Test and Numerical Simulation Research of Casing Crack Failure in Horizontal Wells

Author of the article:WANG Rui1 , ZHANG Le1 , YAN Xiaofeng2 , HAN Dong2 , YANG Peng1

Author's Workplace：1. CNPC Tubular Goods Research Institute, Xi'an 710077, China; 2. Changqing Oilfield Branch No. 6 Gas Production Plant, Xi'an 710018, China

Key Words：horizontal well casing; corrosion; defect; crack; finite element simulation

Abstract：By analysing the working conditions of horizontal well casings and combining experiments and numerical simulations, such as macroscopic observation, physical and chemical property test, microstructure analysis, SEM and energy spectrum analysis, the causes of casing cracking failure in horizontal wells were systematically analysed. The results show that the properties of the casing material meet the requirements of the standard. However, a lot of corrosion pits are found on the inner wall of the casing, and pitting corrosion occurs in the casing during acid fracturing. The fracture analysis shows that the crack originates from the bottom of the corrosion pit, and there are nonmetallic inclusions in the casing. Through the numerical simulation, the pressure bearing capacity of the casing under complete and defective conditions is analysed, which is greatly reduced under corrosion and defects. When the defect depth is 0.5 mm and the internal pressure is 47 MPa, the casing cracks fail along the original defect direction during 52 MPa fracturing, which is consistent with the failure during fracturing operation. Based on the results of the study, some suggestions are put forwards to avoid such failure accidents.