SMY Apr – June 2013

Article

SMY Apr – June 2013

  • Decommissioning of Offshore Platform: A Sustainable Framework
  • Commercial Diver in Oil and Gas Industry
  • Concept Framework: Semi-PSS for Sustainable Decomissioning of Offshore Platformin Malaysia

 

 

Decommissioning of Offshore Platform: A Sustainable Framework

N.A.Wan Abdullah Zawawi, M.S. Liew & K.L.Na
Department of Civil Engineering, Universiti Teknologi PETRONAS
Bandar Seri Iskandar, 31750, Tronoh, Perak, Malaysia
amilawa@petronas.com.my

 

Abstract – The decommissioning activities for fixed offshore platforms in Malaysia are expected to rise significantly. For many of the approximate 300 oil platforms, their service life is approaching the end. Thus far, only a handful of offshore platforms in Malaysian waters have been decommissioned mainly due to lack of regulatory framework and weak decommissioning plans. The shortage of decommissioning yards provides another major challenge in managing onshore disposal. With a number of options viable in decommissioning our used platforms, a review of these possibilities is timely. The scope of this paper entails the decommissioning methods particularly in the Gulf of Mexico, where conditions are similar to Malaysian waters. Evaluations of methodology as well as sustainability implications are discussed. The usual methods of decommissioning involve any of these options: complete removal, partial removal, reefing or re-using. Employing the aspects of sustainability as a pillar of the study, a conceptual framework of a viable decommissioning scheme is drawn. It was conceptually found that refurbishing the whole of the structure as a livable hub has its own unique potentials. Given the calm conditions of Malaysian waters and the sturdy design of the platforms, the restored structures hold possibilities either as ocean townships or futuristic cities such as a ‘sea-stead’. This novel idea of decommissioning is presented and further discussed in the paper. Keywords-Sustainable; Decommissioning; Fixed Offshore Platforms; Malaysia; conceptual framework.

INTRODUCTION

As of the year 2010, regionally, there is an estimated 1733 offshore structures1 in Asia Pacific with Indonesia and Malaysia leading in numbers. Circa the year 2000, Malaysia has roughly 300 shallow water fixed platforms2 operated by various operators in three regions: namely, Peninsular Malaysia Operation (PMO), Sarawak Operation (SKO) and Sabah Operation (SBO). Most of these platforms are shallow water platforms which are especially appropriate in Peninsular Malaysia waters, where water depths range from 50-70 m. In the context of this paper, the water depths no greater than 200m define shallow waters3, in accordance to the PETRONAS Guidelines for Decommissioning of Upstream Installations. Many of these platforms are over 20 years of age and 48% of the platforms have exceeded their 25-year design life. About 28% of these platforms are off Sarawak, 12% off Sabah region, and the remaining 8% off Peninsular Malaysia4. In light of the pivotal protests surrounding Shell’s 1995 proposals for the toppling of the Brent Spar oil operators today are pressured by environmentalists into warranting “sustainable” decommissioning practices5. As an exceptional and flexible performer, steel has long been recognized and acclaimed for its strength, durability, functionality and dry construction method. Hence the usage and disposal of offshore platform steel greatly affects the sustainability aspect of decommissioning.

DECOMMISIONING

The challenges of offshore decommissioning are quite substantial due to rising concerns of sustainable development, the complexity and uniqueness of each removal activity, the high costs involved as well as the complex regulatory structure5. Decommissioning of an oil platform may involve leaving in place, dismantling, removing or sinking disused facilities6. This expression is widely accepted within the oil and gas industry rather than using the terms “abandonment”, “removal” or “disposal”7. Other technical activities include plugging and abandonment of wells, pipelines, risers and related facilities, which will not be discussed in this paper. The decommissioning process differs between countries. For Malaysia, PETRONAS Petroleum Management Unit (PMU) identified four main phases: pre-decommissioning, implementation, post decommissioning and field review8. The scope of works will depend primarily on the type of installation and option for decommissioning.

In Malaysia, there is no governing legislation for decommissioning. However, plans would have to be in compliance with at least eight laws: Merchant Shipping Ordinance, Continental Shelf Act, Exclusive Economic Zone Act, Environmental Quality Act, Fisheries Act, Occupational Safety and Health Act, Natural Resources and Environmental Ordinance and Conservation of Environment Enactment9. The regulatory framework of Malaysia is the 2008 PETRONAS Guidelines for Decommissioning of Upstream Installations, requiring “decommissioning of facilities to be evaluated on a case by case basis based on the standards imposed”3. It is very much based on key international conventions such as the London Dumping Convention 1972/1996; United Nations Convention on the Law of the Sea (UNCLOS) 1982; and the International Maritime Organization‟s (IMO) Guidelines and Standards 199210.

