The Potential of Greenhouse Gas Emission During Flowback Process in Weiyuan Shale Production Site, China

Abstract Objectives/Scope: Greenhouse gas emission (carbon dioxide and methane, etc.) during shale gas production could decide whether it is a cleaner energy source than coal. However, the methane and carbon dioxide emission from flowback process during shale gas production remains unclear. The withdrawn of fracture water both from underground and surface water, and the relatively high gas pressure from the wellhead have made flowback water highly potential as a significant greenhouse gas emission source. Methods, Procedures, Process: In this study, the estimation of greenhouse emission potential was provided based on the flowback water samples collected from shale production sites of China. The buffer capacity of carbon dioxide was estimated based on the parameters measured including temperature, pressure, conductivity, salinity, dissolved inorganic carbon (DIC), pH, chloride etc. The possible methane emission was also estimated based on the solution/dissolution curve from gas-water equilibrium during the flowback process. Results, Observations, Conclusions: The results showed that: the relatively high salinity of the flowback water has provided a considerable buffer capacity for carbon dioxide. The water residence time in the water tank/pond largely determines air-water greenhouse flux. When the flowback water pass through the three-phase separator to the water outlet, the dissolution capacity of methane reduced sharply dropped. By switching to a higher water level in the separator, methane emission could be reduced. However, a higher water vapor ratio may be detected in the gas phase, as well. Besides the fugitive methane emission from pneumatic pumps, valves, etc., greenhouse gas emission from flowback water is a significant source which needs to be reduced in future shale gas production. Novel/Additive Information: The determination of greenhouse gas emission from flowback could better defined the life cycle of shale gas, while provide baseline analysis for the development of greenhouse gas control technology during flowback water treatment and three-phase separator optimization.