Volatile organic carbon emissions in oil and gas industry: Impact and mitigation

Aside from its significant contribution to the environmental degradation, the oil and gas industry is also one of the largest polluters due to the emission of volatile organic compounds (VOCs) into the atmosphere. Chemicals within this large group of hydrocarbons called volatile organic compounds (VOCs) play a significant role in polluting the atmosphere, both in urban and industrial environments.^1,2 

The presence of certain VOCs in the environment, such as benzene, 1,3-butadiene, vinyl chloride, and trichloroethylene, has been linked to adverse health effects in humans, such as chronic poisoning and acute poisoning.​^3​ Several VOCs have been shown to play a role in causing tropospheric ozone pollution, in part because of their function as precursors to the formation of ozone during the oxidation process.​⁴​ It has become increasingly important to focus on the environmental impact of VOC emissions because of the adverse effect they have had on air quality, human health, and climate change in recent years. 

Historical perspective. Since 1990, oil and natural gas production in the United States has been growing steadily and now account for more than half of the country's energy consumption because of a sustained increase in production.⁵ Since the early 1990s, the consumption of natural gas has increased substantially in nearly all areas of the U.S. economy, including in the industrial sector (41%), the commercial sector (38%), the residential sector (42%), and the electrical power generation sector (33%). In general, there are a few types of unprocessed natural gas, which typically contains 60% methane (CH4); impurities such as non-methane volatile organic compounds (NMVOCs) such as alkanes, cycloalkanes, aromatics, etc., and the remaining fraction consists of non-organic compounds such as hydrogen sulfide, carbon dioxide, water vapor, nitrogen, and helium, among other things. There are approximately 2.49 million tons of volatile organic compounds that are produced from the upstream oil and gas production processes every year, making this industry the most significant source of VOCs in the U.S.⁵ 

NMVOC in natural gas. A number of NMVOCs, such as benzene, toluene, ethylbenzene, ortho-, meta-, and para-xylenes (collectively referred to as BTEX), have been found to play a significant role in air quality impact and human health risks caused by natural gas (NG) emissions. This can be attributed to their toxicity, carcinogenicity, and atmospheric reactivity, which contributes to the formation of secondary organic aerosols (SOA).⁶ The presence of BTEX in unprocessed natural gas has been well documented, but the presence of BTEX in distribution-grade natural gas has not been well documented due to the lack of direct measurements made on this topic. There is therefore a need to characterize NMVOCs in the end-use NG stream in more detail due to the fact that many NMVOCs present a health risk whenever NG leaks or incompletely burned on a large scale. Hydrocarbon contamination that results from well-to-refinery operations is proportional to the size of those operations, and a larger size of well-to-refinery operations will entail a greater possibility of contaminated crude oil that will be released into the environment.⁷ 

Fig. 1. Methane emissions in compliance with 2015 UN Paris Agreement.​8​

Figure 1 shows the evolution of the mean global atmospheric mixing ratio (green open circles) over the course of the year compared with the Representative Concentration Pathway (RCP2.6) used in the 2015 Intergovernmental Panel on Climate Change Assessment and as defined by the Paris Agreement.⁸ Taking into consideration the RCP 2.6, carbon dioxide (CO₂) emissions are expected to start declining by 2020 and reach zero by the year 2100. The agreement will result in a reduction in methane emissions (CH4) to approximately half what they were in 2020, while sulphur dioxide emissions (SO₂) will be reduced to approximately 10% of what they were in 1980-1990 as a result of the agreement.  

There has been a plateau in the concentrations of RCP2.6 in 2012, and those of the RCP4.5 (dashed) pathway will peak around 2045, while the mole fractions of RCP8.5 (dotted) will continue to rise well into the 21st century. The lower panel in the figure shows the difference in radiative forcing from the RCP2.6 pathway in comparison to the evolution of methane (green circles), CO2 (red circles), and nitrous oxide (blue circles) in the actual atmosphere over the past few decades. There is a strong correlation between RCP 4.5 and RCP 2.6 as indicated by the dashed lines. 

