Reviewer comment on “Analysis of deformation bands associated with the Trachyte Mesa intrusion, Henry Mountains, Utah: implications for reservoir connectivity and fluid flow around sill intrusions” by Penelope I. R. Wilson et al.

Abstract. Shallow-level igneous intrusions are a common feature of many sedimentary basins, and there is increased recognition of the syn-emplacement deformation structures in the host rock that help to accommodate this magma addition. However, the sub-seismic structure and reservoir-scale implications of igneous intrusions remain poorly understood. The Trachyte Mesa intrusion is a small (~ 1.5 km2), NE–SW trending satellite intrusion to the Oligocene-age Mount Hillers intrusive complex in the Henry Mountains, Utah. It is emplaced within the highly porous, aeolian Entrada Sandstone Formation (Jurassic), producing a network of conjugate sets of NE–SW striking deformation bands trending parallel to the intrusion margins. The network was characterized by defining a series of nodes and branches, from which the topology, frequency, intensity, spacing, characteristic length, and dimensionless intensity of the deformation band traces and branches were determined. These quantitative geometric and topological measures were supplemented by petrological, porosity and microstructural analyses. Results show a marked increase in deformation band intensity and significant porosity reduction with increasing proximity to the intrusion. The deformation bands are likely to impede fluid flow, forming barriers and baffles within the Entrada reservoir unit. A corresponding increase in Y- and X- nodes highlights the significant increase in deformation band connectivity, which in turn will significantly reduce the permeability of the sandstone. This study indicates that fluid flow in deformed host rocks around igneous bodies may vary significantly from that in the undeformed host rock. A better understanding of the variability of deformation structures, and their association with intrusion geometry, will have important implications for industries where fluid flow within naturally fractured reservoirs adds value (e.g. hydrocarbon reservoir deliverability, hydrology, geothermal energy and carbon sequestration).

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Analysis of deformation bands associated with the Trachyte Mesa intrusion, Henry Mountains, Utah: implications for reservoir connectivity and fluid flow around sill intrusions

Solid Earth ◽

10.5194/se-12-95-2021 ◽

2021 ◽

Vol 12 (1) ◽

pp. 95-117

Author(s):

Penelope I. R. Wilson ◽

Robert W. Wilson ◽

David J. Sanderson ◽

Ian Jarvis ◽

Kenneth J. W. McCaffrey

Keyword(s):

Fluid Flow ◽

Host Rock ◽

Deformation Band ◽

Seismic Structure ◽

Deformation Bands ◽

Hydrocarbon Reservoir ◽

Deformation Structures ◽

Porosity Reduction ◽

Igneous Intrusions ◽

Henry Mountains

Abstract. Shallow-level igneous intrusions are a common feature of many sedimentary basins, and there is increased recognition of the syn-emplacement deformation structures in the host rock that help to accommodate this magma addition. However, the sub-seismic structure and reservoir-scale implications of igneous intrusions remain poorly understood. The Trachyte Mesa intrusion is a small (∼1.5 km2), NE–SW trending satellite intrusion to the Oligocene-age Mount Hillers intrusive complex in the Henry Mountains, Utah. It is emplaced within the highly porous, aeolian Entrada Sandstone Formation (Jurassic), producing a network of conjugate sets of NE–SW striking deformation bands trending parallel to the intrusion margins. The network was characterized by defining a series of nodes and branches, from which the topology, frequency, intensity, spacing, characteristic length, and dimensionless intensity of the deformation band traces and branches were determined. These quantitative geometric and topological measures were supplemented by petrological, porosity and microstructural analyses. Results show a marked increase in deformation band intensity and significant porosity reduction with increasing proximity to the intrusion. The deformation bands are likely to impede fluid flow, forming barriers and baffles within the Entrada reservoir unit. A corresponding increase in Y- and X-nodes highlights the significant increase in deformation band connectivity, which in turn will significantly reduce the permeability of the sandstone. This study indicates that fluid flow in deformed host rocks around igneous bodies may vary significantly from that in the undeformed host rock. A better understanding of the variability of deformation structures, and their association with intrusion geometry, will have important implications for industries where fluid flow within naturally fractured reservoirs adds value (e.g. hydrocarbon reservoir deliverability, hydrology, geothermal energy and carbon sequestration).

