Environmental Sustainability and Efficiency of Offshore Platform Decommissioning: A Review

Abstract

Malaysia has inherited many aged offshore platforms that have reached their decommissioning deadline. Many platforms need to be detached through subsea processes. Although there are good techniques for this, they are usually costly and necessitate a great deal of post-cut checking to ensure complete detachment. Explosive cutting techniques, on the other hand, are cost-effective and reliable for offshore decommissioning as they ensure complete cutting with little uncertainty. Until 2019, statistics showed that almost 35% of offshore platform decommissioning processes involved the use of explosive materials and other mechanical severance options. The method was reliable and cheap, but it had a large environmental impact. During blasting procedures utilizing pressure waves, many sea animal species are threatened, such as fishes, turtles, and dolphins. Depletion of already scarce fish stocks through the unsustainable use of explosive removal should be prevented by reducing the environmental impact of underwater explosives. Moreover, due to safety hazards, vessel and aircraft movement around the explosion zone is prohibited. Therefore, this paper provides a comprehensive review of using a highly vacuum-sealed pile for the explosion to control and reduce shock wave propagation. This effort appreciates the benefits of the explosive cutting technique and reduces its environmental side effects. Our findings indicate an accurate and clean-cut method serving the efficiency of offshore platform decommissioning as well as environmental sustainability. Finally, recommendations for future perspectives have been provided based on the decommissioning of offshore platforms, such as topside removal, planning, time scale, and optimization of available space.

1. Introduction

At the end of the lifecycle of any oil and gas platform, decommissioning is required. Decommissioning as a word can be represented by words such as abandonment, removal, or disposal [1,2,3]. Likewise, the completion methods for offshore oil and gas platforms through bringing the seafloor and ocean to their pre-lease stage are known as offshore platform decommissioning [4]. The offshore decommissioning procedure varies between countries [5,6]. In Malaysia, more than 350 offshore platforms are being hosted and require investigations on decommissioning techniques, particularly in Malaysian waters. Decommissioning in Malaysian waters is a relatively new area of practice.

Decommissioning is much more complex than reversing the installation process. Current opinions on applying cutting techniques vary. Explosives, water jets, abrasive waterjets, hydraulic shears, mechanical drilling, and diamond wire cutting are some of the common ideas [7]. However, the offshore oil and gas experience suggests blasting [8]. Explosives have been regularly employed in the oil business since its inception. Explosives have been used in seismic activities, formation perforation, trench construction for pipelines, and extinguishing oil well explosions [9,10]. It is impossible to document the initial use of explosives in decommissioning and recovering offshore structures [11]. Generally, explosives have been used in many regions to remove platforms [12,13,14]. Explosives were most likely first employed by severe well conductors in the mid-to-late 1950s. In the Gulf of Mexico (GOM), most offshore platform removals eventually employed explosives [12,15]. In the early 1980s, there were no fewer than ten businesses offering explosive services for platform decommissioning. Many of the organizations that provided explosive services were actually diving and wireline operations. In addition, in the mid-1980s, environmental concerns about endangered species forced a significant shift in the way offshore explosives were employed. Before then, there were hardly any laws or guidelines. For example, the general rule was that if 5 pounds did a decent job, 10 pounds did a heck of a good job.

When an explosion starts, the solid explosive material is converted into incandescent gas under extreme pressure. The manner in which an explosive’s energy is transformed into an explosion, as well as the shape of the ensuing pressure wave, are determined by the type of explosive and how it is employed. Detonation is the process by which high explosives, such as trinitrotoluene (TNT) and other nitroglycerine-based explosives, detonate. A strong chemical reaction occurs in the aftermath of the shock front spreading through the explosive, converting the solid into a gas at extremely high pressure. The impact zone is, without a doubt, the region (a horizontal radius around a decommissioning target) in which a protected species may be harmed by the pressure and/or acoustic energy emitted by the explosion of an explosive-severance charge. Explosives are the preferred method for separating buildings from their foundations. Although mechanical severance procedures are available, they are less reliable and more expensive, especially as water depth increases. Explosives are often positioned beneath the mudline, either within or outside of target members. Specialized explosive devices are occasionally required to cut targets in the open sea above the mudline, such as chains, cables, and pipelines [16,17]. Figure 1 shows the statistic for 2017–2040; a total of 45 subsea tie-back structures are expected to be decommissioned worldwide between 2031 and 2040 [18].

