Analysis of Cementing Strength of Sidetracking Cement Sheath Based on 3D Model

During sidetracking in old wells,the drill bit may destroy existing casings and cement sheaths,and meanwhile,the cementing strength of the first and second cementing surfaces near the window will be decreased,which will affect the safety of sidetracking directly.In order to ensure the practice safety,taking a sidetracking old well as the study object,a 3D model of casing-cement sheath-formation was established by use of the finite element method to analyze the variation of cementing strength of cement sheaths during sidetracking.The calculation results show that,after sidetracking,the failure area for the first cementing surface is from 1.60 m above the sidetracking point to 4.00 m below the sidetracking point,in which the cementing surface between 0.20 m above the sidetracking point and 1.65 m below the sidetracking point fails completely in circumferential direction.The failure area for cement sheaths ranges from 1.80 m above the sidetracking point to 3.95 m below the sidetracking point,and the failure area for the second cementing surface ranges from 1.90 m above the sidetracking point to 4.10 m below the sidetracking point.