Engineering Offshore Structures PDF

1 Engineering Offshore Structures 1.1 General background In the initial stages of development of offshore oil platforms, the designs evolved from land-based structures and were constructed on site. The engineering design knowledge was either borrowed or ex...

1 Engineering Offshore Structures 1.1 General background In the initial stages of development of offshore oil platforms, the designs evolved from land-based structures and were constructed on site. The engineering design knowledge was either borrowed or extrapolated from traditional fields of civil engineering and naval architecture. During the 1950s, new technology began to be developed for this type of structure. Since then many advances have been made, particularly in the field of materials. Governments’ legislation in the various host countries with offshore oil has also played a role in shaping the design of production platforms and the various other structures seen offshore. Economics are very important and play a leading role in platform design. For example, it is only possible to justify the expenditure for a massive eight-legged steel or a huge concrete gravity platform, when the hydrocarbon reserves in a particular field are large enough to, not only warrant the initial capital cost but will also guarantee a good income for a long period of time. There is also a growing concern for the environment and this consideration influences certain aspects of structural design. Another factor of prime importance is safety of personnel. There are two facets to this: 1.1.1 Safe to operate The first facet is the usual concern of engineers to design a structure which is elegant if possible, conservative in its use of materials, fit for the design purpose, able to operate for the prescribed length of time, safe to operate and within the allowed budget. 1.1.2 Government Legislation The other facet is Government Legislation. This is put in place to ensure that structures are fit in all aspects, including safety, for the purpose they are designed to fulfil. 1.2 Design specifications The requirements for an offshore platform will necessitate the consideration of a number of factors and involve drawing up design specification. The full design specification will contain many different factors, so by way of illustration, the following list should serve to indicate some of those affecting load bearing and cost. 1.2.1 Materials Should be readily available from suppliers in the required form and should meet the requirements of the design specification. Rev 2 February 2014 Engineering Offshore Structures 1-1 Copyright © TWI Ltd 2014 1.2.2 Working life This may typically be 25 years. 1.2.3 Loading The platform should provide a safe working environment for the purpose of recovering hydrocarbon reserves. It must be capable of withstanding the loads imposed on it by the drilling and other works performed in and on the work areas and it must withstand the forces imposed by wind and wave action. 1.2.4 Environment Open sea conditions will impose very harsh conditions on the entire structure but especially the Jacket. Due consideration must therefore be made to the effects of corrosion because of this environment. 1.2.5 Maintenance This should be kept to a minimum. Consideration must be given to the underwater maintenance, being especially singled out with a view to not only minimising it but also to use the most cost effective means of achieving any necessary works. 1.2.6 Weight The weight of the deck modules must be considered, so that the Jacket can be designed to support this weight. The all-up weight will have ramifications on the cost and on the seabed design of the foundations. 1.2.7 Dimensions The size of the structure will be dictated by the work functions and will be strongly affected by the requirements to keep the topside weight to the minimum. 1.3 Construction activity monitoring system At the same time as the design specification is drafted, it is possible for the Quality Assurance (QA) function to be implemented. This can take the form of an Activity Monitoring System that would comprise: Full certification for the location of all components, normally by way of as- built drawings. This would usually include any concessions, repairs and the actual location of J tube and temporary access holes. Full material certification. Non-destructive testing (NDT) and inspection certification, which would include personnel qualifications. Rev 2 February 2014 Engineering Offshore Structures 1-2 Copyright © TWI Ltd 2014 1.4 Guidance on design and construction With these engineering requirements in mind as the basic starting point, design and structural engineers will be able to obtain guidance as to what minimum standards are acceptable to the appropriate authority or government body, whatever country they are operating in. Changes in UK regulations In 1988, there was a substantial leakage of gas condensate on Piper