Flamborough Chalk Outcrops

DrillItOrDie Plc.

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

Stylolites

Location 1: Plan view annotation of fractures

Bed thickness = 20 cm

1m

1m

fault

Location 2: Plan view annotation of fractures

1m

1mBed Thickness = 30 cm

Location 3: Plan view annotation of fractures

Bed Thickness = 29 cm

1m

1m

Rose Diagrams

Location 2 Location 3

Thicker beds ~ 30cm

N N

Location 1

Thinner bed ~ 20cm

N

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

Conclusions

Large joints/fractures and faults determine level of vertical connectivity

The majority of permeability is distributed horizontally

We believe that the data collected and models proposed give us the best understanding to analysis the suitability of the outcrop as a reservoir