Comparison of deformation mechanics for two different carbonates: oolitic limestone and laminites

Stephanie Zihms, Helen Lewis, Gary Couples, Stephen Hall, James Somerville

Research output: Contribution to journalMeeting Abstract

Abstract

Carbonate rocks form under a range of conditions which leads to a diverse rock group. Even though carbonatesare overall mineralogically simple, the solid-space distribution ranges from simple compositions such as ooliticlimestones to highly complex networks of pores and solids as seen in coquinas. Their fundamental mechanicalbehaviour has been identified to be like clastic rocks (Vajdova 2004, Brantut, Heap et al. 2014). However itis very likely that this observation is not true for more complex carbonates. Triaxial tests were performed oncylindrical samples of two different carbonates; a) oolitic limestone (Bicqueley quarry, France) and b) laminite(Ariripe basin, Brazil). The samples were deformed under confining pressures of 8, 12 and 20MPa, and 20, 30 and40MPa, respectively. All tests were stopped as soon as peak load was observed to preserve as many deformationcharacteristics as possible. Photographs of the samples were taken before and after deformation to allow surfaceanalysis of deformation features. Additionally, samples were analysed post-deformation with X-ray tomography(XRT) (using the Zeiss XRadia XRM 520 at the 4D Imaging Lab at Lund University). The 3D tomography imagesrepresent the post-deformation samples’ density distribution, allowing detailed, non-destructive, 3D analysis ofthe deformation features that developed in the triaxial testing, including the complex geometries and interactionsof fractures, deformation bands and sedimentary layering. They also provide an insight into the complexity ofdeformation features produced due to the carbonate response.Initial results show that the oolitic limestone forms single shear bands almost the length of the sample, exhibitingsimilar characteristics to sandstones deformed under similar conditions. These features are observed for all threeapplied loads. The laminate sample deformed at the lowest confining pressure exhibits compactive features.However, the laminite samples deformed at the two higher confining pressures both show highly complex fracturenetworks comprising open fractures and fracture propagation. This suggests that the laminate changes fromcompactive to dilational responses over the selected confining conditions. The XRT analysis indicates that a morecomplex fracture distribution could be linked to rock component properties e.g. grain size and composition. Forthe laminite these are variable with the layers. This is in agreement with field observations of laminite microfabrics(Calvo, Rodriguez-Pascua et al. 1998). Additionally, the typical grain size of the laminate (m) is much smallerthan the oolitic limestone (mm), which suggests that fracture network complexity can also be linked to bulksystem complexity i.e. pore & grain network.These deformation experiments show that, as previously observed, oolitic limestones seem to behave similarly tosandstones. However this observation is not true for laminites and it is very likely that more complex carbonateswill develop even more complicated deformation behaviour. It is therefore necessary to systematically testdifferent carbonate rocks to understand the impact of geometry and composition, as well as the interplay with thepore network.
Original languageEnglish
Article numberEGU2016-173
Number of pages1
JournalGeophysical Research Abstracts
Volume18
Publication statusPublished - Apr 2016
Externally publishedYes
EventEuropean Geosciences Union General Assembly 2016 - Vienna, Austria
Duration: 17 Apr 201622 Apr 2016
https://egu2016.eu/home.html

Fingerprint

mechanics
limestone
carbonate
confining pressure
tomography
carbonate rock
grain size
geometry
fracture propagation
shear band
comparison
clastic rock
fracture network
triaxial test
quarry
rock
photograph
low pressure
sandstone
basin

