Christopher J. Schenk James W. Schmoker 1994 <p>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 (R_o) is slightly over 0.7% in the northern part of the study area (Clarke County, Mississippi). Median porosity is reduced to 8% where R_o<span>&nbsp;</span>approaches 2.7% in the southern part of the study area (state waters of Mobile Bay).</p><p>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 R_o<span>&nbsp;</span>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.</p><p>Based on comparisons at similar R_o<span>&nbsp;</span>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.</p> application/pdf 10.1306/BDFF9050-1718-11D7-8645000102C1865D en American Association of Petroleum Geologists Regional porosity trends of the Upper Jurassic Norphlet Formation in southwestern Alabama and vicinity, with comparisons to formations of other basins article