Natural Gas Midstream
Emission Inventories from Natural Gas Storage Facilities using Regional Frequency Comb Laser Monitoring and Aircraft Flyovers Last Reviewed
May 2018

DE-FE0029168

Goal
The University of Colorado at Boulder, in collaboration with University of California at Davis, Scientific Aviation, and the National Institute of Standards and Technology (NIST) will quantify emissions from natural gas storage facilities and provide an emissions estimate suitable for the Environmental Protection Agency’s (EPA's) Greenhouse Gas Inventory (GHGI). The measurements include ground-based regional-scale measurements at a variety of storage facilities for extended periods (continuous measurements over multiple months), each using a unique laser technology with minute time resolution and sensitivity to leaks down to 0.1 kg hr-1, together with broad ranging aircraft measurements at those and additional facilities. The campaign will achieve 1) continuous capture of diurnal to seasonal variability of emissions from entire facilities with component-level resolution (e.g. specific compressor, sealed well head, etc. emissions rates), 2) complementary and wide-spread aircraft surveys to assess and characterize the mean seasonal total emissions rates of many different facilities, and 3) combination of the detailed ground based and aircraft measurement data with Large Eddy Simulation transport models for determining emission inventories and reducing uncertainties. The integration of these independent-yet-highly-complementary datasets will provide, for the first time, quantification of the mean state and temporal variability (diurnal to annual) of emissions from natural gas storage.

Performer
University of Colorado, Boulder, CO 80309
University of California, Davis, CA 95616
Scientific Aviation, Boulder, CO 80301
National Institute of Standards and Technology, Boulder, CO 80305; Gaithersburg, MD 20899

Background
Very few research studies have concentrated specifically on quantifying methane emissions from underground natural gas storage wells and fields, which can involve complex infrastructure spread over hundreds or thousands of acres (5-10 square miles). The vast underground gas reservoirs may be connected to dozens of surface access points — for example old well heads in the case of a depleted reservoir field. Each is capable of leaking methane, as are the arrangements of handling equipment and compressor stations located on site. The EPA’s GHGI includes an estimate for underground natural gas storage, but that estimate is limited in scope and based on emissions from compressors. Amidst a climate of increasing scientific and public interest in quantifying the amount of methane lost to the atmosphere along the natural gas supply chain, the storage sector has quickly become recognized as a critically under-studied component. In addition, new state and federal safety regulations for the storage sector are already in process following the recent Aliso Canyon blowout event. An understanding of emissions from this sector will be critical for informed policymaking.

Impact
The project provides a highly cost-effective method for quantifying the entire cross-industry spectrum of underground natural gas storage wells and fields. From a scientific standpoint, this research fills an important gap in knowledge of the midstream natural gas supply chain — the storage sector. The comprehensive nature of the study — covering all important aspects of emissions quantification (total emissions across many fields, time history and variability, and uncertainty analysis) — will create a complete emissions inventory for the sector. Furthermore, the project will have long-term benefits for the environmental impacts of the natural gas storage system by providing important information about leak rates and frequencies, and specific high-risk components in use in the storage sector to operators and policymakers. Finally, this approach is a more cost- and resource-efficient means to quantify methane emissions from underground storage facilities than is currently available, and may represent a new paradigm for emissions studies in other sectors with regional footprints.

Accomplishments (most recent listed first)
The aircraft team is collecting emissions data from underground natural gas storage sites across the U.S. (including Alaska).

The ground-based dual-comb spectrometer was completed, underwent testing at the Table Mountain Test Site 8 km north of Boulder. It was then successfully deployed at the first storage site. The team has demonstrated collection of data from the first storage facility with 100% remote operation.

The inversion/modeling team has performed inversions using data collected from the first storage site concurrent with aircraft mass-balance estimates from the same site.

The team demonstrated the acquisition of time-resolved aircraft- and ground-based data from the first storage site. The team provided time-resolved methane emissions estimates using ground-based and aircraft measurements, which demonstrated the successful integration of all components of the observing network (ground, aircraft, modeling/inversions) at the first storage site.

Operations data has been obtained from facility managers of the first storage site for comparison with measured results of the time variability in emissions rates.

Initial conversations have taken place with a data aggregation group to investigate the feasibility of obtaining injection and withdrawal information for sites being studied with the ground and aircraft systems.

A list of possible EPA representatives has been compiled in anticipation of establishing contact for discussions regarding emissions inventories.

The preparation and development of the micrometeorological instrument package, as well as preparation of a low-rate (~1 Hz) horizontal wind speed measurement instrument that can be used to infer micrometeorological parameters, has been completed. The installation team continues to await FAA approval for installation on the aircraft. In the meantime, the team has developed an alternate method of calculating surface heat fluxes (and thus convective velocity scales) by similar relationships. The team has also developed micrometeorological analysis tools to compare heat fluxes and turbulence statistics between the ground- and aircraft-based systems. Initial comparisons agree well.

Two major publications were released in May 2018, which garnered significant press coverage.

Current Status (May 2018)
A long-running timeseries of atmospheric measurements and inversions has now been obtained at the first storage site. The frequency of aircraft measurements slowed in the winter months due to insufficient convective activity in the lower atmosphere to allow for robust gathering of information regarding gas fluxes from the storage site. Aircraft measurements have increased in frequency in the last month, as convective fluxes that allow for optimal measurement conditions have increased.

Aircraft measurements at sites additional to the first storage site have been momentarily put on hold until a heat flux camera can be obtained for the remote sensing of the percentage of compressor stations operating at a given site. The team is in the process of pricing and selecting a low-cost thermal camera for this purpose. This added tool will allow for the gathering of new information about site activity. This new information is anticipated to be highly relevant to emissions.

Project Start: October 1, 2016
Project End: September 30, 2019

DOE Contribution: $1,323,130
Performer Contribution: $330,773

Contact Information
NETL – Eric Smistad (Eric.Smistad@netl.doe.gov or 832-603-0435)
University of Colorado Boulder – Greg Rieker (greg.rieker@colorado.edu or 303-492-6802)