Abstract:

Study shows that the surface area of the ancient lake of the west slope at northern Songliao basin is largely exposed during the initial deposit period of Yaojia Formation, and a regional unconformity surface as the channel of westward migration for oil and gas is formed later. Therefore, it is significant to study the deposition system of upper part of Yaojia Formation and its controlling factors on the oil and gas exploration and development. According to the analysis on the distribution of heavy minerals and the percentage of sandstone in each small layer, it is revealed that the SⅡ+Ⅲ sand groups deposition of Yaojia Formation in the west slope of northern Songliao basin is controlled by the two-way provenance of Qiqihar and Yingtai; after analyzing the controlling factors of paleo-topography layer, palaeogeomorphic and water energy environment, combining with the study on the core data of 49 wells and the drilling logging data of 202 wells in the study area, the fact can be clarified that seven major micro-facies types in the SⅡ+Ⅲ sand groups deposition of Yaojia Formation in the west slope area are developed, which includes underwater distributary channel, under water interdistributary bay, distal bar, mouth bar, sand flat, mud flat and sand-mud mixed flat; and the sedimentary micro-facies plane distribution feature and their changing law of the SⅡ+Ⅲ₄, SⅡ+Ⅲ₃, SⅡ+Ⅲ₂ and SⅡ+Ⅲ₁ four small layers are summarized. After studying the micro-facies under control of the south and north two-way provenance, it is proven that the underwater distributary channel and mouth bar are the favorite reservoir sandstones, and the sand flat and sand-mud mixed flat micro-facies formed at the environment of water erosion are likely to be the potential targets for exploration in the latter part of lakes area.

Key words: Yaojia Formation, the SⅡ+Ⅲ sand groups, provenance analysis, sedimentary micro-facies, the west slope of northern Songliao basin, petroleum gas