Alpha, which was a large North Sea oil platform. The leakage led to an explosion and large fires, which engulfed the Piper Alpha platform and led to the loss of 167 lives. A Public Inquiry was established with the aims of establishing the causes of the disaster and making recommendations for changes to the safety regime. The enquiry was chaired by Lord Cullen and made its recommendations in 1990. There were 106 recommendations aimed at improving the regulation of Health and Safety Offshore and all were accepted by the Government. A central recommendation was subsequently developed and implemented by the UK Regulator, Health and Safety Executive (HSE), in the form of ‘the Offshore Installations (Safety Case) regulations’, which came into force in 1992. These regulations require the operator/owner (known as the Duty Holder) of every fixed and mobile installation operating in UK waters to prepare Safety Cases for each installation on the UK continental shelf, which the HSE must accept before operations are permitted. The Safety Case is expected to demonstrate that the Duty Holder has the ability and means to control major accident risks effectively. This requires that the Duty Holder has identified the major accidents, hazards, assessed the major accident risks, implemented control measures to ensure that the risks are reduced to as low as reasonably practicable (ALARP), in compliance with all relevant statutory provisions and made adequate arrangements for auditing and reporting. The new Safety Case regime effectively replaced the pre-1988 prescriptive system for SIM with risk based and goal setting activities structured around the management of safety critical elements (SCEs). SCEs are defined as the parts, or components of an installation and its plant, whose failure could cause, or contribute substantially to a major accident, or whose purpose is to prevent, control or limit the effects of a major accident. The Safety Case regulations were revised in 2005, to reflect 13 years of experience. Under the 1992 regulations, a Safety Case lasted three years before it had to be resubmitted for acceptance. According to the 2005 regulations, a Safety Case will last the life of the installation, without the need for routine resubmissions. However, the Safety Case is intended to be a living document, kept up-to-date and revised as necessary to ensure it remains current and reflects actual operational conditions on the installation. Rev 2 February 2014 Engineering Offshore Structures 1-3 Copyright © TWI Ltd 2014  The Duty Holder is required to conduct a thorough review of the current Safety Case at least every five years, or as directed by the HSE. In addition, revisions that make a material change are required to be resubmitted to the HSE for acceptance (a material change is one that changes the basis on which the original Safety Case was accepted, such as significant modifications or repairs, introduction of new activities, extension of life beyond original design life or major changes in technology). In addition to the Safety Case Regulations, the new goal-setting regulation (replacing the previous prescriptive regulations) were introduced, as outlined below. 1.4.1 Guidance in UK regulations The regulatory requirements for the asset integrity management of structures operated on the UK continental shelf are specified in the following documents (Stacey, OMAE-49089): The Offshore Installations (Safety Case) Regulations 2005 (SCR05), which make preparation of a Safety Case a formal requirement (described above). The Offshore Installations And Wells (Design And Construction, etc.) regulations 1996 (DCR), which require the Duty Holder to ensure that suitable arrangements are in place for maintaining the integrity of the installation, through periodic assessments and carrying out any remedial work in the event of damage or deterioration. The DCR place a requirement on the Duty Holder to design installations to withstand such forces acting on it that are reasonably foreseeable and that in the event of foreseeable damage it will retain sufficient integrity to enable action to be taken to safeguard the health and safety of personnel on or near it. The Offshore Installations (Prevention Of Fire And Explosion And Emergency Response) Regulations 1995 (PFEER), which require that the duty holder takes appropriate measures for the protection of persons on offshore oil and gas installations from fire and explosion and for securing effective ‘emergency response’, which means action to safeguard the health and safety of persons on such installations in an emergency. The Duty Holder is expected to perform ‘an assessment’ which consists of: (a) the identification of the various events which could give rise to a major accident involving fire or explosion; or the need for evacuation, escape or rescue to avoid or minimise a major accident; (b) the evaluation of the likelihood and consequences of such events; (c) the