AAPG/GSTT HEDBERG CONFERENCE

“Mobile Shale Basins – Genesis, Evolution and Hydrocarbon Systems”

June 4-7, 2006 – Port of Spain, Trinidad & Tobago

Remobilization of Mud Volcano Cones: Shah Deniz, South Caspian Sea, Azerbaijan

Joshua Creviere Turner

BP, Houston, Texas

The interpreted geometry of mud volcanos at depth is often a source of heated debate and concern when exploring for hydrocarbons in the South Caspian Basin.  Proposed geometries have varied from wide diapirs to narrow pipes with significant overburden collapsed into the mud source interval, or narrow conduits with intrusive mud chambers.  Advanced 3D seismic processing over Shah Deniz gas field, has produced an image showing the more likely interpretation of an evacuated and remobilized mud volcano cone forming a shallow syncline that does not significantly impact the productive series below. 

On the Shah Deniz structure, I observe a mud volcano, characterized by a relatively small syncline, lying disharmonically over the top of the larger anticline that sets up the field.  It is not significantly perturbed by faulting or subsidence in the mud volcano’s vicinity.  Additionally, the evaporite beds of the upper Surakhany are usually absent where cones have been remobilized. However, these same evaporites onlap cones that have not been remobilized.  Therefore, I believe Shah Deniz’ mud volcanoes were, in general, initially extruded at the surface near the end of the Surakhany period, but before the deposition of the evaporite beds initiated; extrusion coincides with the onset of increased regional shortening.  The topographically high cone was then onlapped by evaporites and subsequently buried by marine sediments.  In the late Pleistocene the cone was remobilized and evacuated, and the overburden collapsed to form a shallow and local depression.  This theory is encouraging for those developing resources in the Caspian because it reduces risk of reservoir compartmentalization in the vicinity of a mud volcano and increases the chances that the reservoir is more extensive and producible beneath mud volcano cones.