Lithology and Pore Structure Driven Rock Physics Model for Consolidated Siliciclastic Rocks

Summary Upon studying data from a Norwegian Sea well log, penetrating mid-Jurassic consolidated sands, we found a very steep increase in bulk and shear modulus for rocks with constant saturation and lithology, and decreasing porosity. This trend posed problems when attempting to calibrate standard constant cement or inclusion based models. However, we achieved a good fit when using a mixing model between a low porosity end-member, where all the porosities were made up of spherical pores, and a high porosity end-member, modelled using the constant cement model. Furthermore, the porosity-volume of spherical pores had to be drastically reduced to achieve a good fit with pure shales. We believe compaction has resulted in closing the softer, low-aspect ratio pores, while only reducing the volume of the stiffer, spherical pores; making the pore spectrum only consist of spherical pores at low porosities.