Compared to other climate change solutions, methane mitigation from the oil and gas sector is relatively cheap. Some measures actually save money, when the extra revenue from selling gas that would otherwise be released into the air is factored in. The International Energy Agency estimates that globally, a 75% reduction in oil and gas methane is possible with today’s technology, and a 50% reduction is possible at no net cost. Just a 50% cut would have the same long-term climate impact as closing all the coal plants in China. Many national and sub-national governments have already moved forward with strong oil and gas methane regulations that require mitigation from some or all of these sources. Some of the strongest current regulations can be found in Canada, Colorado, California, and Mexico.
The biggest mitigation opportunities, of course, are the largest emitters. These pages describe some of these large mitigation opportunities. What is the source – what role does the equipment or process that is emitting gas play in the oil and gas industry, and why does it emit? How can it be cleaned up? What other jurisdictions have put programs and rules in place to clean up each source?
- Pneumatic equipment venting
- Compressor seal venting
- Tank venting
- Well completion venting
- Oil well venting and flaring
- Dehydrator venting
Leaks and Improper Venting
A huge portion of emissions from oil and gas arise from leaks – a broad category that includes what we typically think of as a “leak” (that is, gas escaping past a seal that is failing, through a crack or corroded material on a vessel, etc.), in addition to other improper operations and “mistakes” such as valves that are stuck open, hatches that are left open, flares that are unlit, and other problems on site that lead to emissions.
While EPA’s U.S. Emissions Inventory estimates that the oil and gas industry leaks 3 million tons of methane per year (37% of industry emissions), a host of independent, peer-reviewed research has demonstrated that this figure is far too low. In 2018, a study in Science written by twenty-four scientists at sixteen universities and institutions analyzed on-the-ground methane measurements from over 400 wellpads and other facilities across the gas industry, and aircraft based studies of several oil and natural gas production basins; these basins account for over 30% of U.S. natural gas production. Their analysis showed that nationwide methane emissions from the oil and gas industry are actually 60% higher than EPA estimates, and the ‘missing emissions’ are largely due to leaks and improper venting. This means that an enormous quantity of methane – 7.1 million tons – arises from leaks and improper venting. Over the near-term, the methane from these leaks heats our climate as much as 160 coal-fired power plants.
Leaks are widespread, and there is no single cause for these leaks. Thermal or mechanical stresses can degrade seals, as can human error (e.g., improper installation, operation, or maintenance), while normal operations and exposure to weather conditions can wear out equipment over time. Leaks will eventually occur at all oil and gas facilities; failing to fix them in a timely matter is a wasteful and harmful practice that leads to clearly avoidable emissions. The biggest source of these emissions are very large, but uncommon, “super-emitters” which happen due to some improper operation (stuck valve, hatch left open, or unlit flare). Research has demonstrated that super-emitters cannot be predicted, and can occur at any site.
Fortunately, most leaks are straightforward to repair (and fixing leaks is paid for by the value of the gas that is saved by repairing them). Further, finding leaks has become efficient with modern technology. The standard approach today is to use special cameras that can detect infrared light (think of night-vision goggles) which are tuned to make methane, which is invisible to our eyes, visible. They allow inspectors to directly image leaking gas in real time, with the ability to inspect entire components (not just connections and other areas most likely to leak) and pinpoint the precise source, making repair more straightforward. And, technology promises to make this process even more efficient (and cheaper) over the coming years.
These technologies can be utilized to reduce harmful leak emissions, by using regular inspections as the lynchpin of rigorous “leak detection and repair” (LDAR) programs. These programs require operators to regularly survey all of their facilities for leaks and improper emissions, and repair all the leaks they identify in a reasonable time. For example, California requires operators to survey all sites four times a year. Colorado has a different approach, requiring operators of the largest sites to survey them monthly, but requiring less frequent inspections for site with smaller potential emissions.
Pneumatic Equipment Venting
Gas-driven automatic pneumatic equipment uses the pressure energy of natural gas in pipelines to control and operate valves and operate pumps. This approach allows operators to automate equipment at sites without electricity – which is very typical for oil and gas sites in some nations. In these nations, pneumatic equipment is ubiquitous at oil and gas production and compression facilities, and it is designed to vent natural gas to the atmosphere.
Pneumatic valve controllers automatically operate valves based on factors like liquid level in a liquid-gas separator, pressure, or temperature. They can be classified based on whether and how rapidly they vent or “bleed” natural gas and whether they bleed continuously or intermittently (typically only when performing some function). Controllers can either be classified as high-bleed or low-bleed, and it has been demonstrated that the conversion from high- to low-bleed is feasible and cost-effective in almost all cases. However, it has also been shown that controllers specified as “low-bleed” often malfunction, causing emissions that are much higher than than the low-bleed threshold.
Thus, a more effective mitigation strategy is the use of “zero-bleed” controllers , which vent no natural gas, by either utilizing compressed air or electrical power to operate instead of pressurized natural gas, or by capturing for further use the natural gas that would otherwise be vented. Some zero-bleed devices are powered with solar-generated electricity, while others require electricity from the grid or an on-site gas-powered generator, or air compressed with a natural gas-powered engine. Significant methane emission reductions can be achieved by replacing natural gas-driven pneumatic controllers with zero-bleed devices, including at wellsites that are off-the-grid.
