Planning application no. LCC/2014/0096 by Cuadrilla Bowland Limited - - PowerPoint PPT Presentation

Planning application no. LCC/2014/0096 by Cuadrilla Bowland Limited to drill at Preston New Road, Lancashire: Objection on grounds of geology and hydrogeology

by

Professor David Smythe

Emeritus Professor of Geophysics, University of Glasgow

Introduction

Shale is a very common kind of rock (UK not special) Shale basins of the UK very different from USA Royal Society etc. :

• fracking environmentally safe if ‘well regulated’.

Geology sections concentrated on:

• Induced seismicity
• Fracture growth by fracking

Hardly a mention of pre-existing faults as conduits

Relied on a US industry (Halliburton) study:

• Ten thousand fracked wells in the

USA collated

• None of the fracks penetrate

upwards anywhere near the local aquifers

• So pollution of groundwater by

fracking not a problem

• in the USA

Faulting: a crucial problem in Europe

USA and UK at same scale Oklahoma England Pennsylvania Texas

Details in later slide

Shale basin sizes: UK: 5-50 times thicker than US, but 10-100 times smaller in area

Northern England Weald ( ) USA

Bowland Basin

Faulting and fracked wells

Marcellus Shale, Bradford County, NE Pennsylvania

Geology shown in colour, dots are wells

Faults in the Fylde and Bowland Fells

at same scale

UK basins have 500 times more faults than US average

Preston New Road

Problem of pre- existing faults as conduits

Target horizon Groundwater layer

German study 2012

France: groundwater circulation to over 3 km depth Faults are proven conduits

Source: University of Montpellier

Bath-Bristol area: groundwater circulation to over 2 km depth (British Geological Survey) Faults are proven conduits

The Sherwood Sandstone Group (SSG) at the surface: the the most important groundwater aquifer in the north of England. West of the Woodsfold Fault and south of the Wyre the SSG is covered by younger rocks, and the aquifer is highly saline. SSG covered by younger rocks Sherwood Sandstone Group (SSG) at surface

W

• d

s f

• l

d F a u l t Bilsborrow Fault

Bowland Fells

Coastline

• R. Wyre

Bilsborrow Fault Woodsfold Fault

Recharge

Fresh

Saline Recharge Dissolution

Bowland Fells to Fylde: Groundwater movement across faults (Environment Agency) Faults are proven conduits

Perspective view looking north Woodsfold Fault EA cross-section Bilsborrow Fault Bilsborrow and Woodsford Faults diverge southwards from Garstang (G). Since the former fault is transmissive, it is highly unlikely that the latter is a sealing fault, especially in the blue-ringed zone where sandstone is juxtaposed against sandstone. G Sherwood Sandstone at surface in West Cumbria: United Utilities drills water wells into geological faults “to give the best access to the yields”.

Preston: Groundwater movement across faults (Environment Agency 2006)

Aquifer Flow through faults

Faults are proven conduits

Preston New Road

• Cuadrilla - potential upward fluid migration will be “prevented by

management” during fracking.

• Well to be drilled through a fault - interpretation is unlikely and

unconvincing.

• Seismic data on which this sketch is based have not been released.
• All layers above fracked shale, except the thin Manchester Marls,

are very permeable.

• Many potential migration pathways exist.

Progressive decrease of 3D quality

Fracked shale

1 4 3 2 A B

Fault-1

Fluid flow paths:

• 1. Directly upwards from the Upper Bowland Shale into the permeable Millstone Grit Group.
• 2. Up the transmissive fracture zone of Fault-1.
• 3. Along the highly permeable Collyhurst Sandstone, generally up-dip to the east, and only partially confined by

the Manchester Marls.

• 4. Directly upwards from all the preceding sources through the Permian and superficial deposits to the surface.

Cuadrilla's Fault-1 is geologically improbable; therefore it is reinterpreted on the right at point A (monoclinal flexure made into a fault) and at

B (continuation of the fault up to the sub-Permian unconformity at the base of the Collyhurst Sandstone).

Preston New Road

Preston New Road NW SE Woodsfold

F a u l t

Permian and younger rocks

Extension of Cuadrilla cross-section to south-east

11 km

Thistleton Fault

Two main varieties of fault:

• Pre-Permian - only cut the Carboniferous
• Faults which cut all rocks up to the surface

Carboniferous

The 3D seismic survey:

Location of the 2011 tremors Fault identification

Bottom of wellbore deviated to east

Cuadrilla 2011: faults at Preese Hall-1 on 2-D seismic image

Faults Wellbore probably deviated to avoid faults

3D survey coverage incomplete and inadequate

100% limit Quality 0% at outer edge Preston New Road

Cuadrilla interpretation

Preese Hall-1

Modified fault interpretation 1000 m vertical

Earthquake hypocentre Oblique view of horizontal plane

Preese Hall-1 Cuadrilla 2014: The ‘tremor’ fault near the bottom of Preese Hall-1

2800 Deformed bore Stage 2 Stage 1 Cuadrilla fault interpretation Better fault interpretation

500 m

Scaled cross-section through Preese Hall-1 wellbore

Hypocentre 2400 2500 2600 2700 2900 3000 2930 m depth

TVD ss depth (m)

Preese Hall-1 did penetrate the ‘tremor’ fault

• matches the 3D seismic image better
• explains the well pipe deformation
• accounts for why tremors started just after stage 2 fracking

West East Wellbore

Lessons from Preese Hall-1 and the 3D survey

• 3D survey not up to scratch
• Faults very hard to recognise in shale
• PH-1 went through ‘tremor’ fault
• Poor understanding of faults

• US shale experience is no guide to UK
• Faulting important in Bowland Basin
• Faults often act as conduits for fluids
• Cuadrilla PH-1 drilled a fault in 2011
• (just like Balcombe, Sussex)
• 3D seismic survey mediocre quality
• Cuadrilla fault interpretation unreliable
• (just like Balcombe, Sussex)
• EA self-contradictory, over-optimistic
• Rocks above shales poor fluid barrier
• More earthquake triggering likely

Applying the precautionary principle to the risk of contamination by fluids and methane -

the application should be refused Conclusions