PSI - Issue 22

Yihua Dou et al. / Procedia Structural Integrity 22 (2019) 33–42 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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materials either. Therefore, the perforated casing remaining strength is often higher than the actual remaining strength of perforated casing. Huang et al. (2008) showed that if the test and production pressure difference is determined based on this condition, the pressure difference over the remaining strength of the perforated casing will be abnormally damaged. Therefore the perforating tubing string will get stuck. In view of the above reasons, this paper studies the deficiencies of existing literature, especially the stress concentration properties around the perforations, so as to obtain practical guiding results. It can not only provide basis for mechanical analysis of perforated casing, but also provide reference for reasonably determination of acid pressure and testing pressure difference. The experimental study and finite element analysis of perforated casing stress concentration will be focused, and the criterion of strength and safety analysis of perforated casing will be determined by comprehensively considering perforating stress concentration and hole cracking. 2. Experimental analysis of stress concentration of perforated casing As shown in Fig. 1, according to the stress concentration theory, on the original "complete" casing, the geometric continuity of the casing structure is destroyed after perforating according to a certain phase angle, perforations density and aperture, the stress concentration will inevitably occur near the hole.

Fig. 1 schematic diagram of spiral perforated casing expansion According to the method of stress concentration analysis of circular hole on the plate, if the hole is used as a u shaped notch, a simplified algorithm can be adopted to obtain the approximate calculation formula of stress concentration coefficient k at the edge of the perforated hole (Masahiro (1986)).

4 3 2 1 1.8 3.6 7.3 71          k

(1)

2 0.25 0.465 (1 ) / (   

) D t t  ； D － norminal outer diameter ； t － thickness ； φ － diameter of





where ，

perforations ； μ － poison ratio. However, taking the commonly used casing of 51/2  9.17mmP110, assuming the diameter of perforated hole is 12.7mm, the stress concentration factor is calculated for about 3.0 through equation (1), which is obviously too large. Therefore, it is not feasible to calculate the stress concentration factor of perforated casing simply by "applying" plate opening. According to the stress concentration theory, the stress concentration coefficient of perforated casing should be related to the yield strength, casing diameter, phase angle, perforations density, aperture and other perforating parameters of casing material. According to the theory of solid mechanics, perforated casing is equivalent to opening several round holes on the cylindrical shell. In addition, due to the fact that the holes on the perforated casing are shot by different combinations of charges and charges carrier, there are tiny burrs and micro cracks at the edge of the perforated hole under the action of the shaped charge jet. Therefore, the problem is more complicated. It is necessary to measure the stress concentration coefficient of perforated casing through physical experiment to guide the perforating practice.