There is very important practical significance for borehole stability to oil and gas drilling and production. When the mud density is too large (mud column pressure too high),the formation will be fractured. When the the mud density is too low (mud column pressure too low), the borehole wall will be collapsed, and hole will be enlarged. In this paper, the fracture pressures of the formations were determined by using the maximum tensile stress theory. The formation collapse pressures were determined by using the Coulomb - Moore intensity criteria. According to the fracture pressure and collapse pressure to evaluate the borehole stability. The two wells stability evaluation examples were given, and the borehole security mud window were calculated.
The magnitude, distribution of earth stress are important parameters. In this paper, based on the hydraulic fracturing test data and logging data, the model of earth stress has been established. The vertical stress (Sv),the maximum horizontal stress (SH), the minimum horizontal stress (Sh) can be calculated by logging data with this model. The profiles of earth stress along the depth with continuous distribution can be determined, and stress spatial distribution has been described.
The freezing and freeze-thaw cycles may reduce the mechanical strength of the material for a concrete faced rockfill dam (CFRD), resulting in the risk of structural damage to the dam under the design load. In order to study the influence of freezing and freeze-thaw on the stress and deformation of the CFRDs, some experimental results and theoretical analysis for the influence of freezing and freeze-thaw cycles on the mechanical parameters of concrete face slab and rockfill were introduced at first. The finite element method (FEM) was adopted for the structural analysis of a CFRD in the high altitude area of Qinghai-Tibet Plateau of China. Using the FEM analysis results, the distribution of stress and deformation of concrete face slab and dam body were obtained and a comparison was made with the analysis results when the freezing and freeze-thaw cycles were not taken into account. Some conclusions were drawn from these analysis results and the research results provide a reliable basis for the design and construction of the CFRD in the future.
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