Authigenic Clay Mineral Distribution, Lower Tuscloosa Formation, Southwest Mississippi: Impact on Sandstone Reservoir Quality, North Hustler Field Area.
Abstract
This research assesses the clay mineral distribution in terms of sandstone petrology, gross lithology, and depositional and diagenetic history; and compares the nature of lower Tuscaloosa diagenesis to that of other Gulf Basin Clastic Formations. Data from 256 x-ray diffraction (xrd) and 34 petrographic anaylses (pa) were added to a previously established data base. These new data were collected on a 1-ft interval from eight wells in this field; all had been previously logged and described, and additional xrd and pa data were available. Qualitative and quantitative xrd studies were undertaken to describe the clay minerlogy; percent porosity, framework grains, matrix, and cement were determined from point counting of thin sections. A literature search reviewed available information on Gulf Basin diagenesis. For all known samples, chlorite (c) abundance relative to other clays ranges from 5 to 92 pct (mean 54 pct), kaolinite (k) from 1 to 76 pct (mean 21 pct), illite (I) from 0 to 78 pct (mean 24 pct), and smectite (s) from 0 to 8 pct (mean 1 pct). Compositions of massive sandstones were: c, 67 pct; k, 15 pct; I, 17 pct; and s, 1 pct. For siltstones, c is 54 pct; k is 18 pct; I is 29 pct; and s is i1 pct. For undifferentiated shales and siltstones c is 15 pct; k is 47 pct; i is 38 pct; and s is 0 pct. Comparison of Lower Tuscaloosa and other Gulf Coast siliclastic diagenesis revealed more similarities than dissimilarities. All exhibit aspects of each diagenetic phase. Paragenesis is also similar.
