Liuhua 11-1 Development - ROV Interventions
Authors: Hughes John D. , Paull B. Mark , Serafin Michael , Openshaw Graham , Smith Graeme L. 
Published: October 2008

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.