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Abstract: Geological Controls on Permeability Distribution and Sand Distribution: Tar Zone, Fault Block IIA, Wilmington Field


Lateral and vertical variations of reservoir quality in turbidite sandstones of the Tar Zone (T and D intervals) are controlled principally by original rock texture (specifically grain size and sorting) and diagenesis (specifically compaction). Interaction of these factors has resulted in variable pore geometries. Quantification of pore geometrical attributes allows for identification of 4 sandstone rock types: intervals of rock with similar pore geometry, porosity-permeability relationships, and capillary pressure characteristics.

Permeabilities range over several orders of magnitude for any given value of porosity. Accurate prediction of permeability requires a knowledge of both rock type and porosity. Algorithms have been developed (using core measured data) that allow for prediction of permeability from a knowledge of rock type and porosity. Individual rock types can be identified using a standard wireline log suite (SP, GR, Resistivity, Density, Neutron) - no new logs, no specialized logs are required. Net footage of each rock type can be determined for each well location and zone. This allows for rapid computer-based mapping of the distribution of each Rock Type across the field. There is a close relationship between depositional environment and rock type distribution. Thus maps of rock type distribution can be used to illustrate the lateral and vertical variations in depositional environments.

Search and Discovery Article #90945©1997 AAPG Pacific Section Meeting, Bakersfield, California