The movement of subsea production systems into water depths beyond practical diver working range presents challenges in the ability to install and maintain the equipment. The partitioning of systems into manageable pieces is critical to their successful remote installation and maintenance. Consideration of equipment size and weight with respect to support equipment constraints and ROV capabilities has resulted in a set of equipment that is flexible in its application to deep water requirements. A complete set of support tooling for installation of umbilicals, control pods, electrical and hydraulic distribution modules and their associated interconnections in deep water has been proven.
Many factors affect the configuration of subsea completion systems. One configuration is a template with wells drilled through it, and another is a clustered configuration where wells are drilled separately around a central gathering manifold and connected to it by jumpers. The following discussion is based on a control system which was designed for a field development configuration based on clustered wells around a central gathering manifold. The system has been configured to have dedicated modules for the distribution of electrical and hydraulic functions. These modules are separate from the production manifold (Fig. 1) The wells are located from 100 feet to 400 feet from the control system distribution equipment. This system was chosen to provide a high degree of flexibility in the installation and drilling phases of the system implementation.
The equipment described in this paper has been installed at a water depth of 2000 feet with an offset of 25 miles. Testing is in progress to extend the depth capability to 5000 feet with an offset of 60 miles.
The basis of the design philosophy was to have all components of the control system be retrievable. Another driving factor was to minimize the requirement for rig support and maximize the use of ROV's and ROV support vessel capability. Due to the deep water and long offset distance, a multiplexed electro-hydraulic control systems was chosen. All subsea junctions in the hydraulic distribution system were to utilize metal seal hydraulic couplings. Special tooling was to be minimized.
The major replaceable control system components are:
Umbilicals - Electrical and hydraulic
Distribution systems for hydraulic supplies, chemical injection lines, and annulus access lines
A distribution system for electrical power and communications
Interconnecting jumpers for both electrical and hydraulic functions.
The umbilical connection from the surface to subsea can be combined in two ways. In one configuration a single umbilical contains both the electrical conductors and the hydraulic supply lines for hydraulic power for the control system and chemical injection. The other configuration separates the electrical umbilical from the hydraulic and chemical supply umbilical. The system described here uses separate electrical and hydraulic umbilicals.
The subsea termination is installed first when laying the umbilical. The electrical umbilical termination (Fig. 2) is an oil filled pressure compensated box containing the electrical connectors.