Print this pageAAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
An Investigation of the Petrophysical and Acoustic Properties of Mass-Transport Sediments Within the Oligocene Frio Formation, South Texas Gulf Coast
(1) Bureau of Economic Geology, University of Texas at Austin, Jackson School of Geosciences, Austin, TX.
3D seismic data and wireline logs were utilized to investigate the petrophysical and acoustic properties of a mass-transported, deformed sediment wedge (MTD) within the Oligocene Frio Formation along the South Texas Gulf Coast between the Houston and Noria Deltas. The mass-transport sediments formed when the Upper Frio paralic shelf-edge sediments collapsed as a result of upwelling of over-pressured shale that coincided with listric growth-faulting. Our results show that average porosity within the un-deformed Upper Frio varies from 1 to 23% and increases with decreasing water saturation. Similarly, average permeability increases with decreasing water saturation varying from 0.001 to 20 md. In contrast, porosity and permeability values within the MTD sediments depend on the distance away from the listric growth fault (point of sediment collapse). In areas proximal to the listric growth fault, average porosity and permeability varies from 1 to 15% and 0.001 to 0.3 md, respectively. Both parameters increase with increasing water saturation and are significantly lower than values observed in un-deformed Frio. In the distal areas, average porosity and permeability are much higher than those in the proximal zone ranging from 1 to 30% and 0.001 to 400 md, respectively.
Average interval velocities in the un-deformed Frio vary from about 9,000 to 11,000 ft/s whereas the proximal areas of the MTD are characterized by lower interval velocities ranging from approximately 7,000 to 8,600 ft/s. However, in the MTD distal area, average interval velocity is about 6,600 to 7,700 ft/s. Further investigation reveals that MTD sediments in the proximal area have higher shale content and water saturation than un-deformed Frio and sediments in the distal areas. In addition, proximal sediments are characterized by hummocky, wavy, and chaotic seismic reflections in contrast to the un-deformed Frio which is characterized by parallel seismic reflections. The distal MTD are characterized by sub-parallel to parallel reflections. The low petrophysical and acoustic properties of the proximal MTD could be attributed to the high shale content and chaotic seismic character due to poor sorting, while the higher values in the un-deformed Frio and distal sediments could be due to lower shale content and better sorting of sediments due to transport.