The detection of deep seafloor pockmarks, gas chimneys, and associated features with seafloor seeps using seismic attributes in the West offshore Nile Delta, Egypt

Abstract

The West Delta Deep Marine (WDDM) concession is one of the abundant natural gas resources in the world characterised by the presence of several active gas chimneys conduit feeding pockmarks. The detection of shallow gas accumulations has been gaining importance in hazard assessments before and during offshore drilling operations, whereas there is no way to estimate the exact pressure of the gas content in sediment to expect the potential gas hazards before and during the offshore installations, operations, and drilling. Monitoring of the gas chimneys and pockmarks plays an important role as an early warning for the oil industry to more focus on this kind of activities which may represent a catastrophic event in the future for the offshore installations at the WDDM region. Moreover, the “‘return period” of the pockmark activities is a region-dependence parameter according to the continuity of the gas supply and stability of the seepage pathway. However, in this study, the identification of the direct and indirect evidence of the shallow gas presence and migration pathways to the seafloor is achieved by extracting various-chosen seismic attributes, such as Root Mean Square, envelope, energy, the cosine of the instantaneous phase, variance, and chaos attributes. These attributes improve the imaging of several seismic evidence such as bright anomalies, enhanced reflectors, gas chimneys, and associated seabed features formed by the migration of the fluids from deep reservoirs through gas chimneys up to the seafloor. The presented profiles clearly show that gas chimneys and pockmarks combined with other associated features represent common features of the WDDM concession that can severely impact during and after offshore drilling operations in the aspects of safety, environment, and cost.