Environmental Consequences and Remediation Strategies for Abandoned Oil and Gas Infrastructure

. This study investigates the environmental problems associated with abandoned oil and gas infrastructure in industrial areas and explores potential remediation and restoration strategies to address these issues. Through a comprehensive literature review, the research examines the environmental consequences of abandoned infrastructure, including soil and groundwater contamination, methane emissions, and physical hazards. The study also evaluates various remediation technologies and restoration approaches, such as soil treatment and stabilization, groundwater treatment and monitoring, methane mitigation, and ecological rehabilitation. Furthermore, the research presents case studies from different regions, including Russia, demonstrating successful remediation and restoration projects. Based on the synthesis of findings, the study provides recommendations for future research and policy development to enhance the management of abandoned oil and gas infrastructure and improve the effectiveness of remediation and restoration efforts. This study contributes to the understanding of the environmental challenges posed by abandoned oil and gas infrastructure and offers valuable insights for researchers, policymakers, and practitioners in the field of environmental management and protection.


Introduction
The oil and gas industry has played a critical role in meeting global energy demands over the past century. As new fields are discovered and developed, older infrastructure often becomes obsolete, resulting in numerous abandoned well sites, pipelines, and processing facilities. It is estimated that there are over 2.6 million abandoned oil and gas wells in the United States alone [1]. In Russia, it is estimated that there are over 20,000 abandoned oil and gas wells, with a significant portion located in Western Siberia [2]. Globally, this number is expected to be much higher. In many cases, these sites are inadequately decommissioned, posing significant environmental and public health risks.
The abandonment of oil and gas infrastructure can occur for various reasons, such as resource depletion, economic factors, or technological advancements. With the increasing global focus on renewable energy sources and efforts to reduce greenhouse gas emissions, the number of abandoned oil and gas infrastructure sites is expected to rise. The proper management and remediation of these sites is crucial to mitigating their environmental impacts and ensuring public safety.
Abandoned oil and gas infrastructure poses several environmental and public health concerns. The most pressing issues are soil and groundwater contamination, which can result from leaks, spills, and residual contaminants at the site. According to the U.S. Environmental Protection Agency (EPA), over 1,300 significant spills occurred in the U.S. oil and gas industry between 2006 and 2016, releasing approximately 12 million gallons of oil and other hazardous substances [3]. In Russia, more than 2,500 incidents of oil spills were reported in 2019, with a total volume of over 5,000 tons of oil. These contaminants can include hydrocarbons, heavy metals, and toxic chemicals, which can have long-term effects on ecosystems and agricultural land, as well as human health.
Methane emissions are another significant concern, as abandoned wells and pipelines can serve as sources of fugitive methane emissions, contributing to climate change. A study by the U.S. Geological Survey found that abandoned wells could emit between 4 and 7 million metric tons of methane annually, equivalent to the greenhouse gas emissions from approximately 2 million passenger vehicles [4]. Although comprehensive data on methane emissions from abandoned oil and gas infrastructure in Russia is limited, it is expected that the emissions are significant, given the vast number of abandoned wells. Physical hazards, such as exposed wellheads, collapsed structures, or unsecured pipelines, also present risks to public safety, particularly in areas where these sites are located near residential or recreational areas.
Addressing these environmental and public health concerns requires a comprehensive understanding of the extent of the problem, as well as the development and implementation of effective remediation and restoration strategies. In the following sections, we will explore the environmental consequences of abandoned oil and gas infrastructure, along with the best practices and technologies for site remediation and restoration.

Materials and Methods
This review study utilized a comprehensive and systematic approach to gather and analyze data related to the environmental problems of industrial areas in the oil and gas industry, specifically focusing on abandoned infrastructure. The following materials and methods were employed: Literature search. A thorough search of scientific literature was conducted using electronic databases, including Web of Science, Scopus, and Google Scholar. The search strategy involved the use of relevant keywords and phrases, such as "abandoned oil and gas infrastructure," "environmental impacts," "remediation," "restoration," and "case studies." Articles were selected based on their relevance to the study objectives and the quality of the research.
Grey literature search. In addition to peer-reviewed scientific literature, grey literature sources, such as government reports, conference proceedings, and technical documents, were also reviewed. These sources provided valuable information on the regulatory context, remediation technologies, and best practices for managing abandoned oil and gas infrastructure.
Data extraction and synthesis. Relevant information from the selected literature was extracted and organized into thematic categories, including environmental consequences, remediation strategies, restoration approaches, and case studies. This information was then synthesized to provide a comprehensive overview of the environmental problems associated with abandoned oil and gas infrastructure and the potential solutions for addressing these issues.
This systematic review study provides a solid foundation for understanding the environmental problems associated with abandoned oil and gas infrastructure and the potential solutions for mitigating these issues. The materials and methods employed ensure a rigorous and comprehensive analysis of the available literature, providing valuable insights for researchers, policymakers, and practitioners in the field of environmental management and protection.