establishment of appropriate standards of performance to be attained by anything provided by measures for ensuring effective evacuation, escape, recovery and rescue to avoid or minimise a major accident. This requires inherent safety by design, preventive, detection, control and mitigation measures (which include plant and management systems). Rev 2 February 2014 Engineering Offshore Structures 1-4 Copyright © TWI Ltd 2014  The Pipelines Safety Regulations 1996 (PSR), which require the operator to ensure that a pipeline has been designed adequately (it can withstand internal and external forces arising from its operation); it is maintained in an efficient state, in efficient working order and in good repair throughout its service life; all hazards relating to the pipeline with the potential to cause a major accident have been identified and the risks arising from those hazards have been evaluated and that the Safety Management System is adequate. The Provision And Use Of Work Equipment Regulations 1998 (PUWER), requires employers to ensure that work equipment is fit for the purpose for which it is used; where the safety of work equipment depends on the installation conditions, inspection of the equipment after installation is required to ensure correct installation and safe operation, where the work equipment is exposed to conditions causing deterioration which is liable to result in dangerous situations, inspection of the equipment during service at suitable intervals is required to ensure that health and safety conditions are maintained and that any deterioration can be detected and remedied in good time. In short, employers are required to identify and control potential risks from hazards due to equipment failure; put in place appropriate inspection procedures after installation; and appropriate inspection and maintenance procedure during service to ensure that the work equipment is in efficient working order and in good repair. ISO standards for offshore structures Standards have been (and are being) developed in the ISO 19900 series giving guidance on the design, construction, transportation, installation, integrity management and reassessment of offshore installations. Structures covered by these standards include: bottom-founded fixed steel structures; fixed concrete structures; floating structures, such as mono-hull FPSOs, semi-submersibles and spar platforms, arctic structures and site-specific assessment of jack-up platforms. The following ISO offshore structures standards have been published: ISO 19900: 2002 General requirements. ISO 19901 Specific requirements. ISO 19901-1: 2005 Metocean design and operating considerations. ISO 19901-2: 2004 Seismic design procedures and criteria. ISO 19901-3: 2010 Topsides structures. ISO 19901-4: 2003 Geotechnical and foundation design considerations. ISO 19901-5: 2003 Weight control during engineering and construction. ISO 19901-6: 2009 Marine operations. ISO 19901-7: 2005 Station keeping systems for floating offshore structures and mobile offshore units. ISO 19902: 2007 Fixed steel offshore structures. ISO 19903: 2006 Fixed concrete offshore structures. ISO 19904-1: 2006 Floating offshore structures – mono-hulls, semi- submersibles and spars. ISO 19905-1: 2013 Site specific assessment of jack-ups. ISO 19906: 2010 Arctic offshore structures. Rev 2 February 2014 Engineering Offshore Structures 1-5 Copyright © TWI Ltd 2014  ISO standards for oil and gas production are expected to have primacy in most regions of the world, including the UK continental shelf, for the design of new offshore installations and for modification to and reassessment of existing offshore structures. 1.5 General design considerations Typical design considerations are outlined below (extract from DNV-OS-C101: 2011 – General Design of Offshore Structures, LRFD method). 1.5.1 Aims of the design Structures and structural elements are designed to: Sustain loads liable to occur during all temporary, operating and damaged conditions, if required. Maintain acceptable safety for personnel and environment. Have adequate durability against deterioration during the design life of the structure. 1.5.2 General design considerations The design of a structural system, its components and details is required, as far as possible, to account for the following principles: Resistance against relevant mechanical, physical and chemical deterioration is achieved. Fabrication and construction comply with relevant, recognised, techniques and practice. Inspection, maintenance and repair are possible. 