KEY TECHNIQUES FOR PREDICTION OF LATE EOCENE FAN DELTAIC RESERVOIR COMPLEX ON SOUTHERN SLOPE OF WEIXINAN DEPRESSION AND THEIR PETROLEUM GEOLOGICAL SIGNIFICANCE

Fan deltaic systems formed during the Liushagang Stage of Late Eocene are well developed on the southern slope of the Weixinan Depression from south to north. Multi-periodic deltaic lobes are superimposed in both vertical and horizontal sequences. Owing to the complexity of deposits, it is quite difficult to identify and predict lithologic traps in oil exploration. In this paper, we made detailed description of sand bodies, prediction of complex reservoir and evaluation of oil and gas geological systems under the constraints of sequence stratigraphy. The vertical change in facies sequences, the distribution pattern of high quality reservoirs, and the oil and gas enrichment zones are identified as the basis for further evaluation of the region. It is found by the research that there are two fourth order sequences in the lower part of the L1 Member, as well as five stages of delta lobes and thirteen single sand bodies are superimposed vertically and horizontally. The changes in depositional hydrodynamic conditions are supposed to be the basic reason leading to the strong heterogeneity and the physical differences of reservoirs. Based upon the study of major control factors of oil accumulation, we, for the first time, proposed three exploration zones in an order from north to south. The results are believed useful for future oil exploration and production in the Weixinan Depression.