Dolomite diagenesis and porosity preservation in lithic reservoirs: Carmopolis Member, Sergipe-Alagoas Basin, northeastern Brazil

The lithic sandstones and conglomerates of the Carmopolis Member of the Muribeca Formation (Aptian) were deposited by fan deltas, alluvial fans, and braid deltas that prograded from low-grade metamorphic terrains into the Sergipe-Alagoas rift basin during the opening of the South Atlantic. Initial carbonates in the Carmopolis reservoirs (presently at depths of 180-2200 m) were marine (high-Mg calcite/aragonite) grain rims, allochems, stromatolitic laminites, and meteoric calcite. Rocks lacking early cements were strongly compacted, losing their primary intergranular porosity and permeability, whereas massively cemented rocks show only minor compaction and further diagenetic modifications. -from Authors