There are three main decommissioning alternatives. The first one is to leave a platform in place. Proper shutting down and stripping of all equipment directly involved in oil extraction are the key components of this option. This involves the plugging of wells in addition to the complete removal and severance of conductors, while all other parts of the platform remain. This scenario would entail the lowest costing due to minimal planning, engineering, and mobilization and disposal costs. Secondly, a partial removal with either offshore/onshore disposal of material that is toppled in place or taken to another location. Topsides must first be completely removed. Removal here would entail the most expensive removal costing. The third option is to completely remove a platform from the ocean. Materials from platform are removed for multiple destinations for reuse or recycling purposes after ensuring all wells are plugged. No other parts of the platform would remain above 4.5 meters below the mudline.

Remnants of the structure could be disposed of at a deep ocean disposal site, on the sea floor near the original site of operations, or removed to shore for salvage. Onshore disposal involves cutting up the structure into manageable pieces which are then transported to shore for either recycling purposes or disposal. Often, operators opt for the latter as waste consists of mainly steel which has a recovery rate of 98%6.

SUSTAINABLE DECOMMISSIONING

With increased environmental awareness and the rising costs of material fabrication, the recycling and reusing of fixed offshore platforms are being examined carefully in view of sustainability feasibility. On average, an offshore platform is constructed out of 1000 – 20,000 t or more of steel (depending on the type of platforms).

Figure 1 above illustrates the material flow of a typical decommissioned platform. Abandoning these weathered yet possibly functional massive steel structures out in the ocean would be a waste of resources. In 2008 alone, about 475 x 106 t of steel scrap were recycled worldwide. This number tops the combined reported total for other recyclable materials such as glass and paper11. Moreover, steel recycling and reusing account for significant raw material and energy savings as well as CO2 emissions reduction. If 475 x 106 t of hot rolled steel were produced purely from scrap steel, the total CO2 savings is approximately 811 x 106 t a year11.

Reuse takes place when end-of-life steel is reclaimed and reused, mostly retaining its original state of material. The embodied energy of steel is saved and the environmental impacts of creating new steel would be reduced. Reusing offshore platforms potentially removes thousands of tonnes of steel from the waste stream and reduces the input energy required for reprocessing or recycling. Taking salvaged steel as an instance, in 2007 the emissions cost of recycling over reuse cost the UK the energy equivalent of the output of two power stations12. Reuse is an important aspect of sustainability as the energy used for remanufacture or refurbishment is relatively small compared to the energy of the recycling process.

Figure 2. The new European 5-Step Waste Hierarchy which classifies waste management strategies according to their desirability14

As illustrated in Figure 2, reuse is the second most viable option in the new European Waste Framework Directive (2008/98/EC) aimed at promoting recycling among EU member states13. The framework applies to all materials, but the durability nature of steel makes reuse particularly pertinent. Thus, from an environmental, and often economic, point of view it is desirable that as many components of an offshore structure as possible are extracted from the waste stream for reuse at the end of their useful life. Although reuse has primarily been used in the Gulf of Mexico, as artificial rigs, the trend is picking up in other locations, such as the North Sea14 and Southeast Asia1.

The potential of reusing the bare structure or components of the platforms is theoretically boundless. For instance, the steel column from the Frigg platform is now a breakwater while the topside is utilized as a training centre for offshore personnel6. These platforms also could be used as bases for search-and-rescue operations or centres for waste processing and disposal.

REUSING OF OFFSHORE PLATFORMS

Decommissioned offshore platforms have also long been recognized as a component of artificial reefs (AR) in the Gulf of Mexico. In fact, the Louisiana artificial reef program (LARP) is the largest rigs-to-reef program in the world. To date, it covers over 83 sites with approximately 120 decommissioned platforms15. The rigs-to-reefs programme is said to have improved biodiversity of the Gulf of Mexico, where flat and sandy sea beds create minimal shelter for sea creatures. These decommissioned platforms are ideal as artificial reefs as their open design attract fish16. Additionally, the platforms increase the amount of available hard substrate needed for coral communities, which are natural fish habitats. This important feature results in a more complex food chain, leading to better fishery exploitations. Fish densities surrounding the artificial reefs have been found to be an amazing 20 to 50 times higher than in open water17 (this number is highly site dependent).

The controversy as claimed by conservative environmentalists is that the practice is viewed as a simple and easy excuse to dispose of the used oil rigs into the ocean. The end-of-life oil rigs as artificial reefs would inevitably lead to a certain degree of habitat damage, localized contamination and spreading of hydrocarbon invasive18, 19. Malaysia holds much potential in rig-to-reef programmes due to its relatively shallow water depths. This is because the performance of AR as fisheries habitat was found to be highly dependent on the depth of deployment. This is due to the vast changes in temperature, salinity, turbidity and light across a vertical water column, which in turn affects the changes in plankton components with influences the plentiful presences of marine life20. The success of this practice in shallow waters of the Gulf of Mexico where around 200 platforms have been converted so far is a great motivator14.

