Terry; #90135 (2011)

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The Correlation between Natural Fracturing and Gas Shales

Engelder, Terry 1
(1)Department of Geosciences, Penn State, University Park, PA.

Gas shales commonly carry systematic joint sets. The correlation between joint density and proximity to gas shales is consistent with the Lacazette-Engelder (1992) and the McConaughy-Engelder (1999) conclusions that gas-shale joints are gas-driven natural hydraulic fractures whose orientation is controlled by tectonic stress (which does not cause these joints). Presumably, the source of the pressure drive is the maturation-related reaction that converts kerogen to petroleum and natural gas through an endothermic, volume increase reaction. If the pressure drive is specific to source rocks (black shale), then one might expect to see a plume of natural hydraulic fractures that dissipates with distance above the source rock. In principle, the dissipation hypothesis should be testable with outcrop observations. However, outcrop observation is only effective to the extent that the operator has a strategy for distinguishing between deep-formed fractures and exhumation-related surface fractures. In fact, exhumation-related fractures have a much different morphology and are easily distinguished from NHF. Evidence for the plume-like behavior of gas-driven fracture will be offered from the Appalachian Basin where is Devonian Marcellus gas shale is so productive.

 

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.