Soil contamination
Soil contamination in abandoned oil and gas infrastructure sites can result from various sources, including leaks and spills from storage tanks, pipeline ruptures, improper disposal of drilling mud, and residual contaminants from processing facilities. These contaminants can be classified into several categories: Hydrocarbons: Petroleum-based substances, such as crude oil, diesel, and gasoline, are the most common contaminants at abandoned oil and gas sites. They can cause soil pollution by adhering to soil particles, reducing soil fertility, and posing risks to plants, animals, and humans.
Heavy metals: Metals such as lead, mercury, cadmium, and arsenic can be found in drilling mud and other waste materials. They can accumulate in the soil and pose health risks to humans and wildlife when ingested or inhaled. Heavy metals can also enter the food chain, affecting plants and animals at various trophic levels.
Toxic chemicals: Chemicals used in the extraction and processing of oil and gas, such as biocides, corrosion inhibitors, and surfactants, can contaminate the soil and pose risks to the environment and public health. These chemicals can be toxic to plants, animals, and humans, causing adverse effects on growth, reproduction, and overall health.
The long-term ecological and agricultural impacts of soil contamination at abandoned oil and gas sites can be significant, affecting both natural ecosystems and agricultural productivity. Key impacts include: Reduction in soil fertility: Soil contamination can disrupt the balance of nutrients and microbial activity, leading to reduced soil fertility and productivity. This can result in a decline in plant growth, limiting the availability of food and habitat for wildlife.
Bioaccumulation and biomagnification: Contaminants, particularly heavy metals, can accumulate in plants and animals through the food chain, resulting in higher concentrations at higher trophic levels. This can lead to adverse effects on the health of wildlife and humans, including reproductive issues, developmental abnormalities, and other health problems.
Loss of biodiversity: Contaminated soil can lead to a decline in biodiversity, as species sensitive to pollutants may be unable to survive or reproduce in affected areas. This can have cascading effects on ecosystems, altering food webs and disrupting ecological processes.
Agricultural impacts: Soil contamination can reduce the productivity and safety of agricultural lands, affecting crop yields and the quality of food produced. This can have economic consequences for farmers and pose health risks to consumers, as contaminated crops may contain unsafe levels of pollutants.
Addressing soil contamination at abandoned oil and gas infrastructure sites requires thorough site assessment, the implementation of appropriate remediation technologies, and long-term monitoring to ensure the effectiveness of remediation efforts and prevent future contamination.

Groundwater contamination
Groundwater contamination at abandoned oil and gas infrastructure sites can occur through various pathways. Leaks and spills can result in the migration of contaminants through the soil, eventually reaching the underlying aquifers. Additionally, improperly decommissioned wells can provide a direct conduit for contaminants to enter groundwater systems [5]. Groundwater can also be affected by the infiltration of contaminants from surface water bodies that have been polluted due to runoff or discharges from these sites [6].
In the United States, it was estimated that between 2 and 12 percent of oil and gas wells had a significant risk of groundwater contamination due to well integrity issues [7]. In Russia, a study conducted in the Samotlor oil field found that 58.8% of groundwater samples exceeded permissible limits for total petroleum hydrocarbons [8]. These findings underscore the need for proper well decommissioning and remediation measures to protect groundwater resources.
Contaminated groundwater can have significant impacts on drinking water sources, as well as aquatic ecosystems. Contaminants in groundwater, such as hydrocarbons, heavy metals, and toxic chemicals, can pose health risks to humans and wildlife when consumed or absorbed through the skin [9]. Moreover, the migration of these contaminants into surface water bodies can harm aquatic life by disrupting physiological processes, impairing reproduction, and reducing biodiversity [10]. A study in the United States revealed that 6.5% of drinking water wells located near oil and gas development sites were contaminated with methane, with higher levels found in areas with a high density of gas wells. In Russia, an estimated 1.4 million people live in areas with contaminated groundwater, with the oil and gas industry being a significant contributor to this contamination.

