The parameters of grain size, contents of silica, kaolinite, hydromica, calcite, and a geological time of tight sandstone reservoirs in Upper Paleozoic in Ordos basin were researched thoroughly, and the impact of the diagenetic evolution process of different sandstone types on porosity and throats was analyzed, based on the quantitative statistics from thin sections, measurements of porosity and permeability, and conventional and constant-rate mercury injection tests. We not only build the evolution of porosity through process-oriented numerical simulations during the geological time but also establish effect-oriented numerical simulations between porosity and different diagenesis parameters. Furthermore, we set up a fitting relationship between diagenetic factors and pore throats in different gas-bearing reservoirs. Differentiation results in the evolution of porosity and a pore-throat system of sandstone types have clear characteristics, such as lithic quartz sandstones of the He 8 Member in the Sulige area and quartz sandstones of the Shan 2 Member in the Yulin area. The fitting results show that the main factors influencing the evolution of porosity and a pore-throat system are grain size and siliceous cement, which can also be validated by the measured data on two gas-bearing intervals. The results are important to a deep understanding of the relationship between the reservoir continuing to experience porosity and permeability evolution and the timing of petroleum charging into the reservoir and can also be applied elsewhere as a quick means in high grading areas of risks during field development.
The Paleozoic strata are widely distributed in the northwest of the Ordos Basin, and the provenance attributes of the basin sediments during this period are still controversial. In this paper, the detrital zircon LA-MC-ICPMS U-Pb age test was conducted on the drilling core samples of the Shanxi Formation of the Upper Paleozoic in the Otuokeqi area of the Ordos Basin, and the provenance age and the characteristic of the Shanxi formation in the Otuokeqi area in the northwest were discussed. The cathodoluminescence image shows that the detrital zircon has a clear core-edge structure, and most of the cores have clear oscillatory zonings, which suggests that they are magmatic in origin. Zircons have no oscillatory zoning structure that shows the cause of metamorphism. The age of detrital zircon is dominated by Paleoproterozoic and can be divided into four groups, which are 2500~2300 Ma, 2100~1600 Ma, 470~400 Ma, and 360~260 Ma. The first two groups are the specific manifestations of the Precambrian Fuping Movement (2.5 billion years) and the Luliang Movement (1.8 billion years) of the North China Craton. The third and fourth groups of detrital zircons mainly come from Paleozoic magmatic rocks formed by the subduction and collision of the Siberian plate and the North China plate. The ε Hf t value of zircon ranges from -18.36 to 4.33, and the age of the second-order Hf model T DM 2 ranges from 2491 to 1175 Ma. The source rock reflecting the provenance of the sediments comes from the material recycling of the Paleoproterozoic and Mesoproterozoic in the crust, combined with the Meso-Neoproterozoic detrital zircons discovered this time, indicating that the provenance area has experienced Greenwellian orogeny.
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