Mudrocks serve as geological seals for carbon sequestration or hydrocarbon formation where mudrock capillary seals having high capillary entry pressure prevent leakage of underlying fluids. However, seal failure can occur if the trapped nonwetting fluid escapes by porous flow or by induced tensile fractures caused by elevated nonwetting phase pressures. Since mudrocks are mainly composed of silt and clay size grains, a silt bridging effect has been observed when there are sufficiently abundant silt size grains. This effect creates force chains across the rock to help preserve large pores and throats and can reduce the sealing capacity of a mudrock. We used network models and discrete element (DEM) models to determine the conditions under which silt abundance will cause a mudrock seal to fail and allow a non-wetting fluid like CO₂ or natural gas to flow. We show that when larger grains in a grain pack become 40-60 % of total grain volume, the drainage capillary pressure curves display two percolation thresholds, and the percolation threshold transitions to a lower value allowing seal failure even below tensile fracture pressure. The DEM compaction simulations found that strong force chains are mostly formed across grain contacts between large grains and their neighbors and not between small grains, which decreases coordination numbers and shields pore space from compaction before reaching a stress limit. Thus, through better understanding of grain concentrations and sizes on fluid flow behavior, we can improve risk management efforts in anthropogenic storage and estimates of reserve capacity of reservoirs.