ORGANIC FACIES AND SPATIAL DISTRIBUTION OF TRANSITIONAL MARINE SOURCE ROCKS IN WESTERN SOUTH AFRICAN COASTAL BASIN

Marine source rocks contribute a lot to oil and gas generation in the world and are widely distributed on the earth. So far, the research on marine source rocks mainly focuses on its hydrocarbon generation mechanism, but lacks the research on its identification, prediction and evaluation technology in particular in the exploration and production stage of an oil field. In order to establish a set of feasible technical methods for marine source rock evaluation by organic facies analysis, this paper selected the Western South African Coastal Basin as a case. Comprehensive organic facies analysis of the main marine source rocks has been carried out by integrated analysis of sedimentary facies, paleoecologicalfacies, organic geochemical facies and seismic facies, or so called "four facies integrattion", and then the main marine source rock in this basin is systematically evaluated. The marine source rock consists of mixed terrestrial and marine organic matters. It can be further subdivided into four organic facies zones from the land to the sea, i.e.the coastal terrestrial organic facies A, the inner shallow sea mixed organic facies B, the outer shallow sea mixed organic facies C, and the upper slope autochthonous organic facies D. In a plane view, the distribution of hydrocarbon is characterized by a pattern of "inner part gas-prone and outer part oil-prone" in the basin.