Pneumatic pumps use the pressure of natural gas to supply the energy required to circulate and pressurize liquids. For example, they are used to introduce liquid chemicals such as corrosion inhibitors into gas pipelines. Electric pumps, which are often solar-powered, completely eliminate methane emissions and are technically feasible in many locations.
Several jurisdictions have implemented strong standards to reduce emissions from pneumatic controllers and pneumatic pumps. For example, California requires all new pneumatic equipment to be zero emitting, and it requires all existing pumps to emit below the low-bleed threshold. Operators must measure emissions from each device annually to ensure that they are in fact emitting below this threshold. British Colombia also requires that all new pneumatic equipment to be zero emitting, and it also requires zero bleed controllers at all large compressor stations (>3 MW).
Seals on natural gas compressors are a significant source of preventable methane emissions.
Reciprocating compressors use pistons to compress gas. These compressors have seals on the rods that transmit motion from the engine to the pistons inside the high-pressure compressor cylinders; these seals are often referred to as rod packing and are a large source of emissions. Even when new, the seals let some gas escape. Over time they wear, letting more gas out. If not regularly replaced, emissions can become very large: the older the seals are, the more methane they emit. Fortunately, these methane emissions can easily be reduced. First, proper maintenance practices— regular replacement of rod-packing—minimize emissions and should be required. An available additional or alternative approach is to capture gas that escapes from rod packing and utilize it, such as by adding it to the fuel/air mixture for the compressor engine. This can be a superior approach since some gas escapes even from newly installed rod-packing.
Centrifugal compressors use a spinning turbine to pressurize gas. The rapidly rotating main shaft of the compressor is generally sealed with one of two technologies. Wet seals circulate oil to seal the narrow gap between the shaft and its housing. This oil absorbs significant amounts of the high-pressure natural gas that must be removed from the oil before recirculation. Typically, the gas removed from the seal oil is vented, resulting in substantial emissions. Dry seals, in contrast, use a more modern design to avoid the use of seal oil, with much lower emissions. Methane emissions can be cheaply and substantially reduced by requiring centrifugal compressors to use dry seals or to redirect gas that would be vented from a wet-seal compressor back into the pipeline system or another use.
Storage tanks are used to hold oil, condensate, and produced water from oil and gas wells. These wells are usually kept at a high pressure, but oil, water, and other liquids are typically stored at wellsites in tanks held at or near atmospheric pressure. When the liquids are moved from the high-pressure well to the atmospheric-pressure tank, methane and other volatile hydrocarbons that are dissolved in the liquids bubble or “flash” out of the liquid, just as bubbles come out of soda when you take the cap off the bottle, reducing the pressure in the bottle. Many tanks have no controls, so the methane is released into the atmosphere, together with the other volatile hydrocarbons. These other hydrocarbons are potent precursors of regional ozone smog, and they also include toxic air pollutants.
Tanks emissions can be controlled, and the hydrocarbons conserved for sale, by using vapor recovery units – small compressors that are designed to capture these hydrocarbon vapors so that they can be pressurized and sent into a pipeline.
Well Completion Venting
Methane emissions from hydraulically fractured oil and gas wells can be significant. Fortunately, there are low-cost and effective waste mitigation measures for this source. The same Reduced Emissions Completions (REC) approach to gas well completions—whereby operators capture natural gas with specialized equipment and direct it into pipelines, instead of allowing it to escape into the air—can be applied to associated gas produced during oil well completions. RECs reduce methane emissions from both oil and gas wells by more than 95 percent.
Oil Well Production Venting and Flaring
Operators often vent and flare natural gas at oil wells. This waste occurs when oil producers, driven by the rush to sell oil, simply dispose of the gas from producing oil wells instead of building infrastructure (such as pipelines) to capture gas as soon as production begins. (In some cases, pipelines are never built and all of the gas the well produces over its lifetime is wasted in this way, as can be seen in sales records for individual wells available from state regulators.) While a substantial portion of this gas is flared off—wasting energy and producing large amounts of carbon dioxide and other pollutants—some is just dumped into the air, or vented. Even in cases where a gas pipeline is not connected, there are a variety of other technologies that operators can use to reduce associated gas flaring at oil wells.
Venting is even more harmful than flaring, since methane warms the climate so powerfully, and VOC and toxic pollutants are released unabated. Venting of this gas should be prohibited in all cases as an absolutely unnecessary source of harmful air pollution. There are numerous lowcost (and usually profitable) ways to utilize natural gas from oil wells. Flaring should be a last resort: only in the most extreme cases should oil producers be allowed to flare gas, and it should be strictly a temporary measure. Rules prohibiting venting of natural gas can easily reduce emissions by 95 percent.
Dehydrators remove water from the natural gas stream. When emissions from glycol dehydrators, the type most commonly used, are not controlled, the dehydrators vent a large amount of methane and other pollutants. Dehydrators are also large sources of VOC, and particularly large sources of toxic air pollutants. Cleaning up methane from dehydrators will reduce HAP emissions too, with important benefits for air quality. There are a number of approaches to reducing emissions from dehydrator venting, such as adjusting circulation rates of the glycol fluid; routing the vent gas to a burner used to heat the glycol, so methane and toxics are combusted; use of a condenser to capture heavier VOC and toxics from the vent gas (which does not capture methane); and routing emissions to a flare or incinerator.