In addition, some countries are faced with older platforms that need to be decommissioned. For example, in Malaysia, there are many recognized techniques with which to carry out this process, but they are expensive and require post-cutoff checks to ensure the success of the cutting procedure. Explosive cutting is one of the most cost-effective and reliable methods among well-known techniques. However, the usual implementation of explosive methods adversely affects the environment. Between 2002 and 2004, 84 sea turtles were exposed to detonations annually in California [19]. Statistics reveal that there could be more than 2900 sea turtles affected over the next six years [19]. A variety of sea animals are killed by blast wave shock, and many suffer from disabilities in hearing and breeding. Due to safety regulations, this practice causes a huge delay in the movements of vessels and aircraft in the explosion zone. It is also a major life threat to divers and the crew on the vessel.

More recent evidence [20] investigates the potential to make a valuable contribution to the developing domain of sustainable business models related to the decommissioning of offshore platforms. A novel approach recommends the utilization of offshore wind power projects as a viable substitute for the abolishment and permanent disposal of infrastructures, which could serve as a prospective resolution to the decommissioning of offshore structures in Brazil [21]. However, to implement a suitable design methodology, it is imperative to obtain a comprehensive understanding of the failure mechanisms associated with these piles. Adding to this, the authors concentrate on the advancement in failure mechanism analysis and design practice of monopile foundations for offshore wind turbines through theoretical and experimental investigations carried out worldwide [22].

To reduce such incidences, therefore, the application of explosive or vacuum-sealed piles in offshore platform decommissioning is crucial. The significance of this study is that it provides a comprehensive review of the effectiveness of explosives within a vacuum-sealed pile in reducing or preventing wave propagation to harmless levels in the surrounding marine environment. It is expected that the utilization of the explosive technique will result in a substantial reduction in expenses during the decommissioning process of offshore platforms. Additionally, the main aim of this paper is to provide an extensive review of state-of-the-art studies related to vacuum-sealed piles for explosive cutting procedures and the environmental sustainability of this cutting method for offshore platform decommissioning.

This review study consists of seven sections and is organized as follows: Section 1 comprises the introduction, Section 2 provides the review methodology, Section 3 provides the principles and history of decommissioning, Section 4 provides systems for decommissioning and environmental impact, Section 5 provides environmental sustainability of using vacuum-sealed piles in offshore platform decommissioning, Section 6 presents a future perspective, and Section 7 concludes.

2. Review Methodology

In this section, the current review’s process is described. Related databases used in the literature review’s search strategy and development of the selection criteria are provided. Figure 2 shows the review flowchart for the data collection process by using specific keywords to search available related documents from database sources, followed by keyword filtering, screening, final inclusion, and critical evaluation.

3. Principles and History of Decommissioning

In this section, we provide the principles and history of decommissioning where an offshore installation is considered for abandonment. Decommissioning is considered when asset production is no longer economically viable [23]. It was argued that the two words should not be used interchangeably [24]. Conventionally, a successful decommissioning is achieved when no fluid flow is possible across the wellbore and the communication between the permeable formation and the seabed via the annulus is completely sealed off. Decommissioning involves the dismantling of abandoned structures so that the land or sea can be reclaimed as much as possible and then used for other purposes [24]. Although most hydrocarbon-producing countries have no workable regulations to initiate and enforce decommissioning after the well has been plugged and abandoned, some (such as the US and the UK) have established a legal framework to ensure that offshore facilities are removed at least one year after they are no longer in use [1,25]. The two countries have been known to be very proactive in field decommissioning, as evidenced by their efforts in the 1950s to establish an international treaty on platform abandonment. In recent years, however, due to the negative effects of in situ decommissioning on the marine environment, the UK and other European countries have decided against it, while the US has continued to embrace this approach with its rig-to-reef programs and the recent adoption of a legislature that supports partial decommissioning.

Currently, more than 7000 oil and gas installations and platforms are located on the continental shelves of more than 53 countries, and most of them have been abandoned, while some have been in operation for 15–20 years [26]. The industry will face the prospect of decommissioning thousands of installations in the coming years [1,25,26]. Offshore platforms vary greatly in weight and size depending on the water depth and the intended applications, which invariably affects the kind of disposal option to be considered during decommissioning. Complete removal, in situ decommissioning (leaving the installation intact or with the topside removed and legs toppling), relocation offshore, and partial removal (removing certain sections and leaving others in situ) are all choices [23]. The discovery of artificial reefs that form around the platform leads to the development and enhancement of marine habitats and biota. These days, therefore, more emphasis is paid to offshore relocation and in situ decommissioning.