1.5.3 Limit States In a Load and Resistance Factor Design (LRFD) standard, load factors are applied to characteristic reference values of the loads acting on the structure and resistance factors are applied to characterise the resistance of the structure or resistance of materials in the structure. The design considers a number of limit states such as: Ultimate Limit States (ULS) corresponding to the ultimate resistance for carrying loads. Fatigue Limit States (FLS) related to the possibility of failure due to the effect of cyclic loading. Accidental Limit States (ALS) corresponding to damage to components due to an accidental event or operational failure. Serviceability Limit States (SLS) corresponding to the criteria applicable to normal use or durability. Examples of limit states within each category: Ultimate limit states (ULS) Loss of structural resistance (excessive yielding and buckling). Failure of components due to brittle fracture. Loss of static equilibrium of the structure, or of a part of the structure, considered as a rigid body, eg overturning or capsizing. Failure of critical components of the structure caused by overloading (in some cases reduced by repeated loads). Transformation of the structure, for example, due to buckling, plastic collapse or excessive deformation. Rev 2 February 2014 Engineering Offshore Structures 1-6 Copyright © TWI Ltd 2014  Fatigue Limit States (FLS) Cumulative damage due to repeated loads. Accidental Limit States (ALS) Structural damage caused by accidental loads. Ultimate resistance of damaged structures. Maintain structural integrity after local damage or flooding. Loss of station keeping (free drifting). Serviceability Limit States (SLS) Deflections that may alter the effect of the acting forces. Deformations that may change the distribution of loads between supported rigid objects and the supporting structure. Excessive vibrations producing discomfort or affecting non-structural components. Motion that exceed the limitation of equipment. Temperature induced deformations. 1.6 Pipelines Offshore pipelines are used to transport oil or gas from platform to loading towers or to shore. They are fabricated from high-grade steel pipe (eg API/5LX), which is bitumen wrapped for corrosion prevention and coated with a layer of reinforced concrete to provide a weight coating, which gives additional protection as well. The sizes normally vary from 50mm (2 inch) to 914mm (36 inch) and the wall thickness normally varies according to the pressure rating required. 1.6.1 Pipeline laying The methods for laying pipe has evolved since the 1950s and uses lay barges on which standard 12m lengths of pipe are welded together along the centre of the specially designed and fitted out deck of the vessel. Each joint is inspected by X-ray, then coated with bitumen and wrapped with a protective sheathing. Modern day inspection involves automated ultrasonic techniques. As new lengths of pipe are added, the assembly is fed over the stern and the barge is moved forward, usually by pulling on anchors, which have been laid by an associated anchor-handling vessel. An alternative approach is laying pipe from a reel barge. The earliest application of this technique occurred during World War II when a 76mm (3”) diameter pipe was laid across the English Channel in operation PLUTO (Pipeline Under the Ocean). This early application used floating reels with the pipeline being unwrapped from them as they were towed along. The modern application requires the pipe to be prepared on land and then wound onto the reel, which is mounted on the stern of the reel laying vessel, which itself is moored at a specially designed pier. The vessel then proceeds to the required site and lays the pipeline by un-reeling it over the stern as the barge steams forward. Rev 2 February 2014 Engineering Offshore Structures 1-7 Copyright © TWI Ltd 2014  The welding and preparation work on land is carried out in a spooling yard, where the pipe sections are supplied in 12m (40ft) lengths. These are welded together to form stalks, usually about 518m (1700ft) long. All the welds are X-rayed (or inspected by automated ultrasonic testing), coated and the stalks are stowed in racks alongside the spooling dock. At the start of spooling, the first stalk is moved into the roller system. The end is welded to a stub of pipe on the reel and is pulled onto the reel. The second length is then welded to the end of the first, the weld is X-rayed and coated and the procedure is then repeated for subsequent stalks. All welding and loading operations are performed at the shore facility and therefore are less affected by weather conditions. The major area of criticality is establishing and maintaining even tightness of the wraps on the reel, this is to avoid potential breakthrough of one wrap into another, which would cause damage to the pipe. The reeling and unreeling of the pipe actually causes yielding of the steel and the maximum diameter pipeline that can be laid is 600mm (24 inch). Figure 1.1 MSV Norlift, laying the 10 inch pipeline between the Neptune and Mercury fields. 