An experimental model of episodic gas release through fracture of fluid confined within a pressurized elastic reservoir

22 Mar 2018

We present new experiments that identify a mechanism for episodic release of gas from a pressurized, deformable reservoir confined by a clay seal, as a result of the transition from bulk deformation to channel growth through the clay. Air is injected into the center of a thin cylindrical cell initially filled with a mixture of bentonite clay and water. For sufficiently dry mixtures, the pressure initially increases with little volume change. On reaching the yield stress of the clay‐water mixture, the lid of the cell then deforms elastically and an air‐filled void forms in the center of the cell as the clay is driven radially outward. With continued supply of air, the pressure continues to increase until reaching the fracture strength of the clay. A fracture‐like channel then forms and migrates to the outer edge of the cell, enabling the air to escape. The pressure then falls, and the clay flows back toward the center of the cell and seals the channel so the cycle can repeat. The phenomena may be relevant at mud volcanoes.