Keywords

  • carbonates
  • geomechanics
  • laminites
  • Limestone

Cite this

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title = "Comparison of deformation mechanics for two different carbonates: oolitic limestone and laminites",
abstract = "Carbonate rocks form under a range of conditions which leads to a diverse rock group. Even though carbonatesare overall mineralogically simple, the solid-space distribution ranges from simple compositions such as ooliticlimestones to highly complex networks of pores and solids as seen in coquinas. Their fundamental mechanicalbehaviour has been identified to be like clastic rocks (Vajdova 2004, Brantut, Heap et al. 2014). However itis very likely that this observation is not true for more complex carbonates. Triaxial tests were performed oncylindrical samples of two different carbonates; a) oolitic limestone (Bicqueley quarry, France) and b) laminite(Ariripe basin, Brazil). The samples were deformed under confining pressures of 8, 12 and 20MPa, and 20, 30 and40MPa, respectively. All tests were stopped as soon as peak load was observed to preserve as many deformationcharacteristics as possible. Photographs of the samples were taken before and after deformation to allow surfaceanalysis of deformation features. Additionally, samples were analysed post-deformation with X-ray tomography(XRT) (using the Zeiss XRadia XRM 520 at the 4D Imaging Lab at Lund University). The 3D tomography imagesrepresent the post-deformation samples’ density distribution, allowing detailed, non-destructive, 3D analysis ofthe deformation features that developed in the triaxial testing, including the complex geometries and interactionsof fractures, deformation bands and sedimentary layering. They also provide an insight into the complexity ofdeformation features produced due to the carbonate response.Initial results show that the oolitic limestone forms single shear bands almost the length of the sample, exhibitingsimilar characteristics to sandstones deformed under similar conditions. These features are observed for all threeapplied loads. The laminate sample deformed at the lowest confining pressure exhibits compactive features.However, the laminite samples deformed at the two higher confining pressures both show highly complex fracturenetworks comprising open fractures and fracture propagation. This suggests that the laminate changes fromcompactive to dilational responses over the selected confining conditions. The XRT analysis indicates that a morecomplex fracture distribution could be linked to rock component properties e.g. grain size and composition. Forthe laminite these are variable with the layers. This is in agreement with field observations of laminite microfabrics(Calvo, Rodriguez-Pascua et al. 1998). Additionally, the typical grain size of the laminate (m) is much smallerthan the oolitic limestone (mm), which suggests that fracture network complexity can also be linked to bulksystem complexity i.e. pore & grain network.These deformation experiments show that, as previously observed, oolitic limestones seem to behave similarly tosandstones. However this observation is not true for laminites and it is very likely that more complex carbonateswill develop even more complicated deformation behaviour. It is therefore necessary to systematically testdifferent carbonate rocks to understand the impact of geometry and composition, as well as the interplay with thepore network.",
keywords = "carbonates, geomechanics, laminites, Limestone",
author = "Stephanie Zihms and Helen Lewis and Gary Couples and Stephen Hall and James Somerville",
year = "2016",
month = "4",
language = "English",
volume = "18",
journal = "Geophysical Research Abstracts",
issn = "1029-7006",
publisher = "Copernicus Gesellschaft mbH",

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Comparison of deformation mechanics for two different carbonates : oolitic limestone and laminites. / Zihms, Stephanie; Lewis, Helen; Couples, Gary; Hall, Stephen; Somerville, James.

In: Geophysical Research Abstracts, Vol. 18, EGU2016-173, 04.2016.

