Experimental and Theoretical Study on the Mechanical Characteristics of Perforated Casings

• DOI: 10.1016/j.prostr.2020.01.005
• Publication Date: 2020-02-25T21:25:53Z
• Authors: Yihua Dou; Yinping Cao; Mingfei Li; Yafei Zhang
• Keywords: 0211 other engineering and technologies; 0202 electrical engineering, electronic engineering, information engineering; 02 engineering and technology

Abstract Due to the perforated holes on casings after perforating, the strength of perforated casings will be decreased and the well integrity will be influenced during sequential well services. To get the remaining strength of perforated casings, experimental and theoretical study were completed. The samples of perforated casings were obtained from conventional oil field casings perforated in simulation well according to oilfield perforating practice, and the stress concentration coefficients around perforated holes were measured and confirmed by experiments and finite element analysis. Taking the perforated holes as semi-elliptical surface cracks on casings, the formula for calculating stress intensity factors and revised coefficients of perforated holes were derived. Then, both strength safety and stress intensity factors were applied to evaluate the safety of perforated casings. So, the safety analysis method for perforated casings is improved and more considerate. Considering the similarity of compressed rod and pipe, the formula for calculating the remaining collapse strength of thin walled casings were developed, taking account the stress concentration of perforated holes. The experimental and theoretical study shows that: the stress concentration coefficients around perforated holes were about 1.3 and the remaining strength will be decreased more when both stress concentration and stress intensity factors are took into consideration. Taking the mostly used perforating parameter as an example, the collapse strength of a perforated casing with 16 perforations/m and 90°helix may be decreased 12%. Based on the results of the experimental and theoretical study of this paper, the working parameters were decided and guidelines were developed to ensure the safety of perforated casing and well integrity.