涪陵页岩气井射孔及滑移段套管变形特征分析

Analysis on Casing Deformation Characteristics in Perforation and Slip Section of Wells in Fuling Shale Gas Block

涪陵区块页岩气老井在分段多级压裂后滑移段套管变形严重,将会影响后期优化改造效果,且目前对该区块套管变形特征分析较少。为此,通过结合现场测井数据,建立不同射孔参数、水泥环材料属性、页岩滑移量的套管-水泥环-地层耦合模型,并采用经典Lame公式验证模型的正确性。数值分析结果表明:ø139.70 mm×10.54 mm的P110无损套管受周向挤压与上覆压力时的应力变化率相近,但射孔后套管的周向挤压应力变化加快,此时套管易产生较大变形,45°、90°相位角射孔比30°、60°、120°和180°相位角射孔对套管强度的影响小;45°方向页岩滑移下,套管最大等效应力位于滑移面上接触点,微小的滑移量将导致套管严重变形,页岩滑移量为4.243 mm时,套管的总变形量为3.957 mm;增大水泥环在页岩滑移处的弹性模量能减少套管的最大等效应力,但套管的总形变量也相对增加。水泥环弹性模量为7 GPa时,减小或增大泊松比至0.26以上均能降低套管的最大等效应力,但对预防套管变形效果不明显。设计的套管受内压地面试验装置及搭建室内试验平台,可为套管变形分析提供试验指导。

After sectional multistage fracturing of shale gas old wells in Fuling block,the casing seriously deforms in the slip section,which affects the later optimization and stimulation effect;furthermore,there is little analysis on the deformation characteristics of casing in the block.Therefore,combined with field well log data,a casing-cement sheath-formation coupling model with different perforating parameters,cement sheath material properties and shale slippage was built,and the classical Lame formula was used to verify its correctness.The numerical analysis results show that the stress variation rates ofø139.70 mm×10.54 mm P110 nondestructive casing under circumferential compression and overlying pressure are similar,but after perforation,the circumferential compression stress of the casing changes fast,the casing is prone to significant deformation,and the impact of 45°and 90°phase angle perforation on the casing strength is smaller than that of 30°,60°,120°and 180°phase angle perforation;under shale slip in the 45°direction,the maximum equivalent stress of the casing is located at the contact point on the slip plane,a small slippage causes severe deformation of the casing;when the shale slips for 4.243 mm,the total deformation of the casing is 3.957 mm;the increase of the elastic modulus of cement sheath can reduce the maximum equivalent stress of the casing at the shale slip point,but the total deformation of the casing also increases correspondingly;when the elastic modulus of cement sheath is 7 GPa,the decrease or increase of the Poissons ratio to more than 0.26 can reduce the maximum equivalent stress of the casing,but it has little effect on preventing deformation of the casing.In addition,a ground experiment device for casing under internal pressure was designed,and an indoor experiment platform was built to provide experimental guidance for casing deformation analysis.