There have only been two major rigs-to-reef programmes in Malaysian waters to date. BARAM-8, now more known as the Kenyalang Reef, was one of the first rigs-to-reef in this region. BARAM-8 was a single well 3-legged wellhead with a protection jacket located 8 nautical miles from Tanjung Baram of Miri. Decommission first started in 2001 after intensive consultation with external stakeholders (local fishermen, local councils, etc.) and approval of PETRONAS21. A series of marine surveys showed that the sunken BARAM-8 platform was housing dendronephthya soft corals and fish were in fact using the rig as migratory points. Additionally, in Brunei, there was a marked difference between the 1996 and 1999 surveys indicating significant increase in marine life10.

CONCEPTUAL FRAMEWORK FOR DECOMMISSIONING IN MALAYSIA

Ocean colonization is another potential platform reuse option. Conceptualized and even practiced since the 1980’s, Seastead is a concept of self-sustaining permanent dwellings at sea. Mega cruises and ships resembling cities are the closest floating cities there is in reality. However, they are not designed for permanent stays and self- sustainability. The notion of seasteading is now refined by Patri Friedman, executive director of The Seasteading Institute (STI). STI describes their mission as creating “next generation governance” at sea, outside the jurisdiction of any nation and the idea has $1.25 million in backing from Peter Thiel, the PayPal co-founder. STI has already drawn up plans for the construction of a homestead on the Pacific Ocean off San Francisco22. The prototype was described as similar to a cruise ship and was loosely designed based on oil rigs, but with important modifications23.

According to TSI‟s official website24, seasteads run on diesel-fueled-generators for electrical power. Instead of being self-sustaining resource-wise immediately, seasteads are to specialize in industries where they have a competitive advantage (such as aquaculture) and trade for goods which are produced more resourcefully onshore.

Figure 3. Conceptual design of the un-named seastead off San Francisco waters21

Figure 3 illustrates the conceptual design of a seastead which consists of (1) a 160,000 ft2 living platform; (2) its water supply systems; (3) its foot tanks which hold the seastead above water and minimize the impact of rouge waves; and (4) the engine room which houses 4 diesel engines. These engines generate electricity and enable the structure to travel up to 2 knots. Instead of producing new steel for such mammoth project, it is feasible that existing oil platforms could be enhanced, structurally and facilities-wise, and re-used as a floating city. Being modular in nature ensures the ease in expansion and design of the cities. With hundreds of oil platforms scheduled to be decommissioned within decades to come, the possibility of decommissioned oil platforms functioning as liveable hubs may come to realization soon. The winning entry of the 2008 Radical Innovation in Hospitality Awards, designed by Morris Architects, showcased a self-sustaining and eco-friendly hotel offshore. As offshore construction is costly, the architects proposed building prefabricated rooms and transporting them by ship25.

A special viewing balcony can be extended from each room and it can be retracted if the weather turns bad. Attractions of the “Oil Rig Resort, Spa and Aquatic Adventure” would no doubt be the various on-water activities and the rich ecosystem which would appeal to eco tourists. John Hardy, president of the John Hardy Group and co-sponsor of the competition, reckoned “the Resort offers a potentially commercially viable solution to an environmental hazard by providing alternative adventure travel opportunities based on a natural setting, simultaneously creating new jobs previously non-existent in the area”25. To maximize use of the existing infrastructure, a core of water is placed in the central of the platforms, allowing light to penetrate and acts as ballast in stabilizing the rig26.

Figure 4. Conceptual design of the „Oil Rig Resort, Spa and Aquatic Adventure‟ design by Morris Architects and the transformation of the modular rooms

Figure 4 shows the conceptual design of an alternative use for decommissioned oil platforms and the mechanisms of its modular rooms.

One of the finalists of the 2011 Skyscraper Competition explored the idea of transforming abandoned oil rigs into livable cities, above and below the ocean level. The general population could reside above waters while specialized researchers work in underwater. The in-between zone will be used as housing and recreational areas. The existing structures are strengthened with the use of exterior steel beams that allow for high velocity wind to filter through the platform27. The entry by Malaysian design students Ku Yee Kee and Hor Sue-Wern exploits solar energy harvested with a large roof-top photovoltaic membrane. Wind turbines are located at strategic points along the façade while tidal turbines are installed at the bottom of the installation.

Figure 5 outlines the conceptual design of the „Residential Oil Rig‟ with retrofitted facilities.

