Mud volcanoes and structural development on Shah Deniz

Abstract

Shah Deniz is a large four-way dip closed structure in the South Caspian located approximately 35 km to the southeast of Bahar and 70 km southwest of the Guneshli–Chirag–Azeri (GCA) Oil Field. A large 3D survey (800 km 2) was acquired over the PSA area in the summer of 1997 and the first exploration well was spudded in the summer of 1998, the second in the summer of 1999. 3D data has shown many interesting details about the development of mud volcanoes and associated features over Shah Deniz and this information has been used to help in the drilling of exploration wells. Mud volcano features on Shah Deniz range from small (hundreds of square-meter) cones to a large “collapse caldera” (10–15 km 2) that overlies much of the northern part of the crest. All mud volcano features appear to be associated with the crests of deep (pre-Maykop) structural highs. Isochron maps of seismic intervals within the Quaternary and Apsheron show that the Shah Deniz structure started to form at around the end of Productive Series deposition and continued through into the upper Quaternary. Mud volcano activity did not begin until middle Apsheron. There is therefore a delay between the start of structural development and the appearance of mud volcano flows of approximately 0.5 million years. Mud volcanoes appeared first at the southern end of the structure, while the major mud volcano on the crest did not start to develop until slightly later within the Apsheron. This is consistent with the observation that the structure initially developed in the south, before the major direction of shortening, NW–SE, seen today, became more dominant in the Mid-Apsheron. The mud volcano flows that are relatively high amplitude seismically can be clearly seen on the seismic, using voxel-based volume visualization, when stratigraphy parallel time slices are viewed. The opacity of the amplitude spectrum can be varied such that any particular amplitude ranges can be highlighted. This technique has shown moderate to high amplitude flows coming from the major central mud volcano that have a lateral extent of up to 17 km and widths of around 0.5 km. The impact of seabed topography can also be seen on the flows as well as the different characteristics of the individual mud volcanoes.