00 The Alternative Hypothesis Of Gas Chimney Formations In Hanging Walls – Fluid Migrations Along Pre-Existing Vertical Fractures - Fluid Venting System - Hydrocarbon Leakage Indicators
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Ho, Sutieng 2013. Evolution of complex vertical successions of fluid venting systems during continental margin sedimentation. PhD Thesis, Cardiff University.            
Official copyright matieral - Ho et al. 2018
httpss://doi.org/10.5194/se-9-1437-2018-supplement
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The Alternative Hypothesis Of Gas Chimney Formations In Hanging Walls – Fluid Migrations Along Pre-Existing Vertical Fractures
in Section 5.2.4. of
«Formation of linear planform chimneys controlled by preferential hydrocarbon leakage and anisotropic stresses in faulted fine-grained sediments, Offshore Angola»


Sutieng Ho, Martin Hovland, Jean-Philippe Blouet, Andreas Wetzel , Patrice Imbert, Daniel Carruthers
2018


We suggest an alternative mechanism for the formation of chimneys; "apart from overpressured fluid (gas) creating new fractures, overpressured gas may also pass through, filling pre-existing sub-vertical cracks/fractures in the hanging wall bottoms along the main fault surface (see fig. 2 in Gaffney et al., 2007). Pre-existing vertical fractures in hanging walls originating from the movements of normal faults have been previously demonstrated by analogue models of van Gent et al. (2010). Fluids may open and extend pre-existing sub-vertical cracks/fractures in the hanging wall only if the pressure required for the fluid entering the hanging wall fractures is less than the one for creating a new fracture (Gaffney et al., 2007)", as published in Section 5.2.4 in the initial version of Ho et al. May 2018 and the final version of Ho et al. December 2018.




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Cited figures and references in section 5.2.4.
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  • Figures below redrawn based on figure 2a-b in Gaffney et al. (2007), show the hypothesis of Gaffney et al. (2007) that overpressured fluid intruded and used the pre-existing fractures in hanging wall to migrate vertically upward, hence the vertical expansion/extension of the fractures forming vertical fluid chimneys.



  • Figure below modified from figure 9f in van Gent et al. (2010) shows vertical fractures formed in the hanging wall due to normal faults movements.
In van Gent et al. (2010) multiple smaller fractures occurring in the hanging wall are demonstrated to evolve into segmented fault arrays afterwards.
 
See also their Youtube video httpss://www.youtube.com/watch?v=MmgYBsHuVHk
References
 
Gaffney, E. S., Damjanac, B., & Valentine, G. A. (2007). Localization of volcanic activity: 2. Effects of pre-existing structure. Earth and Planetary Science Letters, 263(3-4), 323-338.
 
van Gent, H. W., Holland, M., Urai, J. L., & Loosveld, R. (2010). Evolution of fault zones in carbonates with mechanical stratigraphy–Insights from scale models using layered cohesive powder. Journal of Structural Geology, 32(9), 1375-1391.

Key words: Sutieng Ho pockmark Sutieng Ho gas chimney seismic Sutieng Ho polygonal fault Sutieng Ho methane authigenic carbonate Sutieng Ho Lower Congo Basin Angola