Regional porosity trends of the Upper Jurassic Norphlet Formation in southwestern Alabama and vicinity, with comparisons to formations of other basins
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Abstract
Sandstone porosity of the Upper Jurassic Norphlet Formation in southwestern Alabama and vicinity decreases systematically as depth and thermal maturity increase over a wide range. Median porosity is about 25% where equivalent vitrinite reflectance (Ro) is slightly over 0.7% in the northern part of the study area (Clarke County, Mississippi). Median porosity is reduced to 8% where Ro approaches 2.7% in the southern part of the study area (state waters of Mobile Bay).
Porosity of the cemented, tight zone at the top of the Norphlet in downdip locations is roughly 10% lower than porosities of facies underlying the tight zone, but nevertheless is slightly above the norm for other sandstones at similar Ro levels. Porosity of dune facies is consistently 2-5% higher than that of interdune facies, other factors being equal. Our data show 3-6% higher porosity in chlorite-dominated intervals relative to intervals where illite is the dominant clay mineral. Norphlet porosity has little or no correlation with position relative to the present-day hydrocarbon-water contact.
Based on comparisons at similar Ro levels, median (50th-percentile) Norphlet porosity exceeds porosities of "typical" sandstones in other basins by more than a factor of two throughout the study area. Even the lower (10th-percentile) Norphlet porosities are higher than median porosities of sandstones in general.
Study Area
Publication type | Article |
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Publication Subtype | Journal Article |
Title | Regional porosity trends of the Upper Jurassic Norphlet Formation in southwestern Alabama and vicinity, with comparisons to formations of other basins |
Series title | American Association of Petroleum Geologists Bulletin |
DOI | 10.1306/BDFF9050-1718-11D7-8645000102C1865D |
Volume | 78 |
Issue | 2 |
Year Published | 1994 |
Language | English |
Publisher | American Association of Petroleum Geologists |
Contributing office(s) | Central Energy Resources Science Center |
Description | 15 p. |
First page | 166 |
Last page | 180 |
Country | United States |
State | Alabama, Mississippi, Florida |
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