Mechanical properties of a coiled tubing blowout preventer ram in the shearing process

• Main Authors: Bing Liu, Tao Li, Yongjie Zhao, Jingang Chen, Tingting Zhou, Yaoguang Qi
• Format: Article
• Language: English
• Published: KeAi Communications Co., Ltd. 2019-12-01
• Series: Natural Gas Industry B
• Online Access: http://www.sciencedirect.com/science/article/pii/S2352854019301135

A shear ram is of great significance to ensuring the safe operation of oil/gas well drilling and production, but the mechanical properties of the ram itself in the shearing process are rarely researched. Based on the basic motion law of the shear ram, combined its structural and operating parameters comprehensively, a model for solving the stress on the cutting edge was established corresponding to three stages (i.e., shear point contact, cutting and penetrating the drill pipe) according to the wedge stress theory. Then, based on the novel shear ram, the numerical simulation and indoor shear experiment were carried out on CT90 coiled tubing to understand the variation laws of ram stress and shear point stress in the shearing process. And the following research results were obtained. First, when the shear point doesn't contact with the CT90 coiled tubing, the stress at the V-shaped angular center of the ram is the largest, and that at the shear point is extremely small. Second, when the shear point just touches the CT90 coiled tubing, the phenomenon of stress concentration occurs in the vicinity of the shear point of the ram cutting edge. Third, when the shear point cuts into the CT90 coiled tubing, the stress on the shear point and on both wedge edges is the largest, reaching the strength limit of the ram (1050 MPa). Fourth, when the shear point enters the annulus after penetrating the CT90 coiled tubing, the ram stress on both sides of the junction between the cutting edge chamfer and the vertical plane is the largest. Fifth, After the CT90 coiled tubing is cut, crack damage occurs in the vicinity of the shear point of the ram cutting edge. In conclusion, the research results can better reflect the stress state of the ram cutting edge and its interaction with the drill pipe in the shearing process, and can provide an important reference for the design, manufacturing and the correct field application of shear rams. Keywords: Coiled tubing, Blowout preventer, Shear ram, CT90 coiled tubing, Ram stress, Shear point, Cutting edge chamfer, Stress test