Testing and Installation Costs
The Factory Acceptance Test (FAT) is a test of subsea equipment before installation, which is always performed on newly manufactured equipment, to check whether the equipment satisfy the performance and function requirements or not. Extended Factory Acceptance Test (EFAT) may be only applicable for several equipment or subsea structures, e.g. subsea trees with sub-assemblies. The System Integrity Test (SIT) is performed to verify the whole system no matter from one supplier only or different suppliers, which shall interface with each other acceptably. Typical FAT items of subsea equipment are:
- Flushing, functioning and pressure testing of hydraulic control circuits;
- Assembly hydrostatic pressure testing;
- Function testing of ROV interfaces;
- Gas testing;
- Testing for installation and function SCM;
- Thermal insulation test;
- Continuity check for cathodic protection (CP);
The following are typical items for SIT:
- To confirm the interchangeability of individual assembly, e.g. tubing hanger and tree system, pigging loop and manifold;
- To confirm the physical interface of individual equipments, e.g. the tree on the wellhead stack , and the jumper landing on the hub of manifold;
- To identify any interface issues between the individual equipment;
- To confirm the physical interface of ROV tools to the control panel of the equipment;
- To determine the maximum angular offset that will allow for proper installation of well jumper kit. The testing may need special tools or equipment, which should be considered for the cost estimation:
- Water filled test pool;
- ROV hot stab assembly;
- Handling wire rope sling;
- Running tool & tool kits;
- Test stumps;
- Inspection stands;
Subsea Cost Estimation 179 Normally the FAT and EFAT cost are included in the procurement of the individual equipment.
Installation costs for a subsea field development project are a key part of the whole CAPEX, especially for deepwater and remote areas. Planning for the installation needs to be performed at a very early stage of the project in order to determine the availability of an installation contractor and/or installation vessel, as well as a suitable weather window. Also, the selection of installation vessel/method and weather criteria affects the subsea equipment design. The following main aspects of installation need to be considered at the scope selection and scope definition stages of subsea field development projects:
- Weather window;
- Vessel availability and capability;
- Weight and size of the equipment;
- Installation method;
- Special tooling.
Different types of subsea equipment have different weights and sizes and require different installation methods and vessels. Generally the installation costs for a subsea development are about 15% to 30% of the whole subsea development CAPEX. The costs of subsea equipment installation include four major components:
- Vessel mob/demob cost;
- Vessel day rate and installation spread;
- Special tooling rent cost;
- Cost associated with vessel downtime or standby waiting time.
The mob/demob costs range from a few hundred thousand dollars to several million dollars depending on travel distance and vessel type. The normal pipe-laying vessel laying speed is about 3 to 6 km (1.8 to 3.5 miles) per day. Welding time is about 3 to 10 minutes per joint depending on diameter, wall thickness, and welding procedure. Winch lowering speeds range from 10 to 30 m/s (30 to 100 ft/s) for deployment (pay-out) and 6 to 20 m/s (20 to 60 ft/s) for recovery (pay-in). For subsea tree installation, special tooling is required. For a horizontal tree, the tooling rent cost is about USD $7000 to $11,000 per day. For a vertical tree, the tooling rent cost is about USD $3000 to $6000 per day. In addition, for a horizontal tree, an additional subsea test tree (SSTT) is required, which costs USD $4000 to $6000 per day. Tree installation (lowering, positioning, and connecting) normally takes 2 to 4 days.
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