Evolution model for the Absheron Mud Volcano: from stratified sediments
to fluid mud generation
Abstract
We propose a semi-quantitative model of the initiation and early
evolution of a mud volcano. Basin modeling was calibrated against our
previous seismic interpretation of the Absheron mud volcano and
surroundings in the South Caspian Basin on the one hand, analysis of
geological samples from seabed and two exploration boreholes on the
other. Some input parameters of the model were derived from laboratory
testing of samples from the mud volcano and we used a constitutive law
obtained from a previous laboratory study showing the extent to which
gas exsolution may damage host sediments, eventually leading to mud
generation from compacted sediments. The study identified key geological
and physical conditions that led to mud volcano formation: coupling
diffusion processes with hydrofracturing and fluid advection, we were
able to simulate conditions required to generate mud 3.5 km below the
Absheron mud volcano. We also modeled mud remobilization up to the
seabed using Navier-Stokes equations modified to account for the impact
of gas expansion on mud density. Considering density inversion only,
simulations indicate that mud would be extruded at the seabed 100 years
after its generation, an ascent rate similar to extrusion rates measured
at some active mud volcanoes in Azerbaijan, e.g. the Kotyrdag mud
volcano. These models considering eruption dynamics provide
semi-quantitative support to purely conceptual formation models based on
seismic interpretation of subvolcanic stratal geometry.