Methane emissions and climate change implications
Abandoned oil and gas infrastructure can contribute to methane emissions, a potent greenhouse gas with a global warming potential 28 times greater than carbon dioxide over a 100-year time scale. Fugitive methane emissions can result from leaks in abandoned wells and pipelines, as well as from residual gas in decommissioned facilities. These emissions contribute to climate change, which has far-reaching consequences, including more frequent and severe weather events, sea-level rise, and impacts on ecosystems and human health. Methane emissions from the oil and gas sector accounted for approximately 25% of global methane emissions in 2020. In Russia, the oil and gas industry is estimated to be responsible for 42% of the country's total methane emissions. Addressing fugitive methane emissions from abandoned oil and gas infrastructure is crucial for mitigating climate change impacts.

Physical hazards and risks to public safety
Physical hazards associated with abandoned oil and gas infrastructure can include exposed wellheads, collapsed structures, and unsecured pipelines. These hazards pose risks to public safety, particularly in areas where these sites are located near residential or recreational areas. Injuries or fatalities can occur from falls, exposure to toxic substances, or explosions resulting from the ignition of residual gas or vapors. In the United States, between 2000 and 2009, there were 125 fatalities and 1,644 injuries related to the oil and gas extraction industry, with a significant portion resulting from contact with equipment or objects [11]. In Russia, a total of 3,345 accidents were reported in the oil and gas sector between 2010 and 2016, resulting in 215 fatalities. These statistics highlight the need for effective management and remediation of abandoned oil and gas infrastructure to minimize public safety risks.

Regulatory framework and responsible parties
The regulatory framework for addressing abandoned oil and gas infrastructure often involves multiple government agencies and stakeholders, including the responsible oil and gas companies. In many countries, the primary responsibility for site cleanup and restoration lies with the operators or property owners, while government agencies enforce regulations and provide oversight. In many countries, including the United States, the regulatory framework for the remediation of abandoned oil and gas sites involves several levels of government, with state or provincial authorities often taking the lead in overseeing site cleanup and restoration. In Russia, the Ministry of Natural Resources and Environment is responsible for overseeing the remediation of contaminated sites, with regional authorities also playing a role. However, regulatory enforcement can be inconsistent, and not all sites receive adequate attention.

Site assessment and characterization
Prior to remediation, a thorough site assessment and characterization process is conducted to identify the types and extent of contamination, the affected environmental media (soil, groundwater, surface water), and potential exposure pathways for humans and wildlife. This information is critical for developing an appropriate remediation strategy and evaluating its effectiveness over time. A crucial step in the remediation process is the assessment and characterization of the contaminated site. This involves identifying the types and extents of contamination, the affected environmental media (soil, groundwater, surface water), and potential exposure pathways for humans and wildlife [12]. In Russia, approximately 100,000 potentially contaminated sites have been identified, with oil and gas infrastructure representing a significant portion of these sites.

Remediation technologies
Various technologies exist for treating and stabilizing contaminated soil, including excavation and disposal, soil washing, bioremediation, and solidification/stabilization. The choice of technology depends on factors such as the nature and extent of contamination, site conditions, and regulatory requirements. In Russia, bioremediation is a commonly employed technique, with studies showing that it can be effective in reducing hydrocarbon contamination levels by up to 85% [13].
Groundwater remediation methods include pump-and-treat systems, in-situ bioremediation, permeable reactive barriers, and monitored natural attenuation. The choice of technology depends on factors such as the nature and extent of contamination, hydrogeological conditions, and regulatory requirements. Monitoring is a critical component of groundwater remediation to evaluate the effectiveness of the chosen technology and ensure the protection of water resources. In Russia, there is limited data on the specific technologies employed for groundwater remediation, but available information suggests that pump-andtreat and in-situ methods are commonly used [14].
Methane mitigation strategies for abandoned oil and gas infrastructure include well plugging and abandonment, gas capture and utilization, and the installation of vapor recovery units. These approaches can help reduce greenhouse gas emissions and mitigate climate change impacts associated with abandoned infrastructure. In Russia, efforts to mitigate methane emissions have focused on improving well integrity and reducing leakage from pipelines.

Restoration and ecological rehabilitation
Restoration and ecological rehabilitation efforts at remediated sites can involve planting native species, creating wetlands or other habitat features, and managing invasive species. These activities help promote the recovery of ecosystems and provide valuable habitat for wildlife. In Russia, some successful restoration projects have been implemented, including the re-vegetation of disturbed lands in the Khanty-Mansiysk Autonomous Okrug, where over 27,000 hectares have been restored between 2000 and 2019.
Long-term monitoring and adaptive management are essential for ensuring the success of remediation and restoration efforts. This can involve periodic sampling of soil, water, and biota, as well as regular inspections of physical structures. Adaptive management allows for adjustments to the remediation and restoration plan as new information becomes available or conditions change over time. In Russia, there is limited data on the extent of long-term monitoring at remediated sites, but the need for ongoing management and oversight is recognized.