Understanding VOCs in the oil and gas industry. As the name implies, volatile organic compounds are organic compounds that evaporate at room temperature when they are exposed to air. In addition to production wells, storage tanks, refineries, and distribution systems, there are a number of other sources of these gases. This sector produces several VOCs, such as benzene, toluene, ethylbenzene, and xylene (BTEX), as well as methane emissions.⁹ Figure 2 shows the trend in VOC emissions in the United States from 1970-2002, which clearly indicates that Industrial Processes are the largest contributors to the emissions.¹⁰

Fig. 2. Trends in VOC emissions in the U.S. by major sector, 1970-2002.​10​

Production of oil and gas involves more than just drilling; it involves preparing the well for production, starting it up, and overseeing it until production begins, as well as routine maintenance. In this part of the process, it is not uncommon for different gases, including methane, to be vented or flared, depending on the stage of the process. The possibility exists that methane may also escape from natural gas leaks as well as power devices that use natural gas as a source of electricity. The purpose of gas flares is to release methane and other gases directly into the atmosphere after controlled combustion. Venting is the direct release of methane and other gases into the environment, occurring through losses and leaks throughout the oil production/refining process. Flares should be preferred over vents in most cases because they are capable of preventing accidental fires and explosions, while also reducing the amount of pollution produced by the oil and gas industry and minimizing its environmental impact.¹¹ 

All aspects of oil and gas infrastructure can produce methane emissions, from pipeline connections to storage tanks, and it can be released at any time. As an example, there are pneumatic controllers that are designed to vent gas, which can be used in order to release methane emissions from oil and gas production.¹² In addition, there are some activities in the oil industry that can also emit methane in the field, such as venting of associated gas from oil wells, storage tanks, and equipment used in the production process of oil. It is possible for venting to occur in some equipment designs as well as in certain operational practices, such as continuous gas bleeding from pneumatic controllers (which regulate gas flow, liquid levels, temperatures, and pressures in the equipment), or venting from well completions due to the design of the equipment or certain operational practices. There is a lot of evidence to suggest that pneumatic devices powered by natural gas emit the most methane as compared to other industries, according to Environmental Protection Agency (EPA) statistics.¹³ Furthermore, there is also a possibility that methane may be released unintentionally. If the hatch on a tank is accidentally left open, there can be fugitive emissions that are produced.  

There is also a possibility that fugitive methane emissions can occur as a result of improper installation or maintenance of a system, aside from the normal wear and tear. The production of oil and gas also releases VOCs, which contribute to smog and ground level ozone. In sunlight, VOCs react with oxygen to produce nitrogen oxides and carbon monoxide, commonly referred to as ground level ozone, which pose serious health risks.¹⁴ However, the EPA standards only apply to a limited number of VOCs that are considered reactive enough to cause ground-level ozone concerns. The EPA now has direct authority to regulate methane emissions due to the VOC control measures implemented in the oil and gas industry, which emits greenhouse gases in large quantities and is expected to continue to do so in the future. 

CHALLENGES AND IMPACTS 

Air pollution. A major cause of air pollution is the reaction of VOCs with nitrogen oxides (NOx) in the presence of sunlight to create ground-level ozone or smog in the atmosphere.⁹ There is no doubt that ozone poses a severe threat to human health in the form of respiratory problems, and increased vulnerability to respiratory infections.¹⁴ To gain a deeper understanding of the relationship between oil extraction projects, regional air pollutions, and their adverse impact on human health, it is important to carefully observe the health status of communities living near major crude oil exploration developments. 

Climate change. A significant factor contributing to global warming is the release of methane during the production of oil and gas, which is one of the world's most potent greenhouse gases. There is no doubt that the increase in greenhouse gases will have a significant impact on global climate change over the course of the next century, as it is estimated that methane alone will have a 28 times bigger impact over that period as compared to carbon dioxide.¹⁵ Oil and natural gas emissions are likely to contribute to local ozone production, which may offset the mitigation gains made in other emission sectors.¹⁶ 

Health risks. A number of factors can contribute to the health of workers in the oil and gas industry when they are exposed to VOCs. It has been proven that benzene is one of the most well-known carcinogens in the world, and has been linked to a variety of blood cancers, including leukemia.⁹ In addition, neurological disturbances, organ damage, and respiratory problems can also occur as a result of it. 