1.7 Offshore oil terminals Large oil tankers are cheaper to run than small ones. This philosophy of building large tankers was reinforced in the 1950s, when the Suez Crisis forced tankers from the Gulf to detour around the South of Africa to reach Europe. As tanker sizes increased, the number of ports that could handle these large vessels decreased and public opinion was against allowing such tankers too close to inhabited areas. Many solutions were proposed to solve this problem of shrinking docking facilities, which included artificial harbours, artificial offshore islands, multiple buoy mooring systems, tower mooring systems and single point mooring (SPM) or single buoy mooring (SBM) systems. The SPM is the most widely used because of its relatively low operational cost, reliability and flexibility and is shown in section 2. Rev 2 February 2014 Engineering Offshore Structures 1-8 Copyright © TWI Ltd 2014 1.8 Future trends We are likely to see continued development of current trends and techniques in all areas of offshore engineering, with the probability of new techniques being evolved to enable the exploitation of reserves, which are currently marginal or beyond the range of present day techniques. 1.8.1 Drilling This is a branch of engineering which has seen numerous developments, the results of which have made recovery of reserves more efficient and effective. Cost reduction and further development of marginal reserves will, no doubt, cause a continuation of developments of the present techniques and trends. There will surely be, for instance, increased use of: Horizontal drilling enables more formations to be exposed to production and reduces reservoir problems, such as associated gas and water production. It is useful for thin and tight, low permeability reservoirs. Fewer wells are needed to achieve optimum reservoir production than with conventional drilling. Extended reach drilling can reduce the number of platforms required to develop a field as a greater reservoir area can be drained from one central platform. Horizontal distances up to 7000m have been achieved. Slim-line well design involves cost-effective casing design around an optimal production conduit; this can also reduce the number of wells needed to achieve optimum reservoir drainage. Rig automation allows several labour intensive tasks, such as pipe handling, to be carried out automatically. For instance, on the rig package developed for Norske Shell’s Troll platform, only one driller and an assistant man the rig floor. On a conventional rig, between five and seven people would be needed to carry out equivalent tasks. All pipe-handling operations are carried out from a specially designed control cabin. Removing personnel from the drill floor means more cost-effective and potentially safer operations. Temporary (lightweight) topsides on platforms can make production platforms lighter and cheaper than traditional platforms, which include permanent integrated drilling facilities. For example, Norske Shell’s Draugen and Troll platforms are designed so that the derrick set can be removed at the end of the drilling and completion phase. By removal of the drilling derrick and modules the load is decreased on the platform and the stress on the welds reduced. Shell’s Gannet Platform is another lightweight design. Rev 2 February 2014 Engineering Offshore Structures 1-9 Copyright © TWI Ltd 2014  Figure 1.2 Gannet Platform North Sea central sector. Tender assisted operations also help to minimise the weight of the production platform by providing most drilling support equipment on a floating, anchored, ship-shaped tender in calm waters or an anchored semi- submersible unit for deeper or harsher environments. Mobile drilling units are jack-up or semi-submersible rigs, depending on water depth. They can be used to drill production wells (with well completion on the seabed and production pipelines led to a nearby facility) where size and economics of the reservoir do not justify the installation of a platform. Rev 2 February 2014 Engineering Offshore Structures 1-10 Copyright © TWI Ltd 2014 1.8.2 Design practices Fixed platforms are now lighter, slimmer and simpler than the giant platforms built in the 1970s. There is scope for further simplification, for example of topsides, which account for more than half the capital cost of a platform. Platform development Sub-sea Satellite at 20Km Figure 1.3 Comparisons of capital costs. Topside costs can be reduced, for instance by standardising designs and reducing sparing (duplication of equipment). Another option is to examine alternatives to conventional platform designs. Studies of a purpose-built production jack-up unit, a concrete gravity structure and a tripod tower platform have shown that all three are technically viable and could offer cost saving for applications in water depths around 100m. Greater use of sub-sea satellite technology instead of building a platform can reduce costs, especially where infrastructure already exists nearby, which can be used as a host platform. As indicated by the relative sizes of the pie charts in Figure 1.3, the capital costs of constructing a sub-sea satellite 20km from