In addition to water depth, platform mass, lifting vessel, environmental considerations, safety, weather and climate, legislation, and destination of the steel materials are key factors that determine the disposal option [1,25]. However, in deep-water environments (oceans), international policy and law are crucial in providing a framework for decommissioning (disposal). The Geneva Convention on the Continental Shelf, which was held in 1958 (earliest), advocated for the complete removal of out-of-service offshore installations [24]. Both the United Nations Convention on the Law of the Sea (UNCLOS) and the London (Dumping) Convention did not use the word “decommissioning“ but emphasized the need to remove aged offshore facilities. However, the term “abandonment” was more commonly used. UNCLOS affirmed that abandoned offshore infrastructure must be removed in accordance with an internationally recognized standard developed by a globally recognized organization [23]. In response to the provisions of UNCLOS, the International Maritime Organization (IMO) provided Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in Exclusive Economic Zones. The guidelines stipulate that all components of offshore infrastructure must be evaluated separately if any are allowed to remain on the seabed, with the following factors as key determinants: ease and safety of navigation, the risk associated with the removal of the structure, rate of deterioration, effects on marine habitat, costs, technical feasibility, and potential injury from the cause of removal. In addition to these, references were also made to the determination of ”new use” (artificial reef) and disposal in situ. For shallow waters and structures with a weight of less than 4000 tons, the guidelines made provision for complete removal, allowing other concrete and steel structures to remain on the seabed provided there is 55 m of clearance (IMO, 1989), cited by [23].

The following offshore installations are decommissioned once the field is no longer productive:

• Platforms that are composed of support structures and topsides;
• Floating vessels;
• Subsea equipment and supporting structures;
• Infield and export pipelines;
• Ancillary facilities (heavy concrete mattresses, rocks used for pipeline stability);
• Wells.

4. Systems for Decommissioning and Environmental Impact

This section provides a system for decommissioning considering environmental impact, where topsides, wells, substructures, and subsea infrastructure are among the key equipment items slated for removal during decommissioning, with topsides and substructures being the largest [27,28]. If the process is to be successful and cost-effective, the choice of a suitable decommissioning option is critical. However, currently, operators tend to shy away from decommissioning because of the huge cost involved. The cost of decommissioning varies based on the size and number of structures. Decommissioning costs are very high and difficult to estimate due to the complexity of decisions in the decommissioning environment [29]. of the impact COVID-19 must also be considered [28]. More recently, it was estimated that the UK spent GBP 1.1 billion in 2020. In addition to cost, Ars and Rios [30] reported that future liability and government regulations contribute to the reasons why the expected decommissioning rate has never been achieved. Therefore, companies are currently facing major challenges and risks in the planning and execution of decommissioning projects [31]. These include:

• Lack of experience required for the removal of deep-water platforms;
• Poor infrastructure and an exorbitant cost of vessel mobilization;
• Inappropriate onshore processing materials and disposal options;
• A complex regulatory framework;
• Strong emphasis on the protection of marine life;
• Restrictive air emission requirements;
• Uncertain site clearance requirements for shell mounds.

4.1. Decommissioning Phases and Their Environmental Concerns

There are three major phases of decommissioning: pre-decommissioning, decommissioning execution, and post-decommissioning. Environmental concerns about these phases have been addressed in many decommissioning articles. For example, in Malaysia, it has been stated that decommissioning must comply with national laws and international rules on the best available approach and environmental practice, health and safety, precaution, risk, and waste hierarchy principles [32]. Similarly, according to the PETRONAS Procedures and Guidelines for Upstream Activities (PPGUA 4.1), the purpose of decommissioning and abandonment is to enhance the safety, time, and cost efficiency of the end life of the asset; “PPGUA saves life while maximizing value” [33]. On the other hand, due to the high risk of pollution and environmental concerns, a platform waste-handling company, Modern American Recycling Services (MARS), built a facility for handling waste at a cost of USD 200 million in the North Sea [34]. Certainly, all the design levels and decisions of decommissioning are made through the Best Practical Environmental Option (BPEO), which are then approved by the authorities [35]. As a result, the most important question here is how best practices in decommissioning can help create a safer and more hospitable environment for all creatures, including animals and humans.

