Natural gas extraction and artificial gas injection experiments in Opalinus Clay, Mont Terri rock laboratory (Switzerland)

Agnès Vinsot,Philippe De Donato,Pierre De Cannière,Catherine Lerouge,Mélanie Lundy,C Anthony J Appelo,Stefan Wechner,Cristelle Cailteau-Fischbach,Jacques Pironon,Yanick Lettry

doi:10.1007/s00015-016-0244-1

Abstract

Two experiments have been installed at Mont Terri in 2004 and 2009 that allowed gas circulation within a borehole at a pressure between 1 and 2 bar. These experiments made it possible to observe the natural gases that were initially dissolved in pore-water degassing into the borehole and to monitor their content evolution in the borehole over several years. They also allowed for inert (He, Ne) and reactive (H2) gases to be injected into the borehole with the aim either to determine their diffusion properties into the rock pore-water or to evaluate their removal reaction kinetics. The natural gases identified were CO2, light alkanes, He, and more importantly N2. The natural concentration of four gases in Opalinus Clay pore-water was evaluated at the experiment location: N2 2.2 mmol/L ± 25%, CH4 0.30 mmol/L ± 25%, C2H6 0.023 mmol/L ± 25%, C3H8 0.012 mmol/L ± 25%. Retention properties of methane, ethane, and propane were estimated. Ne injection tests helped to characterize rock diffusion properties regarding the dissolved inert gases. These experimental results are highly relevant towards evaluating how the fluid composition could possibly evolve in the drifts of a radioactive waste disposal facility.

Highlights

Opalinus Clay pore-water contains dissolved natural gases: N2, CO2, CH4 and other light alkanes, He and other noble gases
The composition monitoring of the gas circulating in boreholes BPC-C1 and BHT-1 showed the inflow of N2, light alkanes up to C6 and CO2
Two gas circulation experiments in Opalinus Clay at Mont Terri, that have been monitored for 12 and 7 years respectively, made it possible to evaluate the chemical and carbon isotopic compositions of the natural gases dissolved in the pore-water

Summary

Introduction

Opalinus Clay pore-water contains dissolved natural gases: N2, CO2, CH4 and other light alkanes, He and other noble gases. CO2 is of key interest regarding the understanding of the processes that control the pore-water composition (Gaucher et al 2009; Pearson et al 2011; Tournassat et al 2015) and He data enables to characterize transport properties of solutes within Opalinus Clay rock (Rubel et al 2002; Mazurek et al 2011). Data regarding dissolved gas concentration distribution in Opalinus Clay may give some insight on both transport properties of solutes in this argillaceous rock and processes that control the pore-water composition. Data interpretation meets broader research topics on the relationships between their chemical and isotopic composition and the questions about their origin along with the kinetics associated to their production, their potential migration paths, their potential retention properties on clay minerals etc. Data interpretation meets broader research topics on the relationships between their chemical and isotopic composition and the questions about their origin along with the kinetics associated to their production, their potential migration paths, their potential retention properties on clay minerals etc. (Prinzhofer and Pernaton 1997; Zhang and Krooss 2001; Sherwood Lollar et al 2008; Prinzhofer et al 2009; McCollom et al 2010; Stolper et al 2015)

Results

Discussion

Conclusion