Numerical Analysis of Residual Strength in the Perforated Casing of Ultra Deep Wells

A three-dimensional model for the numerical simulation of casing-cement behavior is used to investigate residual strength in the perforated casing of ultra deep wells.The influence of the hole diameter,hole density and phase angle on the residual strength of the casing under non-uniform stress and fracturing conditions is revealed through the consideration of different perforation parameters.It is shown that the residual strength of the casing increases with the hole diameter and periodically changes with the hole density;the phase angle is the main factor that affects the residual strength of the perforated casing,and the perforation should be avoided in the direction of the minimum principal stress to reduce stress concentration at the perforation hole.Moreover,as shown by a companion orthogonal experiment,the descending order of influence of the different influential parameters is:phase angle,hole diameter,hole density and the thickness of casing.

模糊边界剥离聚类

提出了一种模糊边界剥离聚类(fuzzy border-peeling clustering,FBP)算法。首先,采用了一种基于Cauchy核的动态密度估计方式来计算数据点密度;然后,使用逐层剥离策略区分边界数据和核心数据;接着,利用核心数据间的可达性实现核心区域聚类;最后,采用模糊分配策略实现边界数据的软划分。在人工数据集和真实数据集上与10种算法(包含6种密度聚类算法和4种模糊聚类算法)作了对比。实验结果表明,在所有数据集上,FBP的调整兰德系数ARI指标平均提高了21%~60%,FBP的标准化互信息NMI指标平均提升了12%~47%,基于Cauchy核和模糊分配策略优化后的边界剥离聚类算法显著提高了聚类的准确性。