Research output: Contribution to journalMeeting Abstract

TY - JOUR

T1 - Comparison of deformation mechanics for two different carbonates

T2 - oolitic limestone and laminites

AU - Zihms, Stephanie

AU - Lewis, Helen

AU - Couples, Gary

AU - Hall, Stephen

AU - Somerville, James

PY - 2016/4

Y1 - 2016/4

N2 - Carbonate rocks form under a range of conditions which leads to a diverse rock group. Even though carbonatesare overall mineralogically simple, the solid-space distribution ranges from simple compositions such as ooliticlimestones to highly complex networks of pores and solids as seen in coquinas. Their fundamental mechanicalbehaviour has been identified to be like clastic rocks (Vajdova 2004, Brantut, Heap et al. 2014). However itis very likely that this observation is not true for more complex carbonates. Triaxial tests were performed oncylindrical samples of two different carbonates; a) oolitic limestone (Bicqueley quarry, France) and b) laminite(Ariripe basin, Brazil). The samples were deformed under confining pressures of 8, 12 and 20MPa, and 20, 30 and40MPa, respectively. All tests were stopped as soon as peak load was observed to preserve as many deformationcharacteristics as possible. Photographs of the samples were taken before and after deformation to allow surfaceanalysis of deformation features. Additionally, samples were analysed post-deformation with X-ray tomography(XRT) (using the Zeiss XRadia XRM 520 at the 4D Imaging Lab at Lund University). The 3D tomography imagesrepresent the post-deformation samples’ density distribution, allowing detailed, non-destructive, 3D analysis ofthe deformation features that developed in the triaxial testing, including the complex geometries and interactionsof fractures, deformation bands and sedimentary layering. They also provide an insight into the complexity ofdeformation features produced due to the carbonate response.Initial results show that the oolitic limestone forms single shear bands almost the length of the sample, exhibitingsimilar characteristics to sandstones deformed under similar conditions. These features are observed for all threeapplied loads. The laminate sample deformed at the lowest confining pressure exhibits compactive features.However, the laminite samples deformed at the two higher confining pressures both show highly complex fracturenetworks comprising open fractures and fracture propagation. This suggests that the laminate changes fromcompactive to dilational responses over the selected confining conditions. The XRT analysis indicates that a morecomplex fracture distribution could be linked to rock component properties e.g. grain size and composition. Forthe laminite these are variable with the layers. This is in agreement with field observations of laminite microfabrics(Calvo, Rodriguez-Pascua et al. 1998). Additionally, the typical grain size of the laminate (m) is much smallerthan the oolitic limestone (mm), which suggests that fracture network complexity can also be linked to bulksystem complexity i.e. pore & grain network.These deformation experiments show that, as previously observed, oolitic limestones seem to behave similarly tosandstones. However this observation is not true for laminites and it is very likely that more complex carbonateswill develop even more complicated deformation behaviour. It is therefore necessary to systematically testdifferent carbonate rocks to understand the impact of geometry and composition, as well as the interplay with thepore network.

AB - Carbonate rocks form under a range of conditions which leads to a diverse rock group. Even though carbonatesare overall mineralogically simple, the solid-space distribution ranges from simple compositions such as ooliticlimestones to highly complex networks of pores and solids as seen in coquinas. Their fundamental mechanicalbehaviour has been identified to be like clastic rocks (Vajdova 2004, Brantut, Heap et al. 2014). However itis very likely that this observation is not true for more complex carbonates. Triaxial tests were performed oncylindrical samples of two different carbonates; a) oolitic limestone (Bicqueley quarry, France) and b) laminite(Ariripe basin, Brazil). The samples were deformed under confining pressures of 8, 12 and 20MPa, and 20, 30 and40MPa, respectively. All tests were stopped as soon as peak load was observed to preserve as many deformationcharacteristics as possible. Photographs of the samples were taken before and after deformation to allow surfaceanalysis of deformation features. Additionally, samples were analysed post-deformation with X-ray tomography(XRT) (using the Zeiss XRadia XRM 520 at the 4D Imaging Lab at Lund University). The 3D tomography imagesrepresent the post-deformation samples’ density distribution, allowing detailed, non-destructive, 3D analysis ofthe deformation features that developed in the triaxial testing, including the complex geometries and interactionsof fractures, deformation bands and sedimentary layering. They also provide an insight into the complexity ofdeformation features produced due to the carbonate response.Initial results show that the oolitic limestone forms single shear bands almost the length of the sample, exhibitingsimilar characteristics to sandstones deformed under similar conditions. These features are observed for all threeapplied loads. The laminate sample deformed at the lowest confining pressure exhibits compactive features.However, the laminite samples deformed at the two higher confining pressures both show highly complex fracturenetworks comprising open fractures and fracture propagation. This suggests that the laminate changes fromcompactive to dilational responses over the selected confining conditions. The XRT analysis indicates that a morecomplex fracture distribution could be linked to rock component properties e.g. grain size and composition. Forthe laminite these are variable with the layers. This is in agreement with field observations of laminite microfabrics(Calvo, Rodriguez-Pascua et al. 1998). Additionally, the typical grain size of the laminate (m) is much smallerthan the oolitic limestone (mm), which suggests that fracture network complexity can also be linked to bulksystem complexity i.e. pore & grain network.These deformation experiments show that, as previously observed, oolitic limestones seem to behave similarly tosandstones. However this observation is not true for laminites and it is very likely that more complex carbonateswill develop even more complicated deformation behaviour. It is therefore necessary to systematically testdifferent carbonate rocks to understand the impact of geometry and composition, as well as the interplay with thepore network.

KW - carbonates

KW - geomechanics

KW - laminites

KW - Limestone

UR - https://meetingorganizer.copernicus.org/EGU2016/orals/21388

M3 - Meeting Abstract

VL - 18

JO - Geophysical Research Abstracts

JF - Geophysical Research Abstracts

SN - 1029-7006

M1 - EGU2016-173

ER -