松软地层套管损坏的影响因素研究

Casing damage mechanism in sand producing formations

建立松软出砂地层中套管的三维有限元力学模型,分析出砂段高度、套管内压以及垂向地直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;出砂套管损坏的危险程度与出砂段高度呈抛物线关系;最大当量应力与内压的关系基本为双段线性;垂向地应力对套管应力大小影响很大。防止和减少出砂地层套管损坏的措施,除采用合理的防砂工具、选用高强度套管外,还应使出砂段高度避免接近临界出砂段高度,并且尽量使套管内压力接近临界内压。

Mechanical model for casing damage in sand producing formations is established with the finite element method. The factors influencing casing strength, including height of sand production, internal pressure of casing, and the vertical earth stress, are investigated, indicating that sand production interval increases the risk of casing damage greatly. The damage degree is in parabolic relation to sand production height, and the maximum equivalent stress is in bi-linear relation to the internal pressure. The vertical earth stress has significant impact on casing strength. Then in order to avoid or decrease casing damage, except for the conventional methods such as using appropriate sand prevention tools and high strength casing, the critical height for sand production should be avoided as far as possible, with the internal casing pressure approaching critical value as close as possible.