A Detailed Examination of the Mechanics of Slip Crush When Landing Heavy Casing Strings

Abstract

Over the last 50 years, the oil & gas industry has continually pushed the limits of exploration, riding the wave of recent technological advances to pioneer ultra-deepwater areas of the globe. Not until the early 80s, though, did operators start delving below the salt canopy, into reserves like the Wilcox in the Gulf of Mexico. This sub-salt (or pre-salt) trend expanded well program depths in excess of 30,000 ft MD, in water depths exceeding 10,000 ft, necessitating longer, heavier casing/landing strings. Meanwhile, new government regulations have begun mandating well designs capable of sustaining Worst Case Discharge (WCD). Deeper casing strings, in turn, must now be constructed to withstand higher collapse loads, shallow casing strings to handle more robust burst loads. Certain well designs must even feature an intermediate tieback able to endure WCD, where previously a nested liner was sufficient. This confluence of increasingly deep wells and stringent regulations presents challenges. Longer, heavier casing/landing strings push the limits of existing tubular tensile capacity, but as important, they also raise concerns about handling equipment possibly crushing landing strings due to excessive radial load (slip crush). In response, since the mid-80s, a research and testing program has been analyzing and quantifying specific factors involved when crushing loads affect tubular goods failure. Some of the identified causatives behind these increased tubular stresses are handling equipment design, vessel heave-induced dynamic loading, dynamic loading during tripping, and handling equipment-related slip crush loading. A detailed analysis of the mechanics of slip crush revealed modifying certain parameters has a material effect on the radial load imparted onto the pipe by the slips. The research shows that modifying and optimizing the combination of these parameters can not only lead to the design of handling equipment with higher slip crush capacities, but it also leads to the development of a comprehensive model that can more accurately predict the failure of tubular goods due to slip crush.