In an attempt to improve the decommissioning process, a hybrid approach/model (Figure 3) for decommissioning oil and gas offshore installations was presented in [29]. However, it has been suggested that standards and compliance with decommissioning could be improved by using an independent third party and/or Joint Industry Group that could design a Work Breakdown Structure (WBS) [30]. This leads to the execution of the decommissioning in a systematic approach [36]. Therefore, for all decommissioning-related projects, it becomes a compliance process rather than a case-by-case operation. The design could inform the Certificate of Compliance, taking into cognizance the recommended industry practices from well cost estimates, Plug and Abandon (P&A) programs, and decommissioning plans (

Table 1. The summary of Malaysia P&A requirements [35].

Item	Minimum Requirements	Legislation Driving Requirement
Do P&A activities need to be planned in advance?	Yes	PETRONAS Guideline
Barrier Type (Material)	As permanent barriers, solidified cement or mechanical plugs in conjunction with cement are appropriate. Permanent barriers are impermeable and nonshrinking barriers or combinations of barriers that create a seal with permanent or eternal qualities.	PETRONAS Guideline
Verification	You may perform a weight or tag test by attaching a minimum pipe weight of 10,000 pounds to the plug. During a 15 min period, pressure tests the casing against the plug with no more than a 10% pressure loss.	PETRONAS Guideline
Plugging Reservoir Requirements	A balanced cement plug should be installed opposite all open holes, reaching at least 30 m above and 30 m below the perforated interval or down to the casing plug, whichever would be the least.	PETRONAS Guideline
Intermediate Zone	Cement plugs must be placed 30 m below the bottom and 30 m above the top of all hydrocarbon zones and freshwater zones that are less than 300 m below the surface. This will keep any hydrocarbon-bearing zones apart from each other and from water-bearing formations, and it will keep fluids from moving to the surface.	PETRONAS Guideline
Surface	A cement plug at least 45 m long, with a top 45 m or less below sea level, must be installed in the smallest string of casing that reaches the sea floor.	PETRONAS Guideline
Annular Barrier Requirements	Any annular area that connects to an open hole and extends to the sea floor must be filled with cement.	PETRONAS Guideline
Casing Stump Requirement	A stub that terminates below a conductor casing must be filled by installing a cement plug 30 m below the stub.	PETRONAS Guideline
Control Line and Cabling	No Guidance
Seabed	All casing, wellhead equipment, and pilling shells must be removed as far below the sea bottom as reasonably practicable (minimum of 1 m).	PETRONAS Guideline
Post-Abandonment Monitoring	No Guidance

and Figure 4). The aim is to have an accurate cost estimate in addition to improving project performance.

The first step in asset decommissioning is to establish minimum standard criteria that meet all regulatory, safety, and environmental requirements [37]. The second step focuses on the evaluation of the Net Present Value (NPV) of the selected option (one with the lowest NPV). Finally, all nonfinancial issues, such as legal requirements, safety needs, public requirements, environmental effects, technological feasibility, and income generation, must be identified and accessed. This improves the evaluation of the Benefit to Cost (BTC) of each option.

4.2. Removal Option

Based on the report by Bull and Love [35], it is stated that decommissioning and removal are common techniques for the removal of platforms, including the use of explosive and mechanical methods below the seafloor, allowing them to be carried free and taken to shore for limited recycling and/or ultimate disposal in landfill. To demolish installations on islands, both explosives and mechanical means may be employed to break up large pieces of concrete and metal [39]. The global reefing of the submerged portions of offshore platforms at the time of decommissioning has resulted from discussions about the future fate of fish and invertebrates beneath platforms. Reefing decommissioned platforms has been debated for years. Many years of scientific research on California platforms have resulted in a California State statute that now enables the subject to be considered [39].

Moreover, considering the four decommissioning options considered by [37,40], they concluded that the reuse of offshore platforms for wind power generation is the best decommissioning option for deep-water platforms compared to complete removal, partial removal, and reuse for artificial reefs. Their analysis was based on the NPV, the weighted evaluation technique, and the BTC of the proposed options [5,9]. The work of Chan et al. [38] discussed the various removal options considered for the removal of the Miller Platform, located on the Miller Field of the central North Sea. The techniques were evaluated in accordance with UK laws and regulations, which include environment, society, economics, risks, and technical execution [41]. The removal options evaluated were:

• Piece-small removal method (offshore demolition method);
• Piece-large removal method involving a heavy-lift vessel (HLV), cargo barges, and tugs;
• Piece-large removal technique via HLV with extended lift operations;
• Single-piece removal method using a single-lift vessel (SLV).

