HR: 14:35h
AN: S43A-05    [Abstracts]
TI: Overpressure generation and episodic dewatering in the Delaware basin, western Texas: The dual nature of a fault zone
AU: * Hansom, J
EM: jhansom@cdge.com
AF: Auburn University, Department of Geology, Auburn, AL 36849 United States
AU: Lee, M
EM: leeming@auburn.edu
AF: Auburn University, Department of Geology, Auburn, AL 36849 United States
AU: Wolf, L W
EM: lwolf@geology.auburn.edu
AF: Auburn University, Department of Geology, Auburn, AL 36849 United States
AU: Kosuwan, T
EM: leeming@auburn.edu
AF: Auburn University, Department of Geology, Auburn, AL 36849 United States
AB: This study combines numerical modeling techniques with field data to investigate overpressure development and episodic dewatering processes in the Delaware Basin and the Central Basin Platform (CBP). Low-permeability shales in the eastern Delaware Basin are characterized by elevated pore fluid pressures that are much greater than hydrostatic pressures. Observed geophysical anomalies such as low resistivity, high conductivity, and high seismic transit time are consistent with the presence of fluid-filled, fractured and mechanically weak rocks in the eastern Delaware Basin. Our new geophysical analyses also indicate that the overpressures likely extend further into the shallower western basin in Culberson County near the sulfur mineralization area. The predicted present-day gas window is located within the overpressure zone, suggesting that overpressure may be maintained by active oil-to-gas conversion. A basin hydrology model Basin2 is modified to evaluate the pore pressure increases by oil-gas conversion from the equation of state (EOS) for the CH4-CO2-H2O system. Our modeling shows that source beds in CBP have been rather shallowly buried and did not become thermally mature to generate gas directly. Overpressure and episodic dewatering processes appear to be the most plausible mechanism to move deep-basin hydrocarbons eastward into the CBP and westward into the shallow margin of the Delaware Basin. The model of long-distance fluid migration from the eastern Delaware across the fault zone into the CBP is supported by the geochemical similarities of oils from the two basins. A model that invokes episodic release of overpressured fluids by hydrofracturing processes can simultaneously provide mechanisms for achieving transient overpressure preservation and substantial, episodic fluid movement. The episodic dewatering through hydrofracturing processes thus can better explain the observed overpressure preservation, long-distance fluid migration, and related mineralization and alteration of evaporitic strata in the Permian Basin.
DE: 1719 Hydrology
DE: 1829 Groundwater hydrology
DE: 1832 Groundwater transport
DE: 3210 Modeling
DE: 5100 PHYSICAL PROPERTIES OF ROCKS
SC: Seismology [S]
MN: 2005 Joint Assembly