an existing platform are much lower than the costs of constructing an additional platform. However, in such an instance, the long term technical integrity of existing facilities, platforms and pipelines must be ensured, given that they may be in continued use beyond the original design life, which was probably in the order of 20 years anyway. Rev 2 February 2014 Engineering Offshore Structures 1-11 Copyright © TWI Ltd 2014  Engineering Offshore Structures General background Initially, the designs used for offshore platforms were borrowed from traditional fields of civil engineering and naval architecture. CSWIP 3.1U Course During the 1950’s new technology developed and many advances were made. Engineering Offshore Structures Section 1 Government legislation in various countries with offshore oil played a role in shaping the design of offshore structures. Economics, the environment and safety of personnel have also had great influence on structural design. Copyright © TWI Ltd 2014 Copyright © TWI Ltd 2014 Considerations in Design Design Specifications Safe to operate Materials Designers strive to achieve a structure which is Should be readily available in the required form elegant if possible, conservative in material, fit for and meet the design specification. purpose, able to operate for the prescribed length of time, safe to operate and within budget. Working life This may typically be 25 years. Government legislation This is put in place to ensure that structures are fit Loading in all aspects, including safety, for the purpose they The platform should provide a safe working were designed to fulfill. environment capable of withstanding all loads imposed upon it such as drilling, wind and waves. Copyright © TWI Ltd 2014 Copyright © TWI Ltd 2014 Design Specifications Design Specifications Environment Weight Consideration must be given to the effects of The weight of the deck modules must be corrosion and to offshore conditions. considered so that the jacket can be designed to support this weight. The all-up weight will have Maintenance ramifications on the cost and on the design of This should be kept to a minimum. Underwater the seabed foundations. maintenance being especially singled out with a view to not only minimising it but also to use the Dimensions most cost effective means of repair works. Size is dictated by the work functions but topside weight should be kept to a minimum. Copyright © TWI Ltd 2014 Copyright © TWI Ltd 2014 1  Construction Activity Monitoring System Guidance on Design and Construction At the same time as the design specification is With these engineering requirements in mind as drafted, the quality assurance (QA) function can be the basic starting point, design and structural implemented. engineers will be able to obtain guidance as to what minimum standards are acceptable to the This can take the form of an activity monitoring appropriate authority or government body, system that would include: whatever country they are operating in. Full certification for the location of all components, normally by way of as-built drawings, including concessions, repairs and actual location of J tube and temporary access holes. Full material certification. Non-destructive testing (NDT) and inspection certification, including personnel qualifications. Copyright © TWI Ltd 2014 Copyright © TWI Ltd 2014 Changes in UK Regulations Changes in UK Regulations In 1988 a gas condensate leak on the Piper Alpha The safety case is expected to demonstrate that the duty holder caused an explosion and large fires which destroyed the has the ability and means to control major accident risks effectively. This requires that the duty holder has identified the platform and cost 167 lives. A public enquiry ensued and major hazards, assessed the major accident risks, implemented it’s chairman, Lord Cullen made 106 recommendations control measures to ensure that the risks are reduced to as low as aimed at improving safety offshore. reasonably practicable (ALARP), in compliance with all relevant statutory provisions, and made adequate arrangements for The Health and Safety Executive (HSE) developed ‘The auditing and reporting. Offshore Installations (Safety Case) Regulations’ in The Safety Case Regulations were revised in 2005, to reflect 13 1992, which require the operator/owner known as the years of experience. Under the 1992 regulations, a safety case Duty Holder to prepare safety cases for each installation lasted three years before it had to be re-submitted for acceptance. in UK waters, which the HSE must accept before According to the 2005 regulations, a safety case will last the life of operations are permitted. the installation, without the need for routine re-submissions. Copyright © TWI Ltd 2014 Copyright © TWI Ltd 2014 Changes in UK Regulations General Design Considerations However, the safety case is intended to be a living document, kept Aims of the design up-to-date and revised as