Abstract: Mud volcanoes occur in many petroliferous basins and are associated with significant drilling hazards. To illustrate the type of information that can be extracted from limited petrophysical datasets in such geomechanically complex settings, we use P-wave velocity data to calculate the mechanical properties and stresses on a two-dimensional vertical section across a mud volcano in the Azeri-Chirag-Guneshly field, South Caspian Basin. We find that: (1) the values of the properties and stresses calculated in this way have realistic magnitudes; (2) the calculated pore fluid pressures show spatial variations around the mud volcano that potentially highlight areas of fluid recharging after the most recent eruption; and (3) the information obtained is sufficient to provide helpful indications of the width of the drilling window. Although calculations of this kind may be readily improved with more sophisticated petrophysical datasets, the simplicity of this approach makes it attractive for reconnaissance surveys designed to identify targets worthy of further investigation in developing our understanding of mud volcano geomechanics, or which could be used to help formulate drilling strategies. Correction notice: The original version was incorrect. All instances of mbsf (metres below seafloor) should have read mbsl (metres below sea-level).

In contrast to volcanologists, sedimentologists are not only interested in “classical” volcanoes, but also in a second type, viz. sedimentary volcanoes. This type of volcano is helpful for sedimentologists in understanding the processes that occur in the (commonly unconsolidated) subsoil, even after deep burial. Sedimentary volcanoes can be grouped in three classes: mud volcanoes, sand volcanoes, and associated structures such as water-escape and gas-escape structures. Mud volcanoes on deep-sea floors can become partially abraded in the course of time by ocean currents, and then are recognizable on seismic profiles as so-called pockmarks. A brief review of the various types of sedimentary volcanoes is provided, and representative examples of an active mud volcano and of a dormant mud volcano are dealt with in some more detail. Sedimentary volcanoes have several characteristics in common with “classical” volcanoes, including their shapes and the processes that contribute to their genesis; they therefore deserve the name volcanoes, which implies that the term volcano has to be redefined.