Their report revealed that the removal of the large top and derogated jacket using HLVs with extended lifts was the first of its kind and showed no damping effects from the water column. In addition to meeting all environmental and technical criteria, it was the most cost-effective and efficient option. Eke et al. [27] summarized the analysis of decommissioning the Hermosa Platform located offshore of California using a technique of multi-criteria decision analysis (MCDA) called AHP, or Analytic Hierarchy Process. Five criteria were adopted in their analysis: safety, environmental impact, technical feasibility, cost, and public perception.

4.2.1. Complete Removal Option

The environmental, social, and economic consequences of decommissioning initiatives in the Gulf of Mexico are more recent issues considered in the decommissioning business and are rapidly gaining traction. It is difficult to identify and evaluate the environmental costs and advantages of removing and managing pipes, jackets, wellheads, and sediment deposits [14]. We must now consider that a complete asset removal can help the environment and people more than a partial asset removal [42]. Ultimately, it is important to understand how ecology has evolved in response to the exposure of drill-cutting structures below and on the seabed. Determining how much of the structure can or should be eliminated is a major difficulty here. We must determine whether demolishing the whole facility or only particular components of offshore structures provides the maximum advantage or has the least detrimental influence on environmental, economic, and social situations. In many cases, structures have proven advantageous to the site’s biological condition, increasing the number and variety of fish in the area. As a result, there may be more recreational and commercial prospects. This raises another important question for the region’s Decommissioning Program Leads: where should the line be drawn? It is difficult to determine where the line should be drawn between beneficial and negative consequences in environmental, social, and economic situations [43]?

Much of the hard infrastructure that has already been established has reached or is approaching the end of its useful life, at least for the purposes for which it was installed. Decommissioning is underway, while new structures are being built at the same time (such as wind turbines). Decommissioning, for example, accounted for just 10% of industry investment in the United Kingdom in 2020, leaving 90% for exploration, development, and operations [44]. Over 7500 oil and gas platforms in the oceans of 53 countries are expected to become obsolete in the next few decades. Under current rules, most of these platforms will have to be taken down completely [40]. Platform removal can be a challenging engineering process due to size, weight, and, in some cases, age, and will require some of the largest lifting operations ever performed at sea. Although oil and gas industries contribute a considerable amount of money to the national budget through taxes, the global cost of removal has been estimated at USD 210 billion, and the industry receives a significant share of this cost in the form of tax breaks [45]. As oil and gas production declines (for example, in the North Sea), some countries have committed to reducing greenhouse gas emissions (for instance, the Climate Change Act requires the United Kingdom to reduce greenhouse gas emissions by 80 percent by 2050 compared to 1990 levels). Massive enhancements in offshore wind energy capacity are frequently employed in emission reduction strategies.

The rapid expansion of offshore wind farms (OWFs) is expected over the next ten years [46], resulting in the construction of hard infrastructure for offshore wind farms in large regions of the seabed. However, as with oil and gas platforms, the eventual decommissioning of OWFs (anticipated for approximately 1800 offshore wind turbines between 2020 and 2030 [47]; note that the decommissioning of OWFs has already occurred in some places [9]) would produce environmental problems. Based on reports gathered from different research and evaluation processes on decommissioning options, the complete removal option is the best for many countries.

4.2.2. Partial Removal Option

For large structures, partial removal is permitted under IMO criteria. To allow safe travel, the structure must be partially dismantled so that an unobstructed water column exists. The bottom half of the jacket is left on the seabed once it is cut to the desired depth. The upper section of the jacket can be carried to a deep-water disposal site, transported offshore for recycling or disposal onshore, or placed on the seabed next to the bottom piece [48]. According to Eke et al. [27], partial removal of the Hermosa platform was the best option, irrespective of the preferences of the stakeholders. Those who believe that removing the entire structure is the sole choice for decommissioning are unlikely to examine the total environmental implications of their actions and, thus, are unlikely to make an informed decision [42].