Environmental footprint. There has been a significant degradation in the planet's ecosystem as a result of the widespread use of oil and oil products in industry and daily life.¹⁷ As the pressure is growing for emissions of greenhouse gases to be reduced, there is an increased need to control the release of VOCs. The oil and gas industry contributes significantly to global carbon footprints through VOC emissions. A number of factors contribute to VOC pollution, including oil storage facilities, oil depots, and railroad transportation. Hydrocarbon contamination of soil, especially by volatile organic compounds (VOCs), has far-reaching consequences for ecosystems. VOCs can enter the soil because of spills, leaks, and improper disposal of petroleum products and their by-products.¹⁸ The compounds can persist in soil for extended periods, disrupting the ecosystem's natural balance and functionality. The mineralization process can be hindered due to VOCs, which is crucial to breaking down organic matter in soil.¹⁹ 

TECHNOLOGY ENABLED MITIGATION 

There have been a number of technologies developed by technology companies over the past several years that have been able to aid operators in detecting and determining the source of fugitive methane emissions that are caused by equipment that doesn't operate properly or in a manner consistent with normal operations. It is possible for some technologies to detect and measure these emissions which are generated because of oil and gas operations. There are several ways in which optical and remote sensors can be deployed, such as on piloted aircraft, drones, satellites, or they can be placed on the ground as ground-based sensors to provide continuous monitoring of the environment using optical and remote sensors.²⁰ Through the technological examples provided below, it is possible to gain a better understanding of methane emissions on a variety of spatial and temporal scales with different degrees of detection sensitivity. 

Optical gas imaging cameras. Hydrocarbon emissions, particularly methane, in industrial settings can be detected using optical gas imaging (OGI) technology, specifically handheld instruments like OGI cameras. By capturing infrared images of methane plumes, these devices reveal otherwise invisible emissions. Hydrocarbon emissions can be detected using video cameras equipped with cooled detectors which are sensitive to the 3.2-3.4 m spectral band.²¹ By using the OGI method, both the hydrocarbon plume and the background absorb and emit infrared radiation, which is then detected by the OGI camera. The effectiveness of OGI surveys depends on the contrast between the plume and the background.  

The technology offers advantages over traditional leak detection and repair programs conducted by U.S. government agencies. In the past, agencies like the Environmental Protection Agency (EPA) have used portable hydrocarbon probes, specifically Method 21 (M21), to check industrial components for leaks. In spite of M21's sensitivity and precision, it requires a substantial investment of resources. It is the inspector's responsibility to document, physically touch, and thoroughly inspect each potential leak interface. OGI technology, on the other hand, has several advantages. With its ease of use, higher spatiotemporal coverage, and ability to collect component-level information without physical contact, it is a more efficient alternative to traditional methods like M21. By doing so, resource consumption is reduced and inspection speed is increased. 

Piloted aircraft. An airplane, for example, can be equipped with a variety of instruments that are designed to monitor wind speed, temperature, and methane emissions around areas with oil and gas operations.²⁰ During a survey, a pilot flies in a predetermined path (such as a circle or a zigzag pattern) around the well site or a basin to collect data and determine emission rates. Compared to ground crews, aircraft can cover large areas more quickly, which is advantageous for operators of well sites that cover a large state or region. 

Drones.  Due to the weight thresholds of the drone platform, drones operate in a similar way to piloted aircraft, however their sensors are generally less robust due to the smaller size and more fragile design. When fitted with sensors, drones can fly closer to a well site in tighter circles, thus providing a more accurate measurement of methane emissions compared to piloted aircraft. As a result of their ability to hover for up to 15 minutes at a time, multi-rotor drones have become increasingly popular due to their ability to monitor or sample ambient air pollutants.²² Traditionally, captive balloons and stiff wing unmanned aerial vehicles (UAVs) have been used to monitor or sample ambient air pollutants. A lightweight, easy-to-operate drone can be used to collect atmospheric samples, monitor air pollution, and trace industrial emissions. As a part of the gas sampling process, drones are equipped with stainless steel canisters, adsorptive tubes, and Teflon sampling bags for collecting gas samples. The use of gas chromatography coupled with a mass spectrometer (GC-MS) has become widely accepted as a method of analyzing VOCs​.²² 

Satellite. Monitoring and detecting methane emissions requires satellites equipped with advanced sensors, positioned miles above the Earth's surface. Using these satellites, continuous monitoring can be provided for specific geographical areas. Satellite-based monitoring can be useful for industries with geographically dispersed operations or for those looking to monitor specific areas when a satellite is overhead.²³ For identifying air pollution levels, satellite images are analyzed using a variety of remote sensing techniques. VOCs are monitored by satellite platforms such as METOP-A, ENVISAT, and ERS-2. A large-scale, high-resolution approach such as this can help fill in gaps left by other monitoring techniques at the regional, national, and continental levels. Monitoring of environmental conditions is further enhanced by integrating ground monitoring networks with satellite platforms. 

