Stress and deformation of offshore piles under structural ...
THE STRUCTURAL EVOLUTION OF DEFORMATION BANDS
1
Deformation bands alter the way fluids move through the subsurface. Deformation bands are useful indicators of discrete changes in the local stress regime. There is a research gap relating deformation band studies to sedimentary-hosted mineral deposits. Shallow depth deformation bands have a greater effect on fluid flow than deeply buried deformation bands. Deformation bands analysis may provide insight into uranium-fluid pathways. 6. 6. SUMMARY 5. 5. The role deformation bands play in the minerals sector is poorly constrained; specifically, their effects on uranium-bearing fluid migration between source and deposit. This project focuses on understanding the structural evolution of four basins in South Australia and Saskatchewan. Our overall goal is to develop a model to delineate the impact of deformation bands in sedimentary-hosted mineralization, focusing on the impacts of fluid flow as it relates to structural permeability (Fig. 8; Fig. 9). The data collected will help source a new set of tools for both petroleum geoscientists modelling basin structure and evolution, and mineral exploration geologists targeting uranium fluid pathways and deposits. APPLICATION TO MINERAL SYSTEMS Figure 8. (top) A dilation band forming at the palaeoredox interface of a roll front viewed under plane polarized light (top), and reflected light (bottom). Figure 9. (bottom) Skematic model of the Paralana Fault system and Four Mile uranium deposits. 2.5 cm A A A 1 mm 1 mm Mesoproterozoic metasediments and radiogenic inlier Meteoric fluids leach uranium and thorium from radiogenic granite Namba Formation Quaternary Sediments Eyre Formation Cretaceous Sediments Wooltana Fault Dead Tree Section High permeable deformation band fluid conduit network Frome Embayment Paralana Fault Four Mile Fault 2 1 Legend Deformation band Four Mile West deposit Four Mile East deposit Fault 2 1 4. 4. image image Figure 6. Deformation band cluster in the Entrada Sandstone, Utah, after Fossen and Bale (2007). Figure 7. Deformation band non-uniform thickness in the Entrada Sandstone, Utah, after Fossen and Bale (2007). Figure 5. Conjugate deformation bands in the Entrada Sandstone, Utah, after Fossen and Bale (2007). The petrophysical properties of deformation bands are known to cause large reductions in porosity and permeability (reductions of up to 6 orders of magnitude) (Fossen et Al. 2007). Permeability is the prominent characteristic controlling fluid flow patterns in the subsurface, making these discrete structures good indicators of fluid flow. There are no documented cases where a deformation band has acted as a structural petroleum trap due to their poor connectivity and non-uniform thickness (Fig. 6; Fig. 7). However, de- formation bands may alter fluid flow patterns in the vadose or shadow zones, if they have a preferred orientation (Sigda et al. 1999). PETROLEUM GEOSCIENCE e 20 cm 2 cm 3. 3. Deformation bands form as either compaction or dilation features; therefore, they can act as fluid baffles or fluid conduits (relatively). Moreover, compaction band failure re- sults in fracture and slip-surface, further developing fluid conduits. Deformation bands form the main element to fault zones (Fossen et al. 2007), and may result in permeabil- ity anisotropy (Fig. 3) (Farrel et al. 2014), or compartmentalization of fluids dependent on the arrangement of deformation bands (Fig. 4; Fig. 5) (Manzocchi et al., 1998). Fossen & Bale, 2007 concluded that deformation bands are unlikely to maintain any significant pressure difference within a reservoir due to their poor connectivity and thickness variation along a single band; however, flow pattern may be effected and sweep efficiency reduced where injection and recovery of fluids are involved. image image Figure 3. Skematic illustration of a fault zone with deformation bands after Fossen & Bale, (2007). Figure 4. Potiental small scale arrangement of deformation bands that could result in permeability anisotropy and/or fluid compartmentalization. PETROPHYSICAL PROPERTIES Kmax Kmin Drill hole image Deformation bands form as a result of localised scale faulting, folding, slump- ing, and growth and collapse of salt and shale diapirs (Fossen et al. 2007). They are classfied based on their formation mechanics, resulting from either pure- or simple-shear kinematics that can form dilatant or compaction features. Disaggregation bands form as a result of grain boundary sliding, grain rolling, and breaking of grain-bonding cements (Fig. 2a). Phyllosilicate bands form as platey minerals preferentially align (>10% bulk composition) (Fig. 2b). Cataclastic bands invoke grain crush- ing to facilitate pore space collapse (Fig. 2c). Solution/cement bands form as a result of pressure solution and subse- quent cementation, in addition to prefer- entially cementing disaggregation and cataclastic bands due to their highly re- active surfaces (Fig 2d). 