Burial History Modeling and Paleogeomechanics of the Barnett and Haynesville
Williams, Kenneth E.
Burial history analysis of the Barnett source-rock reservoir (SRR) area shows a complex history of burial and uplift/erosion. The initial deep burial of the area as part of the Fort Worth foreland basin in front of the advancing Ouachita fold belt resulted in hydrocarbon generation and expulsion of oil and gas in the Pennsylvanian and Permian basins. This was accompanied by high overpressures that are capable of fracturing the source rock to allow the primary migration of hydrocarbons. The regional stress field at that time was related to foreland basin tectonics and was different than the current stress field. In the Triassic and Jurassic periods, when the Gulf of Mexico basin opened, the Barnett core area was uplifted, and 7,000 ft (2,134 m) of overburden was removed in some areas, which contributed to the filling in of the Permian basin to the west. The stress field was likely deviatoric, away from the uplifted eroding highlands, and another set of fractures may have been induced. At the present time, the stress regime is oriented such that the younger set of induced fractures are critically stressed. Hydraulic fracturing opens these younger fractures and reconnects the borehole to the older set of fractures, thereby creating a complex fracture system and allowing the production of hydrocarbons at a commercial rate.
Burial history analysis of the Haynesville SRR reveals a paleogeomechanic and paleogeographic explanation for horizontal fractures that have been observed in core. A compressional stress regime that allows the development of horizontal fractures requires that vertical or overburden is the minimum principal stress. Often, this is accompanied by the presence of thrust faults; however, thrust faulting is not readily observed in the Haynesville area, but horizontal fractures are present. The stress regime was developed during the mid-Cretaceous unconformity when the ancestral Sabine uplift was active. A deep-seated volcanic intrusion may be the ultimate cause of the uplift, which would have provided an increased heat flow that coincided with the maximum burial of the SRR. High internal pressures from hydrocarbon generation and migration, therefore, coincided with overburden removal with little horizontal compression, and the overburden was uplifted to allow the emplacement of horizontal mineral-filled fractures.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013