Example 1: Decommissioning of an abandoned well site
The decommissioning of an abandoned well site in Alberta, Canada, provides an example of a successful remediation and restoration project. In this case, a multidisciplinary team, including biologists, engineers, and soil scientists, collaborated to remove contaminated soil, plug the well, and restore the surrounding ecosystem. The project successfully reduced the risk of groundwater contamination, eliminated physical hazards, and restored the site to its pre-development conditions [15]. In the decommissioning of the abandoned well site in Alberta, Canada, the primary technology used was well plugging and abandonment. This involved placing cement plugs at specific intervals within the wellbore to prevent the flow of fluids, followed by cutting and removing the well casing and capping the wellhead. Additionally, contaminated soil was removed and disposed of in accordance with regulatory requirements, and the site was re-graded and re-vegetated to restore the natural ecosystem.

Example 2: Remediation of a contaminated pipeline corridor
The remediation of a contaminated pipeline corridor in the United States demonstrates the successful application of a range of remediation technologies. The project involved the removal of impacted soil, the treatment of contaminated groundwater using pump-and-treat systems, and the implementation of natural attenuation processes. As a result, the site achieved regulatory closure and was deemed suitable for unrestricted use [16]. For the remediation of the contaminated pipeline corridor in the United States, a combination of technologies was used. Impacted soil was excavated and removed, while contaminated groundwater was treated using a pump-and-treat system. This involved pumping groundwater to the surface, treating it using a water treatment system to remove contaminants, and then discharging the treated water in compliance with regulatory requirements. Additionally, monitored natural attenuation was employed to allow natural processes to further reduce contaminant concentrations over time.

Example 3: Restoration of a former gas processing facility
The restoration of a former gas processing facility in the United Kingdom serves as an example of successful ecological rehabilitation. After the removal of contaminated soil and treatment of impacted groundwater, the site was re-vegetated with native species, and habitat features such as ponds and wetlands were created. The project resulted in the establishment of a diverse and functioning ecosystem that supports a range of wildlife species [17]. In the restoration of the former gas processing facility in the United Kingdom, the primary technologies used were the excavation and removal of contaminated soil and the treatment of impacted groundwater. Specific treatment methods for groundwater are not detailed in the source; however, they likely involved physical, chemical, or biological processes to remove contaminants. Following the remediation, the site was re-vegetated with native species, and habitat features such as ponds and wetlands were created to promote the establishment of a diverse and functioning ecosystem.

Example 4: Bioremediation of oil-contaminated soil in Russia
A successful remediation project in Russia involved the bioremediation of oil-contaminated soil at a site in the Republic of Tatarstan. Researchers used a combination of indigenous hydrocarbon-oxidizing microorganisms and nutrient amendments to enhance the biodegradation of oil contaminants. Over the course of 18 months, the total petroleum hydrocarbon (TPH) concentration in the soil was reduced by 92%. This project demonstrates the potential of bioremediation as an effective and environmentally friendly approach to remediating oil-contaminated soils in Russia [13].

Conclusion
Abandoned oil and gas infrastructure poses significant environmental and public health risks, including soil and groundwater contamination, methane emissions, and physical hazards. Remediation and restoration strategies play a crucial role in mitigating these risks and promoting the recovery of impacted ecosystems. Various technologies, such as soil treatment and stabilization, groundwater treatment and monitoring, and methane mitigation, can be employed to address contamination and reduce risks. Successful restoration and ecological rehabilitation efforts, including re-vegetation and habitat restoration, contribute to the longterm health and resilience of ecosystems.
Proactive and collaborative approaches to addressing the environmental problems of abandoned oil and gas infrastructure are essential. This involves the engagement of responsible parties, including oil and gas companies, government agencies, and local communities, in the planning, implementation, and monitoring of remediation and restoration efforts. By working together, stakeholders can develop and apply best practices, share knowledge and resources, and ensure the long-term success of these initiatives.
To further enhance the management of abandoned oil and gas infrastructure and their associated environmental problems, several recommendations for future research and policy development are proposed: Improve data collection and reporting on the extent, condition, and risks associated with abandoned infrastructure to inform decision-making and prioritize resources.
Develop and promote the use of innovative remediation technologies and approaches that are cost-effective, efficient, and environmentally sustainable.
Strengthen regulatory frameworks and enforcement mechanisms to hold responsible parties accountable for the cleanup and restoration of abandoned sites.
Encourage the integration of remediation and restoration efforts into broader land use planning and ecosystem management initiatives, to maximize ecological, social, and economic benefits.