The Research On Upper Palaeozoic Sedimentary System Of H8Interval Of Shihezi Formation, Southwest Ordos Basin

On the basis of existing exploration and research with predecessors, as the guiding ideology of sedimentology, and combined with geophysical and geochemical data, treating H8interval of the upper paleozoic in area, Southwest Ordos Basin as the study object, by drilling core and outcrop observations, sample analysis, well log interpretation and other means to systematically measure the study area H8segments stratigraphic division and sandstone reservoirs provenance research, and established a depositional model, integrated multi-method carved out of the H8sand body distribution rules and controlling factors. The following results were obtained and cognition.By observation outcrop and core site field, identification in the southwestern section of the Ordos Basin in H8of lateral accretion of large cross-bedding, bedding identify the characteristics discussed in detail, conduct environmental and mechanism of their formation discussed. Its significance has four research:First, restore ancient flows, thin intersecting layers of lateral accretion role and the role of pre-formed product of a different relationship with the ancient tendency to flow, so the only distinction between the front side of the plot and the plot cross-bedding in order to correctly determine paleocurrent. Secondly, the side plot interlaced layers can be used to explain part of the geological phenomena. For example, often even in fine-grained sandstone and siltstone layer is seen in more than lm thickness in large staggered layers, which is hydraulically unexplained geological phenomena. Third, the lateral accretion cross waterways praseodymium layer of sand to migrate aggradation side product, so its size can be used to restore the depth of the ancient water flow. Fourth, due to the migration of lateral accretion staggered layers of sediment aggradation product lateral waterways, so the thin layer of occurrence and flow direction nearly perpendicular to the characteristics of the restoration work lithofacies paleogeography is also important to help.In previous studies, a lot of information to digest the premise, from a large outcrop H8section measurement and correction of cross-bedding, combining in-depth study of indoor rock components:including sandstone debris particles, debris type and metamorphic lithic composed of feldspar content distribution, heavy mineral composition analysis; foundation shale distribution study, pointed out that there are three comprehensive source area of the study area, the source area Yin basin in the north, north-west edge of the basin Qilian and Qinling provenance West, North Qinling source area south of the basin, and noted that the intersection of the three major sources of big things to the Central County-Huachi area.By outcrop and core observation, micro-site field sedimentary facies analysis, identify three kinds of sedimentary system in the Ordos Basin, Southwestern H8segment, the three kinds of sedimentary facies, six kinds of sub-phase,12kinds of micro-phase type, and its micro-phase characteristics are discussed in detail, clearly pointed out that compared with H8member braided river, braided river delta and lacustrine three kinds of phases. Sedimentary facies studies show that during the deposition of paragraph H8, the performance of northern source river transport capacity enhancement, Southern relatively weakened, during the deposition of a segment in terms of relative mountains, northern overall braided river delta front southward advance of nearly40km, the river diversion frequent migration. This conclusion is forecast for the latter part of the reservoir has a positive effect.Through in-depth study of the distribution law sand H8show that the purpose of the study area layer of sand bodies in the main channel sand body, including the heart riverbed sand beach and delta distributary channel sand bodies. In the study area north of the delta front underwater distributary channel sand lanes thin strip, woven into a mesh connectivity is better; south of the study area, sand with ribbon-based, wide belt, the overall lateral connectivity is poor.By sedimentary facies and sand features in-depth study clearly pointed controlling factors in southwestern Ordos Basin target layer large reservoir sandstones and distribution are:the nature of the provenance rock sand control material composition; tectonic setting control sand vertical distribution of sedimentary facies control sand genetic types, hydrodynamic conditions control structure of sand.