About This Item
Share This Item
Reservoir carbonates in the Bryan's Mill area of east Texas are ooid-dominated grainstones that occur toward the top of stacked coarsening-upward sequences. Individual grains were coated by isopachous circumgranular cements producing early lithification of the grainstones with retention of a modified intergranular porosity. This was patchily
occluded by later equant intergranular cements. Grainstones in each sequence were subject to at least 2 phases of facies-selective dolomitization. The earliest phase mimicked the preexisting texture, whereas the later phase was texture-destructive with rhombic dolomite crystals.
Dolomitized grainstones have highest porosities and permeabilities resulting from calcite dissolution and physical compaction. Calcite dissolution within ooids occurred after the second dolomitization phase; thus, oomoldic porosities are not related to meteoric leaching during or after Smackover deposition. Subsequent physical compaction enhanced permeability. Later, partial porosity occlusion was by anhydrite calcite.
Dolomitization was caused by refluxing brines during deposition of the overlying Buckner evaporites. Dolomite ^dgr13C values are compatible with Smackover/Buckner seawater; ^dgr18O values become lighter with time, a probable function of dolomitization during progressive burial. A change to coarse clastic sedimentation coupled with syn-Buckner faulting modified the hydraulic regime of the area. This may have been the stimulus for calcite dissolution and hence porosity development within the Smackover grainstones.
End_of_Article - Last_Page 264------------