Pneumatic Vent Gas Measurement

Brian Van Vliet (P. Eng), Spartan Controls

April 24, 2018


Executive Summary

Air emission inventories are becoming an increasingly important method of monitoring and reporting on industry emissions, for the public, governments and individual companies. Governments are using emission inventories to negotiate international treaties, establish air emissions policy measures and targets and develop emission forecasts. It is important that upstream oil and gas operators have access to effective emission monitoring technologies and, more importantly, emissions factors obtained from adequate quantity and duration field measurements. Reported facility emission reductions are more realistic when tracked using standardized methodologies and accurate emission factors with low uncertainty. Inaccurate emission factors can result in an imprecise portrayal of the emission profile of pneumatic devices used in the oil and gas industry. Pneumatic efficiency is a key focus area specific to chemical injection pumps and instruments used at upstream oil and gas sites. Clear targets and means of de‐risking expected emission reductions with equipment retrofits are key to enabling vented methane reductions in the field.

The development of technically defensible and effective emission management policies and regulations is reliant upon good quality emission data. Analysis of high quality data identifies potential opportunities for emission reductions and can be used to quantify industry Greenhouse Gas (GHG) performance as well as track emission reductions achieved. There are opportunities in the upstream oil and gas sector for improvements in emission data quantification (emission factors, measurement technologies and methodologies), monitoring, data management and reporting.  The goal of this study was to establish more accurate and repeatable means for determining emissions from pneumatic devices including chemical injection pumps and instruments.

Industry benefits from field verified emission factors that can be applied for equipment retrofits.  Most current measurement techniques focus on measuring the amount of gas vented from, not supplied to, a pneumatic device. Measuring the upstream pneumatic supply does not impact device performance nor cause pneumatic device backpressure, which are a source of error in the current published data sets.  The data is also not subject to error if the case of the pneumatic device is not pressure containing. The enhanced‐Measurement Emission Accuracy Solution (eMEASTM) quantified the volume consumed by measuring pressure reduction with temperature compensation from a known volume, pressure, temperature and quality gas. Better quantification of current methane emission rates from pneumatic devices, as well as the reduction and associated carbon dioxide equivalent (CO2e) after retrofit, has a direct monetary impact on operations.  Establishing better margin of error on positive displacement measurement emission rates published to date reduced the risk associated with emission uncertainty for such retrofits and provided a better level of certainty on measurements made and presented in published reports.

The e-MEASTM measurements obtained also achieved better quantification of dynamic, transient and static emission contributions. This analysis provided insight into the amount of pneumatic gas consumed beyond steady state instrument vent rates. Specific to level controllers, quantifying the dynamic vent contribution drew attention to the potential additional volume available for GHG offset credits beyond steady state vent rate reductions. This is of importance in Alberta, Canada because about 40 percent of pneumatic instruments in service at upstream oil and gas sites are level controllers (GreeenPath Energy Ltd., 2017) and those devices are currently considered pneumatically efficient. Focus on vent reductions for these devices provides opportunity for greater than 0.5Mt CO2e per year in vented methane reductions in Alberta.

Current regulations are focused on emissions specific to a low vent steady state threshold of 0.17 meters cubed per hour (m3/hr.) or six standard cubic feet per hour (scfh). The emissions from pneumatic devices are more than just steady state. The steady state rate of gas consumption is not a good predictor of the total gas consumption as shown in (Allen, et al., 2015) and (Prasino Group, 2013). Consequently, the total consumption of a given control loop can be optimized by improving more than just steady state consumption. There are few details on just how to optimize pneumatic efficiency because the consumption in a pneumatic control loop, attributed to the final control element, is difficult to segment from the instrument. Furthermore, the pneumatic device’s contribution to the total emission in the dynamic state is not well understood. By trending the gas consumption, the static and dynamic components of gas use for a pneumatic device could be separated. Giving consideration for the dynamics in a control loop provided reference for determining the uncertainty associated with a given emission factor. By gaining a detailed understanding of the dynamic gas consumption of pneumatic devices, it is possible for policy makers to implement outcome‐based GHG regulations that are both practical and achievable. This study provides both producers and regulators with the necessary tools to better quantify GHG reductions from pneumatic devices.


Main Body of Report

Technical Appendices

Full Report

Best Management Practices

# 17-ARPC-06 / 18-ARPC-04