By early planning of a subsea development it is possible to consider remote intervention as a means of reducing both capital and operating expenditure. This is achieved by up-front cooperation between subsea equipment suppliers and subsea contractors, with detailed input from oil companies. A major development project has been undertaken by Subsea Intervention Systems Ltd (SISL) to demonstrate the design, manufacture and testing of equipment to meet this objective.
The project described here is used as an example of how a low-cost solution to remote intervention can be achieved. The savings are not the result of one unique design solution or operating practice, but are obtained by continued attention to simple and readily available technologies.
The Integrated Intervention Systems for Subsea Production Equipment (IISSPE) project was set up as a joint industry project. The experience of a subsea equipment manufacturer, an ROV operator and the direct guidance of participating oil companies through a Technical Advisory Committee (TAC) have provided the basis for an integrated solution to intervention.
The IISSPE Project will design, manufacture and test equipment for the remote maintenance of subsea production trees The subsea equipment designs are suitable for use on satellite, cluster and template developments. The tree design includes purpose-built interfaces to optimize the use of ROV-based intervention techniques.
The intervention system will interface with a range of ROVs and can be deployed rapidly for field maintenance or emergency repairs. The system will be capable of operation from monohull vessels in existing North Sea depths but is also applicable to future deep-water fields.
The intervention required on a subsea production tree will include a variety of tasks and techniques such as inspection, repair and maintenance. These operations will be performed over a wide range of component shapes, sizes and weights. If an intervention system is to be utilized cost-effectively, it must be (Fig. 1 is available in full paper)
capable of operating throughout the entire work spectrum described in Fig. 1. The lighter work duties such as visual inspection will be performed regularly, possibly as part of a planned maintenance schedule. The heavier tasks such as major component replacement will only be performed as a result of equipment malfunction. Such an event will be a rare occurrence during the lifetime of a tree. For these situations, intervention can be considered as he primary task for subsea equipment.
Conceptual solutions were examined for the range of intervention tasks identified. The requirements were considered as part of a system approach such that the infrequent heavy-lift requirement would not detract from the features required during light work, and vice versa. It was also a requirement that any solution be compatible with existing ROV technology.
The approach selected as a result of this system approach is to provide two complementary pieces of intervention equipment as shown in Fig. 2. An ROV toolskid provides general-purpose intervention support with a manipulator and tooling services. The toolskid carries specific light intervention tooling and functions and also supports the heavy-lift facility.