Fluid venting phenomena are prevalent in sedimentary basins globally.
Offshore, these localised fluid-expulsion events are archived in the geologic
record via the resulting pockmarks at the sea-floor. Venting is widely
interpreted to occur via hydraulic fracturing, which requires near-lithostatic
pore pressures for initiation. One common driver for these extreme pressures is
horizontal tectonic compression, which pressurises the entire sedimentary
column over a wide region. Fluid expulsion leads to a sudden, local relief of
this pressure, which then gradually recharges through continued compression,
leading to episodic venting. Pressure recharge will also occur through pressure
diffusion from neighboring regions that remain pressurised, but the combined
role of compression and pressure diffusion in episodic venting has not
previously been considered. Here, we develop a novel poroelastic model for
episodic, compression-driven venting. We show that compression and pressure
diffusion together set the resulting venting period. We derive a simple
analytical expression for this venting period, demonstrating that pressure
diffusion can significantly reduce the venting period associated with a given
rate of compression and allowing this rate of compression to be inferred from
observations of episodic venting. Our results indicate that pressure diffusion
is a major contributor to episodic fluid venting in mudstone-dominated basins