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Aims
Provide detailed information to allow the distribution of permeability to be evaluated.
Define the most likely fluid flow model for the outcrop
To demonstrate that GetRichQuick will not get rich, quickly or otherwise
Methods for data collection
Sub-team 1 – jointing Fracture frequency for individual beds Fracture orientations Vertical connectivity of the fracture
systems: In plan In section
Methods for data collection
Sub-team 2 – faulting and fracturing Frequency of faults versus throw Clustering of faults Impact of faults – retard or enhancement of
flow Fault timing relationship with joints
Jointing
9 Centimetres
0
10
20
30
40
50
60
70
80
90
Joint Spacing
Joint Distrubution
9 Centimetres
10 Centimetres
15 Centimetres
28 Centimetres
50 Centimetres
56 Centimetres
Interpretation
In section the joints and fractures are spatially dependant on the thickness of the bed
Thicker beds have more distance between fractures and lower fracture density
The fractures in thicker beds tend to continue through the surrounding thinner beds
Vertical connectivity
Thinner beds are typically bound by clay rich layers above and below
Stylolites present in thick beds and are laterally extensive prohibiting vertical permeability
Governed by larger joints through thick and thin beds
Location 1 Location 2 Location 3
Fracture length vs area:
15.6m/m2 5.9 m/m2 5.5 m/m2
No. of fracture junctions:
130 14 16
Connectivity (no. of connections / fracture length per m2)
8.3 per m 2.4 per m 2.9 per m
Fracture density and connectivity analysis
Bed 20cm thick Bed 30cm thick Bed 29cm thick
1m21m2 1m2
From fracture plan analysis… Near 100% connectivity in all chalk beds 20cm thick units have an 4x greater
degree of fracturing as those measuring 30cm
Dominant fracture orientation ~125°(+/-10°), sub-parallel to faults
Fracture density increases around fault planes
Impact on fracture permeability
Lateral fluid flow better in thinner chalk beds, but still active in thicker units
General preferential orientation to fluid flow in SE-NW direction (fault controlled)
Vertical fluid flow determined by fracture permeability of thicker units as smaller fractures (apparent in thin beds) do not translate
Implications for Reservoir Model Fracture analysis has shown that fluid flow will
be dominantly horizontal in thinner beds which are heavily fractured
Degree of vertical flow is controlled by larger joints that propagate through beds of various thickness
Fractures and joints play a major role in the permeability of the chalk
To maximise production: Fluid flow will produce a higher yield laterally rather than
vertically Possible horizontal drilling may maximise flow out of
reservoir
NE
Brecciated Zone
Releasing Faults.
Displaced Limestone Beds.
Typical short offset dextral faulting.
Releasing Faults.
SW
20 cm
Short offset faultsRadial Fractures
Fault bend
Clay layer
Clay layer thins towards bend from 3cm to 0.5cm
•Majority of faults contain fault bends and not extensional oversteps (fracture refraction)
•The beds around the fault bends are highly fractured
Longer Offset Fault
•The effect of larger displacements on a fault plane result here in a thin straight fault zone lined by clay
•These are likely to be barriers to horizontal flow
Clay lining of fault
Planed off fault bend
Large Offset Fault, example of fault gouge & a damage zone
Calcite Precipitation filling highly fracturedDamage Zone
2-3m wide gouge zone
Damage Zone
Fault Morphology
Two main fault trends W-E & ENE-WSW The amount of offset determines the likely role of the
faults as fluid conduits or barriers. Short offset faults contain highly permeable fault bend
zones. This suggests a refraction style of growth, this being the case the position of fault bends is determined by competency of the unit which it propagates through so that: Clay layers & less competent chalk layers are more likely to
result in fault bends concentrating fractures & flow Thinner layers (more fractures) are less competent and may
cause minor fault bends
Characteristics of small offset faultsCumulative frequency against spacing
1
10
100
0.1 1 10
Spacing (m)
Cu
mu
lati
ve f
req
uen
cy
Displacement vs cumulative frequency
1
10
100
0.01 0.1 1
Displacement (m)
cum
ula
tive
fre
qu
ency
Fault clustering for low offset faults at South Landing
0
10
20
30
40
50
60
1 5 9 13 17 21 25 29 33 37 41 45 49 53 57 61 65 69 73
Relative position of faults
Len
gth
of
fau
lts
Effects of Offset
The large offset faults appear are likely to act as barriers unless their damage zones contain open zones i.e vugs that could concentrate flow through the fault gouge, however the extensive damage zone would likely form a barrier to flow over a production timescale
Short offset faults increase permeability although there needs to be further research carried out into all the factors that determine clay smear along the faults
Incorporation of fault data into a reservoir model Definition of seismic scale faults & there
spatial extent will allow for potential compartments to be identified.
To maximise production Drill through sealing compartmentalising faultsUtilise the dominant trend of intra reservoir
small scale faults to maximise production
Limitations of Flamborough as an Analogue
Uplift and erosion may affect the structural features recorded i.e the width of fractures could be significantly less, reducing permeability