地震作用下岩盐层套变规律研究

Study of casing deformation in halite bed under earthquake

5.12汶川特大地震发生后,某气田在岩盐层段发现了多口井套变,为了能有效地治理,急需了解其套变的原因和规律。为此,利用真三维接触有限元分析方法研究了震前套管应力和变形分布规律,并在原有边界条件基础上,在模型的顶面进一步施加不同震级地震载荷,重新分析套管应力和变形的分布规律。对比二者分析的结果发现:无论是震前还是震后都显示岩盐层段套管的应力和变形水平明显高于套管其他部位,且基本规律是震级越高套管在岩盐层段的应力水平和变形越大。对比有限元计算震前和震后套管应力和变形的结果还发现,仅5.12特大地震载荷的竖向分量所产生的应力水平已经超过了套管的屈服强度极限,因此,可以判定此次地震是导致该气田盐岩层段出现套变的真正原因。

Casing deformation and damage have been found in halite beds in many gas wells of a gas field after 5.12 Wenchuan Earthquakes.It is very important to find out the reasons and laws of the casing deformation in order to control and repair them.Distribution laws of the casing stress and deformation are found out by applying true three-dimensional contact finite element analysis before the earthquake.Based on the above,applying extra different earthquake loads to top face of the model,the casing stress and deformation are studied again.Careful contrast of the two results shows that the level of casing stress and deformation is higher in halite bed than that in other beds whether before or after earthquakes;and the basic laws are that the higher earthquake power is,the higher level of casing stress and deformation is in halite bed.Finite element calculation results also reveal that 5.12 Wenchuan Earthquakes are the direct reasons for casing deformation and damage because the Mises stress of the casing in halite bed is already over the yield limit of its material only under the influence of vertical component load of 5.12 Wenchuan Earthquakes.