The Effects of Geologically-Realistic Heterogeneity on Stray Gas Migration and Mass Transfer
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Authors
Davidson, Mitchell
Date
2021-11-03
Type
thesis
Language
eng
Keyword
Stray Gas , Mass Transfer , Light Transmission , Hydrogeology
Alternative Title
Abstract
Natural gas production is expected to be sustained until 2030 in North America, with demand rising, in part due to ‘coal-to-gas switching’. Natural gas wells can leak, resulting in stray gas migration, which can be detrimental to the environment. The goal of this research was to investigate stray gas migration and mass transfer in geologically-realistic bed-scale heterogeneity, for the purposes of better conceptualization and improving field-scale modelling and monitoring techniques. This goal was achieved by conducting methane injection and dissolution experiments in a medium scale (39.6 cm × 40 cm × 1.15 cm) quasi-two-dimensional flow cell packed with heterogeneous or homogeneous deposits. Geologically-realistic bed-scale microheterogeneous structures were created using a newly developed modified 3D printer depositional apparatus. Sand packs were assessed for structural similarity to replications of themselves, and replication of gas migration was assessed between and within packs by injecting gas once into five replicate packs and injecting gas five times into a sixth replicate. Gas saturations throughout injection and after relaxation were quantified using the light transmission method (LTM). After gas relaxation, water was pumped through the cell and integrated aqueous samples were collected to measure concentration in time.
The printer-based packing method showed good reproducibility of the geologically realistic microheterogeneous structures (herringbone cross beds). It showed good reproducibility of the macroscopic characteristics of the gas migration structure within the same and between different packs, but at the near-pore scale replication cannot be achieved. LTM results showed that methane migration is significantly impeded by capillary barriers created by heterogeneous deposits, and that the gas storage capacity can be as high as 12.2% of the pore volume at the scale of the flow cell for the heterogeneity configurations tested. Dissolved methane concentrations compared with estimates of source mass showed the rate of mass transfer to be close to a 1-to-1 relationship, and it is less sensitive to initial source mass conditions than has been reported previously for upscaled DNAPL mass transfer due to gas persistence and a reduced change in interfacial area.
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ProQuest PhD and Master's Theses International Dissemination Agreement
Intellectual Property Guidelines at Queen's University
Copying and Preserving Your Thesis
This publication is made available by the authority of the copyright owner solely for the purpose of private study and research and may not be copied or reproduced except as permitted by the copyright laws without written authority from the copyright owner.