Insight into the Sealing Capacity of Mudrocks determined using a Digital Rock Physics Workflow

Primary objective: To better understand seal capacity in mudrocks and to determine the conditions under which a mudrock seal fails by allowing a non-wetting fluid to percolate. Hypothesis: Mudrock seals can fail below the fracture pressure if there exists a percolating pathway formed due to a continuous and sufficiently large pore-throat system. Procedure: We used SEM images of uncemented muds obtained at various depths (< 1.1 km burial) in the Kumano Basin offshore Japan for the study. Image mosaics were filtered and segmented using conventional and machine-learning techniques to identify the pore space, silt, and clay grains. We applied a 3D stochastic technique for pore space reconstruction from the SEM images and simulated capillary drainage in the resulting 3D volumes by the lattice Boltzmann method (LBM) using Stampede 2. Conclusion: Results showed that porosity and permeability decreased with depth, and capillary threshold pressure values increased. However, increasing silt content at a particular depth counteracted this behavior, due to better preservation of larger pores and throats.