Burial and Thermal History of the Haynesville Shale: Implications for Overpressure, Gas Generation, and Natural Hydrofracture
Jeffrey A. Nunn
Department of Geology and Geophysics, Louisiana State University, E235 Howe-Russell Complex, Baton Rouge, Louisiana 70803
The Haynesville Shale is an organic rich sedimentary rock found in northwestern Louisiana, eastern Texas, and southwestern Arkansas. It was deposited during the Late Jurassic in a marine environment. Average thickness varies from 200 to 300 ft (60–90 m). The Haynesville Shale is typically found at depths of 10,000 ft (3 km) or more and is characterized by ultra low permeability. It is an area of active exploration and development for natural gas especially in northwestern Louisiana. Results from an earlier thermal-mechanical model suggest that Jurassic temperature gradients were more than twice the current regional value of 0.0135 to 0.02°F/ft (25 to 35°C/km). Thus, Jurassic age sediments have been close to their current temperatures for the last 100 m.y. Using subsurface data, a simple model of heat transport by advection and conduction and fluid flow by compaction was used to estimate temperature, maturation, and fluid pressure through time for the Haynesville Shale. High heat flow in the Early Cretaceous contributed to high temperature gradients and early maturation of hydrocarbons. Rapid sedimentation in the Early Cretaceous resulted in generation of significant overpressure within the Haynesville Shale. This overpressure cannot be maintained over geologic time because the unit is too thin and there was subsequent uplift and erosion. Hydrocarbon generation produced additional overpressure in the Late to mid-Cretaceous and the Late Paleogene. However, under most conditions, model overpressures do not exceed the fracture gradient.
AAPG Search and Discovery Article #90158©2012 GCAGS and GC-SEPM 6nd Annual Convention, Austin, Texas, 21-24 October 2012