Natural gas migration to the near-surface environment as an analogue to potential leakage of CO2—detection and mechanisms

Author(s):  
B SCHROOT ◽  
R HEGGLAND
Author(s):  
J. H. Redding

AbstractBy the end of 1986, over 400 km of high pressure (70 bar) natural gas pipeline will have been constructed in the Irish Republic, much of it laid in sparsely populated rural areas where topography, hydrology, near surface geology and ground conditions can significantly influence construction feasibility and cost. Identifying, quantifying and (where possible) avoiding areas of potential difficulty or hazard are aspects of route selection to which engineering geology can make an important contribution. This contribution is discussed in relation to the Cork-Dublin pipeline completed in 1982, and the Limerick, Waterford and Mallow lines due for completion this year. In particular, the application and merits of stereo aerial photographic interpretation, superficial geological mapping and field study are outlined, together with the use of more traditional methods of site investigation. Attention is focussed on indigenous engineering geological problems associated with shallow rock, limestone karst, peat bog and poorly drained alluvial and morainic soils. Data acquisition and presentation are discussed within the overall context of civil engineering contract preparation and administration. The usefulness of this approach, particularly for predicting and minimising construction costs, forestalling claims and generally facilitating on-site supervision, is emphasised.


2018 ◽  
Author(s):  
Haoyi Yao ◽  
Wei-Li Hong ◽  
Giuliana Panieri ◽  
Simone Sauer ◽  
Marta E. Torres ◽  
...  

Abstract. We report on a rare observation of a mini-fracture in near-surface sediments (30 cm below the seafloor) visualized using rotational scanning X-ray of a core recovered from the Lomvi pockmark, Vestnesa Ridge west of Svalbard (1200 m water depth). Porewater geochemistry and lipid biomarker signatures revealed clear differences in the geochemical and biogeochemical regimes of this core compared with two additional ones recovered from pockmarks sites at Vestnesa Ridge, which we attribute to differential methane transport mechanisms. In the sediments core featuring the shallow mini-fracture at pockmark Lomvi, we observed high concentrations of both methane and sulfate throughout the core in tandem with moderately elevated values for total alkalinity, 13C-depleted dissolved inorganic carbon (DIC), and 13C-depleted lipid biomarkers (diagnostic for the slow-growing microbial communities mediating the anaerobic oxidation of methane with sulfate – AOM). In another core recovered from the same pockmark about 80 m away from the fractured core, we observed complete sulfate depletion in the top centimeters of the sediment and much more pronounced signatures of AOM than in the fractured core. Our data indicate a gas advection-dominated transport mode in both cores facilitating methane migration into sulfate-rich surface sediments. However, the more moderate expression of AOM signals suggest a rather recent onset of gas migration at the site of the fractured core, while the geochemical evidence for a well-established AOM community at the second coring site at the Lomvi pockmark suggest that gas migration has been going on for a longer period of time. A third core recovered from Lunde pockmark was dominated by diffusive transport with only weak geochemical and biogeochemical evidence for AOM. Our study highlights that advective fluid and gas transport supported by mini-fractures can be important in modulating methane dynamics in surface sediments.


2018 ◽  
Vol 123 (7) ◽  
pp. 4930-4969 ◽  
Author(s):  
P. Ola G. Persson ◽  
Byron Blomquist ◽  
Peter Guest ◽  
Sharon Stammerjohn ◽  
Christopher Fairall ◽  
...  

2019 ◽  
Vol 123 (14) ◽  
Author(s):  
Dolev Bluvstein ◽  
Zhiran Zhang ◽  
Claire A. McLellan ◽  
Nicolas R. Williams ◽  
Ania C. Bleszynski Jayich

1995 ◽  
Vol 68 (1) ◽  
Author(s):  
S. Manton ◽  
T. Johnstone ◽  
D. Trivedi ◽  
S. M. A. Hoffmann ◽  
P.N. Humphreys

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