Closer to home, there is a successful example of the reuse of decommissioned structures. Off the east coast of Sabah, stands a refurbished oil platform, now a hotel for snorkelers and scuba divers. Seaventures Dive Resort, nearby Sipadan Island, houses 25 minimalistic guest rooms. Well known by serious divers all over the world, its main attraction is the diving trips around Sipadan Island28.

In view of these realistic concepts, the aging platforms of Malaysia holds potential economic value through more commercialized yet sustainable decommissioning. Leading contractors and researchers could fit into the picture as an Engineering, Procurement, and Construction Contractor (EPCC) in refurbishing the end-of-production-life platforms, marketing the completed structures, and running the place for a contractual period. Prospective ventures include but not limited to research centres, wind farms, tourist attractions and even as long-term living hubs. Once the agreed upon contractual period is up, PETRONAS as the previous operators, could take over possession of the venture.

In terms of metocean characteristics, South China Sea is relatively calmer than other prominent hydrocarbon producing regions. The North Sea is frequently plagued by severe extratropical cyclones, which bring torrential rain and winds. Hurricane Bawbag in 2011 experienced winds up to 264 km/h29.

While tidal currents are quite insignificant in both the Gulf of Mexico and the South China Sea, severe tropical storms affect both basins30. However, it is quite established that destructive tropical cyclones are very rare in the near equatorial zone31. Due to the diminishing Coriolis effect, the belt 300 kilometers on either side of the equator has been generally considered to be tropical cyclone-free32. Hence, Malaysia is relatively shielded from the incidences of cyclones. Save for Typhoon Vamei, which developed near the south of Peninsular Malaysia in 2001. It was the first of its kind recorded within 1.5 degrees of the equator and is estimated to have a return period of once every 100-400 years32.

Conditions of the Gulf of Mexico (GOM) are less advantageous, given the likelihood of intense tropical cycles striking anytime. Circa the 60s, Hurricanes Hilda, Betsy and Camille caused severe damages to 50 out of 1500 platforms. Forty years onwards, hurricanes Ivan, Katrina and Rita destroyed 130 of 4000 fixed platforms along the Gulf33. Moreover, the GOM is also affected occasionally by strong oceanic currents caused by the Loop Current and its anti-cyclonic eddies30. Given the little information available on the comparisons of metocean data of the three seas, an evaluation of the respective platform design guidelines would illustrate the extent of environmental loads of the respective oceans.

TABLE I. COMPARISON OF MAXIMUM AND SIGNIFICANT DESIGN WAVE HEIGHTS FOR OFFSHORE PLATFORMS OF DIFFERENT REGIONS

Table 1 demonstrates the variation in maximum design wave height (Hmax) and significant design wave heights (Hs) for the GOM, the North Sea and Peninsular Malaysia. The difference between these values clearly depicts the environmental conditions of the three oceans. The relatively calmer waters of Malaysian waters are a plus point in terms of safety and ease of the refurbishment of the decommissioned rigs. The crux of the matter would be coming up with the most optimal engineering and economics scheme in realizing this innovative vision. Once the appropriate platforms are identified by the operators, retrofitting works could be done to structurally strengthen the platforms and to integrate sustainability elements. Incorporating the key criteria of the Green Building Index or other equivalent indexes, the refurbished platform houses a coexistence of humans and nature. By improving on the efficiency of mechanical and electrical systems as well as incorporating good passive designs together with proper sustainable maintenance regimes, significant reductions in operational energy and emissions can be realized. For instance, having adequate harvesting of natural lighting, an efficient storm water management and proper control of air flow would greatly reduce carbon footprint and incur long-term savings. Similar to the design by Morris Architects, wind turbines, wave energy generators and photovoltaic panels could be mounted for alternative energies. As for desalination works, Thermo-Ionic technology is implemented. This novel technique applies salinity gradients using low-temperature energies such as sunlight or waste heat, significantly reducing operational and material costs.

VI. CONCLUSION

With the impending rise of regional decommissioning of offshore platforms, it is important for all stakeholders to plan for a sustainable and profitable scheme. Being second in the waste hierarchy, reusing steel has been proven to incur less environmental impact relative to recycling the same amount of steel. Through extensive sustainability and technical comparisons, reusing an end-of-production-life platform can be feasible. The proposed approach of decommissioning as a Build-Operate-Transfer (BOT) commercial project is attainable with the fitting technology.

