Lithofacies Palaeogeographical Study And Oil-Gas Prospect Analysis Of Early Cretaceous In Easten Heilongjiang Basins

Baesd on the strategic requirement of energy resources, Daqing oilfield company purposed the target that "to find the oil and gas in peripheral and deep-seated of Daqing", and one of the key links is the oil and gas exploration for easten basins.On the basis of lots of field investigation, region data analysis and previous researches, it was considered that the easten Heilongjiang basins was the south part of large Sanjiang—Xihuote basin in early Cretaceous. Therefore, this article is mainly upheld by the theory of sedimentology, using the firsthand quantitative information which was obtained from well drilling sections as a foothold. And it was also based on the analysis of petrology and sedimentary facies, using the single factor analysis and multifactor comprehensive mapping method as its methodology. Combined with the regional geotectonic, the 1:500000 quantitative lithofacies palaeogeography map were made to predict the oil and gas prospect zone. The main cognitions and conclusions of this thesis are as follows:1,It collected the materials of the well drilling section systematicly, and it also described 16 drilling wells in details to obtain the first hand datas of petrology and the partitioning standards of sedimentary facies. Rock types are complete and bedding structures are various. It contains many kinds of clastic rocks, such as conglomerate sandstones and mudstones. Coal measure strata are also abundant, many kinds of volcanic rocks which were used as reservoir and cover in this area. The seismites were distinguish alone which were considered to be significance to oil and gas reservoir.2,According to further discussion on the marine environment, the authigenic mineral combinations of glauconite, authigenic monazite and framboid pyrite were found. And the typical tidal flat deposits with two-clay-layer structure are also found in the corresponding layers, which supplied mineralogical and sedimentology evidences to transgression in the cretaceous basins of eastern Hei Longjiang Province.3,Based on the sequence analysis of 5 drilling wells in the study area,10 integrated third-order sequences were divided out, especially the sequence 4, which can be compared in all region and provide strong evidences of that the basins were unified in the early Cretaceous. 4,It also identify two major categories of continental and Marine sedimentary environments. Continental depositional environment are further divided into 3 types, they are meandering river delta, braided delta and lacustrine facies.Furthermore, it identifies 7 kinds of sedimentary sub-facies and 16 kinds of sedimentary micro-facies. Marine sedimentary environment can be further divided into 2 types, they are coastal and shallow shelf facies. Marine deposits were mainly regard as dissections which were located in different layers in the Cretaceous. Because of non-dominant facies, which were not display on planar graph.5,Using the single factor analysis and multifactor comprehensive mapping method, four single factors were selects (formation thickness(m), clastic percentage content(%), conglomerate percentage content (%) and coal and carbon shale content (‰)).to make the quantitative lithofacies and paleogeography maps of Muling period and Chengzihe periods were compiled. There are 3 distiguished characters of Inheritance, development and Staggered from Chengzihe period to Muling period. Form the period of Chengzihe to Muling, it is a water enhanced process. Muling period inherited Chengzihe period deposition, and continues to develop with its base. In the period of the Chengzihe formation, there already formed a unified basin, but the water depth relatively shallow, so that there fromed braidd delta (meandering delt) and shore-shallow lacustrine sedimentary system, accompanied by transgression events. The lake area of Muling period became larger, and water relatively gets deeper. Then it fromed a braidd delta (meandering delt)-shore-shallow lacustrine and semi-deep lake systems.6,The comprehensive study on lithofacies and paleogeography evolution, sedimentary facies distribution and organic geochemical and reservoir properties analysis, defined that Jixi basin, the Sanjiang Suibin hollow and BoDong areas were the favorable facies belt of hydrocarbon source rocks and reservoir facies. It was purposed that BoDong-Qianjin-Fuyuan area was depocenter of the semi-deep lake-deep lake, all above should be the focus for further exploration zone.