Apart from the environmental advantages, operators receive significant cash rewards; millions of dollars might be saved by decommissioning efforts not only in the Gulf of Mexico but globally [15,49,50]. Similarly, Western Europe’s projected decommissioning expenditures of CAD 102 billion through 2040 can accommodate the maturing North Sea basin’s increasingly demanding physical and commercial environment [51]. Some of these savings might be integrated into future restoration projects, which could be tailored to provide advantages that outweigh the risks of leaving a portion of a structure or residual contamination in place [14]. The NEBA technique helps operators to evaluate the risks, advantages, and trade-offs connected with various decommissioning alternatives. This is because it is technically sound and scientifically dependable, which means it is visible to everyone. The method considers established values, which could be important when making a desired decommissioning plan. Decommissioning costs and the risk to people’s lives could be reduced if the industry could do it at a time when oil prices were low [52].

The process of determining the “break-point” of removal is difficult, but it has the potential to be a win–win solution for oil companies, the public, and the environment; costs and risks are significantly reduced, while the public benefits from better environmental values [42,53]. Many offshore platforms have become excellent aquatic habitats that should not be eliminated, stated Tom Campbell, Esq., a Partner in Pillsbury Winthrop Shaw Pittman LLP’s Environment, Land Use, and Natural Resources Section. The NEBA paradigm incorporates this value into societal decision making, allowing regulators and the regulated society to make informed decommissioning decisions. When applied correctly, NEBA can aid both technical and legal processes [48,54]. As an industry, we are continually working to lessen our environmental impact, and such developments show that stakeholders are committed to long-term sustainability.

5. Environmental Sustainability of Using Vacuum-Sealed Pile in Offshore Platform Decommissioning

In this section, we discuss the environmental sustainability of using vacuum-sealed piles in offshore platform decommissioning, a technique with which several structures have already been decommissioned worldwide. The conventional piling technique is a widely recognized approach in which steel piles are inserted into the configuration of a temporary work comprising piling gate beams. These beams are upheld by either piling trestles or spud piles [55]. Some articles have discussed ecological factors and environmental conditions beyond the removal or refeeding of structures. In this review, we discuss the effect of the environment on decommissioning options, considering the impacts of marine communities’ ecosystems regarding structure, general biology, and environmental conditions in other systems [56].

Engineers and technicians need a core crew to oversee daily operations across all areas of a decommissioning project. Therefore, project management is essential for all elements of WBS. This core staff changes over time, depending on how much work there is and what skills are needed [57]. If an OSPAR derogation is necessary, this portion of the WBS covers the development of the comparative assessment (CA), as well as the impact assessment (IA), the decommissioning plan (DP), and any supporting studies required during the project. Operators and practitioners conduct these investigations to acquire data to make informed decisions about decommissioning initiatives based on variables such as safety, technology, the environment, society, and economics. Decommissioning initiatives include a broad spectrum of operations. Consequently, there are many rules and agencies in place to ensure decommissioning activity is safe and successful. Permits, licenses, and consents for decommissioning projects must be carefully managed to keep projects on track [58]. This is described in this section of the WBS. This aspect includes tasks such as forming the core project management team, interacting with partners and stakeholders, conducting research to support the DP and scope definition, developing a method, making any necessary changes to the QRA, and creating the DP. This WBS section includes project-related company overheads, project insurance, compliance and verification costs, donations to any trust funds, project bids, and any paid research work [59]. Extra sources of expenditure should be disclosed in this area for cross-border projects, particularly those involving the UKCS, e.g., preparation of a comparative evaluation (CA) [60]. Any new decommissioning programs are prepared. Close-out reporting to the regulator is complete. Fees due to regulators for the evaluation of the decommissioning program and any other costs must be paid to relevant organizations to support permission applications. Throughout a decommissioning project, the contractors assigned scopes of work are responsible for project management and their correlated endeavors. As needed, the contract’s project management should be incorporated into each WBS element [61,62].

5.1. Extraction and Transfer Platforms

Extraction and transfer platforms, as well as pipes, must be separated and sanitized. This involves removing all sources of pressure and ensuring that the installation is as free of hydrocarbons and contaminants as possible. Topside cleaning includes flushing process equipment from wells and pipes on the platform’s topside. Additionally, it may be necessary to physically clean or remove any solid material from the system’s pressure vessels. Due to the fact that much of the cleaning and disinfection can be performed as part of the onshore disposal, the removal procedure determines the level of cleaning required on an installation. Pipeline cleaning programs are organized in accordance with guidelines to ensure that the hydrocarbon content and any deposits within the pipeline are thoroughly cleaned without jeopardizing future DP or reuse opportunities. This WBS element includes facility draining, flushing, purging, ventilation, physical isolation, cleaning, pipe pigging, recycling, and related waste management duties, as well as pipeline isolation and cleaning. This WBS component should also contain cleaning responsibilities for flowlines that link to wells [63,64,65].

