Developments in Coiled Tubing BOP Ram Design

Abstract

Abstract Significant technical improvements have been made recently in the design of coiled tubing (CT) blowout preventer (BOP) shear and slip rams. This technology is constantly being enhanced and refined as the CT service industry continues to mature and new operational demands are placed on the CT pressure control equipment. Larger CT sizes require better BOP shearing capabilities. Advancements in the understanding of CT fatigue life25 have caused the life reducing affects of the slip ram markings on the pipe to be examined. This paper explores the circumstances that have precipitated these improvements, and the research and development methods involved in developing better BOP rams. CT Shear Rams The CT shear ram should be capable of shearing a specified range of CT with no tension in the string at maximum well head pressure5, leaving a sheared portion of CT with a fishable top profile that has a residual outside diameter equal to or less than the original outside diameter. Equally important is the amount of flow area in the lower fish to permit sufficient circulation through the sheared CT to control the well during the well recovery sequence. With the advent of operations with an electrical wireline installed inside of the CT, it has become an important design criteria that the shear rams cut not only a wide range of CT sizes but also stranded wireline inside the CT. The shear blades must be designed to eliminate any gap between the blades at the point of contact with the stranded wire to prevent trapping small diameterstrands of the cable that would result in an incomplete shear. Also, the ability to repeatedly shear a wide range of sizes and weights of CT offers a definite advantage over previous designs of shear blades which required changing out blades for each size of CT. Earlier designs of shear blades were lacking in their ability to perform multiple cuts, and to shear wireline.hese designs typically had a "V" pocket configuration as is shown in figure 1, with a knife cutting edge fabricated from carburized carbon steel or hardened tool steel. These blades were generally limited to the smaller CT sizes up to 1-1/4" diameter used during that period. They were designed for a one time emergency cut and were to be replaced after each use due to their tendency to fracture on the first closure. Due to demand for a multiple cut blade and advances in CT metallurgy that propagated larger diameters and weights of CT, new innovations in blade design were required. The radius pocket blade was introduced with a square cutting edge to overcome the shearing deficiencies of the earlier "V" blades, This concept proved successful in its ability to repeatedly shear CT and wireline without damaging the blade?s cutting edge. This was achieved by the radius pocket and blunt cutling edge, shown in figure 1, that allow the shearing impressive forces to be distributed over the entire cutting edge. Also, the radius net made a preferable cut that left an elliptical profile.