Hugh Barron Responsive Surveys Scotland · Oil Amorphous Kerogen Structureless debris of algal...

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Potential shale gas/oil resources in Scotland

Hugh Barron

Responsive Surveys Scotland

The British Geological Survey (BGS)

− world's oldest national geological survey (1835)

− public sector organisation

− the UK’s No.1 centre for geoscience information & expertise

− geoscience advisors to UK Government (and Scottish Govt)

− impartial geological advice to industry, academia & the public

− part of NERC, which reports to BIS

− 50% funded (c. £45m) from NERC, rest from public and private commissioned research

BGS Edinburgh office

Murchison House

BGS expertise on shale gas issues− 3D geological modelling

− Hydrocarbon prospectivity

− Organic geochemistry

− Groundwater sustainability and quality

− Seismicity, earthquake hazard & rock stress

What is shale?

− Grey or black, soft

− Fine grained

− Low porosity and permeability

− 70% of the world’s surface rocks are sedimentary; 50% of those are shale

− Contain ~95 % of the organic matter in sedimentary rocks

P521295

Lower Devonian shale, Margie Burn, Edzell

P219686Shales, siltstones and thin sandstones in the Gullane Formation, Linhouse Water, Mid Calder, West Lothian

What is shale?

Land plant material and seawater algae collect in mud

Older, deeper shale layer

Where does the organic material come from?

0 mOld deep shale layer

Burial over millions of years

− Shale buried

− Biological decay –biogenic methane

− Organic matter ‘cooked’ – thermogenic methane

Shale formation

Oil and gas maturation

Geothermal gradient in Scotland = 30 to 45oC/km

Kerogen types and their hydrocarbon potentialEnvironment Kerogen

typeKerogen form Origin HC potential

Aquatic

Alginite Algal bodiesOil

Amorphous Kerogen

Structureless debris of algal origin

IIStructureless planktonic material,primarily of marine origin

Terrestrial

Exinite Skins of spores and pollen, cuticle of leaves and herbaceous plants

Vitrinite Fibrous and woody plant fragments and structurelesscolloidal humic matter

Gas, some oil

Mainly gas

IVInertinite Oxidised, recycled woody debris

Petroleum accumulates instructural closure

Cap rock

Reservoir

Source

www.aapg.org

Cap Rock

Reservoir

Source

Conventional Petroleum System

PERMEABLE

RESERVOIR

What is a Gas Shale ?

LOMPOC Quarry Sample

Monterey Formation, CA

It´s all together:

the source

the reservoir

the seal

it is rich in organic carbon

!! Shale gas is self-contained HC system !

Unconventional Petroleum System− Regionally extensive

− Dry holes are rare

− No HC/H2O contacts

− Poor reservoir

− Production difficult

− Performance unpredictable

− High OPEX

Sand grain

0.25mm

shalesandstone

Conventional − Unconventional

iMethane gas is stored……

In sorbedstate

On the surface of the organic fraction

On the surface of clay minerals

As free gas

Matrix porosity (blue)

Fracture porosity

− Fracture gas is produced immediately

− Adsorbed gas is released as pressure declines

PERMEABLE

RESERVOIR

Unconventional Petroleum Systems

− Shale gas

− Shale oil

− Tight gas sands

− Heavy oil

− Coalbed methane

− Gas hydrates

− Oil shale

Oil shale

− Organic rich

− Immature for oil & gas

− Produces oil and gas when pyrolyzed at around 500°C

P528095Oil-shale from West Lothian

From: frontispiece of Bibliotheca Chemica (Volume 2), 1906, edited by John Ferguson

Scotland − birthplace of the oil industryJames “Paraffin” Young

1811 − 1883− 1850 Patent: distillation of

oil and paraffin wax from cannel coal

− 1851, Bathgate: first commercial oil-works in the world

− Initially torbanite & cannel coal, then oil shale used

− Scotland was the worlds largest oil-producing nation for a few years!

− In production until 1960

P000194

West Lothian oil-shale works

Retorts, distillation plant and condensers in 1927

− Estimated total oil production = 75m barrels (10m tonnes)

− 37m barrels remaining (5m tonnes)

Oil-shale products

P528115

P000199

Spent shale…

Westwood Bing 'The Five Sisters', West Calder, West Lothian

What makes a successful shale play?

− Conventional oil & gas production

− Depth range: 1000 – 3500 m

− TOC; Tmax; HI (maturity)

− Kerogen type (I & II)

− Target unit thickness/volume

− Overpressured zones

− Maturity within the gas/oil window

− Petrography: non-clay minerals

− Good geophysical data

Risk Period Target Basin/setting

Carboniferous Bowland Shale Pennine

Jurassic Kimmeridge Clay Weald

Higher

Carboniferous Dinantian shales Pennine

Jurassic Lias Weald

Carboniferous Oil Shale Group Midland Valley, Scotland

Cambrian Upper Cambrian Midland Microcraton

UK exploration targets

Conventional oil & gas wells

Midland Valley PEDL licences

Resources and reserves ‒ definitions

Resources refers to an estimate of the amounts of oil and gas that are believed to be physically contained in the source rock

Reserves refer to an estimate of the amount of oil or gas that can technically and economically be expected to be produced from a geological formation. Estimates of reserves will develop and improve with increasing exploration drilling

SPE Oil & Gas Reserves Committee (OGRC)

Resources and reserves

ResourceTechnically recoverableresource

Economic reserve ?

Bowland Shale resources

Total Gas in Place (GIP)

= 1,329 tcf (2013)

Midland Valley resources

= ? (2014)

− Bottom-up – In place figure based on geological model, volumetrics and gas contents-BGS approach

− Top-down – Technically recoverable estimate based on well technology, well density, well performance* USGS approach

*more reliable figure but requires production data that we don’t have in the UK

How to estimate

Core and cuttings for:Mineralogy

Organic geochemistry

Vitrinite reflectance

Porosity and permeability

Subsurface models:of shale thicknesses

of underground stress

Downhole data:Geophysical log: Natural/spectral gamma;

resistivity; sonic, nuclear, image etc.

Geothermal gradient

Interpreted 2D/3D seismic

Datasets to aid resource estimations

Workflow

Bowland Shale (lower unit)

− Correlation and dating: establish a geological framework

− Variations in TOC and kerogen types

− Variations in shale mineralogy

− Geological controls on variables:

• Depositional

• Diagenetic

• Basin evolution; Maturation, inversion

− Resource assessment‒ resource to reserve

Geological challenges

− Cracks the shale

− High pressure water or nitrogen, 350-700 bar (350 to 700 atmospheres)

Fracking basics

hfb@bgs.ac.uk

www.bgs.ac.uk/research/ukgeology/scotland.html

Hugh Barron Responsive Surveys Scotland · Oil Amorphous Kerogen Structureless debris of algal...

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