| Xingou oilfield is a complex block faulted one located in the south of Yajiao-Xingou low bulge, Qianjiang depression. Its exploration target has turned from conventional reservoir to the unconventional ones with the feature of masses Dolomite in latest years. With the guidance of the theory of Sedimentology, classic and salt lake Sequence Stratigraphy, reservoir geology, based on the materials of core, well logging and testing,the thesis carry out reservoir sedimentology study which will be the theory guidance of the exploration and development of Xingou oilfield.The deposit source was the Hanshui water system from the north of the basin, based on the analysis of the components and content of heavy minerals, variation in sandstone thickness and seismic attribute. The ancient landform was characterized by high-northeast and low-northwest which were revealed by the way of correction of compaction depth, based on the analysis of paleo-water-depth, tectonization, and the propotion of different lithology summed from well logging.Based on the previous study which divided Xingouzui formation into a second-order sequence and four third-order sequences, we divide the Xinxia II formation into five fourth-order sequence SQ1、SQ2、SQ3、SQ4、SQ5and multiple subsequences according to the regular pattern in the contraction of salt lake.16types of lithofacies were recognized in the570.41m core of4wells. They are red-brown mudstone facies, horizontal bedding vauquelite facies, deformation structure vauquelite facies, ripple lamination calcium-mudstone facies, current bedding calcium-mudstone facies, intraclast calcium-siltstone facies, argillaceous siltstone facies, ripple bedding silty-mudstone facies, swallow-tailed calcium-mudstone facies, deformation bedding argillaceous siltstone facies, horizontal bedding argillaceous dolomite facies, current bedding argillaceous siltstone facies, massive bedding calcium-limestone facies, horizontal bedding calcium-mudstone facies and convolute bedding calcium-limestone facies and so on.Besides,4kinds of sedimentary microfacies were recognized based on the lithofacies assembly. They are shore sandbar, mud flat, dolomite flat and calcium flat.The horizontal distribution and vertical evolution of sedimentary facies were analyzed by the comparison of the well tie. The horizontal distribution is transmeridional stripe and change from calcium flat-dolomite flat-mud flat from north to sounth. The scope of mud-calcium flat,calcium-dolomite flat, mud-dolomite flat have moved to sounth because of the decline of lake level during the deposition of Xinxia II formation, there can be seen thin bedded sandbar deposition in the SQ2, While the argillaceous dolomite, mudstone and dolomitic mudstone deposition were dominated in other four sequences.The reservoir features were studied by the core, rock slice, scanning electron microscope material, and X-Ray. There are mudstone, dolomite and little siltstone in the Xinxia Ⅱ formation,as the main soure rock is mudstone while the dolomite is reservoir which can be featured that the gap and few microcrack were common while the cavern porosity is absent, middle-high porosity and extremely low permeability, it can be orderd from micritic dolomite to micritic argilliferous dolomite,then silty mudstone, based on the order from well to poor physical property.Combine the ancient dolomitisation pattern theory and the dolomite distribution in the study area, we get the conclusion that the dolomite were formed by the evaporative pumping dolomitisation while the process were influenced by the contraction and enlarge of salt lake obviously.The most advantageous sedimentary face is dolomite flat and dolomite-mud flat, the second were mud-dolomite flat,sandbar and calcium-dolomite flat. |
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