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

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 (H 2 ) 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 CO 2 , light alkanes, He, and more importantly N 2 . The natural concentration of four gases in Opalinus Clay porewater was evaluated at the experiment location: N 2 2.2 mmol/L ± 25%, CH 4 0.30 mmol/L ± 25%, C 2 H 6 0.023 mmol/L ± 25%, C 3 H 8 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.

Quantitative Monitoring of Dissolved Gases in a Flooded Borehole: Calibration of the Analytical Tools

“…The collected dissolved gases can thereby be transported from the aquifer or the flooded depth borehole via a gas circulation system to different analytical techniques to be analyzed. Besides, the dissolved concentration or the partial pressure of CO2 can also be derived from the pore water ex-situ analysis, e.g., calculated from the measured alkalinity or the total inorganic carbon content using PHREEQC software [8,24]. However, the pore water extraction requires a careful sampling procedure to avoid any sample chemical alteration (due to the contact with the atmosphere for example) which in turn may result in an error of the measured dissolved gas concentration.…”

In situ continuous monitoring of dissolved gases (N2, O2, CO2, H2) prior to H2 injection in an aquifer (Catenoy, France) by on-site Raman and infrared spectroscopies: instrumental assessment and geochemical baseline establishment

“…[46][47][48][49][50][51] The successive developments have aimed to optimize all measurement systems, to simplify experimental protocols, and to establish gas calibration curves for accurate prediction and simulation of gas dissolution, diffusion and transfer in the surrounding geological medias. [52][53][54][55][56][57][58][59][60][61] The most commonly adopted analytical setups for the purpose of in situ, long-term and continuous gas monitoring comprise three modules: specic completion, gas circulation tubing and sensor(s) compartment, installed in a dedicated borehole from the shallow surface down to À600 m deep. 32,50,53,56,57,60,62 Raman and infrared spectrometers have proven to be suitable sensors: these techniques have been constantly developed from the laboratory measurement scale to the continuous eld measurement scale for soil and underground gas monitoring.…”

“…[52][53][54][55][56][57][58][59][60][61] The most commonly adopted analytical setups for the purpose of in situ, long-term and continuous gas monitoring comprise three modules: specic completion, gas circulation tubing and sensor(s) compartment, installed in a dedicated borehole from the shallow surface down to À600 m deep. 32,50,53,56,57,60,62 Raman and infrared spectrometers have proven to be suitable sensors: these techniques have been constantly developed from the laboratory measurement scale to the continuous eld measurement scale for soil and underground gas monitoring. 32,50,60 The two techniques are complementary (at similar cost) as Raman spectroscopy can detect a lot of gases (e.g.…”

“…32,50,53,56,57,60,62 Raman and infrared spectrometers have proven to be suitable sensors: these techniques have been constantly developed from the laboratory measurement scale to the continuous eld measurement scale for soil and underground gas monitoring. 32,50,60 The two techniques are complementary (at similar cost) as Raman spectroscopy can detect a lot of gases (e.g. N 2 , O 2 , CO 2 , CH 4 and H 2 ) but with a low sensitivity while only CH 4 and CO 2 can be detected by infrared spectroscopy but with higher sensitivity.…”

Development of quantitative detection method for mass spectrometry coupled to an infrared laser spectroscope (Picarro) to monitor in nitrogen matrix a complex gas mixture of H2, He, CO, N2, Ne, O2, Ar, CO2, H2S, CH4, C2H4, C2H6, C3H6, C3H8, i‐C4H10, n‐C4H10, and C5H12

“…However, its spectral range is limited, and the results depend on the gas matrix used. 14 In URL, nonoptical techniques such as MS 4,5 and GC 1,3,7,8 are used for measuring the partial pressures of CO 2 , H 2 , CH 4 , N 2 , O 2 , and noble gases. Cailteau et al 6 used FTIR and nondispersive infrared (NDIR) spectroscopy technique to measure the atmospheric trace species (CO 2 , CH 4 ) under URL conditions.…”