 

Commercial Diver in Oil and Gas Industry

By: Azelin Mohamed Noor, Dept. of Management & Humanities, UniversitiTeknologi PETRONAS and Lim Chia Wei, Dept. of Petroleum Engineering, Universiti Teknologi PETRONAS

Divers may not be a profession commonly associated with the oil and gas industry, but commercial divers are highly demanded specifically in off shore exploration and production. A commercial diver inspects, installs, repairs and removes equipment and structures inthe depths of the sea. Three major functions that makeup the chunk of commercial diving activities in offshore oil and gas exploration and production are subsea pipeline maintenance, inspection and underwater welding.

The maintenance, inspection and installation of offshore pipelines are extremely complicated processes and usually more than one commercial diver is needed. On an annual basis, commercial divers routinely inspect and repair the pipelines. These tasks are meticulously monitored by a diving supervisor who is responsible for all diving operations.The supervisor needs up-to-the-minute information on the whereabouts of divers.

A diver on a routine line inspection

Maintenance

Divers are required to clean pipelines during pipeline inspection through a process fondly known as pigging. Pigging refers to an operation of using a cylindrical or spherical pig which travels along the pipeline for cleaning purposes. Accumulated deposits or debris such as liquid and wax layers are scrapped clear off the lines.

Inspection

Robots are used for a thorough subsurface inspection. Underwater robotics such as the remotely operated vehicle (ROV) and the low cost remotely operated vehicle (LCROV), as the name implies, is a cheaper version of the ROV which combines the latest technology in robotics and mechatronic. The size and performance of the ROV makes it a versatile machine used for shallow and deep water. Commercial divers are tasked to operate these robots during inspection of pipelines.

Installation

Wet underwater welding and dry underwater welding are two main types of welding commercial divers are entrusted with.Divers are exposed to sea water in wet water welding.This method uses the manual metal arc (MMA) welding process and a special electrode to weld. Wet welding is most effective as it allows the welder to move a wet environment freely. Hence, wet underwater welding method has become the preferred choice for inspecting and repairing pipelines underwater.

Dry or hyperbaric welding is done by sealing a chamber around the structure to be welded and then the chamber is filled with gas. Helium is commonly used as it doesn’t react with other chemicals. The gas then fills the chamber to an extreme pressure before water is pushed out. The divers will then carry out their tasks within the chamber.

Risks associated with commercial diving

Divers often work in dangerous circumstances and they require proper training and certification necessary to meet the regulations of local authorities. Commercial divers face two main dangers which are dive related injuries and tool or machinery related injuries. Being totally reliant on complex, often bulky breathing equipment, commercial divers are subjected to turbulent aquatic environments. As if these are not enough, divers have to be mindful of their speed when they come up to the surface. If they ascend too quickly, the abrupt change in pressure will stop blood from flowing and nitrogen bubbles could accumulate in their blood. Commonly called “the bends” or the decompression sickness, can be potentially fatal.The risks related to commercial diving also comes with the job itself. Underwater welders often make difficult welds, in challenging conditions with dangerous tools. The greatest fear a diver would encounter while welding is electrical shock. Other potential fatal hazards are explosions, particularly in applications where both hydrogen and oxygen are used and pockets of gas are formed.

Despite the enormous risks commercial divers have to face, they are a highly sought after profession. Not many are aware that divers are engaged by owners of platforms for maintenance and inspection purposes. In Malaysia, divers are attached to diving contractors such as Borneo Subsea Service and Technip. Among the higher income occupations, commercial divers earn an average annual salary of RM182,000 according to Forbes.com, and commercial divers are America’s best-paying blue collar job! As we continue to scour and exploit the earth’s seabed for hydrocarbons, commercial divers keep on diving their way into the foreseeable future despite thetreacherous tasks waiting for them.

Co-author in one of her open sea dives.

 

Concept Framework: Semi-PSS for Sustainable Decomissioning of Offshore Platformin Malaysia

N.A.Wan Abdullah Zawawi, M.S. Liew & K.L.Na
Department of Civil Engineering, Universiti Teknologi PETRONAS
Bandar Seri Iskandar, 31750, Tronoh, Perak, Malaysia
amilawa@petronas.com.my


Abstract— For many of the offshore jacket structures in Malaysia, their design lives of 25-30 years is approaching the end, signifying the urgent implementation of decommissioning efforts. While current regulatory guidelines strongly recommend complete removal of the structures, in view of sustainability issues, other options of decommissioning should not be overlooked. As a way forward, this paper suggests an approach of reusing offshore jacket platforms as an opportunity to derive economic and/or scientific benefits. To utilize a structure beyond its design life, a thorough control of the structural safety must be executed. Integrating a risk-based structural assessment, weighting factors and the concept of hazard functions, the approach gauges the failure probabilities and risk events involved in the reusing of redundant offshore platforms. The principles of a risk-based structural assessment are thus described and the proposed conceptual framework is illustrated, linking the operational and structural risks in connection with reusing of an offshore jacket structure. This semi-probabilistic support system (Semi-PSS) provides a valuable outline in improving the selection of appropriate platforms to be refurbished and transformed into livable hubs.

