Identification of shallow water flow using multicomponent seismic and GPR attributes in the deepwater basin of the northern South China Sea

Abstract

China has been using large-scale ocean bottom cable (OBC) multicomponent seismic data in deepwater oil and gas exploration since May 2012. In the northern South China Sea, shallow-water flows and over-pressurized zones are major hazards in deepwater drilling projects. Thus, the accurate predrill seismic prediction of shallow-water flow sands is an important practical problem. In this paper, the exact velocity field of sound in deep water is calculated as a function of the density, temperature and pressure of the seawater. Models of various elastic parameters are established. Through drilling data and simulation of the full wave field, new Pp and Ps AVO phenomena of shallow-water flow at various effective pressures are developed. Methods based on multicomponent seismic attributes, such as weighted average frequency and sweetness, are established to predict and characterize shallow-water flow. By studying vertically oriented GPR signals and signals parallel to the well paths in the SWF region, we find a significantly increased polarity inversion and decreased amplitude in the SWF region as effective pressure increases. Methods based on multicomponent seismic attributes and characteristics of the GPR signals may aid in the identification of SWF in the deepwater basin of the northern South China Sea. This may help overcome limitations to research in this area.