Anthropogenic and crustal fluxes of methane constrained from groundwater data in shale gas exploration areas of Quebec, Canada

Daniele L. Pinti

GEOTOP research center for geochemistry and geodynamics Département des Sciences de la Terre et de l’Atmosphère, Université du Québec à Montréal, Canada

Homepage

Abstract 

The increasing number of studies on the determination of natural methane in groundwater in shale gas areas offers a unique opportunity for refining the quantification of geological methane emissions. Here methane  fluxes computed  from  four  potential sources  in the  St.  Lawrence  Lowlands,  Quebec (Canada)  are  reported.  Methane  emissions  can  be  caused  by 

1. Groundwater  degassing  by  human abstraction; 
2. Groundwater  discharge  along  springs  or  rivers; 
3. Migration  to  the  surface  by microseepage. In areas where shale gas is extracted by hydraulic fracturing methane emissions can be related also to
4. The degassing of the flowback waters during recovery.

Methane fluxes related to groundwater discharge  surpass those of microseepage and human abstraction . Exploitation of the Utica shale over a 10- to 20-year horizon would emit from one third to 45 times the methane flux from  groundwater  discharge.  Finally,  using  calibration  against  crustal  helium  fluxes,  it  is  estimated that  a  maximum  global  microseepage  methane  flux  of  2  Tg  yr-1  seeps  from  all  exploited  or prospective shale gas areas around the world. This flux is one tenth of that previously estimated in literature (10-25 Tg yr-1) based on field methane flux measurements over oil and gas provinces.