Sequence stratigraphy of the Lower Cretaceous Aershan-Duhongmu Formation in Baiyinchagan Sag, Erlian Basin

Sequence stratigraphy is a key technology for exploration of stratigraphic-lithological reservoirs. For the purpose of pushing forward the stratigraphic-lithological reservoirs exploration of Baiyinchagan Sag in Erlian Basin, on the basis of previous researches, and through delicate stratigraphical correlation of over 200 wells, detailed core description of 759.42 meters from 33 wells, and analysis of regional tectonic-sedimentary evolution, the authors recognized the sequence stratigraphic characteristics of the main target for petroleum exploration in Baiyinchagan Sag (i.e., the Lower Cretaceous Aershan-Duhongmu Formation) and redefined the sequence boundary properties according to various kinds of data such as tectonic geology, paleontology, petrology, logging and seismic reflection. The results show that the Lower Cretaceous Aershan-Duhongmu Formation of Baiyinchagan Sag can be divided into two super long-term sequences and five long-term sequences. The two super long-term sequences correspond to the Aershan-Tenggeer Formation and the Duhongmu Formation. The five long-term sequences correspond to the 1^st member of Aershan Formation, the 2^nd member of Aershan Formation, Tenggeer Formation, the 1^st member of Duhongmu Formation and the 2^nd to the 3^rd member of Duhongmu Formation. Meanwhile, this paper indicates that the long-term sequence bottom boundary of Tenggeer Formation in Baiyinchagan Sag is a conformity surface, which can not form the favorable pathways for oil-gas migration. In another word, even if there are good trap conditions in bottom boundary of Tenggeer Formation of Baiyinchagan Sag, for example Xi40-Xi43 wellblock, there is no hydrocarbon accumulation due to lacking the favorable pathways of oil-gas migration and the associated insufficient hydrocarbon supply.