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 study also demonstrates and tests a low-cost emissions monitoring system that may help industry drastically lower cost for leak detection and repair. 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 used for determining emission inventories and reducing uncertainties. The integration of these independent-yet-highly-complementary datasets will, for the first time, provide quantification of the mean state and temporal variability (diurnal to annual) of emissions from natural gas storage. 

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

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 compressor stations and arrangements of handling equipment 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 2015 Aliso Canyon blowout event. An understanding of emissions from this sector will be critical for informed policymaking.

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 monitoring by industry.

The aircraft team has finished collecting emissions data from underground natural gas storage sites across the U.S. (including Alaska). In all, 29 unique underground natural gas storage facilities were flown for mass balance estimation of emissions.

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. Publications have been submitted to Environmental Science & Technologies and Environmental Research Letters and as of the time of writing are under peer review.

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. Detailed operations information was collected directly from the operator of the first storage site. A new collaboration has begun with researchers at the Harvard T.H. Chan School of Public Health to explore relationships between well integrity (Harvard dataset) and emissions (our dataset). 

A list of possible EPA representatives has been compiled in anticipation of establishing contact for discussions regarding emissions inventories. A meeting has taken place to present emissions data to representatives from the EPA, DOE and NETL. The exploration of possible additional auxiliary data (e.g. equipment counts) has been started. 

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. FAA approval for the instrument was granted. Flights with the instrument showed validation of the methodology. 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. Comparisons agree well. 

Two major publications were released in May 2018, which garnered significant press coverage.
One year of measurements with both the ground- and aircraft-based systems has now been completed at storage site 1. Operations data for the same time period have been shared with the team by the operator, so that analysis of emissions and operations events can begin.

Deployment at storage site 2 is underway, with key field components in place and operator agreements finalized, and monitoring has begun. New optical components have been tested and implemented to increase the flexibility and scope of the system. Monitoring has uncovered a pattern of emissions related to the change-over of the withdrawal to injection season. The team has initiated a request for operations data. 

The team has field-tested and purchased a heat-sensing camera for the purpose of airborne analysis of compressor activity during aircraft mass balance flights. Heat-sensing cameras were used in many if not most of the additional flights performed during the project period.

A database documenting the spatial extents of underground natural gas storage facilities in the U.S. has been compiled for use in guiding aircraft flight patterns during mass balance flights. 

Large-eddy simulation (LES) modeling has been completed for validation and testing of instrument comparison in model simulations. An initial publication is in preparation for submission to Monthly Weather Review. Submission to the journal is expected in June or July of 2020. A second publication will directly follow, offering full analysis of aircraft and ground-based measurement systems intercompatibility and individual/collective ranges of uncertainty.

 The team continues to collect ground-based DCS Observing System data at Storage Site 2. Data analysis of aircraft- and ground-based data continues, in preparation for final publications. 

$1,323,130

$330,773

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)