2. 2. 2. 2. DEFORMATION BAND MECHANICS Strain in highly porous rocks and sedi- ments is not initially accommodated by fracture, instead by formation of discrete deformation structures (Fossen et al. 2007). A deformation band is a tabular zone of localised compressional strain that forms as a result of compaction due to sediment loading or high horizontal or vertical stress (Fossen et al. 2007). De- formation bands were first, recognized in porous sandstones of the Colorado Plateau in the 1970s; however, they were largely ignored and incorrectly in- terpreted, as they resemble quartz veins and silicified shears. The first docu- mented case study was published by Attila Aydin (1978) (Fig. 1). 2. 2. 1. 1. Figure 1. Attila Aydin standing beside a slip surface associated with a zone of deformation bands in the Entrada Sandstone at Molly’s Castle, San Rafael Desert, Utah (Aydin, 1979). WHAT IS A DEFORMATION BAND? Figure 2. Skematic diagram of deformation band mechanisms, after Fossen et al. (2007). 3 mm 3 mm THE STRUCTURAL EVOLUTION OF DEFORMATION BANDS 1 Centre for Tectonics, Resources, and Exploration (TRaX), Department of Earth Science, University of Adelaide, Adelaide, South Australia 5005 2 Centre for Tectonics, Resources, and Exploration (TRaX), Australian School of Petroleum, University of Adelaide, Adelaide, South Australi 5005 3 Geological Survey of South Australia, Department of State Development, Level 7, 101 Grenfel Street, Adelaide, South Australia 5005 Drew Lubiniecki 1 , Rosalind King 1 , Simon Holford 2 , Mark Bunch 2 , Sam White 1 , Stephen Hore 3 , Steve Hill 3
Transcript of THE STRUCTURAL EVOLUTION OF DEFORMATION BANDS
Deformation bands alter the way fluids move through the subsurface.
Deformation bands are useful indicators of discrete changes in the local stress regime.
There is a research gap relating deformation band studies to sedimentary-hosted mineral deposits.
Shallow depth deformation bands have a greater effect on fluid flow than deeply buried deformation bands.
Deformation bands analysis may provide insight into uranium-fluid pathways.
6.6. SUMMARY
5.5.
The role deformation bands play in the minerals sector is poorly constrained; specifically, their effects on uranium-bearing fluid migration between source and deposit. This project focuses on understanding the structural evolution of four basins in South Australia and Saskatchewan. Our overall goal is to develop a model to delineate the impact of deformation bands in sedimentary-hosted mineralization, focusing on the impacts of fluid flow as it relates to structural permeability (Fig. 8; Fig. 9). The data collected will help source a new set of tools for both petroleum geoscientists modelling basin structure and evolution, and mineral exploration geologists targeting uranium fluid pathways and deposits.
APPLICATION TO MINERAL SYSTEMS
Figure 8. (top)A dilation band forming at the palaeoredox interface of a roll front viewed under plane polarized light (top), and reflected light (bottom).
Figure 9. (bottom)Skematic model of the Paralana Fault system and Four Mile uraniumdeposits.
2.5 cm
A
A
A1 mm
1 mm
Mesoproterozoic metasedimentsand radiogenic inlier
Meteoric fluids leach uraniumand thorium from radiogenic
graniteNamba Formation
Quaternary Sediments
Eyre Formation
Cretaceous Sediments Wooltana Fault
Dead Tree SectionHigh permeable deformation band
fluid conduit network
Frome Embayment
Paralana Fault
Four Mile Fault
2
1
Legend
Deformation band
Four Mile West deposit
Four Mile East deposit
Fault
2
1
4.4.
image image
Figure 6. Deformation band cluster in the Entrada Sandstone, Utah, after Fossen and Bale (2007).
Figure 7. Deformation band non-uniform thickness in the Entrada Sandstone, Utah, after Fossen and Bale (2007).
