Climate change is a recurring theme in conversations about oil and gas operations and other industrial-scale human activities. Contentiously, the primary forcing function of global climate change is the atmospheric accumulation of anthropogenic greenhouse gases (GHGs). There are a number of natural and anthropogenic sources of GHG emissions globally. Whether natural or anthropogenic, different GHGs have differing potentials to impact global warming based on how long they stay in the atmosphere and how strongly they affect the atmosphere.
Global Warming Potential
The Global Warming Potential (GWP) is a method to compare the global warming impacts of different gases. The GWP measures how much energy the emissions of 1 ton of a gas will absorb over a given period of time, relative to the emissions of 1 ton of CO2. The larger the GWP, the more a particular gas warms the Earth compared to CO2 over that period of time. The time period used for GWPs is typically 100 years. This common unit of measure allows analysts to add up emissions estimates of different gases (e.g., a national GHG inventory), and allows policymakers to compare emissions reduction opportunities across sectors and gases.1U.S. Environmental Protection Agency. (2022, May 5). Understanding Global Warming Potentials. Retrieved 1/9/2023 from https://www.epa.gov/ghgemissions/understanding-global-warming-potentials.
Carbon dioxide, as the reference gas, has a Global Warming Potential (GWP) of 1 regardless of the time period discussed. Emissions from CO2 cause increases in atmospheric concentrations of the gas that last thousands of years.¹
Methane (CH4) has a GWP of 27-30 over 100 years. Methane emitted today lasts about a decade on average, which is much less time than CO2. But CH4 also absorbs much more energy than CO2. The net effect of the shorter lifetime and higher energy absorption is reflected in the larger GWP numbers.¹
Locating Methane Emissions
Point sources for CO2 emissions are usually easy to locate. Any facility engaging in large-scale combustion emits significant quantities of CO2. Because thermoelectric power production is the main source of anthropogenic CO2 in the United States, and also a point source, power plants are of primary interest for atmospheric CO2 mitigation.
On the other hand, CH4 emissions are much more difficult to locate. These are frequently labeled “fugitive” because they are unintentional releases of gas. Because CH4 is a commercial product (the main component of natural gas) and an environmental hazard (much more potent greenhouse gas), oil and gas operators have both a financial and an environmental incentive for locating and mitigating CH4 emissions. Identifying and monitoring leaks presents a sizeable challenge to oil and gas operators, but increased monitoring and improved equipment maintenance present several long-term benefits including more product available for sale and fewer GHG emissions. One of our experts outlines both common sources and detection methods for fugitive CH4 emissions.
Transcript
Fugitive Gas Emissions from Oil and Gas Production Facilities – Mike Parker – Parker Environmental and Consulting, LLC
Fugitive emissions are unintentional releases of gases or vapors from equipment at oil and gas production facilities. Individually fugitive emissions are usually very small but cumulatively they can be more significant both in terms of economic loss and potential environmental impact. When we’re dealing with complex systems like those used for oil and gas production finding and fixing fugitive emissions can be a challenging process.
Every component with a seal or connection can be a potential leak point. So what are the most common sources of fugitive emissions? Seal or gasket failure or a seal or gasket has deteriorated can occur from a number of sources. These include regular wear of movable parts, improper or uneven bolt torque, missing flange bolts, excessive pressure, corrosion or vibration.
Leaking valves are a common source of fugitive emissions. A single valve can has as many as five potential leak points. These include the valve flange, the valve seat, the bonnet seal, the stem seal and the stem cap. Even a relatively simple production facility can have over 50 valves so it’s easy to see how complex monitoring for fugitive emissions can become. Regular inspection and routine maintenance is a key to ensuring that valves and other equipment are functioning properly.
Another common source of leaks are their control lines and their connections. Pressurized natural gas is often readily available on site so it’s commonly used to control equipment and devices. A bad connector or a cracked control line can be a potential leak point. Tanks and stuffing boxes round out the list of common sources. With tanks, fugitive emissions can come from a thief hatch that is not fully closed or one with a bad seal. Pressure relief devices on tanks and other pressurized equipment can also be a source of leaks.
Stuffing box seals help control the flow of fluids on a rod pump well. They require routine maintenance and monitoring due to the potential for wear from frequent movement. The main goal of the methane reduction plan of the Environmental Protection Agency, or EPA, is to reduce the fugitive methane emissions through increased monitoring and improved equipment maintenance. The intent of these EPA rules is to ensure that operators perform periodic leak detection surveys.
The results of these surveys must be reported to EPA. The record keeping requirements allow the EPA and the operator to track leak performance which will determine how often follow up surveys must be conducted. The fugitive emission surveys are initially performed twice a year. If any leaks are discovered, all repairs must be made within 15 days of surveying. Finally, the EPA rewards good performance by reducing the survey frequency for facilities that demonstrate a low leak rate.
So how do we identify fugitive emissions? There are several common methods. Optical gas imaging uses infrared cameras to detect heat differences found with most gas emissions. The advantage of this method is that infrared cameras quickly detect leaks but because this technology only detects heat differences, it cannot identify specific gases such as methane, volatile organic compounds or carbon dioxide. These cameras can alert us that a leak is occurring but they cannot tell us what gases are leaking.
Other common tools include combustible gas detectors also known as gas sniffers. There are many types of these tools. Depending on the complexity of the tool, they can simply sound an alarm when they detect combustible gas or they can identify specific gases. They work by detecting either electrical or chemical properties of a gas. One type of electrical detector uses an electrode that is specific to a particular gas or group of gases. As gas flows over the electrode, it is either oxidized or reduced. The detector then measures the type and strength of that reaction. This allows it to identify the gas and to quantify its concentration.
Another tool that measures electrical properties is an infrared or IR point detector. This tool pulls a known quantity of gas across an infrared sensor beam. The amount of energy absorbed from the sensor beam identifies the gas and quantifies the concentration. A semiconductor device is a tool that uses chemical detection. It works by initiating a chemical reaction when the gas contacts a sensor. The reaction creates a change in resistance that is used to identify the type of gas and quantify the concentration.
With all of these detection technologies, it’s important to understand how they work and what they can tell you and what they can’t tell you. None of these devices can quantify the volume of leaking gas. The process for quantifying the volume of a leak is decidedly low tech. First, you wrap the leak point with a plastic bag. Next, you measure the time the bag is in place and then you remove the bag and measure the volume of gas that’s captured in it.
What are some challenges related to fugitive emissions? Monitoring every potential leak point is a challenge because it is time intensive and requires a robust record keeping program. The work involved in cataloging and accurately recording monitoring data can be significant. However, the benefit is in reduced methane emissions and improved product recovery. While there are many potential sources of leaks, regular maintenance and inspection helps prevent fugitive emissions. When a leak is detected, it should be recorded and fixed as quickly as practical. Meeting the challenges of providing routine monitoring, systematic maintenance in detecting and fixing a leak is a long term win for everyone.
Images: “Arctic Methane Sea Ice” by NASA Earth Observatory