Pore-Space Reduction by Solution and Cementation

The amount of pore-space reduction caused by solution of grains at points of contact and the additional reduction that would result from precipitation of this dissolved material has been investigated. For single grains and their associated pore space such reduction in porosity has been calculated for spheres and other geometric forms in various packing arrangements. The relative amounts of porosity reduction may vary greatly, depending on grain shape and angularity, packing, direction of pressure, and amount of solution. The maximum porosity loss by cement relative to porosity loss by solution occurred with spheres in orthorhombic packing, rotated 30°. This is believed to be a maximum for any sand and most closely approached by a well-sorted sandstone made up of very well-rounded grains. A maximum cement-to-solution relation is estimated for sandstones of better or poorer sorting or greater grain angularity. The extrapolation from single grains and their associated pores to sandstones is complicated by the possibility of nonuniform solution or cementation.