The method of the stability calculation of landslide with pore pressure is presented and an amelioration for the imbalance force method is done.A three-dimensional numerical simulation with FLAC3d has been carried out for a landslide of a hydropower station to study the pore pressure,phreatic level and flow discharge,which affected by the subhorizontal drainage holes,during the drainage period.The research of the stability change of the landslide is accomplished by the amelioration imbalance force method with the data achieved from the simulation results of FLAC3d with a program written by FISH language.The results indicate that the procedure of the stability expansion is represented properly by the amelioration method.The degrees of increased stability and the decreased imbalance force are underestimated with normal methods during the drainage period.
Abstract At present, the low-permeability reservoir fluid identification and formation dynamic evaluation mainly relies on the wireline formation test (WFT) technology in China Offshore exploration (Yang 2014 and Zhang 2018). However, because of low permeability, formation fluids cannot be continuously supplied while sampling, which makes it impossible to achieve continuous pumping during sampling operations. Therefore, there are problems such as low success rate and poor timeliness in the sampling operation of low to ultra-low permeability reservoirs. In some extreme cases, formation fluids samples cannot be obtained, which increases operating costs and exploration risks. As a spare and passive sampling method, intermittent pumping is often used for fluid identification and sampling in ultra-low permeability reservoirs. However, at present, there is no systematic analysis and demonstration of the application limit and related feasibility of intermittent pumping in the industry, nor the scientific optimization of intermittent pumping. The rationality of the intermittent pumping scheme affects the efficiency and sampling success rate. This paper aims to find out the influencing factors of intermittent pumping, and to form the optimal intermittent scheme to guide the operation. This paper uses the Modular Formation Dynamic Tester Tool (MDT) formation testing tool as the research object. First, the lower limit of MDT was analyzed. Second, through numerical simulation, the pressure recovery ratios (flowing pressure at the end of pump stop/formation pressure) of 40%, 50%, 60%, 70%, 80%, 90% were respectively defined; 8 in-, 15 in-, 20 in- invasion depths were simulated, which represent shallow, middle, and deep-mud filtrate invasion scenarios, respectively. Three samples of purity at 20%, 50%, and 80% were set as achievement goals; a total of 54 kinds of "intermittent" pumping operations were simulate, and the total operation time in the corresponding situations were obtained as well. During intermittent pumping, the continuous invasion of mud filtrate is the key factor affecting the pumping time and samples assurance. In this study, the mud filtrate invasion rate of different formations and mud systems was confirmed through laboratory and previous WFT data analysis. Moreover, this paper realized the world's first numerical simulation about intermittent pumping while there was mud filtrate continuous invasion. The intermittent pumping performance under different original invasion depths and different continuous invasion rates were also simulated and analyzed to provide guidance for the optimization of subsequent operations. Through the above studies, the optimized intermittent pumping method has been successfully applied to ultra-low to low permeability reservoir WFT sampling in multiple wells, which in the past could only be abandoned or it had to rely on advanced tools.
In Horizontal Directional Drilling (HDD), the hole diameter of clay stratum usually shrinks because of the swell or expansion of the montmorillonite, the kaolin and the illite. In order to control the swelling or expansive phenomenon which leads to the shrinkage hole during drilling in the clay stratum, a new kind of Ionic Soil Stabilizer(ISS) was used to treat the clay slurry and the expensive soils on the wall of hole. The Atterberg limits test, the shrinkage test, the free swell test, the zeta potential and the cation-exchange capacity test of the clay before and after treatment with ISS were carried out. The results show that the plastic index lowers, the shrinkage limit reduces, the free swell falls, the zeta potential and cation-exchange capacity decrease in the clay after treatment by the ISS. The mechanism is that the clay soil is treated by the ISS, which can replace the exchangeable cation of clay particle surface, change the structure of pair-electricity layers of clay particle surface, decrease the thickness of adsorbed water, reduce the cation-exchange capacity, and transfer the hydrophilic clay soil to the hydrophobic by the function of physics and chemistry so as to reduce the shrinkage hole in the clay stratum.
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