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how to measure spacing of fractures
core, image logs, outcrop analogues
data sources for fracture parameters (4)
core, image logs, outcrop analogues, well performance
how to measure fracture aperture size
core, well performance
vug
vuggy fractures
small to medium cavities in a rock
eroded from inside, eg. karst
two names for groups of fractures, usually cross cutting strata
fracture swarms
fracture coridoors
stylolite
serrated surface at which material has been removed by pressure solution
how can fractures interact with strata (two types)
strata bound
non strata bound
what is the reaction of the pressure in a fractured reservoir (from multiple wells)
heterogenous
how many types of fractured reservoir
4, decreasing fracture influence
4 types of fractured reservoir (supply and storage)
I:essential storage and permeability
II:no storage, essential permeability
III:no storage, assist in permeability
IV:only anisotropy
percolation threshold
when fractures are such that their interconnectivity means that transmissability jumps.
curvature of stratigraphy is a good indicator of
fracture density
testing fractures with fluid?
slug like tests with mud pit
two types of borehole image log
acoustic or resistivity
3 pros of borehole image log
orientation
identify open fractures in the subsurface
easy to obtain
3 cons of borehole image logs
resolution
degraded by artefacts and poor hole conditions
expensive
how do fractures affect ultrasound
waves fastest parallel to fractures
(due to effects of fluids in fractures and continuous rock )
problems with relating curvature to fracture density
curvature doesn't indicate strain accommodation mechanism, also only measuring current structural setup.
Guassian curvature?
the product of the two primcipal curvatures of a surface
ie.
Cylindrical folds K′ = 0
Periclinal folds K′ ≠ 0
Productivity index
PI or J
J=rate of production/drawdown
Two types of fault seal
Juxtaposition seal
Fault rock seal
Juxtaposition seal
reservoir against low-permeability unit
fault rock seal
also called
membrane seal
controlled by fault rock properties
what decides if a fault seal leaks
bouyancy forces vs. capillary threshold pressure
fault seal workflow
4 points
structural mapping
assessment of fault rock properties
fluid properties
seal prediction
what part of fault seal workflow can be looked up?
fault rock properties in lit.
fault rock peroperty defining sealing ability
clay content
two measures of fault rock clay content
VSH volume of shale
VCL volume of clay
VSH
volume of shale
VCL
volume of clay
how to calculate clay content of fault rocks
geophysical borehole methods
SGR
meaning and calculation
shale gouge ratio
average clay moved past point on fault
SSF
meaning and calculation
shale smear factor
fault throw/bed thickness
SSF <4 means
continuous smears
SSF 4-10 means
60% continuous smearing
SSF >10 means
70% discontinuous smearing
complications of smearing
variations in breaks of fault
max clay content of marine shale
66%
most models assume a clay content of
100%
different types of breaches of fault seals (4)
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Flashcards
how do fractures affect ultrasound
waves fastest parallel to fractures
(due to effects of fluids in fractures and continuous rock )
problems with relating curvature to fracture density
curvature doesn't indicate strain accommodation mechanism, also only measuring current structural setup.
Guassian curvature?
the product of the two primcipal curvatures of a surface
ie.
Cylindrical folds K′ = 0
Periclinal folds K′ ≠ 0
Productivity index
PI or J
J=rate of production/drawdown