Keywords- Risk-Based Assessment; Sustainable; Decommissioning; Decision-Making Tool; Semi-Probabilistic

I. INTRODUCTION
For decades, offshore jacket platforms have been commonly used in the oil and gas production in the shallow water depths of Malaysia. With many of the 250 (and counting) structures [1] aging over 20 years and approximately 48% of the platforms of the exceeding their 25-year design life [2], decommissioning activities in Malaysia are set to rise significantly. Decommissioning is a general term covering a wide spectrum of activities in closing down and proper abandoning of the production facilities, to the largest extent feasible [3].

At present, conventional decommissioning alternatives fall into four general categories [4]: complete removal, partial removal, toppling (either as in-situ disposal of the structure or as artificial reefs), and reusing. While the complete removal of the platforms is strongly recommended by primary regulatory guidelines such as the 1989 International Maritime Organization (IMO) Guidelines, in light of increasing international attention on sustainability, other options of decommissioning are not to be discounted for.

As jackets are mainly steel-based, the restoration of decommissioned platforms is a conceptually viable possibility. Steel is renowned for its strength, durability and functionality. The sturdy design of Malaysian jackets and the relatively tranquil conditions of local waters are a boon to the reusing of these jackets as an opportunity to derive economic and/or scientific benefits.

For these jackets which have already attained or exceeded their design lives, it is beneficial, if not necessary, that all targeted platforms be structurally assessed beforehand. Furthermore, older platforms; which are constructed prior to the year 1998, are not designed to be decommissioned [5]. For these reasons, a pre-decommissioning reliability-based decision making framework is proposed.

II. SUSTAINABLE DECOMMISSIONING ALTERNATIVE
In Malaysia, there is no governing legislation for decommissioning. The regulating 2008 PETRONAS Guidelines for Decommissioning of Upstream Installations, however, makes complete removal mandatory for all offshore installations [6]. Nevertheless, fundamentally, “decommissioning of facilities is to be evaluated on a case-by¬case basis based on the standards imposed”.

With the rise of sustainability awareness within the industry, considerations of environmental, economic and social performance of decommissioning needs to be assessed.

The mapping of material and energy flow is one approach in evaluating the environmental and economic aspects of decommissioning alternatives. The Institute of Petroleum’s guideline [7] on the estimations of energy usage and emissions in the decommissioning of offshore platforms documented the direct and indirect energy requirements of the processes involved. Taking toppling of a platform as the baseline of its research (due to its lowest overall energy requirement status), the total energy requirements for various decommissioning alternatives are compared in Table I.

TABLE I. COMPARISON OF ENERGY REQUIREMENTS FOR VARIOUS DECOMMISSIONING ALTERNATIVES

Source: ERT 1997, Page 11 table 4
Note: Only the partial ashore/partial in-situ and the complete ashore scenarios are permissible under current OSPAR regulations

 

In this paper, reusing is defined as ‘refurbishing the platform for other non-production uses’, it could be classified under either Scenario B or Scenario C. Based on Table 1 above, the complete removal of a platform entails the highest energy needs among all the scenarios, almost 10% more than the partial removal/reusing alternative. Reusing retains the original properties of steel, with substantial savings in its embodied energy and reduction in environmental impacts associated with the production of new steel as well as recycling.

If there are parts of the structure being reused, the savings in embodied energy and materials achieved would be equal to the embodied energy and materials which would have been built for such a use, in the absence of the reused materials [7]. Moreover, reusing would eliminate tonnes of steel from the waste stream.

The option of reusing the steel-based platform for other purposes other than as oil and gas facilities is unbounded. Some of the viable possibilities include, but not limited to: a) offshore maintenance and logistics bases; b) sites for wind turbines, wave energy generating equipment and(or) photovoltaic panels; c) LNG terminals; d) sites for aquaculture facilities; e) tourism attractions; f) offshore research and training centers; and g) bases for search-and rescue operations

In light of these prospective undertakings, the proposed framework seeks to identify fitting aging platforms to be reused and refurbished accordingly.

III. STRUCTURAL INTEGRITY MANAGEMENT FOR DECOMMISSIONING
With the rising awareness in the importance of managing an aging offshore platform, researches in structural assessment approaches has ultimately led to the development of assessment guidelines within American Petroleum Institute (API) and International Organization for Standardization (ISO) [8].

