This paper provides an overview of the Liuhua infield production and test pipelines, focuses on new technologies used to tie the pipelines into a subsea manifold, and reviews the basis for selection of flexible pipe in preference to steel pipelines. The infield pipelines consist of two 13.5 -in.-ID flexible pipes for production and one 6. O-in.-ID flexible pipe for well test. Each pipeline riser is approximately 10,300 ft (3, 130 m) long and runs from the subsea manifold below the FPS, Nanhai Tiao Zhan, to the FPSO tanker, Nanhai Sheng Li. The technologies used to tie the pipelines into the subsea manifold involved:A transition tie-in base into which the flexible pipe was pulled using ROV-assisted tooling to make up the first end connectorA rigid pipe long jumper from the manifold to the tie-in baseThe survey and measurement tools to set up the jumper welding jigs Each new pipeline tie-in technology was proven through field tests of actual components before completion of manufacturing and installation. Flexible vs. Rigid Pipelines An overview of the manifold-to-pipeline system is provided in Fig. 1. Amoco uses two subsea connection techniques for the Liuhua subsea connection system. To understand how this occurred, a brief history on the Liuhua pipelines is presented. A more detailed discussion of the history and economics of the flexible pipeline selection has been presented previously (Refs. 1 and 2). During the defining stage, the Liuhua pipeline system consisted of three pipelines - two production and one test. The pipelines were to be of all-steel construction, fabricated either onshore or in shallow water and towed to site prior to the arrival of the vessels. Once the FPS was on site, the pipelines and manifold would be connected via a long jumper that spanned up to 150 ft between the manifold and the lead tow sled. At Coflexip's (now Coflexip Stena Offshore) request, Amoco agreed to reconsider the use of flexible pipelines. An all-flexible pipeline system was previously rejected due to its perceived higher cost. Full-cycle economics - including the rental of riser reels, risk of damage to the pipelines and communication cables during tow, and cost of cable crossings, corrosion inhibition chemicals, maintenance, and corrosion monitoring - was performed after receipt of installation bids. The economic result favored two 13.5-in,-ID flexible pipes for production and one 6,0-in, ID-flexible pipe for well testing. In addition, this solution outperformed the rigid pipeline option with respect to risk of damage or failure. Once awarded the work, Coflexip Stena worked with Amoco to develop an acceptable method to tie the pipelines into the manifold. The designed for steel pipelines, did not permit significant horizontal loads on the manifoldduring a flexible pipe lay away. Pile-founded tie-in bases were selected to resist lay-away loads with rigid-pipe long jumpers connecting them to the manifold.

Two 100-hp work-class remotely operated vehicles (ROVS) are a permanent part of the equipment for the Liuhua Field. ROV operations, tooling, and work packages were developed for tie construction installation of the subsea components, and for the daily operation, inspection, maintenance, and repair of these components. Facilities for the Liuhua Field include a floating production system (H%), and a floating production, storage, and offloading vessel (FPSO), the subsea production system, and three pipeline shisers from the manifold to the FPSO, a distance of 1.7 miles. The ROVS are installed aboard the FPS, which is directly above the 20 wells, manifold, and three tie-in bases for the flexible-pipe pipelines. The ROVS perform most of their installation and operational functions from the ITS. One ROV is portable, so it can be used from a workboat or other vessel to service the pipelines, risers, FPSO, or other facilities as required. The Liuhua 11-1 Development Project's use of ROVS is integral to everyday operation, ROV systems, including specially designed tool packages, were included from the early stages of the Liuhua development, and were integrated into the construction, operations, and maintenance planning of the project. The ROVS are able to perform complicated tasks with specialized tooling packages and remain subsea for long durations. The Liuhua Field construction employs a modular or building block approach. The spacing of the wells is not precisely controlled, so their piping connection is by field constructed jumpers. The reservoir requires pumping from the outset so each well employs its own electric submersible pump. The ROVS are designed to assist with the measurement, installation, and construction operations of the various subsea components, including the manifold, the well bases, the pipeline tie-in bases, the jumpers, and the system for the array of 25 risers. Introduction Amoco Orient Petroleum Company (AOPC), China Offshore Oil Nanhai East Corporation (CONHE), and Kerr-McGee China Petroleum Ltd. are completing tie initial development of the largest known offshore oil deposit in the South China Sea. The Liuhua Field is located in 1,020 ft (310 m) of water, approximately 120 miles (200 km) southeast of Hong Kong. OTC paper 8172 gives an overview of the Liuhua project as a whole (Ref. 1). As the South China Sea is an area prone to monsoons, the Liuhua ROVS have to be launched and recovered in severe weather conditions. The ROVS can dive and perform complicated tasks in weather and current conditions that would not be practical for divers. Internal waves with high currents, called solitons, frequently pass through the Liuhua Field, These solitons can cause currents over four knots; the 100-year event is hypothesized to exceed seven knots. The subsea environment at Liuhua presents a challenge for ROV operations due to the solitons. The underwater currents make it necessary to have a vehicle which can perform construction-type tasks in greater-than-normal background current.

Hard-pipe tie-in jumpers, for diverles. subsea connections between production manifolds and export pipelines (or satellite wells), are an economical alternative to additional diverless connection methods like deflection and pull-in: and also to flexible pipe jumpers. A systems level approach to the design of the jumpers. which takes into consideration performance requirements, measurement methods, fabrication and installation constraints, as well as code requirements, is essential to making these connections economical and reliable. A dependable, ROV-friendly measurement stem is key to making these connections possible. The parameter affecting the design of hard-pipe jumpers, and the relationship between these, are discussed in the context of minimizing cost while maintaining reliability. The applicability (Ifpipeline cedes to the design of hard-pipe jumpers is examined. The design construction and installation of the how Liuhua 11-1 pipeline tie-in jumpers are presented as a case study for applying these concepts. Introduction There are numerous advantages to tying in a production facility to an expect pipeline by means of a jumper spool piece. The advantage over a lay-away system is that using the jumper system, two vessels need not be on location at the same time. The cost associated with the lay-away method is particularly high when multiple connections have to be made. Deflection and pull-m method have been used as an alternative to the lay-away method The deflection method requires a large ?sweep' area for deflecting the pipeline terminations to the production manifold and requires a large vessel or stem capable of generating the loads required to deflect the pipeline, The pull-in method has the disadvantage of transferring the pull-in loads on to the production manifold and often requires the use of complex tooling In many instances. particularly when the trend is for small, light weight manifolds, this method is unacceptable Amoco function Company, as part of the development of their generic Deepwater Subsea Production System (DSPS) (Ref. 1), conducted a study in collaboration with Oceaneering Intention engineering (formerly Oil Industry Engineering, inc.) and others to develop the concept of using hard-pipe jumpers to connect a subsea production manifold to both the individual wells and to the export pipeline. The jumpers were to be designed such that they could be constructed on, and installed from, a drilling or production vessel. The ?short- jumpers connecting the wells to adjacent wells and wells to the gathering manifold were designed to be measured and installed using a high precision measurement tool known as the Measurement, Installation and Retrieval (MIR) rod. Another simpler ROV operable measurement tool was also developed as part of this system. This tool, called the Pre- Measurement Tool (PMT), is a mechanical measurement tool which can be operated with ROV hydraulics. The primary purpose of this tool is to make linear and angular measurements for constructing the hard-pipe tie-in spools ('long' jumpers) between the central manifold and the export pipelines.