页岩气井套管剪切-挤压-弯曲组合变形反演分析

Inversion Analysis and Prediction of Shear-extrusion-bending Combination Deformation of Casing in Shale Gas Wells

水力压裂是页岩气井增产的重要手段,也是导致套管失效的主要原因,严重制约了页岩气的高效开发。为了准确预测页岩气井水力压裂过程中地层运移导致的套管变形形态和程度,采用有限元分析方法,建立了剪切、挤压和弯曲多重载荷下页岩气井筒三维有限元模型,分析地层运移作用下套管的应力、变形。采用多臂井径测井曲线,反演分析页岩运移和套管变形的形态和程度,并验证有限元模型。研究结果表明,套管在地层剪切、挤压和弯曲载荷作用下的变形形态分别呈现S形、椭圆形和拱形。当地层发生剪切运移17 mm时,套管变形为13.62 mm;发生单侧运移16 mm时,套管变形为12.67 mm;当地层发生挤压运移每侧23.5 mm时,套管两侧各向内缩径3.328 mm。套管应力集中区域出现在剪切运移地层、单侧运移地层间的缝隙处以及垂直于挤压运移方向的侧面。套管变形量沿轴线方向的数值模拟结果与测井曲线实测结果最大误差为5.73%,平均相对误差为1.89%。研究获得的组合变形预测模型可以准确分析页岩气井套管变形形态和程度,为页岩气井套管变形的预防和防治提供理论依据。

Hydraulic fracturing is an important means of increasing production in shale gas wells and it is also the main reason for casing failure,which makes the efficient development of shale gas seriously restricted.In order to predict the shape and degree of casing deformation caused by hydraulic fracturing in shale gas wells accruately,a 3-D finite model of shale gas wellbore under multiple loads of shear,extrusion and bending based on the finite element analysis method was established to analyze the stress and deformation of the casing caused by formation migration.The multi-arm caliper logging curve was used to analyze the shape and degree of casing deformation in shale gas wells inversely and verify the finite element model.The research results show that the deformation forms of casing under the action of formation shear migration,extrusion and bending loads are S-shaped,elliptical and arched,respectively.When 17mm shear travel occurs in the formation,the casing is deformed by 13.62 mm;when 16 mm unilateral migration occurs,the casing is deformed by 12.67 mm;when 23.5 mm extrusion migration occurs on each side of the formation,both sides of the casing shrink inwards in diameter by 3.328 mm.The areas of casing stress concentration appear in the shear migration formation,the gap between the unilateral migration formations and the top of the casing perpendicular to the extrusion migration direction.The maximum error between the numerical simulation results of casing deformation along the axis and the measured results of the logging curve is 5.73%and the average relative error is 1.89%.The combined deformation prediction model obtained from the study can be used to accurately analyze the deformation form and degree of casing in shale gas wells and provide theoretical basis for the prevention and control of casing deformation in shale gas wells.