Structural Integrity Management (SIM) is an on-going life-cycle process for ensuring the fitness-for-purpose of existing offshore structures [9]. Traditionally, properly applied design codes produce conservative structures with reserves of strength and redundancy [10]. Utilizing the abovementioned properties, SIM has been used extensively to provide decision support from installation through to the decommissioning of offshore production facilities, to determine whether strengthening, repair or other mitigation measures are required [10].

At present, evaluations practiced in the pre-decommissioning process are mainly to identify the relevant resources and logistics of offshore decommissioning operations. As the decommissioning industry is set to grow, the needs to prioritize the order and to determine the appropriate method of approach are significant, if not necessary, for economic and technical reasons.

Incorporating the concept of the API Recommended Practice (RP) for SIM of offshore structures, weighting factors and hazard functions, the propositioned framework aims to offer semi-quantitative assessment of aging platforms which are scheduled to be decommissioned.

The SIM framework based on API has four main aspects namely Data, Evaluation, Strategy and Program [9], as illustrated in Figure 1.

Figure 1. Primary Elements of the SIM Process
Further details on the complementing of these aspects to the proposed framework
will be discussed in the coming sections.

 

IV. STRATEGY AND TOOLS

A. Data and Evaluation

Up-to-date data is crucial in SIM and typically, these data falls under two categories [9]; platform characteristic data and platform conditional data. The former relates to baseline data which describes the structure state at installation while conditional data defines the changes made to characteristics data throughout the service life of the structure.

Information on the initial design, fabrication and installation process, inspections, evaluations, structural assessment, as well as Strengthening, Modification and Repair (SMR) works are all inaugurated elements of the SIM data base.

Such data gathering should be conducted months, if not throughout the platform’s service life, prior to the actual decommissioning activity through periodic structural inspections and analysis of reliability, to gain knowledge on the existing platform and its associated facilities.

To encourage the coherence of data monitoring and management, an extensive online repository is proposed to monitor the movement of data within the operator’s organization. The repository should include key characteristics and conditional data onset of installation through decommissioning. Additionally, to ensure data timeliness and consistency, all available data is thoroughly audited and streamlined regularly. Any data gaps would then prompt the system for further actions. Any missing information on the structure would increase the uncertainty about the structure. Therefore, penalties in the form of larger safety margins are considered in the assessment later.

Evaluation is performed alongside with data collection. It does not necessarily imply a detailed structural analysis as evaluation can also only include competent engineering judgment, references to research data and detailed analysis of similar platforms [10]. Evaluation entails applying qualified engineering solutions to assess the impact SIM data has on the platform and providing insights to the development of strategies for inspection, monitoring and remediation to ensure platform fitness of purpose.

For a realistic estimation of reliability and safety levels of aging platforms to be reused, quantitative evaluations is advocated. Nevertheless, fully quantitative assessments are not industry feasible. To optimize the course of evaluation, the proposed assessment is categorized into three analysis levels.

All coming-of-age platforms are to be assessed from Level One (as depicted below in Figure 2) and would progress through the levels if necessary. At the end of every level, risk ranking is done to categorize the likelihood of a platform’s failure and consequences of such failure.

Figure 2. Flowchart of the proposed three-level-framework  

1) Level One: Qualitative Risk Ranking.
The platforms are ranked accordingly in determining the urgency of assessment, based on the following five components. Exposure category [10] comprises of an estimate of the likely percentage of the personnel manning the facility and expected to be on a platforms at any one time. Similarly, the function of platform [10] is taken into account. In addition, the maturity of a platform provides an idea on its design codes and installation methods [12]. Significant findings proved that platforms designed according to the modern API RP2A standards rarely suffered from extensive damage or failures. The type of jacket bracing configuration [10] also gives an approximate idea on the order of structural robustness. In general, framing schemes, such as the joint-less K and single diagonal bracing, result in less robustness. Lastly, the in service performance history [11] considers the strength and behavior of platforms subjected to extreme environmental loadings and accidental events. Platforms which have survived similar events provide a structural strength and robustness estimation of comparable structures.

2) Level Two: Inspection Based Risk Ranking
Platforms proceeding into Level Two undergo more detailed inspection-based surveys to validate the numbers. The scope of work should fundamentally consider the following main extent of works:

a.    A visual survey of the platform for structural damage and design deficiencies, from the mud line to top of jacket;

b.    A visual survey to verify the presence and integrity of the sacrificial anodes;

c.     A visual survey to confirm on the number of installed appurtenances and their integrity;

d.    Confirmation of the as-installed platform orientation; and e) Excessive corrosion, scour and seafloor instability, excessive marine growth and debris.

