基于多孔介质概念,建立了孔隙度、渗透系数与体积应变的动态演化模型,给出了Mohr-Coulomb 准则与Drucker-Prager 准则之间的强度折减系数换算关系,以Abaqus 为平台,将动态演化模型与有限元强度折减系数法相结合,研究水平定向钻孔壁稳定性。结果表明,使用不同屈服准则所得安全系数有差异,但在一定条件下可相互转换,数值分析结果与理论分析一致;研究了不同泥浆压力对孔壁稳定性的影响,指出在一定的泥浆压力下,随着泥浆压力的提高,孔壁安全系数不断降低。扩孔结束时,泥浆压力为2.4 MPa时,最大塑性半径达到2.34 m,孔壁处最大塑性应变达到0.393,极限平衡状态时,泥浆压力2.4 MPa时,孔壁周围的最大塑性应变增加到1.208,远大于扩孔结束时的最大应变值,相应的最大塑性半径达到5.68 m,约为孔径15 倍。
Based on the concept of porous media, a dynamic evolution model between porosity, permeability coefficient and damage variable volumetric strain is established. The strength reduction factor conversion relationship between the Mohr-Coulomb criterion and Drucker-Prager criterion is given. Based on the Abaqus platform, the dynamic evolution model combined with the finite element strength reduction coefficient method is used to investigate the horizontal directional drilling wall stability. Engineering case calculations show that using different yield criteria may result in different safety factors. However, under certain conditions, they can be equivalent, or the numerical results are consistent with the theoretical analysis. Different effects of pressure on the slurry stability of the hole wall are studied, and it is found that under certain mud pressure, the safety factor continuously decreases with the increase of the mud pressure. At the end of expanding, the mud pressure is 2.4 MPa, the biggest plastic radius is 2.34 m and the maximum plastic strain reaches 0.393 at the hole-wall. In the limit equilibrium state, when the mud pressure is 2.4 MPa, the maximum plastic strain increases to 1.208 around the hole-wall, which is greater than the maximum strain value of expanding. The radius of plastic reaches 5.68 m, which is about 15 times the aperture.
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