Fixed sensors. Fixed sensors play a crucial role in detecting methane emissions, particularly near well sites. Methane emissions are continuously monitored by these sensors at high frequencies, such as every few seconds or even repeatedly per second, around the well site area. Often, sensors are installed around the boundaries of the site to detect emissions as the wind changes direction. With this proactive approach, operators can receive alerts within minutes of detecting a leak, providing real-time monitoring. By deploying continuous monitoring sensors, operators can quickly identify emissions, allowing them to take immediate corrective action.²⁰ 

Real-time monitoring is especially beneficial when it comes to environmental stewardship and regulatory compliance since it minimizes the potential for emissions to extend and go unnoticed. Using sophisticated instrumentation, monitors perform precise, accurate, and reproducible analyses of individual VOCs. These techniques include gas chromatography-mass spectroscopy (GC-MS), gas chromatography-flame ionization detector (GC-FID), differential optical absorption spectroscopy (DOAS), and Fourier Transform Infrared Spectroscopy (FTIR).²⁴ In addition to providing detailed insights into pollutants' composition and concentration, these instruments are particularly useful for analyzing specific VOCs. With gas chromatography-mass spectroscopy (GC-MS), it is possible to separate and identify individual components within complex mixtures. GC-FID is sensitive to hydrocarbons, making it suitable for VOC analysis. It is possible to detect and quantify VOCs in the air using differential optical absorption spectroscopy (DOAS) and Fourier Transform Infrared Spectroscopy (FTIR). 

PROSPECTIVE STRATEGIES 

It is increasingly important to explore options for removing methane emitted from areas with elevated levels. Identifying and detecting methane sources is a major technical challenge associated with the reduction of methane emissions, as well as quantifying specific emission fluxes associated with the sources and developing effective methods of reducing those emissions. 

Leak detection and repair programs. It is essential to establish leak detection and repair (LDAR) programs. LDAR programs that are rigorous to detect and repair equipment leaks as soon as possible. To reduce the emissions of VOCs to the atmosphere, it is important to monitor and maintain storage tanks, valves, and other infrastructure on a regular basis. Hydrocarbon materials and products can leak, vent, or evaporate, releasing VOCs into the atmosphere. A major source of VOC emissions is equipment leaks, which contribute to about 25% of emissions.²⁵ Many factors, including excessive operations, erosion, looseness, and seal cracks, can lead to the leakage of equipment components in processing units and auxiliary facilities. Controlling VOC emissions from leaky equipment has been made easier by the LDAR program. In the United States, the European Union, and Canada, the LDAR program implemented since the 1980s has led to significant reductions in VOC emissions (63% for petroleum refineries).²⁵ 

Improved capture and recovery systems. By installing vapor recovery units (VRUs) and gas capture technologies, VOCs that would otherwise be released into the atmosphere can be captured and recovered.²⁶ VOC emissions are particularly prevalent during storage and transportation processes of crude oil and natural gas. The purpose of vapor recovery units is to capture and process gases emitted from various industrial processes, preventing harmful pollutants from being released into the atmosphere. Often, these units are used in oil refineries, chemical plants, and other facilities that produce VOCs. VRUs contribute significantly to direct emissions reduction and environmental protection by capturing and treating these emissions. To prevent emissions from crude oil and natural gas during storage and transportation, innovative approaches involve advanced materials, such as ionic liquids (ILs).^27,28 

These are liquids containing anion and cation ions which exhibit distinctive physical and chemical properties. A few of these properties include low or no vapor pressure, high thermal and chemical stability, low melting points, and environmental friendliness. These are used to specifically absorb particular VOCs from a mixture of gases. By utilizing VRUs, gas capture technologies, and innovative materials like ionic liquids, emissions can be reduced in a proactive manner. In addition to adhering to environmental regulations, industries can contribute to a cleaner and more sustainable future by preventing VOCs and other pollutants from entering the atmosphere. 