3) Level Three: Semi Quantitative Risk Ranking
Finally, further probabilistic studies are done to reinforce the decision ranking module.
Leading the assessment is a metocean data study. Environmental loads are dominant factors in the design of offshore structures. As wind speeds, wave heights and current speeds are generated by different sources of varied directions and magnitude, it is essential to consider the joint density of these loads to provide comparatively accurate metocean values. As proven by a recent study, joint density analysis yields an accurate mean return interval for regional extreme wind and wave loads [13]. This will mitigate the risks related to the operations of existing offshore structures as well as their decommissioning process.

Through non-linear analyses of the structure, the true capacity and response of the system can be accurately assessed. Pushover analysis is adopted to establish structural ultimate strength, considering the influences of environmental load directions and damaged structure members. Utilizing factored gravity loads followed by the increase of unfactored characteristic environmental loads established from the metocean data study earlier, the range of values of Reserve Strength Ratio (RSR) is determined [8].

Defined as the ratio of the structure’s ultimate strength to a reference level load (usually 100-year-loading), RSR is an assessment of reserve strength of a structure subjected to a specific set of loads [10]. The proposed approach here is to evaluate the platform to survive a longer return period storm, for example 1000-year.

According to ISO 19902, an “extension of the design service life may be accepted without a full assessment if inspection of the structure shows that time dependent degradation (fatigue and corrosion) have not become significant and there have been no changes to the criteria for design” [14]. Nevertheless, for prolonged usage of selected jackets, fatigue analyses are done on the critical joints of the structure, which are basically the areas of stress concentration. A fatigue failure analysis determines the number of cycles taken to reach a threshold failure criterion, which, in this case, is a through thickness crack.

Through a number of push-over analyses, a relationship between wave height and response base is derived. Given a stipulated acceptance criterion, the exceedence probability of structural ultimate strength can be estimated. For existing manned platforms in the Gulf of Mexico (GOM) and North Sea, the value of 0.001 or 10-4 is the acceptable failure probability [8]. To adopt the same acceptance criteria would be conservative given the milder ocean climate in this region.

Similarly, the likelihood of fatigue failure is studied using the same concept. The probability curves evaluate the rate of both small cracks and through thickness cracks as a function of the age of the jacket. Target reliability for fatigue is either as per the design standards or on probability of failure deemed acceptable to the operator.
With inspections, the goal is to keep failure probability to a reasonable level, not exceeding the acceptance reference value, during the extended life of the platform.

Lastly, the Risk Matrix as recommended by the API defines the risk level of a platform, given its probability of failure (PoF) and the consequences of failure (CoF) [9]. Weighting factors are assigned to all assessed attributes and PoF to define the level of relative importance of each attribute, for both qualitative and quantitative aspects. Meanwhile, the consequences of failure encompass the effects of environmental, life-safety and business loss consequences, as shown in Table II below. Similarly, each characteristic is weighted respectively.

The intersection between PoF and CoF in the API recommended risk matrix describes the overall relative risk assessment of soon-to-be-decommissioned platforms. The higher the risk of failure the more critical the platform is to be inspected, assessed and decommissioned. Figure 3 illustrates a risk matrix.

Figure 3. Example of a 3 x 3 risk matrix (Consequence of Failure vs Likelihood of Failure).
Common matrix sizes in practice are 3 x 3 and 5 x 5

With every level of evaluation, follows risk reduction measures to decrease the likelihood of structural failure, assessed professionally by competent engineers. These mitigation efforts encompass operation changes such as removal of certain facilities and structural changes.

B. Strategy and Program
The strategy of the proposed framework will define the frequency of inspection and scheduling of decommissioning of platforms according to the results of the risk matrix. This in turn, identifies the respective actions as described, by example, in Table III.

The strategy will be prioritized accordingly along the operator’s needs and techniques/ tools to be used. While the program represents the detailed scope of work defining the SIM strategy [9]. In the execution of proposed pre-decommissioning program, the results of the weighted risk matrix determine the routine of platform inspection (ranging from above water inspections, baseline inspections, underwater inspections and event driven inspections) and the urgency of decommissioning activities.

All data collected throughout the Program are then incorporated back into the data management framework, to fill up information gap and to ensure accurate and complete records for the framework. In optimizing the processes, analyses performed on a single platform can be used to justify the program for another platform similar in configuration and environment loadings.

V. CONCLUSION
A semi-probabilistic support system for decommissioning of Malaysian platforms is presented. With the impending rise of regional decommissioning of offshore platforms, it is important for all stakeholders to strategize the decommissioning process. Through use of the API recommended risk matrix, weighting factors and the concept of hazard functions, the proposed framework aims to provide an industry-viable solution in improving the selection of appropriate platforms to be refurbished and reused.

ACKNOWLEDGMENT
The encouragement and facilities provided by Universiti Teknologi PETRONAS and the Malaysian Structural Steel Association (MSSA) are gratefully acknowledged.

 

 

REFERENCES
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