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Chemical bleaching indicates episodes of fluid flow in deformation bands in sandstone

AAPG Bulletin ◽

10.1306/b282ef9c-1e90-445d-99e78723c1eb9c77 ◽

2004 ◽

Vol 88 ◽

Author(s):

W. T. Parry, Marjorie A. Chan, and

Keyword(s):

Fluid Flow ◽

Deformation Bands

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Structural control on fluid flow and shallow diagenesis: insights from calcite cementation along deformation bands in porous sandstones

Solid Earth ◽

10.5194/se-11-2169-2020 ◽

2020 ◽

Vol 11 (6) ◽

pp. 2169-2195

Author(s):

Leonardo Del Sole ◽

Marco Antonellini ◽

Roger Soliva ◽

Gregory Ballas ◽

Fabrizio Balsamo ◽

...

Keyword(s):

Fluid Flow ◽

Structural Control ◽

Control Flow ◽

Porous Rocks ◽

Deformation Bands ◽

Seismic Resolution ◽

Porous Sandstone ◽

Reservoir Compartmentalization ◽

Porosity And Permeability ◽

And Control

Abstract. Porous sandstones are important reservoirs for geofluids. Interaction therein between deformation and cementation during diagenesis is critical since both processes can strongly reduce rock porosity and permeability, deteriorating reservoir quality. Deformation bands and fault-related diagenetic bodies, here called “structural and diagenetic heterogeneities”, affect fluid flow at a range of scales and potentially lead to reservoir compartmentalization, influencing flow buffering and sealing during the production of geofluids. We present two field-based studies from Loiano (northern Apennines, Italy) and Bollène (Provence, France) that elucidate the structural control exerted by deformation bands on fluid flow and diagenesis recorded by calcite nodules associated with the bands. We relied on careful in situ observations through geo-photography, string mapping, and unmanned aerial vehicle (UAV) photography integrated with optical, scanning electron and cathodoluminescence microscopy, and stable isotope (δ13C and δ18O) analysis of nodules cement. In both case studies, one or more sets of deformation bands precede and control selective cement precipitation. Cement texture, cathodoluminescence patterns, and their isotopic composition suggest precipitation from meteoric fluids. In Loiano, deformation bands acted as low-permeability baffles to fluid flow and promoted selective cement precipitation. In Bollène, clusters of deformation bands restricted fluid flow and focused diagenesis to parallel-to-band compartments. Our work shows that deformation bands control flow patterns within a porous sandstone reservoir and this, in turn, affects how diagenetic heterogeneities are distributed within the porous rocks. This information is invaluable to assess the uncertainties in reservoir petrophysical properties, especially where structural and diagenetic heterogeneities are below seismic resolution.

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Microstructure and fluid flow in rift border fault-bounded basins – insights from the Dombjerg Fault, NE Greenland

10.31223/x5fp57 ◽

2021 ◽

Author(s):

Eric Salomon ◽

Atle Rotevatn ◽

Thomas Kristensen ◽

Sten-Andreas Grundvåg ◽

Gijs Henstra

Keyword(s):

Fluid Flow ◽

Chemical Reduction ◽

Pore Space ◽

Hanging Wall ◽

Structural Deformation ◽

Tectonic Activity ◽

Deformation Bands ◽

Fracture Formation ◽

Rock Alteration ◽

Fluid Flow Regimes

In this contribution, we elucidate the interaction of structural deformation, fluid flow, and diagenesis in hanging wall siliciclastic deposits along rift basin-bounding faults, exemplified at the Dombjerg Fault in NE Greenland. Due to fault-controlled fluid circulation, fault-proximal syn-rift clastic deposits experienced pronounced calcite cementation and became lithified, whereas uncemented clastic deposits remained porous and friable. Correspondingly, two separate deformation regimes developed to accommodate continuous tectonic activity: discrete fractures formed in cemented deposits, and cataclastic deformation bands formed in uncemented deposits. We show that deformation bands act as partial baffles to fluid flow. This led to localized host rock alteration, which caused a chemical reduction of pore space along the bands. Where cemented, porosity was reduced towards zero and fracture formation created new pathways for fluid migration, which were subsequently filled with calcite. Occasionally, veins comprise multiple generations of microcrystalline calcite, which likely precipitated from an abruptly super-saturated fluid that was injected into the fracture. This suggests that cemented deposits sealed uncemented deposit bodies in which fluid overpressure was able to build up. We conclude that compartmentalized fluid flow regimes may form in rift fault-bounded basins, which has wide implications for assessments of potential carbon storage, hydrocarbon, groundwater, and geothermal sites.

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