Based on the 18-year(1993–2010) National Centers for Environmental Prediction optimum interpolation sea surface temperature(SST) and simple ocean data assimilation datasets,this study investigated the patterns of the SST anomalies(SSTAs) that occurred in the South China Sea(SCS) during the mature phase of the El Ni?o/Southern Oscillation.The most dominant characteristic was that of the outof-phase variation between southwestern and northeastern parts of the SCS,which was influenced primarily by the net surface heat flux and by horizontal thermal advection.The negative SSTA in the northeastern SCS was caused mainly by the loss of heat to the atmosphere and because of the cold-water advection from the western Pacific through the Luzon Strait during El Ni?o episodes.Conversely,it was found that the anomalous large-scale atmospheric circulation and weakened western boundary current during El Ni?o episodes led to the development of the positive SSTA in the southwestern SCS. 相似文献
The effect law of deformation and failure of a jointed rock mass is essential for underground engineering safety and stability evaluation. In order to study the evolution mechanism and precursory characteristics of instability and failure of jointed rock masses, uniaxial compression and acoustic emission (AE) tests are conducted on sandstones with different joint dip angles. To simulate the mechanical behavior of the rock, a jointed rock mass damage constitutive model with AE characteristic parameters is created based on damage mechanics theory and taking into account the effect of rock mass structure and load coupling. To quantify the mechanism of rock instability, a cusp catastrophe model with AE characteristic parameters is created based on catastrophe theory. The results indicate that when the joint dip angle increases from 0° to 90°, the failure mechanism of sandstone shifts from tensile to shear, with 45° being the critical failure mode. Sandstone's compressive strength reduces initially and subsequently increases, resulting in a U-shaped distribution. The developed damage constitutive model's theoretical curve closely matches the test curve, indicating that the model can reasonably describe the damage evolution of sandstone. The cusp catastrophe model has a high forecast accuracy, and when combined with the damage constitutive model, the prediction accuracy can be increased further. The research results can provide theoretical guidance for the safety and stability evaluation of underground engineering.
The Daxing conglomerate reservoir has become an important exploration target in the Langgu Depression of the Bohai Bay Basin. In this paper, gravel composition, void space, poroperm characteristics and hydrocarbon productivity of the Daxing conglomerate in the third member of the Oligocene Shahejie Formation (Es3) are studied in detail to understand the impact of gravel type on reservoir quality based on cores, petrographic thin-sections, scanning electron microscope (SEM) photos, porosity, permeability and well test data. The Daxing conglomerate is composed of limestone and dolomite gravels. The void space of the Daxing conglomerate includes intragravel and intergravel pores as well as fissures. Intragravel pores are dominated by gravel type. They develop as intergranular pores, intergranular dissolved pores, intragranular dissolved pores and few intercrystalline pores in limestone gravels, whereas in dolomite gravels they develop as intercrystalline pores, intercrystalline dissolved pores, dissolved pores and cavities, few intergranular pores and intergranular dissolved pores. The analysis shows that dolomite conglomerates provide better reservoir quality than limestone conglomerates. Microscopically, areal porosity in dolomite gravels is higher than that in limestone gravels. Macroscopically, porosity and permeability of conglomerates that are dominated by dolomite gravels (dolomite conglomerates) are better than those of conglomerates dominated by limestone gravels (limestone conglomerates). The dolomite conglomerates are superior to the limestone conglomerate with regard to hydrocarbon productivity at the level of parent rock and gravel properties. Poroperm characteristics and hydrocarbon productivity of dolomite reservoirs in the middle Proterozoic Changcheng and Jixian Systems (parent rocks of dolomite gravels) are better than those of the limestone reservoirs in the lower Paleozoic, Cambrian and Ordovician (parent rocks of limestone gravels). Gravel properties, including grain structure, physical nature and dissolution velocity cause the dolomite conglomerates to have more intercrystalline pores, fissures and secondary dissolved pores than limestone conglomerates. 相似文献