51 research outputs found
Effects of weld size on stress concentration factors of CHS-CFSHS joints
No full textThis paper aims to disclose the effects of weld size on hot spot stress in the calculation of fatigue performance of the joints. For this purpose, the author explored the hot spot stress of CHS-CFSHS T-joints, which consists of circular hollow section (CHS) braces and concrete-filled square hollow section (CFSHS) chords. After reviewing the previous studies and the relevant specifications on weld size, the author probes into the effects of weld size on the stress concentration factor (SCF) of CHS-CFSHS joints via finite-element analysis. The analysis show that the weld size directly affected the hot spot stress in both conditions, and the influence laws were largely the same; with the increase of weld size, the brace-side SCF plunged when the chord-size weld size remained the same, but the chord-side SCF changed slightly when the brace-side weld size was constant; the brace-side and chord-side SCF declined when the brace-side and chord-side weld sizes increased by the same amount. This research successfully determined the weld sizes that are consistent with the relevant specifications, and safe and simple to apply in actual engineering
Effects of weld size on stress concentration factors of CHS-CFSHS joints
No full textThis paper aims to disclose the effects of weld size on hot spot stress in the calculation of fatigue performance of the joints. For this purpose, the author explored the hot spot stress of CHS-CFSHS T-joints, which consists of circular hollow section (CHS) braces and concrete-filled square hollow section (CFSHS) chords. After reviewing the previous studies and the relevant specifications on weld size, the author probes into the effects of weld size on the stress concentration factor (SCF) of CHS-CFSHS joints via finite-element analysis. The analysis show that the weld size directly affected the hot spot stress in both conditions, and the influence laws were largely the same; with the increase of weld size, the brace-side SCF plunged when the chord-size weld size remained the same, but the chord-side SCF changed slightly when the brace-side weld size was constant; the brace-side and chord-side SCF declined when the brace-side and chord-side weld sizes increased by the same amount. This research successfully determined the weld sizes that are consistent with the relevant specifications, and safe and simple to apply in actual engineering
Petrography, geochemistry, and geochronology of Lower Jurassic sedimentary rocks from the Northern Tianshan (West Bogda area), Northwest China: Implications for provenance and tectonic evolution
No full textResearch on the dynamic trajectory of spatial cable-suspended parallel manipulators with actuation redundancy
No full textOrigin of the Dolomitic Ooids Formed in the Pliocene Shizigou Formation in the Qaidam Basin, Northern Tibet Plateau and Implications for Climate Change
No full textThe concentric layers of ooids from the modern environment are mostly aragonite and those from the ancient are mostly calcite and Mg-calcite. Dolomitic ooids are rare and are usually formed via the replacement of aragonite or calcite. Here, dolomitic ooids were found in the Pliocene Shizigou Formation in the Qaidam Basin, Northern Tibet Plateau. This paper focuses on whether the dolomitic ooids is a primary precipitate. Optical microscope and scanning electron microscope observation, combined with X-ray diffraction and cathodoluminescence analyses, indicate that the primary mineral of the ooid cortices is poorly ordered dolomite. Extracellular polymeric substances and pyrite were found in the ooids, indicating that the microbe participation was involved in the formation of the ooids. Firstly, the ooids grow on the offshore lake floor. Due to the involvement of sulfate-reducing bacteria and dissolved silica, the nanominerals were precipitated on extracellular polymeric substances. Then, the ooids were transported to strong hydrodynamic surf zones, where the random nanominerals were abraded to form flattened plates as a new polished layer. In addition, a comparison between the carbon and oxygen isotopic compositions and minerals of ooids from different periods indicate that the Pliocene lakes had a lower salinity and were more humid than Pleistocene lakes. Therefore, ooids may be an effective proxy for reflecting the climatic change and uplift history of the Tibet Plateau
Helium Resource Evaluation in the Qingyang Area of the Ordos Basin Based on Natural Gamma Logging
No full textTo explore the contribution of helium generation from sedimentary rocks to helium reserves in the Qingyang area of the Ordos basin, natural gamma logging technology is used to reflect the abundance of radioactive elements in rocks by detecting the natural radioactive intensity of U, Th and K in the formation. Combined with core sampling and laboratory energy spectrum analysis, the contents of U and Th elements are calibrated and the natural gamma logging values are fitted to calculate the helium generation amount. The logical chain of "radioactive element abundance—helium generation rate—cumulative amount" is used to evaluate the helium generation potential of potential helium source rocks. Logging data from 23 wells, along with data on formation thickness, density, and area, are used to quantitatively assess the total helium resource generation from major sedimentary rocks in the study area, which is compared with the conventional component method. The research results show that: ①The helium generation potential of different lithologies is bauxite > mudstone > sandstone, and that of different horizons is Taiyuan formation > Shan 2 member > He 8 member ≈ Shan 1 member. ②The total helium generation from sandstone horizons of He 8 member and Shan 1 member in the Qingyang area is 0.911×108 