Flexible pipe risers have limitations in deep water depths and pressure/collapse ratings compared to rigid steel pipe risers. Use of steel pipe systems has therefore attracted the interest of deepwater riser designers, not least to dissociate from the monopoly of the limited few flexible pipe suppliers in the world. Examples are the steel catenary riser and freestanding hybrid riser systems. An all-steel pipe Bottom Weighted Riser (BWR) system and its components are described in this paper. It is a novel approach ideally suited for short to medium term usage for production, injection and export of hydrocarbons in a large range of riser diameters. Its key advantage is the ability to relocate in a re-usable form, and disconnect from the production vessel in severe weather conditions. The feasibility of the BWR is shown in terms of the operating envelopes when connected to a floating production vessel.
The use of a generic re-locatable production riser system for use with a disconnectable Floating Production Storage and Offloading (FPSO) vessel or Floating Production Unit (FPU) in a range of shallow to medium water depths has been the topic of a number of offshore projects in the South China Sea. Such a system is attractive when early production is desirable whilst the reservoir condition remains uncertain, in an area where typhoon is almost a predictable event. A flexible riser system conventionally adopted for this range of water depths is deemed to be less than ideal from an economic standpoint. It is also disadvantaged by typically long delivery schedule, susceptibility to damage during retrieval and re-installation, and inadaptability to different water depths. The Bottom Weighted Riser (BWR) concept was first mooted more than a decade ago (Huang and Hatton, 1995). It was originally intended for large diameter risers operating in deep and harsh environments.
