achieving future development in the subsea industry
Section 1: Introduction
The current technology employed by the industry allows the use of subsea equipment to develop reserves in remote and environmentally sensitive areas. Even though the associated equipment used is innovative, the industry still strives to push the boundaries by developing further innovative solutions.
Section 2: Future for the Subsea Industry
Global growth of the subsea industry is unprecedented. The current market is growing and as shallow water and land reserves decrease the industry is looking towards deep water. Deep water generally refers to water depths of 500m or greater. Despite increased costs and risks, deep water developments will play an important role in future energy requirements.
Many demanding and technically challenging problems will be encountered in deep water as the equipment must be able to deal with changes in temperature and pressure.
Another critical aspect to deeper water developments will be control system requirements. Due to the increase in water depth the offset between the equipment on the seabed and the production facility will be larger. This poses a problem for passing power and communication signals over long distances. As a result this could usher in a change to alternative power and control systems. Subsea completions could be controlled with fibre optics or electricity instead of hydraulics and electro-hydraulics.
With respect to drilling, deepwater riser systems need to be built to cope with the weight and stress put on the long riser strings. High tech solutions like slender well drilling and production systems, as well as riser-less drilling are emerging. These solutions are likely to lower the associated cost of drilling.
Section 3: Current and Developing Technology
With the vast nature of the industry it would be impossible to capture all the aspects of developing technologies. For that reason, this section introduces a number of key subsea technologies which are either in place or in development. (This section is expanded upon in Module 4, Topic 8, Current and Developing Subsea Technology).
Key technologies include:
Subsea Multiphase Pumping
Usually all subsea productions will produce a mixture of oil, gas and water to surface facilities. By adding subsea booster pumps it is possible to increase the pressure energy and increase the production rate.
Subsea Electrical Submersible Pumps
ESP’s are electrically powered submersible centrifugal pumps lowered to the well. Electrical energy from the surface powers the pump via a cable linking the pump to the electrical power. As well as the typical function of aiding lift from wells, ESP’s are also used in water injection schemes and in producing horizontal wells.
Wet Gas Compression
Wet gas requires to be thoroughly dried before transportation. The operation is usually carried out by separators but if it is not possible to gain full removal of liquid this can go on to cause issues with further processing. To extract these reservoirs, subsea wet gas compressors are used. These compressors add pressure energy to unprocessed fluid and result in higher production rates.
Subsea Separation
As a fluid travels along a pipeline, from the well to the facilities, it exerts a back pressure on the wellhead, reducing the production rate. To achieve a higher production rate, subsea separation is used. The separators remove the gas from the liquid, send the gas to the facility and either inject the liquid or pump to an end point. This decreases the back pressure and achieves a higher production rate.
Multiphase Metering
It is difficult to model or predict multiphase flow. Various flow regimes are possible and are dependant on operating conditions, fluid properties, flowrate and orientation of the pipeline. The ability to measure unprocessed multiphase flow can lead to cost saving measures on the surface facilities.
Novel Wellhead Connectors
The wellhead provides all the anchorage for the casing and tubing strings of the well. It also provides access to the annulus between the casing and the production tubing.
ROV Technology
Remotely operated vehicles (ROVs) have been used in the oil and gas sector for many years now. An ROV consists of a power unit, thrusters for movement, control equipment, video equipment, etc. The electricity and hydraulic requirements are supplied to the vehicle by an umbilical cable. Their applications have expanded greatly as tasks that were originally carried out by divers are now completed by ROVs. These tasks include:
• Pipeline Inspection
• Platform Inspection
• Drilling Support
• Cable Laying/Burial
The development of ROVs has led to the increased use of fibre optics for data transfer as well as an increased use of un-tethered ROVs, called Autonomous Unmanned Vehicles (AUVs), which are not connected by umbilical cable.
Pipe-In-Pipe (Bundles)
A key challenge of many new subsea developments is maintaining the appropriate product temperature to avoid the formation of hydrates or wax which may lead to a complete shutdown. Pipe-in-Pipe systems allow a range of advanced and highly efficient insulation material to mitigate this risk. However, as a result of this efficient insulation, thermal expansion challenges are increased and techniques such as probabilistic analysis, upheaval buckling design, snake lay or cooling spools are employed and developed to mitigate the high expansion loads on the PIP system.
Flexible / Dynamic Riser
Flexible pipe / riser have been a successful solution for deep and shallow water environments due to its efficiency in coping with the most severe and complex loading conditions.
Development of flexible riser systems has naturally progressed in recent years due to the need for improvements in pressure ratings, diameters, depth of application and materials for sour service; however the costs remain high. Recent developments of flexible riser include;
Steel Catenary Risers
Hybrid Risers
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