Figure 5. Conjugate deformation bands in the Entrada Sandstone, Utah, after Fossen and Bale (2007).
The petrophysical properties of deformation bands are known to cause large reductions in porosity and permeability (reductions of up to 6 orders of magnitude) (Fossen et Al. 2007). Permeability is the prominent characteristic controlling fluid flow patterns in the subsurface, making these discrete structures good indicators of fluid flow. There are no documented cases where a deformation band has acted as a structural petroleum trap due to their poor connectivity and non-uniform thickness (Fig. 6; Fig. 7). However, de-formation bands may alter fluid flow patterns in the vadose or shadow zones, if they have a preferred orientation (Sigda et al. 1999).
PETROLEUM GEOSCIENCE
e
20 cm
2 cm
3.3.Deformation bands form as either compaction or dilation features; therefore, they can act as fluid baffles or fluid conduits (relatively). Moreover, compaction band failure re-sults in fracture and slip-surface, further developing fluid conduits. Deformation bands form the main element to fault zones (Fossen et al. 2007), and may result in permeabil-ity anisotropy (Fig. 3) (Farrel et al. 2014), or compartmentalization of fluids dependent on the arrangement of deformation bands (Fig. 4; Fig. 5) (Manzocchi et al., 1998). Fossen & Bale, 2007 concluded that deformation bands are unlikely to maintain any significant pressure difference within a reservoir due to their poor connectivity and thickness variation along a single band; however, flow pattern may be effected and sweep efficiency reduced where injection and recovery of fluids are involved.
image image
Figure 3. Skematic illustration of a fault zone with deformation bands after Fossen & Bale, (2007).
Figure 4. Potiental small scale arrangement of deformation bands that could result in permeability anisotropy and/or fluid compartmentalization.
PETROPHYSICAL PROPERTIES
Kmax
Kmin
Drill hole
image
Deformation bands form as a result of localised scale faulting, folding, slump-ing, and growth and collapse of salt and shale diapirs (Fossen et al. 2007). They are classfied based on their formation mechanics, resulting from either pure- or simple-shear kinematics that can form dilatant or compaction features. Disaggregation bands form as a result of grain boundary sliding, grain rolling, and breaking of grain-bonding cements (Fig. 2a). Phyllosilicate bands form as platey minerals preferentially align (>10% bulk composition) (Fig. 2b). Cataclastic bands invoke grain crush-ing to facilitate pore space collapse (Fig. 2c). Solution/cement bands form as a result of pressure solution and subse-quent cementation, in addition to prefer-entially cementing disaggregation and cataclastic bands due to their highly re-active surfaces (Fig 2d).
2.2.2.2. DEFORMATION BAND MECHANICS
Strain in highly porous rocks and sedi-ments is not initially accommodated by fracture, instead by formation of discrete deformation structures (Fossen et al. 2007). A deformation band is a tabular zone of localised compressional strain that forms as a result of compaction due to sediment loading or high horizontal or vertical stress (Fossen et al. 2007). De-formation bands were first, recognized in porous sandstones of the Colorado Plateau in the 1970s; however, they were largely ignored and incorrectly in-terpreted, as they resemble quartz veins and silicified shears. The first docu-mented case study was published by Attila Aydin (1978) (Fig. 1).
2.2.1.1.
Figure 1. Attila Aydin standing beside a slip surface associated with a zone of deformation bands in the Entrada Sandstone at Molly’s Castle, San Rafael Desert, Utah (Aydin, 1979).
WHAT IS A DEFORMATION BAND?
Figure 2. Skematic diagram of deformation band mechanisms, after Fossen et al. (2007).
3 mm
3 mm
THE STRUCTURAL EVOLUTION OF DEFORMATION BANDS 1Centre for Tectonics, Resources, and Exploration (TRaX), Department of Earth Science, University of Adelaide, Adelaide, South Australia 50052Centre for Tectonics, Resources, and Exploration (TRaX), Australian School of Petroleum, University of Adelaide, Adelaide, South Australi 5005
3Geological Survey of South Australia, Department of State Development, Level 7, 101 Grenfel Street, Adelaide, South Australia 5005
Drew Lubiniecki1, Rosalind King1, Simon Holford2, Mark Bunch2, Sam White1, Stephen Hore3, Steve Hill3
