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GetRichQuick Ltd. A.Anigboro, V. Carter, S. Green, R. Hall, P. Jones, G. Markham, M. Thomas. - PowerPoint PPT Presentation

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Investigation of fracture & fault populations in analogue outcrops for use in the Spindrift subsurface reservoir/fluid flow model. GetRichQuick Ltd. A.Anigboro, V. Carter, S. Green, R. Hall, P. Jones, G. Markham, M. Thomas. MSc. Structural Geology with Geophysics,

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Investigation of fracture & fault populations in analogue outcrops for use in the Spindrift subsurface reservoir/fluid flow model.

GetRichQuick Ltd.

A.Anigboro, V. Carter, S. Green, R. Hall, P. Jones, G. Markham, M. Thomas.

MSc. Structural Geology with Geophysics,

Dept. Earth Sciences, University of Leeds.


“ Use of analogue data collected from outcrops at Flamborough Head for input into the Spindrift prospect subsurface fluid flow model.”


Analysis of collected data in terms of;

  • Relationship of fracture spacing/density to bed thickness & vertical connectivity,
  • Lateral connectivity and orientation of fractures,
  • Stratigraphic controls on fault geometries & fault rock properties,
  • Fault throw, orientation, & clustering relationships,

Assessment of all data in terms of predictability of fault & fracture populations permeability.

fracture density1
Fracture density
  • As bed thickness increases fracture spacing increases.
  • In smaller beds (<15cm) fracture spacing rarely exceeds 20cm.
  • In larger beds (>30cm and especially >50cm) fracture spacing reaches as high as 90cm.
  • The greater thickness gives the bed a higher competence, which results in the stress needed to form fractures being greater.
  • Data doesn’t account for fracture clustering around faults.
fracture density3
Fracture density
  • Trend visible suggesting most fractures fit a general rule.
    • 2/3 Bed Thickness + 20cm
  • Data set is not large enough for a definitive equation.
  • Data also suggests that larger beds show more fractures above the general trend.
vertical connectivity
Vertical Connectivity
  • Fractures do not show a tendency to cross from one bed to another.
  • Fractures that do cross from one bed to another are associated with faults.
  • Most beds show well developed Stylolites.
  • Stylolites appear to facilitate more pervasive fracturing.
  • Stylolites were formed before the vertical fractures.
  • Beds show well developed clay layers on their tops, which act as an inhibitor to vertical pervasiveness.
plan fracture connectivity
Plan Fracture connectivity
  • 6 x 1m2 quadrant samples taken from exposed bedding surfaces of several different units.
  • Digital photo mapping & field based measuring implemented in tandem.
  • Orientation, length & density (cumulative length per m2), average fracture length, & bedding thickness recorded.
  • Impact of faulting on fracture populations investigated.
loc 1 loc 2

Bed thickness – 0.25m

  • Fracture frequency - 53
  • Cumulative fracture length per m2 - 11.27m
  • Average fracture length – 0.21m
  • Bed thickness – 0.35m
  • Fracture frequency - 245
  • Cumulative fracture length per m2 - 21.74m
  • Average fracture length – 0.09m



Loc. 1 Loc. 2



loc 3 loc 4

Bed thickness – 0.18m

  • Fracture frequency - 128
  • Cumulative fracture length per m2 - 14.96m
  • Average fracture length – 0.11m
  • Bed thickness – 0.30m
  • Fracture frequency - 227
  • Cumulative fracture length per m2 - 21.53m
  • Average fracture length – 0.09m





Loc. 3 Loc. 4

Faulting increases local fracture density

Conjugate fault set intersecting in cliff face

loc 5 loc 6

Bed thickness – 0.25m

  • Fracture frequency - 19
  • Cumulative fracture length per m2 - 7.95m
  • Average fracture length – 0.42m
  • Bed thickness – 0.75m
  • Fracture frequency - 17
  • Cumulative fracture length per m2 - 5.77m
  • Average fracture length – 0.34m





Loc. 5 Loc. 6
bed thickness vs plan fracture properties
Bed thickness vs. Plan Fracture properties

