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Petroleum Migration and Accumulation
Published in Muhammad Abdul Quddus, Petroleum Science and Technology, 2021
One of the interesting examples of gas leakage is the eruption of mud volcanos. A mud volcano is a leakage through the fracture of gas accumulation under pressure at shallow depth. The mud volcano emits mud with force. A mixture of mud–water–gas forms a cone-shaped ‘mud volcano’. Mud volcanos are found in various parts of the world in argillaceous (clay) sedimentary rock basins. The cone shape of a mud volcano mound is similar to the igneous magma volcano, but its size is much smaller. The mud is emitted out from the mouth, a crater in the middle of the cone, with different eruption speeds. The mud spreads around a wide area depending on the mud/gas volcano pressure. The eruption of mud is not a continuous process. The volcano activity is sandwiched between eruption (active) and quietness (sleeping). The eruption of mud is associated with gases. Methane is the main gas in the emission of mud volcanos. Gas bubbles can be seen coming out from the mud. In case the mud is thick and viscous, the gas bubbling is stopped. When enough pressure is developed, gas bubbling again starts. The amount and duration of gas bubbling are different from time to time and from one volcano to another. A view of mud volcano eruption and bubbling gas is depicted in Figure 3.7.
Geohazards
Published in White David, Cassidy Mark, Offshore Geotechnical Engineering, 2017
Mud volcanoes are eruptions or expulsions of methane gas that have accumulated in the shallow sedimentary deposits, accompanied by watery mud and often large masses of rock. Debris from mud volcanoes can be sent many tens or hundreds of metres into the water column and travel for many kilometres or tens of kilometres across the seabed, especially from large volcanoes that may be several kilometres in diameter. The methane gas may exist in solution in pore water; temperature increases or pressure reductions can lead to ex-solution and expansion of the gas causing an increase in pore pressures. Gas hydrates are solid compounds of gas (typically methane) and water that are physically stable within a particular range of pressure and temperature conditions. Temperature increase or pressure reduction can lead to the dissociation of gas hydrates back into the gas phase (methane) and liquid phase (water) leading to volume expansion. The ex-solution of gas and water from the gas hydrate can increase the volume by a factor of two, leading to a sudden increase in pore pressure and reduction of effective stress in the sediments.
Characteristics of features formed by gas hydrate and free gas in the continental slope and abyssal plain of the Middle Caspian Sea
Published in Marine Georesources & Geotechnology, 2021
H. Gerivani, V.A. Putans, L.R. Merklin, M.H. Modarres
On the abyssal plain, due to horizontal beds and with the lack of weak zones, fluid pressure force up the upper beds and made a gentle diapir. In the case like sequence B, in which the sediments are permeable enough, fluids can easily migrate upward inside the sequence. Where there is a weak zone, high-pressure fluids can find a way to escape and make a mud volcano.