Enhanced flaring and combustion practices. Flares can minimize the emissions of VOCs and methane into the atmosphere as a result of controlled gas combustion. Focusing on finding new combustion technologies that replace traditional flaring with more efficient ones would be the most effective way to minimize routine flaring.²⁹ Systematic studies has been conducted to determine whether dynamic simulation and optimization can be used during chemical plant turnarounds (start-up, shutdown and upset) to minimize industrial flaring.³⁰ Using the steady-state model and dynamic simulation model, the operators are able to virtually run the operation of the plant under normal and abnormal conditions and examine the results. Under the constraints of a given operation, the optimal operating points can be identified. A variety of process designs can be employed to reduce start-up/shutdown flares by experimenting with different design options with and without recycling optimization. It is important to install a flare gas recovery system that is adequate and viable to minimize flare gas emissions during abnormal operations. 

Enhanced regulatory frameworks. Efforts must be made by governments and regulatory agencies to implement emission standards within the oil and gas industry. Investment in clean technology and practices can be encouraged by implementing comprehensive regulations and monitoring systems, as well as imposing penalties for non-compliance in order to encourage companies to adopt them as a matter of business practice. There has been a proposal from the EPA that will substantially reduce the amount of methane that is emitted from any new or existing oil and gas sources.³¹ It would be mandatory for states to reduce methane emissions from hundreds of thousands of existing sources nationwide for the first time in order to meet the new requirements, as well as extending and strengthening existing requirements that are currently in place for new, modified and reconstructed sources of oil and natural gas. 

Adoption of green technologies. By using renewable energy sources and low-carbon technologies, oil and gas companies can reduce VOC emissions. This can be achieved in several ways, such as promoting the electrification of equipment and exploring alternative energy solutions for the extraction and refining procedures. As the power plant is typically the largest point-source emitter of carbon dioxide in a refinery, there is a strong possibility that newer installations could benefit more from utilizing low-carbon power sources, such as solar or wind energy. The temperature of concentrated solar power system (CSP) can reach temperatures of 60°C to 250°C, and in some cases, as high as 400°C.³² There is a possibility that in the future, CSP systems may be directly coupled with carbon capture and storage (CCS) units to reduce the amount of carbon dioxide that is emitted by utility systems. As a practical matter, however, it is difficult to integrate such technologies in refineries in an efficient and effective manner. 

CONCLUSION 

The oil and gas industry faces significant challenges because of the increasing amount of air pollution, global climate change, and health risks resulting from volatile organic compounds released into the atmosphere. It is imperative that industry stakeholders, regulatory bodies, and technology providers work together to resolve this urgent issue to ensure that the people and organizations affected by this crisis are not left stranded. Through the implementation of effective leak detection programs, improvements in capture and recovery systems, and enhancing flaring practices as well as adopting green technologies, the oil and gas industry can substantially reduce the emission of VOCs and contribute to a more sustainable and environmentally friendly future.  

Furthermore, oil and gas companies need to make considerable investments in research and development if they want to ensure a more sustainable and greener future by developing new technologies that are designed to reduce emissions. It is essential that industries, regulators, and technology providers work together to ensure that these solutions are implemented smoothly.  

To further reduce the carbon footprint of the industry, there is a need for companies to invest in the development of renewable energy sources. Governments should also develop incentives to encourage companies to invest in these technologies to ensure the transition to a greener future is swift and effective. 

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About the Authors

Kasturi Laturkar

Validation Associates LLC

Kasturi Laturkar works as a Validation Engineer for Validation Associates LLC and has more than five years of experience working in commissioning, qualification and validation of upstream and downstream bioprocessing equipment and critical utilities. Laturkar graduated with an MS degree in chemical engineering from Syracuse University and a B.Tech degree in chemical engineering from Guru Gobind Singh Indraprastha University, Delhi, India. The author can be reached at kasturi.laturkar@gmail.com.

Kaustubh Laturkar

Facility for Rare Isotope Beams

Kaustubh Laturkar works as an Engineer at the Facility for Rare Isotope Beams, a U.S. Department of Energy (DOE) project in Michigan. He has more than 10 years of experience working in the field of process engineering, refinery operations, utility systems design and operation, with a special focus on design and commissioning of engineering systems. Laturkar earned an MS degree in chemical engineering from University of Florida and a BE degree in chemical engineering from Panjab University, Chandigarh, India. The author can be reached at kos19188@gmail.com.