Cumulative length (m) per m2 vs. bed thickness (m)

  • Weak correlation between measures of plan fracture density and bed thickness;
    • Limited data set
    • Difficult to assess bed thickness

Fracture frequencyvs. bed thickness (m)

  • Local fracture densities related to proximity to faulting
plan fracture orientations
Plan Fracture orientations
  • Data collected from 6 x 1 m2 quadrants (~700 fractures)
  • Wide spread of fracture strike orientations, with 335-155 and 260-080 exhibiting dominant trends
  • Local fault orientations influence fracture density & orientations.
observations from plan fractures
Observations from Plan fractures
  • Near 100% connectivity of joints/fractures
    • Connectivity independent of density of fractures/faulting
  • Increased local density of fracturing around faults
  • Density of fracturing is related to bed thickness, data collected from foreshore difficult to relate to bed thickness.
    • Plan densities should be correlated with cross-sectional data
  • Dominant trends of fractures related to mean fault orientations
    • Need to be correlated with fault orientations
stratigraphic control of faulting
Stratigraphic control of faulting
  • Strain taken up by weaker Marl beds.
    • Which often mark the tip of faults
    • Here they also provide a weak medium for fault propagation and linkage.
    • Some fault planes contain breccia and clay smears

4 metres

fault geometry
Fault geometry
  • Fault geometry is strongly linked to fracture orientation.
  • Flat geometry causes heavy fracturing, mostly in the Hanging-wall
  • This leads to fracturing along strike of the fault orientation.
fault relationship with jointing orientation
Fault relationship with jointing /orientation

Fault orientation.

  • Poles to planes and average great circle
  • Synthetic (left). Antithetic (right).

Mean fault planes 332 / 53 North-east

Mean fault planes 241 / 64 South-west

throw vs transect length
Throw vs transect length
  • Clustering of smaller faults around larger faults
  • Available data suggests larger faults (>15cm) appear approximately every 25m
frequency of fault spacing
Frequency of fault spacing
  • Median spacing of faults = 0.5 metres
  • Trend line fits exponential curve to 94%
fault throw vs cumulative frequency
Fault throw vs cumulative frequency
  • Higher frequency of small displacement faults
  • Low frequency of large displacement faults
large scale faulting examples of damage zone
Large scale faulting – examples of damage zone

Main fault damage zone

Calcite filled fractures/veins (mm-dm width) within the damage zone

Significant reduction if fracture permeability

Barrier to fluid flow

Rotated, dragged & thrusted bedding

Complex filled veins & fractures

prediction of fracture fault permeability
Prediction of fracture & fault permeability
  • Little vertical connectivity of fractures (strata-bound >90%),
  • High degree of lateral connectivity along beds,
    • Higher density of fractures within thinner beds,
  • Small offset faults may provide vertical connectivity,
  • Larger offset faults may produce fault seal gouges/smears leading to potential compartmentalisation.
  • Large offset faults are likely to have a wide, complex damage zone
  • High density of damage around faults (eg. Compressional over steps/damage zones).
uncertainty analysis
Uncertainty analysis
  • Data collection
    • Limited sample size
      • More data required over larger area
    • Measurement errors
    • Orientation of sample lines relative to trends of features
  • Upscaling
    • Do relationships found occur at all scales?
  • Use of analogue data set
    • Uplift induced fracturing, jointing & faulting
    • How ‘closed’ are fractures under subsurface pressure conditions.
implications for reservoir production development
Implications for reservoir production/development
  • Analogue data collection allows for greater understanding of potential reservoir production issues, ie fluid flow during production.
  • Interaction of fractures & small offset faulting creates high lateral permeability allowing efficient drainage of beds.
    • Very High fracture permeability parallel to small offset faults
  • Vertical restriction of fracture permeability & presence of marl units may prevent excessive water cut in wells.
  • Larger offset faults, if open may encourage water production, however complex low perm damage zone & fault gouge likely to create sealing faults.
  • Evaluation of seismic structure & understanding of sub-seismic features & populations is key to successful well planning & development.