Identification and quantification of greenhouse gas emissions from oil and natural gas operations using an aircraft-based mass balance technique

Tegan N Lavoie, Purdue University

Abstract

Rapid advancements in horizontal drilling and hydraulic fracturing techniques have led to a booming natural gas industry. Natural gas is considered a cleaner fuel alternative to coal, producing less carbon dioxide (CO 2) upon combustion per unit energy produced, and therefore has been hailed as a bridge fuel during conversion from fossil fuels to renewable energies for electricity production. The primary component of natural gas is methane (CH4), a potent greenhouse gas with 28 times the global warming potential of CO2 on a 100 year timescale. At oil and natural gas facilities, CH4 leaks are common due to changes in operational modes, scheduled ventings to relieve pressure from equipment, equipment aging, and malfunctions, and it is estimated that a CH4 leak rate of 1.5% of facility throughput is enough to negate the climate benefits incurred by use of natural gas instead of coal. Additionally, the Obama administration has set an aggressive mitigation goal of 26-28% emission reduction by 2025, as compared to 2005 levels. To achieve this target, emission sources must be quickly identified and quantified with high precision and accuracy to best understand where additional controls are required. Here, an aircraft-based measurement technique is used to address this challenge using a high-precision cavity ring-down spectroscopy system to measure atmospheric concentrations of CH4, CO2, and H2O, in conjunction with high-frequency three-dimensional wind measurements and aircraft location tracking from an onboard global positioning and inertial navigation system. Here, an assessment of method accuracy and precision was performed by conducting repeat measurements at a power plant and comparing the calculated CO2 emission rate to the reported hourly emissions measurements made by continuous emissions monitoring systems at the facility. Subsequently, results are presented from a field campaign conducted in the Barnett shale, Texas which quantified CH4 emissions from facilities with atypically large emissions, known as “super-emitters”, and assessed their overall contribution to basin-wide emissions. Calculated emissions were compared to inventory estimates and potential reasons for discrepancies were discussed. Results suggested that super-emitting facilities do not emit at the same rate for extended periods of time, and therefore, their emissions can vary by several orders of magnitude depending on operating conditions. To investigate the degree to which temporal variability of emissions occurs, a separate study was conducted in the Eagle Ford shale, Texas, in which four unique measurement methods were used to conduct repeat measurements at facilities during different operational modes. Results were assessed to suggest potential mitigation strategies that may address this variability to improve national inventories. Finally, a series of measurements were made at natural gas-fired power plants and oil refineries, two facility-types with minimal to no CH4 monitoring requirements due to presumption that they produce negligible CH4 emissions annually. Calculated CH4 and CO2 emission rates were reported and improved emissions factors were presented as an alternative to industry-used emissions factors. Additionally, the source of CH4 emissions was assessed by comparison of CH4 enhancements with combustion- and non-combustion-related enhancements.

Degree

Ph.D.

Advisors

Shepson, Purdue University.

Subject Area

Analytical chemistry|Atmospheric sciences

COinS