套管在单轴压缩载荷下的失效规律

针对均匀载荷下套管挤毁失效规律的研究颇多,并已形成了API 5C3和ISO标准;然而,非均匀载荷对套管的挤毁强度也具有显著影响,目前对其套管挤毁失效规律的探索与试验则较少。为此,利用YAW电液伺服压力试验机,开展了无水泥环和含水泥环的P110SS套管局部受到单轴压缩载荷的非均匀挤毁试验,得到了P110SS套管在单轴压缩载荷下的位移变化规律,套管在挤压过程中始终没有出现任何裂纹,表明该套管在变形过程中不会爆裂而发生井下事故;基于套管外壁粘贴电阻应变片测量套管在测试过程中应变的方法,得到了无水泥环和含水泥环的套管局部屈服载荷、局部失稳载荷以及其在单轴压缩载荷下的变形规律和失效机理,分析了水泥环对单轴压缩载荷下套管局部屈服载荷和局部失稳载荷的影响。结论认为,加载过程中刚开始发生屈服的套管,并不代表其失去承载能力或其承载能力下降,相反其承载能力有较大的提高。

Casing failure laws under uniaxial compressive load

Many studies have been performed on casing collapse failure under uniform load, and API 5C3 and ISO standards have been established. The non-uniform load also has obvious influence on casing collapse strength. There are only few investigations and experiments on casing collapse failure under non-uniform load. In this paper, non-uniform collapse experiments were conducted on P110SS casing with or without cement sheath under uniaxial compressive load by using YAW electrohydraulic servo pressure testing machine. The displacement variations of P110SS casings under uniaxial compressive load were obtained. No cracks occur on the casing in the whole loading process, which indicates that the P110SS casing will not burst and cause downhole accidents during its deformation. The local yield load, local instability load, deformation rule and failure mechanism of P110SS casings with or without cement sheath under uniaxial compressive were obtained by measuring the strain in the process of testing by means of the resistance strain gauge pasted on the outer wall of the casing. Analysis was made on the effect of uniaxial compressive load on the local yield load and local instability load. It is concluded that the initial yield of casing during loading does not mean the load-carrying capacity is lost or drops, on the contrary, its load-carrying capacity may rise greatly.