Sustainability has emerged as a major element for oil and gas companies trying to make significant modifications to their competitive strategies and business models in recent years. This industry, one of the largest in the world, encompasses the global processes of exploration, extraction, refining, transportation (often via oil tankers and pipelines), and marketing of petroleum products, which are essential to many industries and the maintenance of industrial civilization, making it a major concern for many countries. Rising temperatures and climate change, as well as global warming caused by increasingly visible and intensive human activities, as well as exciting atmospheric occurrences and temperature increases, have undeniably highlighted the urgent need for energy corporations to rethink their strategies over the last 20 years [20]. Redefining strategic methods and business models has become an important concern for reducing risks and embracing new opportunities in the context of global changes in energy balances [66,67,68]. Several oil and gas companies have recently changed their focus to sustainability, seeking to assist various governments in mitigating the effects of climate change [69,70]. As a result, potential energy scenarios have been developed to explain business strategies in line with national decarbonization targets and a growing commitment to energy transition. Because they operate in an environmentally, economically, and socially sensitive industry, oil and gas companies must make a reasonable effort to respond to regulators and other stakeholders [70,71,72]. Therefore, given the significant effects and harsh operational environment, assessing sustainability implications supplied by oil and gas supply chain members, as well as implementing a sustainable business strategy, have become critical components for adequate social well-being [72].

5.2. Explosive Removal of Offshore Structures

Sea turtles have been documented as being killed by explosive-severance removals during offshore construction. If a marine protected species is found to be shocked, damaged, or dead, activities are stopped, and attempts are made to collect and resuscitate the animal in collaboration with the Sea Turtle Stranding and Salvage Network Coordinator, resulting in a significant delay in the project timeline [13,73,74]. Figure 5 shows an illustration of a kill zone that was reported in the Gulf of Mexico and occurred during the cleaning up of oil junk [75], where many thousands of fish have been killed.

Another incident happened in July 1988 and was categorized as one of the worst disasters in the history of UK decommissioning: the decommissioning of the Piper Alpha Platform, North Sea [76]. This was an offshore oil and gas platform that witnessed a miserable disaster of an explosion, resulting in the loss of 165 crew members and property damage of around USD 1.4 billion. Nonetheless, if marine mammals are seen in or around the identified zone, the detonation of the zone must be put off until either the marine mammals are out of the zone or actions have been taken to remove them from the zone [77,78].

It is widely acknowledged that explosive blast energy can have a deleterious effect on marine life, which is an immediate threat to the lives of sea animals. It is highly recommended to avoid using explosive material in the sea; however, in cases where detonation is required, it should be sufficiently far from, for instance, seal haul-out sites, fish spawning grounds, and whale migration paths [78,79]. Numerous case studies have proven that animals with a larger size have a greater chance of survival during explosions [80]. The destructive effect of dynamite blasts on fish has been widely acknowledged during the past decades. In addition to fish, dolphins that are exposed to blasts dramatically lose their hearing abilities [81].

During detonation, a lined or unlined chamber produces a high-energy cutting jet. The time required is minimal, and adequate skill in the controlled destruction of structures is of great importance. This method is typically selected if there are many risks, more preparation is required, or more damage to the marine ecosystem is anticipated compared to nonexplosive methods [9]. On the other hand, a statistical account of the explosive removal of offshore structures in the Gulf of Mexico has been provided based on historical data obtained from the US Minerals Management Service. The influence of parameters including water level, planning area, configuration type, structure age, and time on the use of explosive removals has been studied. The business community appears to make accurate assessments. This is because the influence of parameters of explosive methods, such as water depth, structure complexity, and age at removal, appears to be increasing. Moreover, many of the offshore structures removed from the GOM (84%) are in the central planning region, with the remainder scattered throughout the western GOM. A total of 954 of the 1626 structures decommissioned so far have used explosive technology, indicating a 59% explosive removal rate. Caissons were removed equally with explosive or non-explosive methods, while well-protector jackets were removed with explosives 62% of the time and permanent structures with explosives 66% of the time. The use of explosive technologies increases in direct proportion to the complexity of the configuration type, depth of the water, and age of the building being removed. It had no bearing on how they were used during the explosive evacuation. Despite the danger of an explosion, the time dependency was removed from the dataset for the sake of consistency [79].

