Determination of specific surface area and mean grain size from well-log data and their influence on the physical behavior of offshore reservoirs

Specific surface area (ss) is one of the most important and effective geometrical parameters in defining and interpreting petrophysical relationships, textural framework, and fluid–solid interactions in porous media. It is defined as the interstitial surface area of the pores and pore channels for each unit of bulk volume, grain volume, or pore volume, or for a unit of weight of a material. Variations in the specific surface area (ss) and mean grain size (Gs) influence the physical parameters controlling electric current and hydraulic flow, as well as acoustic and seismic wave propagation and attenuation. In this study, the specific surface area per unit of pore volume (sp) and the mean grain size (Gs) were numerically determined from well-log data for 14 wells penetrating the Hibernia and Terra Nova reservoirs of the Jeanne dʹArc Basin (JDB), offshore Newfoundland, Canada. Both parameters (sp and Gs) were derived using the formation resistivity factor, porosity, and permeability. Mathematical and physical concepts of ss (including sp) and Gs were analyzed, and empirical equations linking sp and Gs with various petrophysical parameters were obtained. The lithological components (shale, sandstone, silt, limestone, and marl) were also obtained. The rocks in both reservoirs are generally characterized by fine- to medium grain size and high values of sp.