PSI - Issue 22

Yihua Dou et al. / Procedia Structural Integrity 22 (2019) 33–42

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Author name / Structural Integrity Procedia 00 (2019) 000 – 000

1. Preface Abnormal damage of casings, especially in perforated casings, is a serious problem in the process of exploration and development of oilfield (Wang et al. (1994)). Preliminary research shows that the decrease of casing strength caused by perforations is one of the main reasons for casing damage in the perforated section (Godfrey et al. (1970)).Therefore, as early as the 1980s, scholars at home and abroad paid attention to the remaining strength analysis of perforated casing (Zong et al. (1988), King (1989), King (1990)) .Due to the asymmetry of perforated casing, it is difficult to obtain the remaining strength of perforated casing analytically. Therefore, at present, Finite Element Analysis (FEA) is mostly adopted. Wu et al. (1994) used the finite element method to determine the allowed pressure of high energy gas in 1500 m underground without damaging casing. Xu et al. (1991) studied the combination of different forms of loads by FEA considering the effect of loads and different combination of load ratio on the strength of the perforated casings. Considering the condition of conventional perforating density and the different combination of loads type, the strength deducted factor and the phase angle of perforations helix are given. Wang et al. (2000) analyzed the impact of different perforation diameter, perforating density and phase angle on the casing strength using ANSYS soft, under conditions of fracture, water injection and normal production for casings of  139.7 and  177.8 mm. In paper by Xiang et al. (2002), the influence of perforation on casing strength is studied by using finite element analysis software in the form of solid modeling according to plane elasticity problems. In paper by Yang et al. (2006), nonlinear elastic-plastic finite element method (nonlinear elastic-plastic FEA) was used to establish the spatial finite element mechanical model for the strength analysis of perforated casings with spirally arranged perforated holes. The effects of various factors on the remaining strength and collapse strength of perforated casing were analyzed. Ji et al. (2018) established 3D finite element model of perforated casing, contrasted collapse law before and after the casing perforated, and analyzed the effect of perforations diameter and perforations density and phase angle change on the collapse strength of perforated casing using nonlinear buckling method, because the rule of equivalent stress Mises yield theory is not suitable for evaluating perforated casing collapse strength. Li et al. (2018) firstly analyzed the collapse strength of repeatedly perforated casing by finite element method. Wang et al. (2018) and Tang et al. (2017) conducted a finite element method to study the effect of a new perforating technology on casing strength. Jia et al. (2017) studied the influence of perforating impact phase change on the collapse resistance of perforated casing by using finite element method. In addition to the finite element method, Yu. (2004) presented the elastic differential equations of collapse strength of perforated casing, and a general formula for reduction factor of elastic collapsing by perturbation method. The change rule of plastic zone near the perforated hole with the increase of external pressure of perforated casing is determined by elastic-plastic finite element method. Through the non-uniform outer pressure test, Li et al. (2005) studied the impact of different perforating parameters, such as different aperture and perforations density, and different casing wall thickness on the collapse strength of casing. The results showed that the collapse strength of casing decreased greatly when it is subjected to non-uniform external loads, and the more the non-uniformity, the more the strength decreases. Based on the finite element analysis method, Liu et al. (1991) proposed the approximate calculation formula of stress intensity factor for perforated cracked casing, and studied the critical loading capacity of perforated cracked casing by using the experimental data of fracture toughness of casing material. The fracture toughness criterion of perforating performance of steel grade P110 and J55 casing is given and verified by Chen et al. (2000). In the paper by Dou et al., the approximate calculation formula of remaining strength coefficient of perforated cracked casing is derived by considering the influence of hole edge crack and pipe curvature and referring to the experience of pressure vessel defect evaluation. In the paper by Wang et al. (2004), based on the double criterion method, the concept and calculation method of loading capacity reduction coefficient of inner wall damaged tubing were proposed, which provided a new idea for the analysis of remaining strength of perforated casing considering the stress concentration at the perforating edge and the tendency of perforating cracking. Literature analysis shows that the published literatures mainly considered the slight "weakening" effect of perforations on casing cross section, yet rarely considered the stress concentration near the perforated holes. Only a small amount of experimental research on strength of perforated casings while the "holes" is not perforated. Due to the restriction of the size of the autoclave, the length of the sample “ holed ” casing is only 40 cm, and can not eliminates the fixture of "boundary" effect, which do not conform to the Saint Venant's principle of mechanics of