Historically, explosives were the least costly method of removing platforms. Operational variables such as water depth, platform design, and conductor makeup can all have an impact on cost. In most cases, explosive severance in a large removal operation costs less than 1% of the total project expense. The explosives cost of modest removal efforts could reach 5%. The explosives and technician percentages are consistent. Work boats are drivers of expenses in removal efforts. If a severance process fails on the first attempt, project overruns are primarily due to work vessels and supporting equipment. Depending on the explosive severance target, the success rate on the first attempt is usually between 95% and 100%, according to historical field data. If the variables are known, experienced explosives contractors can calculate the likelihood of hitting a target [12].

6. Future Perspectives

When it comes to the decommissioning of offshore oil and gas platforms, there is still a lot of uncertainty, and one of the most crucial aspects that influences the entire process is a project’s life expectancy. For example, Yttre Stengrund retired after 14 years [9], while Vindeby will be decommissioned after more than 25 years [9,82]. However, they are still minor prototype projects. If projects do not last as expected, this has a significant impact on the actual decommissioning plans and economics of offshore wind farms. One of the primary issues in the offshore business is the lack of specialized vessels. Due to the volatility of the oil price, forecasting future vessel expenses is particularly difficult. One method to mitigate this risk is to create a supply–demand curve for large lift boats [83]. Even if oil prices remain at their all-time lows, a great deal of demand in the future is anticipated because oil and gas wells will be shut down and more marine energy will be generated. The length of time needed for decommissioning depends mostly on the methods used in each step and the method chosen for moving structures. One of the most important factors impacting decommissioning time is the depth of the water, which affects how the foundation is built and how much it weighs. Each MW is believed to take about a day to remove and move to the shore, which means that the estimates in the published decommissioning program are optimistic [9].

Decommissioning, as with installation, is affected by a range of factors specific to each place. These factors regarding primary challenges related to decommissioning are as follows:

• Topside removal: There are several options for dismantling offshore platforms, some requiring fewer but heavier lifts and others requiring more but lighter lifts. Experience is required to determine which are the best to use, but this is unlikely to be a one-of-a-kind solution;
• Planning, time scale, and cost: Planning, schedule, and budget are essential factors to consider. These are the most important aspects of the procedure because if even one of them is not well organized, the costs could skyrocket. Due to the challenging environment in which the task must be completed, the weather must be carefully considered. The procedures should preferably be performed during the summer to avoid the winter. Two summers might be preferable;
• Optimization of available space: The deck areas of ships are limited. To achieve a resourceful mode of transportation, effective space design is required. The way the turbines, transition components, and foundations are fitted and secured once placed on the transportation vessel is an important factor that is often overlooked in decommissioning plans. The components can be welded to the deck or mounted on a prefabricated rack, depending on the vessel’s stability, weight, and space. They can also be placed vertically or horizontally, but their options are limited by the stability, weight, and available space of the vessel.

7. Conclusions

In this paper, we present a review of the environmental sustainability and efficiency of offshore platform decommissioning using vacuum-sealed piles. Due to the rapid development of technology, offshore wells and installations must be decommissioned as soon as possible to reduce financial risks associated with well integrity loss and/or massive cost overruns associated with their decommissioning. Collaboration within the oil and gas industry can provide operators with the most cost-effective solutions, increase competency, retain competent staff, ensure the use of new technology now and in the future, and develop P&A standards and norms. This is the objective of an independent third party specializing in oil and gas offshore decommissioning certificates of compliance, certification, and training. Furthermore, our study provides an extensive review of the efficiency of explosives within a vacuum-sealed pile that can reduce or prevent the pressure of wave propagation to harmless levels in the surrounding marine environment. It is expected that the explosive method will benefit the decommissioning of offshore platforms by significantly reducing the cost of cutting. Using vacuum-sealed piles minimizes the side effects of the explosion method. The method has the following benefits:

• Significantly reduces the decommissioning cost when compared with other cutting techniques;
• Enables control of the propagation of wave shocks;
• Enables understanding of the performance of low-pressure wave pulses;
• Establishes a low-threat technique for sea animals by controlling blast wave shocks (fish, turtles, dolphins, whales, etc.);
• There are no delays for the project due to protecting vessels and overflying traffic;
• Improves the safety of personnel (divers and crew on vessels).

The study findings also indicate an accurate and clean-cut approach to the efficiency of offshore platform decommissioning as well as environmental sustainability. Finally, our work has some limitations, which include the use of vacuum-sealed piles for platform decommissioning.