松软地层套管损坏机理分析

为了防止和减少松软地层套管损坏，采用分析计算方法，建立了松软出砂地层中套管的三维有限元力学模型，分析了出砂段高度、套管内压、以及垂向地应力对套管受力的影响。分析结果表明，出砂段的存在大大增加了套管损坏的危险性：出砂套管损坏危险程度与出砂段高度为二次曲线关系；最大当量应力与内压的关系基本上为双段线性。应使出砂段高度避免接近临界出砂段高度；并尽量使套管内压力接近临界内压。同时根据普氏砂拱效应建立了出砂量和套管最大应力之间的关系，为有效预测松软地层套管的损坏幅供了可行依椐．

Casing damage mechanism analysis in soft formations

In order to prevent and decrease the casing damage in soft formations, the article adopts the analysis-calculation method. Mechanical model for casing damage model in sand-production formations is established with the finite element method. Several factors influencing casing strength are analysed including the interval of sand production, internal pressure on casing. The analysis based on computation indicates sand production increases greatly the equivalent stress magnitude near affected regions compared with that under unaffected cases, causing the casing to be damaged more easily. Furthermore, the relationship between the damage degree and sand production height is parabolic, and the relationship between the maximum equivalent stress and the internal pressure is bi-linear. Then critical height for sand production should be avoided as far as possible, with the critical internal casing pressure approaching as close as possible.