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Controls on rock deformation
environmental
confining pressure, differential stress, temp
lithological
porosity, strength, lithification, mineralogy
cataclasite
a type of cataclastic rock that is formed by fracturing and comminution during faulting
two methods of fault rock characterisation
SEM and CL
SEM is backscatter
backscattered electron emmision
electrons scattered back from target, amount is proportional to average atomic number
three variables of fault rock classification
clay content
fragmentation level (lots of sub-cats)
lithification state
three categories of clay content of fault rocks
clay smear series (40%+ clay content)
phyllosiicate framework fault rock series (15-40% clay content)
Quartz rich (deformation band) (0-15% clay content)
fault rock classification diagram
.
dissaggregation seam characterisitics
common in clean sands, same composition as host
no grain fracture, formed by rolling, resulting quartz cementation
thickness c.10 times host rock grain size
permeability reduction due to disaggregation: relationship to clay content
.
cataclasite characteristics
characterised by grain fracture and grain size reduction
up to 50% composed to grain fragments
thickness not related to host grain size.
anastomosing
permeability reduced by 1-6 compared to host
cataclasis diagram
.
effect of temperature on quatrz cementation:
drastic increase at 90 degrees
permeability reduction factor of low clay cataclasites
100 to 10000
permeability vs. threshold pressure graph
.
phyllosilicate framework fault rocks
appear darker than host
more clay content means:
less grain fracturing
more grain contact quartz dissolution
>25% mechanical compaction
define dissolution
The action or process of dissolving or being dissolved
threshold pressure
pressure at which fluids enters
threshold pressure vs. clay content summary graph
location of the 4 fault zone classifications
.
permeability vs. clay content summary graph
location of the 4 fault zone classifications
.
cementation localisation area
in dilational areas of reactivated faults
Permeability Units
mD
mili Darcy
Densities of oil gas water
oil=0.5-1 g/cm3
gas = ≈0-0.5 g/cm3
water/brines >1 g/cm3
API degree?
hydrocarbon ambient density (as opposed to in situ)
hydrocarbon density dependant on
the amount of dissolved gas
GOR (Gas:Oil Ratio)
graph of density vs. depth/temperature for oil and gas
1
hydrostatic/lithostatic pressure graph
.
lithostatic pressure is
overburden
pressure gradients for
water
oil
gas
in psi/ft
water≈0.45
oil≈0.4
gas≈0.1
psi/ft
SI alternative to psi/ft
kPa/m
≈x20 to get to kPa/m from psi/ft
Bouyancy pressure
Pb = (water density - hydrocarbon density)gH
H=height of hydrocarbon column
variations in fluid pressure with topseal and GOC and OWC
.
ODT
oil depth to
WUT
water up to
capillary threshold pressure
force needed from bouyancy pressure to displace water already in pores
technique to determine capillary entry pressure
inject mercury into a clean and dry sample, get graph, then convert from Hg/air to oil/water with formula
capilliary entry pressure equation
Pc=(2*interfacial tension*cos(contact angle))/radius of pore
wetting surface
if adhesive forces exceed cohesive fluid spreads out
non-wetting surface
If cohesive forces exceed adhesive fluid beads up
wettability is
Wettability is the tendency of one fluid to spread to or adhere to a solid surface in the presence of other immiscible fluids
wettability indicated by
contact angles
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Lernkarten
Permeability Units
mD
mili Darcy
Densities of oil gas water
oil=0.5-1 g/cm3
gas = ≈0-0.5 g/cm3
water/brines >1 g/cm3
API degree?
hydrocarbon ambient density (as opposed to in situ)
hydrocarbon density dependant on
the amount of dissolved gas
GOR (Gas:Oil Ratio)
graph of density vs. depth/temperature for oil and gas
1
hydrostatic/lithostatic pressure graph
.
lithostatic pressure is
overburden
pressure gradients for
water
oil
gas
in psi/ft
water≈0.45
oil≈0.4
gas≈0.1
psi/ft
SI alternative to psi/ft
kPa/m
≈x20 to get to kPa/m from psi/ft
Bouyancy pressure
Pb = (water density - hydrocarbon density)gH
H=height of hydrocarbon column
variations in fluid pressure with topseal and GOC and OWC
.
ODT
oil depth to
WUT
water up to
capillary threshold pressure
force needed from bouyancy pressure to displace water already in pores
technique to determine capillary entry pressure
inject mercury into a clean and dry sample, get graph, then convert from Hg/air to oil/water with formula
capilliary entry pressure equation
Pc=(2*interfacial tension*cos(contact angle))/radius of pore
wetting surface
if adhesive forces exceed cohesive fluid spreads out
non-wetting surface
If cohesive forces exceed adhesive fluid beads up
wettability is
Wettability is the tendency of one fluid to spread to or adhere to a solid surface in the presence of other immiscible fluids
wettability indicated by
contact angles
typical wettability of clastic and carbonate rocks
clastic rocks tend to be water wet
carbonates have mixed wettability
relative permeability
ratio to take into account multiphase fluid
why cementation in dissagregation zones?
as the grains slide past each other they can clean each other and quartz cement preferentiallyt deposits on these clean areas.
how does a change in hydrocarbon saturation change the relative permeability of a medium
as hydrocarbon saturation increases the relative permeability to water decreases.
spill/leak point controls on column height diagram
.
Controls on rock deformation
environmental
confining pressure, differential stress, temp
lithological
porosity, strength, lithification, mineralogy
cataclasite
a type of cataclastic rock that is formed by fracturing and comminution during faulting
two methods of fault rock characterisation
SEM and CL
SEM is backscatter
backscattered electron emmision
electrons scattered back from target, amount is proportional to average atomic number
three variables of fault rock classification
clay content
fragmentation level (lots of sub-cats)
lithification state
three categories of clay content of fault rocks
clay smear series (40%+ clay content)
phyllosiicate framework fault rock series (15-40% clay content)
Quartz rich (deformation band) (0-15% clay content)
fault rock classification diagram
.
dissaggregation seam characterisitics
common in clean sands, same composition as host
no grain fracture, formed by rolling, resulting quartz cementation
thickness c.10 times host rock grain size
permeability reduction due to disaggregation: relationship to clay content
.
cataclasite characteristics
characterised by grain fracture and grain size reduction
up to 50% composed to grain fragments
thickness not related to host grain size.
anastomosing
permeability reduced by 1-6 compared to host
cataclasis diagram
.
effect of temperature on quatrz cementation:
drastic increase at 90 degrees
permeability reduction factor of low clay cataclasites
100 to 10000
permeability vs. threshold pressure graph
.
phyllosilicate framework fault rocks
appear darker than host
more clay content means:
less grain fracturing
more grain contact quartz dissolution
>25% mechanical compaction
