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Permeability heterogeneity of sandstone intrusion fluid-escape systems, Panoche Hills, California: Implications for sedimentary basins globally

Permeability heterogeneity of sandstone intrusion fluid-escape systems, Panoche Hills, California: Implications for sedimentary basins globally
Permeability heterogeneity of sandstone intrusion fluid-escape systems, Panoche Hills, California: Implications for sedimentary basins globally
Natural surface gas seeps provide a significant input of greenhouse gas emissions into the Earth’s atmosphere and hydrosphere. The gas flux is controlled by the properties of underlying fluid-escape conduits, which are present within sedimentary basins globally. These conduits permit pressure-driven fluid flow, hydraulically connecting deeper strata with the Earth’s surface; however they can only be fully resolved at sub-seismic scale. Here, a novel minus-cement-and-matrix permeability method using 3D X-ray micro-CT imaging enables the improved petrophysical linkage of outcrop and sub-surface data. The methodology is applied to the largest known outcrop of an inactive fluid-escape system, the Panoche Giant Intrusion Complex in Central California, where samples were collected along transects of the 600-800 m stratigraphic depth range to constrain porosity and permeability spatial heterogeneity. The presence of silica cement and clay matrix within the intergranular pores of sand intrusions are the primary control of porosity (17-27 %) and permeability (≤ 1 to ~500 mD) spatial heterogeneity within the outcrop analogue system. Following the digital removal of clay matrix and silica (opal-CT and quartz) cement derived from the mudstone host strata, the sand intrusions have porosity-permeability ranges of ~30-40 % and 103-104 mD. These calculations are closely comparable to active sub-surface systems in sedimentary basins. Field observations revealed at decreasing depth, the connected sand intrusion network reduces in thickness and becomes carbonate cemented, terminating at carbonate mounds formed from methane escape at the seafloor. A new conceptual model integrates the pore-scale calculations and field-scale observations to highlight the key processes that control sand intrusion permeability, spatially and temporally. The study demonstrates the control of matrix and cement addition on the physical properties of fluid-escape conduits, which has significance for hydrocarbon reservoir characterisation and modelling, as well as subsurface CO2 and energy storage containment assessment.
Cementation, Permeability, Sandstone intrusion, Seal bypass, X-ray micro-CT, fluid flow
0037-0746
Callow, Ben
15166203-d3e6-4b28-8369-e99e1bd00240
Falcon-Suarez, Ismael
f5cdbc61-326b-424d-a90f-593a8698a4d2
Bull, Jonathan
974037fd-544b-458f-98cc-ce8eca89e3c8
Gernon, Thomas
658041a0-fdd1-4516-85f4-98895a39235e
Ruffell, Sean
0c0c7440-18b3-4b8a-9d8c-a8fb8386d7c7
Grippa, Antonio
f8eaa53e-e5ac-4759-9c1e-27cfa56a5087
Hurst, Andrew
430a6936-b166-4cc3-9673-048e0ed371f9
Callow, Ben
15166203-d3e6-4b28-8369-e99e1bd00240
Falcon-Suarez, Ismael
f5cdbc61-326b-424d-a90f-593a8698a4d2
Bull, Jonathan
974037fd-544b-458f-98cc-ce8eca89e3c8
Gernon, Thomas
658041a0-fdd1-4516-85f4-98895a39235e
Ruffell, Sean
0c0c7440-18b3-4b8a-9d8c-a8fb8386d7c7
Grippa, Antonio
f8eaa53e-e5ac-4759-9c1e-27cfa56a5087
Hurst, Andrew
430a6936-b166-4cc3-9673-048e0ed371f9

Callow, Ben, Falcon-Suarez, Ismael, Bull, Jonathan, Gernon, Thomas, Ruffell, Sean, Grippa, Antonio and Hurst, Andrew (2022) Permeability heterogeneity of sandstone intrusion fluid-escape systems, Panoche Hills, California: Implications for sedimentary basins globally. Sedimentology. (doi:10.1111/sed.12997).

Record type: Article

Abstract

Natural surface gas seeps provide a significant input of greenhouse gas emissions into the Earth’s atmosphere and hydrosphere. The gas flux is controlled by the properties of underlying fluid-escape conduits, which are present within sedimentary basins globally. These conduits permit pressure-driven fluid flow, hydraulically connecting deeper strata with the Earth’s surface; however they can only be fully resolved at sub-seismic scale. Here, a novel minus-cement-and-matrix permeability method using 3D X-ray micro-CT imaging enables the improved petrophysical linkage of outcrop and sub-surface data. The methodology is applied to the largest known outcrop of an inactive fluid-escape system, the Panoche Giant Intrusion Complex in Central California, where samples were collected along transects of the 600-800 m stratigraphic depth range to constrain porosity and permeability spatial heterogeneity. The presence of silica cement and clay matrix within the intergranular pores of sand intrusions are the primary control of porosity (17-27 %) and permeability (≤ 1 to ~500 mD) spatial heterogeneity within the outcrop analogue system. Following the digital removal of clay matrix and silica (opal-CT and quartz) cement derived from the mudstone host strata, the sand intrusions have porosity-permeability ranges of ~30-40 % and 103-104 mD. These calculations are closely comparable to active sub-surface systems in sedimentary basins. Field observations revealed at decreasing depth, the connected sand intrusion network reduces in thickness and becomes carbonate cemented, terminating at carbonate mounds formed from methane escape at the seafloor. A new conceptual model integrates the pore-scale calculations and field-scale observations to highlight the key processes that control sand intrusion permeability, spatially and temporally. The study demonstrates the control of matrix and cement addition on the physical properties of fluid-escape conduits, which has significance for hydrocarbon reservoir characterisation and modelling, as well as subsurface CO2 and energy storage containment assessment.

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Callow_et_al_2022_SED-2021-OM-119 - Accepted Manuscript
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Sedimentology - 2022 - Callow - Permeability heterogeneity of sandstone intrusion fluid‐escape systems Panoche Hills - Accepted Manuscript
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More information

Accepted/In Press date: 22 March 2022
e-pub ahead of print date: 5 April 2022
Keywords: Cementation, Permeability, Sandstone intrusion, Seal bypass, X-ray micro-CT, fluid flow

Identifiers

Local EPrints ID: 456206
URI: http://eprints.soton.ac.uk/id/eprint/456206
ISSN: 0037-0746
PURE UUID: 302a82d2-a1ff-472e-96d5-7ec9e4908e80
ORCID for Jonathan Bull: ORCID iD orcid.org/0000-0003-3373-5807
ORCID for Thomas Gernon: ORCID iD orcid.org/0000-0002-7717-2092

Catalogue record

Date deposited: 26 Apr 2022 17:03
Last modified: 25 Jun 2022 04:05

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Contributors

Author: Ben Callow
Author: Ismael Falcon-Suarez
Author: Jonathan Bull ORCID iD
Author: Thomas Gernon ORCID iD
Author: Sean Ruffell
Author: Antonio Grippa
Author: Andrew Hurst

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