Understanding Permeability and Porosity of Sandstones Using Digital Rock and Lattice-Boltzmann Method

Porosity and permeability are sediment properties most important in petroleum and environmental applications. Porosity determines how much fluid can be stored in rock and permeability determines how fast it can flow. The sediment transport mechanism (air, water, and gravity forces) determines the initial texture whose quantitative measures are grain size, sorting and grain shape. The post-depositional alteration and diagenesis change the texture by compaction, cementation, replacement, and re-crystallization. All these factors affect the pore-space topology, thus porosity and permeability. We quantify the effect of the initial texture and consecutive alterations on permeability by directly simulating viscous fluid flow through the pore space in 3-D. The simulation is based on the Lattice-Boltzmann numerical method that allows us to accurately describe fluid flow through the pore space of any complexity, without replacing actual pores with idealized shapes such as pipes and spheres. We construct 3-D digital rock by first numerically constructing the basic grain of desirable shape and size. Statistical codes based on existing theoretical development will be used to reconstruct 3-D pore space from thin section images of sandstone samples available for this project. An experimental desktop setup is available for this project by the Stanford Rock Physics Laboratory. True 3D images of the pore space of selected samples will be acquired via X-ray tomography at facilities outside of Stanford. Bringing the grains closer together and digitally depositing cement on the grain surface respectively simulates the compaction and diagenesis effects. The permeability/porosity curves are computed for digital sediments of varying sorting and grain shape and also during the digital compaction and diagenesis processes. The resulting trends are validated by comparing them to laboratory data obtained on sandstone samples of varying initial texture and degree of diagenesis.