Research Of The Sedimentary Facies And The Distribution Law Of Sand Bodies Of Fuyu Oil Layer In Well Min73-well Min7, Northern Songliao Basin

Chaoyanggou terrace-Changchunling anticline zone is located in the southeastern Sanzhao depression, which is an important resource areas in Daqing Oilfield for continued stable production. Through many rounds of selection to favorable exploration target area in Chaoyanggou terrace-Changchunling anticline, we consider that well Min73-Min7 areas have great exploration potential, it can be used as the focus of tight oil exploration, increasing reserves on production in next step. With the deepening degree of exploration, the accumulation of particularity and complexity becomes even more obvious. In order to accelerate the progress of Fuyu reservoir exploration, micro-phase characteristics and distribution of sand deposition at high frequency sequence stratigraphic framework control fine characterization is particularly important.With the guidance of theory of sedimentology, high resolution sequence stratigraphy, logging geology and petroleum geology, on the basis of fine core observation and well logging data interpretation, combined with regional geological background, the paper conducted sequence stratigraphic division and correlation for Fuyu reservoir (ie. FI and FII) in well Min73-Min7 areas, and then established Fuyu oil layer sequence stratigraphic framework, systematically studied characteristics of sedimentary system which controlled by high-frequency sequence stratigraphic frame. Finally, the paper researched the distribution feature of sand bodies in the study area. It summarizes the sedimentary characteristics the reservoir sand bodies in the vertical, the cross section and plane angle. It focuses on the size of the meandering river. The main results achieved and recognized as follows:1) With the guidance of core, well logging data, established a study area Fuyu oil HFS interface identification mark. Based on the theory of high resolution sequence stratigraphy, take plane cycle and sediment thickness as a constraint condition, the paper divided Fuyu oil layer (ie FI and FII) into 12 short-term cycles. Among them, FI group is divided into seven short-term cycles, FII group is divided into five short-term cycles.2) On the basis of fine core observation, this paper identified several kinds of lithofacies in the study area. It pointed out that there mainly exits three categories of rock facies in Fuyu reservoir:such as mudstone, siltstone and fine sandstone, which can be further divided into five categories of mudstone, six categories of siltstone, four categories of fine gravel-fine sandstone phase. By analyzing petrographic facies types and combinations of features, combined with logging flag, a meandering river-shallow delta depositional system is developed in the study area, which can be further divided into five kinds of sub-phases, ten kinds of micro facies. Wherein the meandering river is the most developed, mainly for river subfacies, river banks and diffuse subfacies subfacies, followed by shallow water delta, which can be subdivided into shallow water delta plain and delta front, delta plain can be further divided distributary channel, crevasse splay, flood sedimentary microfacies; delta front subfacies can be divided into underwater distributary channel, underwater crevasse splay, bay tributaries between micro-phases.3) In high resolution sequence stratigraphic framework, characteristics of sedimentary facies distribution in each of the small layer and evolution law were deeply studied. The results showed that Fuyu oil layer in well Min73-Min7 areas primarily develop a meandering river-shallow delta depositional system. During the period of Q3-SSC1, it mainly develops delta plain facies which is controlled by southern provenance; during the period of Q3-SSC2-Q4-SSC3, meandering river deposition by southern provenance control, the whole channel show a tendency to increase; during Q4-SSC4 to Q4-SSC5 period, it mainly develops meandering river and delta plain. Sedimentary water gradually becomes deeper, showing a channel width narrowing tendency; During the period of Q4-SSC6-Q4-SSC7, it mainly develops delta front deposition, the deposition of water further deepened, the river generally narrower width. Vertically, changes of depth of water showing such procedure:it starts from deep to shallow, and then gradually varying from shallow to deep, indicating changed back deep lake-lake transgression deposition process.4) Fine analysis of different types of channel sandstones and depositional characteristics of Fuyu oil layer, and then studied reservoir sand body sedimentary cycle, a cross-sectional study and analysis of its features and cloth plane exhibition. Meandering channel sand with fine-grained sandstone, siltstone sediments, bedding larger scale, trough-shaped, tabular cross bedding, massive bedding, parallel bedding mainly sand scale relative to the delta distributary channel underwater distributary channel and significantly larger, its main internal sedimentary cycle times of 3 to 10 times. Along the direction of the source material, the connectivity of sand body is preferably well, showed multiple strip; and perpendicular to the direction of the source material, the connectivity of sand body is relatively poor, takes the shape of lenticular sand.5) The distribution of sand bodies in the study area were studied, and then we summarized the sedimentary characteristics of reservoir sand bodies in the vertical, cross-sectional, plane angle. Quantitatively analysis the sand scale of the meandering river in well Min 73-well Min 7, and depicts the internal configuration of reservoir sand body. Within each segment layer units are generally two channel sand body development. Using empirical formulas, statistics shows that the meandering channel thickness changes in the range of 2-12.5m, the scale of them range between 300～1450 m.