Geological characteristics and exploration objectives of hydrocarbons in the northern continental margin basin of South China Sea

All the Cenozoic basins on the continental margin of the northern South China Sea experienced two structural phases: Palen-gene rift-fault subsidence and Neogene post-rift subsidence. There exist evident differences among the basins, which can be divided into two types as pull-apart and extensional ones. The later can be further classified into fault-subsidence and fault-sag superimposed subtypes. Their source rocks include lacustrine shale, coastal plain swamp shale and marine shale, and the reservoirs are composed of marine sandstone, bioherm and continental sandstone. Source-reservoir-seal assemblages in this area include three different types, such as continental source-marine reservoir, continental source-continental reservoir and marine source-marine reservoir ones. Secondary structures for hydrocarhon potentials in different basins are characterized by drape and bioherm in uplift, faulted zone in the abrupt slope of sags, and faulted zone, diapire zone and gentle, slope within sags. Explorations in this area are defined as precision exploration in the proven hydrocarbon-rich sags, frontier exploration and gas hydrate exploration. The precision exploration in the proven hydrocarbon-rich sags aims at new traps, types and layer systems, while the frontier exploration aims at Tertiary and pre-Tertiary basins. Explorations in the northern South China Sea have an enormous potential because hydrocarbon-generative sags control hydrocarbon distributions and the proven hydrocarbon-rich sags are major targets for explorations in the near future. The natural gas exploration in high-temperature and high-pressure formations and the exploration in deepwater areas are succeeding fields to increase the reserve next. It is crucial for the next progress in explorations in the South China Sea to actively open up and explore new areas and fields. Major problems remaining in current explorations are how to identify and deal with high-temperature and high-pressure reservoirs, low-porosity and low-permeability or low-resistivity oil layers as well as to collect and process geophysical data under specific geological conditions.