Begin with the end in mind. You’ve probably heard it before. It’s one of Stephen Covey’s Seven Habits of Highly Effective People. When your target is minimizing methane emissions, design is where you begin. Using a proactive low emissions design for new facilities provides the fundamental basis for minimizing emissions and ultimately, the best end result. With existing facilities, a review of design will identify important changes that are needed to reach your target.
No matter what segment of the natural gas value chain, dealing effectively with methane emissions is vital to the future of this important energy source. Achieving the lowest levels of methane emissions starts with a design that incorporates equipment, systems and technologies to minimize the release of natural gas, maximize its capture and return that gas to the system for use or sale. Design sets the basis for one of the key factors in determining expected emissions intensity.
Design, combined with a culture of low emissions, can position your company as a leader in low methane intensity.
Each sector, from production through distribution, uses different types of equipment that may be a source of methane emissions. Each also operates under different conditions (weather, temperature, availability of power) which vary the economics of equipment selection not only across sectors but also for the same sector in different regions. Even with those differences, establishing a target of low emissions provides a basis for design decisions and selection of equipment that will reduce the methane emitted. Design determines the number of devices that are potential sources of emissions and the level of emissions expected (emission factor), which impact the calculated emissions level and emissions intensity.
Designing for minimum emissions includes understanding the potential sources, both planned and unplanned, considering tools available to minimize or prevent emissions, evaluating the economics of implementing solutions and making decisions based on the value of action. Some common sources of emissions include flanges, pneumatic controllers, valve leakage, rod packing, compressor seals, flash gas management, storage tank vents, equipment blowdown, dehydrator vents and liquid unloading. Each of these sources of emissions can be minimized through different processes, technologies and operating practices.
The complex system of equipment and controls that are used in oil and gas production and delivery can be evaluated by potential emissions source when designing a low emissions system:
1. What are the potential sources of methane emissions?
2. What options are available for reducing or eliminating emissions for a single source?
a. What is the cost of the potential solution?
b. What are the benefits from each alternative?
c. Are there interactions between sources to be considered?
3. Can solutions be combined to reduce cost?
4. What are the maintenance costs to keep equipment operating as originally designed?
5. Would a broader system solution be more cost effective?
Consider the example of pneumatic controllers, one common source of methane emissions frequently used for operational control in oil and gas operations, including upstream, gathering and processing and transmission pipeline systems. These controls are powered through use of natural gas pressure and emit small amounts of methane during normal operation. Because there are a large number of these devices in use, they can represent one of the larger sources of cumulative methane emissions.
There are several options for minimizing or eliminating emissions from pneumatic controllers. The lowest cost option most frequently used is intermittent controllers that release gas to the atmosphere only on actuation. The level of emissions in this case is dependent on the frequency of actuation. An alternative is to use continuous vent low-bleed controllers to minimize the gas released during higher frequency operations. While these choices can help, the range of emissions can vary and, in some cases, may be much higher than expected. Maintenance is a critical factor, as poorly maintained equipment can emit much higher levels of methane than new or properly maintained equipment. For this reason, it’s important that monitoring programs include a check for excessive emissions from pneumatic controls.
Another option is to use a power source other than natural gas, through the installation of a compressed air system to provide the pneumatic pressure needed. This eliminates the release of methane, but adds additional equipment requiring maintenance. Installation of electrically actuated controllers can also eliminate this source of emissions, although the initial cost of these controllers may be higher than pneumatics and requires a reliable source of power. Mechanical controls can be used for some applications and don’t require pneumatics or electrical power. For example, in tank applications an internal float can operate a mechanical lever to actuate a valve to maintain a desired level. For each alternative the costs to be considered include the initial equipment cost, operation and maintenance cost (or savings) and the savings from reduction in emissions.
Finally, , a broad system approach to design can be considered such as centralizing facilities to eliminate well-site equipment and shifting certain processing and storage to a central location. This approach can reduce the controls needed at each location and shift requirements to a larger central facility reducing the overall equipment required. Some companies have taken this approach with tankless, reduced emissions site design. Through careful design both the calculated and actual emissions can be reduced, helping to achieve the objective to minimize methane emitted to the atmosphere.
Changes in the design for controls impacts the calculation of expected methane emissions for GHG reporting. These calculations include a device count (number of emission sources), application of an emissions factor specific to the source and (for some devices) applying an activity factor representing a frequency of emission. The use of intermittent or low-bleed pneumatic devices or a non-emitting alternative result in a smaller emission factor or zero emissions associated with these devices in the calculation of expected emissions. Through careful design both the calculated and actual emissions can be reduced, helping to achieve the objective to minimize methane emitted to the atmosphere.
Beginning with a low methane emissions design, combined with a culture of environmental excellence will position your company as a leader in delivering natural gas that is responsibly produced for the future. Effective programs for detection, measurement and data analytics provide the remaining keys to effective methane management.