Shale diagenesis: an important factor in development of secondary porosity

Abundant secondary porosity due to the dissolution of feldspar grains, volcanic rock fragments, and carbonate cement has been observed in thin-section studies of reservoir sandstones in the McAllen Ranch field in south Texas. Secondary porosity develops in fluid flow pathways within the sandstones. Potentiometric profiles indicate that within the overpressured Oligocene strata, head gradients cause pore fluids to flow from the shales into the...