Field Operation of Drilling Marine Risers

Abstract

Structural analysis techniques have been used since the 1950's to predict stresses in marine riser systems. However, little effort has been focused on the input design criteria, their interpretation, and field application. Taking into consideration the rig's characteristics, mooring capability, and riser system, this paper presents design and operating criteria for the engineer and rig personnel. Introduction Since the first marine riser (or mud riser) was run and operated in the late 1950's off the coast of California,1,2 the industry has analyzed and studied the structural aspects of drilling riser systems rigorously. Literally millions of dollars have been spent on computer programs and their refinement in an effort to analyze accurately the beam column structure as it is used on a floating drilling vessel.3–6 In search of field verification of developed analytical techniques, additional large sums of mopney have been spent for strain gauge and accelerometer measurements along with digital and analog recording systems.7 As of the mid-1970's, the industry generally had come to the conclusion that, from an analytical standpoint, the analysis techniques and conclusions were sound. This is apparent from the publication of API Bull. 2J8 as compiled by the Marine Riser Task Group, in which close agreement was obtained between nine different independent contributors. The literature is full of presentations on riser structural analysis. However, no major piece of work has been presented on the methodology of taking the beam column computer output and implementing it on a daily basis in actual field operation. Because of this lack of attention, some interesting and varied results on how to design and operate a drilling riser in the field have taken place. It is our purpose (1) to show the tremendous divergence in approaches currently being used to determine a recommended tension and (2) to present a specific method for analysis that is based on operational considerations as well as riser structural stability. We also will discuss field operations such as riser space-out, riser tensioner wire rope slip programs, and the inspection of marine riser joints and connectors.