THE ROLE OF RISER OPERATIONS IN EFFECTIVE DEEP WATER PRODUCTION SYSTEMS
Stephen J Rowe and William J Brendling, BMT Fluid Mechanics Limited Charles N White, Conoco Inc.
Introduction
Field development opportunities in very deep waters and harsh environments demand very efficient reservoirs and production systems. The high costs of drilling operations and production and drilling facilities are exacerbated by the great water depths, and exposure to complex and potentially dangerous metocean conditions.
Serious efforts to reduce the cost of deep water developments are being vigorously pursued by many operators. However, it takes a balanced perspective, and a mature appraisal of the uncertainties and risks, to manage the implications of front-end cost savings that may have potentially detrimental consequences on immediate and long term revenue streams in this challenging environment.
The work described in this paper has generated the means to calculate the relative operating efficiency of competing development approaches so that the cost of delayed (o r lost) production can be properly accounted for in economic models. Software development, careful modelling, and analysis have produced results that characterize critical performance issues for 'wet' and 'dry' deep water production scenarios under a range of conditions and constraints.
The study has clarified the critical roles associated with riser and well system operations in building a n effective field development plan. Analysis of the sensitivity of the operational performance to key uncertainties (eg., reservoir performance) has permitted the quantification of the commercial risks that may be hidden in what may appear to be lower cost production solutions.
EFFECT OF TENSION FLUCTUATION ON THE DYNAMIC BEHAVIOUR OF MARINE RISERS
Amiya K Basu, School Civil & Structural Engineering, Nanyang Technological University, Singapore 639798
ABSTRACT
The main purpose of the paper is to show how periodic fluctuation of the top tension affects the dynamic behaviour of rigid risers when under the combined action of regular waves, current and vessel motion. The nodal displacements of the riser associated with finite difference discretization are computed in the frequency domain using an iterative procedure which is capable of accurate multi-harmonic treatment of the nonlinear drag load and the 'load' associated with the time dependent component of the tension. This procedure is applicable also to constant tension cases, and is explained in some detail. The example problems included in the paper are designed to illustrate the additional response harmonics generated as a result of interaction of the frequencies of tension fluctuation and riser curvature.
