Multiscale Site Investigation of a Giant Mud-Volcano Offshore Azerbaijan - Impact on Subsea Field Development.

Abstract

AbstractA 3D seismic, AUV and geotechnical data integration has been conducted in order to assess the potential impact of a large Mud Volcano (MV) activity and its related mudflows for subsea field development.The studied area is located within the South Caspian Basin (SCB). The tectonic compression of the SCB led to the development of horizontal stresses within the sedimentary sequence and to the formation of anticlinal folds throughout the basin, pierced by large mud volcanoes affecting up to the seabed.The potential future material expulsion and associated seabed mudflows may represent a significant threat for any subsea installation (flowlines, wellhead, templates…) of E&P activities. The 3D seismic dataset has therefore been used to identify and describe the MV complex interaction with large regional Mass Transport Complexes (MTC). AUV data were essential to provide high resolution informations regarding the geometry and succession of the different mud flows through time, associated with the MV activity.A large pseudo-circular topographic high forming the crater of the MV at seabed is located into a wider low circular relief. In more details, within the crater, smaller steep side cones associated to seabed high seismic amplitudes are identified as gryphons (secondary small vents), from where recent seabed mud flows have been expulsed. The surrounding depression around the MV has canalized the recently expulsed mudflows southward thanks to lower relief and the present bathymetry. Five recent seabed mudflows have been clearly discriminated, indicating that the MV has been active during the last 5000 years B. P. As a consequence and since the latest catastrophic event (dated 735 years BP) exceeds the estimated mud expulsion recurrence time (500 years), the mud flow zone is considered as a hazardous area for the time being leading to a "No Go" classification for any drilling activity and subsea installation.This study demonstrates the added value of HR geophysical (AUV) data and geotechnical ground truthing integration with the regional shallow geological understanding derived from 3D seismic data to assess geohazards in a complex and active shallow geological context.