Structure and emplacement of mud volcano systems in the South Caspian Basin

Abstract

The term “mud volcano system” is coined to describe the set of structures associated with a constructional edifice (mud volcano) and feeder complex that connects the volcano to its source stratigraphic unit. Three-dimensional (3-D) seismic data from the South Caspian Basin are used to investigate the structural elements and evolution of these systems. Mud volcano systems initiate via early, kilometer-scale, biconic edifices termed “pioneer” cones. These are fed by fluidization pipes tens of meters in width. Subsequent kilometer-scale mud volcanoes grew via persistent extrusion, fed by numerous additional fluidization pipes injected in the country rock. This subvolcanic intrusion complex creates a densely intruded, cylindrical zone, similar in cross section to gryphon swarms observed at an outcrop onshore. Wall rock erosion and compaction of the intruded zone leads to the collapse of a downward-tapering cone enveloping the cylindrical zone, capped by ring faults that define a kilometer-scale caldera that downthrows the overlying mud volcano. Mud volcanoes get buried during basin subsidence and can look like intrusive laccoliths at first glance on seismic data. Reactivation of mud flow through a conduit system generates a stack of superimposed mud volcanoes through time. Large volcanoes continue to dewater during burial and may locally remobilize. This model of mud volcano evolution has similarities with igneous and salt tectonic systems. To reduce drilling and geologic uncertainty, mud volcano system extent and impacts on a reservoir can be assessed on 3-D seismic data. Simon Stewart received his Ph.D. from the Imperial College London in 1992. In 1992–2000, he was seismic interpreter at Amerada Hess, in support of exploration and appraisal drilling in the North Sea. In 2000, he moved to BP and has since worked on structural geology and well planning in the Americas, Middle East, and the former Soviet Union. His special interest is in the integration of structural geology and seismic interpretation. Richard Davies received his Ph.D. from the University of Edinburgh in 1995. In 1995–2003, he was with Mobil and ExxonMobil, working on field development and exploration, the North Sea, the west of Shetlands, and the west Niger Delta deep-water slope. In 2003–2005, he was a senior lecturer in earth sciences at Cardiff University, United Kingdom. Currently, he is professor and director of CeREES (Center for Research into Earth Energy Systems), Durham University, United Kingdom. His special interest is in seismic-scale expression of fluid migration and diagenesis.