m3, that from mudstone horizon of Shan 2 member is 11.116×108 m3, that from bauxite horizon of Taiyuan formation is 4.431×108 m3, with a total of 1.646×109 m3, and the Heshui area and its surrounding regions have high helium generation potential. ③The calculated helium generation potential of sandstone in Shan 1 member is slightly higher than the measured helium content, the calculated value of bauxite in Taiyuan formation is close to the measured value, the calculated value of He 8 member is significantly lower than the measured value, and the total helium generated by the sedimentary rock series in the study interval is higher than the measured helium content in the Qingyang gas field. ④The genetic method can quantify the helium resource generation, predict resources in undeveloped areas, and reduce exploration risks, but it is highly dependent on data and may overestimate resources, the component method can directly calculate recoverable resources but cannot dynamically evaluate gas reservoirs or predict undeveloped horizons. It is concluded that the helium generated by the sedimentary rock series can be the main helium source rock. The genetic method, based on the analysis of the genetic mechanism of helium resources, can calculate the theoretical resource amount more accurately and can be used for preliminary prediction of favorable helium exploration areas
Geochemical Characteristics of the Chang 7 Source Rocks of the Triassic Yanchang Formation in Ordos Basin, China: Implications for Organic Matter Accumulation and Shale Oil Potential
No full textThe Chang 7 member of the Upper Triassic Yanchang Formation in the Ordos Basin is considered to hold the main source rocks for conventional and unconventional oil and gas. The lamination or lithology alteration in vertical and lateral directions, even over a short distance, is a common feature in lacustrine source rocks. The differences in the geochemical characteristics of black shales, dark mudstones and interbedded sandstones have been scarcely reported, and their influences on the petroleum generation potential and shale oil potential are not clear. To this end, 22 core samples were collected from the Lower and Middle Chang 7 (C7-3 and C7-2) members of the Triassic from well CYX in the Qingcheng area. By conducting a series of geochemical analyses including TOC, Rock-Eval pyrolysis yields, bitumen extraction and quantification, and the separation and quantification of saturates, aromatics, resins and asphaltenes, along with biomarker analyses, several results were found. Firstly, the C7-3 and C7-2 source rocks are thermally mature and have entered into the stage of hydrocarbon generation. The C7-3 and C7-2 source rocks have a good to very good hydrocarbon generation potential especially the C7-3 black shales. Secondly, terrigenous source input is more abundant in C7-2, whereas the source input of phytoplankton, algae or microbial lipids is more abundant in C7-3. Moreover, a high TOC content basically corresponds to low wax indexes, terrigenous/aquatic ratios (TARs), and Pr/nC17 and Ph/nC18 ratios and high C27/C29 regular sterane ratios, which suggests that the source input of phytoplankton, algae or microbial lipids is favorable for OM accumulation. Third, analyses of the molecular composition of saturated fractions in shales and interbedded sandstones and the production index demonstrate the migration of petroleum from organic-rich source rocks to their organic-lean counterparts. The C7-2 dark mudstones could be considered as a potential “sweet spot” since their oil saturation index (OSI) was the highest among all the studied samples and they are more enriched in light aliphatic fractions
Diagenetic fluids evolution of Oligocene Huagang Formation sandstone reservoir in the south of Xihu Sag, the East China Sea Shelf Basin: constraints from petrology, mineralogy, and isotope geochemistry
No full textNanoscale Pore Network Evolution of Xiamaling Marine Shale during Organic Matter Maturation by Hydrous Pyrolysis
No full textCharacteristics and controlling factors of pore structure of shale in the 7th member of Yanchang Formation in Huachi area, Ordos Basin, China
No full textTo clarify the influence of organic matter and mineral composition on the pore structure of shale reservoirs in the 7th member of the Yanchang Formation (Chang 7 Member) in the Ordos Basin, we characterized the pore structure of Chang 7 shale reservoirs using argon ion polishing-field emission scanning electron microscopy (FE-SEM) and low-pressure nitrogen adsorption (LP-N2A). This characterization was combined with whole-rock mineral composition and organic geochemical experiments to analyze the main controlling factors of the pore structure of Chang 7 Member shale. The results reveal the presence of various pore types in shale, including organic matter pores, intergranular pores, intercrystalline pores, dissolved pores, and micro-cracks. The LP-N2A isotherms of shale consistently exhibit type Ⅱ isotherms with H3 and H4 hysteresis loop characteristics, indicating the relatively developed nature of mesopores and a pore morphology characterized by parallel lamellar and “ink bottle” shapes. The primary determinants of shale pore structure are identified as organic matter, clay minerals, quartz, feldspar, and pyrite. Among these factors, clay mineral phase transformation generates a substantial number of micropores and mesopores within the mineral crystal layers, serving as the main source of shale pores in the study area. Additionally, liquid hydrocarbons generated, solid bitumen, and euhedral pyrite fill inorganic mineral pores, thereby reducing the pore space of Chang 7 shale to a certain extent. These results provide a new cognition into understanding the pore structure characteristics and controlling factors of Chang 7 shale
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