necessary to ensure it remains current Structures and structural elements are designed and reflects actual operational conditions on the installation. to: The duty holder is required to conduct a thorough review of the Sustain loads liable to occur during all current safety case at least every five years, or as directed by the temporary, operating and damaged conditions, HSE. if required. Maintain acceptable safety for personnel and In addition, revisions that make a material change are required to environment. be re-submitted to the HSE for acceptance (a material change is one that changes the basis on which the original safety case was Have adequate durability against deterioration accepted, such as significant modifications or repairs, introduction during the design life of the structure. of new activities, extension of life beyond original design life, or major changes in technology). Copyright © TWI Ltd 2014 Copyright © TWI Ltd 2014 2  General Design Considerations General Design Considerations General design considerations Limit states The design of a structural system, its ULS (Ultimate): Relating to the ultimate components and details is required, as far as resistance for carrying loads. possible, to account for the following principles: FLS (Fatigue): Related to the possibility of Resistance against relevant mechanical, failure due to the effect of cyclic loading. physical and chemical deterioration is ALS (Accidental): Corresponding to achieved. damage to components due to an Fabrication and construction comply with relevant, recognised, techniques and practice. accidental event or operational failure. Inspection, maintenance and repair are SLS (Serviceability): Corresponding to the possible. criteria applicable to normal use or durability. Copyright © TWI Ltd 2014 Copyright © TWI Ltd 2014 Pipelines Pipelines Offshore pipelines are used to transport oil or gas from platform to a loading tower or to shore. They are fabricated from high grade steel pipe (eg API-5LX) which is bitumen wrapped for corrosion prevention and coated with a layer of reinforced concrete to provide a weight coating which also gives physical protection. Pipeline laying from a lay barge 12m lengths are welded together on the deck of a lay barge. Each joint is X-rayed and bitumen wrapped. As joints are made up the pipe is fed over the stern as the barge is moved forward. Copyright © TWI Ltd 2014 Copyright © TWI Ltd 2014 Pipelines Pipelines Pipeline laying from a reel barge Lengths of pipe kilometres long are made up ashore and wound onto reels mounted on special vessels. The vessel then lays the pipe by un- reeling it on location. (Maximum diameter of the pipe is 600mm). Reel barge MSV Norlift laying 10in pipe Copyright © TWI Ltd 2014 Copyright © TWI Ltd 2014 3  Offshore Oil Terminals Future Engineering Offshore Trends Large oil tankers are cheaper to run than small ones. This Drilling philosophy of building large tankers was reinforced in the 1950s Horizontal drilling: Using directional drill assemblies. when the Suez Crisis forced tankers from the Gulf to detour around Extended reach drilling: Using longer drill strings. the South of Africa to reach Europe. As tanker sizes increased, the Slim line well design: Using cost effective casing to number of ports that could handle these large vessels decreased minimise wall thickness and diameter of the well casing. and public opinion was against allowing such tankers too close Rig automation: Using automatic pipe handling inshore. equipment to remove personnel from the drill floor. Temporary (Lightweight) topsides on platforms: Many solutions were proposed to solve this problem of shrinking Removable derrick after completion of drilling. docking facilities, which included artificial harbours, artificial offshore Tender assisted operations: Drilling support equipment islands, multiple buoy mooring systems, tower mooring systems kept on vessel anchored alongside. and single point mooring (SPM) or single buoy mooring (SBM) systems. The SPM is the most widely used because of its relatively low operational cost, reliability and flexibility and is shown in section 2. Copyright © TWI Ltd 2014 Copyright © TWI Ltd 2014 Future Engineering Offshore Trends Future Engineering Offshore Trends Temporary topsides on platforms Design practices The thrust of design is to continue the This design innovation trend to make structures slimmer and allows for the removal of simpler. the derrick after drilling The main emphasis for the future is likely is completed. to be the topside modules. Concurrently there will be a greater use of sub-sea satellite technology. Both of these trends will reduce production costs. Gannet platform Copyright © TWI Ltd 2014 Copyright © TWI Ltd 2014 Future Engineering Offshore Trends Comparison of capital costs for offshore production methods Platform development Subsea satellite at 20km ANY QUESTIONS? Copyright © TWI Ltd 2014 Copyright © TWI Ltd 2014 4