AAPG/GSTT HEDBERG CONFERENCE

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

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

Mud volcanoes in Azerbaijan: implications for sediment and fluid migration in active piercement structures

Sverre Planke^1,2, Adriano Mazzini¹, Henrik Svensen¹, Grigorii G. Akhmanov³,

& Anders Malthe-Sørenssen¹

¹Physics of geological processes (PGP), University of Oslo, Norway

²Volcanic basin petroleum research (VBPR), Oslo Research Park, Oslo, Norway

³Department of petroleum geology and geochemistry, Faculty of geology, Moscow State University, Russia

Piercement structures, such as mud volcanoes, are common in many sedimentary basins. It is currently difficult to incorporate such piercement structures in basin modeling theories, therefore these features are commonly ignored when studying fluid flow in sedimentary basins. A number of issues need to be addressed in order to get a better understanding of the role of piercement structures in the evolution of sedimentary basins. These relate to processes in the source region, in the conduit zone, and the hydrology of the seepage stage between eruption events.

Results from active seepage systems may furthermore provide important constraints on hydrothermal piercement structures which are common in volcanic sedimentary basins. Recent fieldwork and geochemical studies on eight mud volcanoes in Azerbaijan aims at understanding both the eruptive and dormant stages of mud volcanoes.

Mud volcanic eruptions in Azerbaijan normally last for less than a few days, and are characterized by vigorous eruptions of mud breccias, hydrocarbon fluids (liquids, gas), and water. The dormant period activity ranges from quiet to vigorous flow of mud and fluids. In both cases, the driving force of the system appears to be methane of thermogenic and biogenic origin. Eruption events are accompanied by active tectonics and sometimes graben formation. Subsidence and caldera formation leads to extensive faulting even during the dormant stage. Geochemical analyses of expelled waters during the dormant stage of mud volcanoes show a wide range in solute concentrations, suggesting the existence of a complex plumbing system. The waters expelled at mud volcanoes represents complex mixtures of deep and shallow waters, with chemistries affected by processes like mineral dehydration, adsorption and desorption on clay minerals, mineral precipitation and dissolution, redox reactions, decomposition of organic material, and microbial-driven processes. The salinity of expelled waters, expressed as the Cl concentration, is as high as 35,000 ppm, exceeding both seawater concentration and oil reservoir brines. Main and trace element composition suggest that the fluids have a deep origin mixing with meteoric waters. This is consistent with a deep-seated origin (>5 km) of the extrusive mud breccias.