2 Million-lbm Slip-Based Landing String System Pushes the Limit of Deepwater Casing Running
Authors: Brock James N. , Chandler R. Brett , Jellison Michael J. , Sanclemente Leianne W. , Robichaux Richard J. , Saleh Muhammad 
Published: October 2008

With water depths increasing to over 10,000 feet, offshore well depths exceeding 34,000 feet and extended reach targets pushing out over 35,000 feet; operators are deepening the setting depths of larger diameter and heavier casing strings. These offshore designs require landing strings with hoisting capacity approaching 2-million pounds. These requirements have exceeded the limits of previous tubular manufacturing and handling capabilities. This paper documents the design, development, manufacture and deployment of a 2-million pound landing string system to meet these requirements. The system incorporates three components: pipe, elevators and slips. The 6 5/8-inch, heavy wall, 150-ksi yield strength pipe incorporates an innovative thick-walled section in the slip contact area for resistance to slip crushing loads and a uniquely designed dual-diameter tool joint to increase elevator capacity. Slips were specially engineered to equalize radial and axial loads, increase the slip-to-pipe contact area, and optimize the contact angle to minimize the crushing loads on the pipe body. Combined with 1,000-ton elevators, the system utilizes conventional rig-up and operating procedures. The design criteria developed for landing string applications and the solutions to the unique manufacturing challenges associated with the heavy wall, high strength pipe are presented. In addition, laboratory and case studies are presented for landing operations, some with axial tension loads approaching 1.75-million pounds.

Introduction

In addition to the issues mentioned above, the nature of deep water and ultra-deep water well designs is driving the requirement for higher tension capacity landing strings. Not only is water depth increasing but well target depths below the mudline are being extended. This, combined with the often narrow margin between pore pressure/mud weight and fracture gradient, is causing well designers to set more intermediate casing strings and this in turn is pushing large diameter, heavy casing strings to deeper setting depths to maintain hole size and reach the intended hydrocarbon targets.

In the past, casing liners and offshore casing strings set in sub-sea well heads were simply run on the drill pipe that was used to drill the well. The axial tension loads encountered created no significant concerns and were well within the capabilities of the standard drill pipe and pipe handling tools traditionally used to drill the well. As the loads increased, it became apparent that more specialized systems for running these longer and heavier casing strings in ever increasing water depths would be required. It became clear that the pipe handling and running tools that had been used successfully for decades to run and set pipe were not designed for axial tension loads that were now exceeding 1.5-million pounds and approaching 2-million pounds. Initially, evolutionary changes to the landing string pipe and handling/running tools were able to address the issue successfully. Later, limitations in the pipe and handling equipment were realized. It was no longer sufficient to simply increase wall thicknesses, increase slip segment lengths, increase material strengths, enlarge cross-sectional areas, etc.; more revolutionary design changes were required.