TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractSteel catenary risers (SCR) have been an attractive choice for recent deep-water field developments. However, design of SCRs for harsh environment is a great challenge, especially from large motion host platforms such as semi-submersible platforms. The key driver for the design of SCR in harsh environment is the fatigue near hang-off and at touch down point.This paper describes the concept of weight optimized SCR design for deep water harsh environment fulfilling both strength and fatigue requirements. The concepts incorporate presently available materials and technology. For the fatigue critical cross-sections, some qualified cost-effective and easily installable solutions are proposed. These proposed concepts are demonstrated through case studies of a few common riser sizes for such deep water field development with large vessel motions.
BP-Amoco operated Wytch Farm has installed fibre optic distributed temperature systems on 2 of their recent ERD (extended reach drilling) wells in order to provide real time reservoir surveillance. This novel new approach to reservoir monitoring has provided important information about the well and reservoir performance. This type of zonal contribution and fluid data would normally be acquired by running production logs on the end of coiled tubing at infrequent intervals, however the dual completion on Wytch Farm's M-12 well made conventional production logging impossible. Distributed temperature data has been recorded over 2 years throughout well tests and shut-ins, as well as during normal periods of production. Data analysis is performed both visually, by correlating time related thermal events observed in the well with known reservoir and production anomalies, and theoretically by comparing recorded temperature data with that predicted by thermal profiles generated using nodal analysis fluid flow and heat transfer software*. Use of this software* allows estimates of production by zone to be compared to actual recorded temperature data, enabling a variety of production scenarios to be investigated and the most likely identified. The installation of real time fibre optic distributed temperature monitoring on Wytch Farm field has enabled the asset to recognise flow behind casing and cross flow during shut-in in the M-12 well and water finger encroachment to be identified in the M-17 well. This data has provided important information about both the reservoir and well performance in real time, which would not usually have become available until later in the wells life. Introduction BP-Amoco's operated Wytch Farm Sherwood reservoir has latterly been developed with horizontal extended reach (ERD) wells drilled to a TVD of 1,500m and measured depths of over 10,000m under Poole harbour and the English Channel Fig 1. The producing intervals are typically in excess of 1000m long, cased with 7 inch pipe and perforated. Production is by Electrical submersible Pump (ESP). The Triassic fluvio-lacustrine sandstone reservoir is 120m thick, consisting of the Lower Sherwood high net to gross sands separated from the Upper Sherwood low net to gross sands by a field wide shale. The Lower sands have a porosity of 18% and permeability greater than 1.5D while the Upper sands range from 10 to 15% porosity with permeability about 150mD. The reservoir is bounded and divided by faults, some sealing and some conductive, and this has resulted in some compartments and layers exhibiting different reservoir pressures, as a result of production. In 1997 Wytch Farm installed a fibre optic distributed temperature monitoring system in their K-7 well. This system was intended to monitor the ESP pump temperature during start-up and to evaluate the ease of installation of the fibre optic monitoring system. Following the success of this operation, two ERD wells (M-12 and M-17) were subsequently fitted with fibre optic temperature monitoring over the reservoir in 1998 and 1999 respectively.
Loading hoses in an offshore loading buoy system in the North Sea were investigated with respect to extreme load resistance and fatigue durability. Both experimental work and fatigue life analyses were carried out. The FLS test is based on the principle of a service simulation test according to the American Petroleum Institute (API) 17B guidelines. The test results given in number of endured cycles from the laboratory test are scaled to the in-service conditions. Although the life estimate is based on one full scale test only, an attempt has been made to account for the inherent scatter in fatigue life. Furthermore, the results are validated by large test series with small scale test specimens for the critical reinforcement components in the composite structure of the hose wall. Test series with steel wires and samples of the steel helix were carried out. Statistically based S-N curves with characteristic scatter are established. Finally, all experimental facts were assembled and fatigue life predictions made. Redesign is considered and a scheduled inspection and replacement program is presented. The rubber-steel composite structure has sufficient strength for both the ULS and FLS case. For a planned replacement interval of 10 years the thickness of the standard steel end fittings has to be increased and the shape of the fitting should be optimized with respect to fatigue.
A multi-strip numerical method, combining solution of the incompressible Reynolds Averaged Navier-Stokes (RANS) equations with a finite-element structural dynamics response, has been developed to analyze the flow-structure interaction of long, flexible risers. This solution methodology combines a number of individual hydrodynamic simulations corresponding to individual axial strips along the riser section with a full 3D structural analysis to predict overall VIV loads and displacements. The hydrodynamic loading for each riser strip is derived from a 2D finite-volume discretization of the governing RANS equations which is applicable to both single and multiple riser configurations. The entire flow-structure solution procedure is carried out in the time domain via a loose coupling strategy, such that the hydrodynamic loads from each riser strip are summed to obtain the overall loading along the span of each riser. This loading is then used to integrate forward a single time-step in the riser equations of motion to obtain an updated riser displacement profile. Closure of the coupled flow-structure method is achieved by updating the riser displacements for each of the corresponding hydrodynamic strips in the next time-step integration. The developed multi-strip method is applied to a single bare riser subjected to both uniform and shear current profiles. The flow conditions and riser configuration were chosen to match the Marintek rotating rig experiments, and comparisons between experimental and numerical results are presented for several flow configurations and axial tensions. In addition, a parametric study is presented using 16, 32, and 64 hydrodynamic strips for a given flow configuration to ascertain the sensitivity of the results to the number of strips chosen.
The accuracy of current modelling is critical when considering deepwater riser fatigue damage caused by vortex-induced vibrations (VIV). In the present study the use of empirical orthogonal functions (EOF) to extract the governing characteristics from huge amounts of current measurements has been assessed. The amplitudes of the time varying principal components (PC) have been organized into bins in scatter diagrams. The accuracy of this scatter diagram approach with different numbers of EOF modes involved has been evaluated in terms of riser VIV fatigue damage.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.