Technically Recoverable Shale 

Oil and Shale Gas Resources:

United Kingdom

Independent Statistics & Analysis

www.eia.gov

U.S. Department of Energy

Washington, DC 20585

September 2015
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U.S. Energy Information Administration | Technically Recoverable Shale Oil and Shale Gas Resources i

This report was prepared by the U.S. Energy Information Administration (EIA), the statistical and 

analytical agency within the U.S. Department of Energy. By law, EIA’s data, analyses, and forecasts are 

independent of approval by any other officer or employee of the United States Government. The views 

in this report therefore should not be construed as representing those of the Department of Energy or 

other Federal agencies.
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Contents

Executive Summary.......................................................................................................................................3

Introduction.............................................................................................................................................3

Resource categories.................................................................................................................................3

Methodology ...........................................................................................................................................5

Key exclusions..........................................................................................................................................6

United Kingdom.......................................... .........................................................................................................XI-1
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Executive Summary

Introduction 

Although the shale resource estimates presented in this report will likely change over time as additional 

information becomes available, it is evident that shale resources that were until recently not included in

technically recoverable resources constitute a substantial share of overall global technically recoverable oil and 

natural gas resources. This chapter is from the 2013 EIA world shale report Technically Recoverable Shale Oil 

and Shale Gas Resources: An Assessment of 137 Shale Formations in 41 Countries Outside the United States.

Resource categories 

When considering the market implications of abundant shale resources, it is important to distinguish between a 

technically recoverable resource, which is the focus of this supplement as in the 2013 report, and an 

economically recoverable resource. Technically recoverable resources represent the volumes of oil and natural 

gas that could be produced with current technology, regardless of oil and natural gas prices and production 

costs. Economically recoverable resources are resources that can be profitably produced under current market 

conditions. The economic recoverability of oil and gas resources depends on three factors: the costs of drilling 

and completing wells, the amount of oil or natural gas produced from an average well over its lifetime, and the 

prices received for oil and gas production. Recent experience with shale gas and tight oil in the United States 

and other countries suggests that economic recoverability can be significantly influenced by above-the-ground 

factors as well as by geology. Key positive above-the-ground advantages in the United States and Canada that 

may not apply in other locations include private ownership of subsurface rights that provide a strong incentive 

for development; availability of many independent operators and supporting contractors with critical expertise 

and suitable drilling rigs and, preexisting gathering and pipeline infrastructure; and the availability of water 

resources for use in hydraulic fracturing. See Figure 1.

Figure 1. Stylized representation of oil and natural gas resource categorizations

(not to scale)

Crude oil and natural gas resources are the estimated oil and natural gas volumes that might be produced at 

some time in the future. The volumes of oil and natural gas that ultimately will be produced cannot be known 
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U.S. Energy Information Administration | Technically Recoverable Shale Oil and Shale Gas Resources 4

ahead of time. Resource estimates change as extraction technologies improve, as markets evolve, and as oil and 

natural gas are produced. Consequently, the oil and gas industry, researchers, and government agencies spend 

considerable time and effort defining and quantifying oil and natural gas resources.

For many purposes, oil and natural gas resources are usefully classified into four categories: 

• Remaining oil and gas in-place (original oil and gas in-place minus cumulative production at a 

specific date)

• Technically recoverable resources

• Economically recoverable resources

• Proved reserves

The oil and natural gas volumes reported for each resource category are estimates based on a combination of 

facts and assumptions regarding the geophysical characteristics of the rocks, the fluids trapped within those 

rocks, the capability of extraction technologies, and the prices received and costs paid to produce oil and natural 

gas. The uncertainty in estimated volumes declines across the resource categories (see figure above) based on 

the relative mix of facts and assumptions used to create these resource estimates. Oil and gas in-place estimates 

are based on fewer facts and more assumptions, while proved reserves are based mostly on facts and fewer 

assumptions.

Remaining oil and natural gas in-place (original oil and gas in-place minus cumulative production). The volume 

of oil and natural gas within a formation before the start of production is the original oil and gas in-place. As oil 

and natural gas are produced, the volumes that remain trapped within the rocks are the remaining oil and gas 

in-place, which has the largest volume and is the most uncertain of the four resource categories.

Technically recoverable resources. The next largest volume resource category is technically recoverable 

resources, which includes all the oil and gas that can be produced based on current technology, industry 

practice, and geologic knowledge. As technology develops, as industry practices improve, and as the 

understanding of the geology increases, the estimated volumes of technically recoverable resources also 

expand.

The geophysical characteristics of the rock (e.g., resistance to fluid flow) and the physical properties of the 

hydrocarbons (e.g., viscosity) prevent oil and gas extraction technology from producing 100% of the original oil 

and gas in-place.

Economically recoverable resources. The portion of technically recoverable resources that can be profitably 

produced is called economically recoverable oil and gas resources. The volume of economically recoverable 

resources is determined by both oil and natural gas prices and by the capital and operating costs that would be 

incurred during production. As oil and gas prices increase or decrease, the volume of the economically 

recoverable resources increases or decreases, respectively. Similarly, increasing or decreasing capital and 

operating costs result in economically recoverable resource volumes shrinking or growing.

U.S. government agencies, including EIA, report estimates of technically recoverable resources (rather than 

economically recoverable resources) because any particular estimate of economically recoverable resources is 

tied to a specific set of prices and costs. This makes it difficult to compare estimates made by other parties using 

different price and cost assumptions. Also, because prices and costs can change over relatively short periods, an 

estimate of economically recoverable resources that is based on the prevailing prices and costs at a particular 

time can quickly become obsolete.
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Proved reserves. The most certain oil and gas resource category, but with the smallest volume, is proved oil and 

gas reserves. Proved reserves are volumes of oil and natural gas that geologic and engineering data demonstrate 

with reasonable certainty to be recoverable in future years from known reservoirs under existing economic and 

operating conditions. Proved reserves generally increase when new production wells are drilled and decrease 

when existing wells are produced. Like economically recoverable resources, proved reserves shrink or grow as 

prices and costs change. The U.S. Securities and Exchange Commission regulates the reporting of company 

financial assets, including those proved oil and gas reserve assets reported by public oil and gas companies.

Each year EIA updates its report of proved U.S. oil and natural gas reserves and its estimates of unproved 

technically recoverable resources for shale gas, tight gas, and tight oil resources. These reserve and resource 

estimates are used in developing EIA's Annual Energy Outlook projections for oil and natural gas production. 

• Proved oil and gas reserves are reported in EIA’s U.S. Crude Oil and Natural Gas Proved Reserves.

• Unproved technically recoverable oil and gas resource estimates are reported in EIA’s Assumptions

report of the Annual Energy Outlook. Unproved technically recoverable oil and gas resources equal 

total technically recoverable resources minus the proved oil and gas reserves.

Over time, oil and natural gas resource volumes are reclassified, going from one resource category into another 

category, as production technology develops and markets evolve.

Additional information regarding oil and natural gas resource categorization is available from the Society of 

Petroleum Engineers and the United Nations.

Methodology 

The shale formations assessed in this supplement as in the previous report were selected for a combination of 

factors that included the availability of data, country-level natural gas import dependence, observed large shale 

formations, and observations of activities by companies and governments directed at shale resource 

development. Shale formations were excluded from the analysis if one of the following conditions is true: (1) the 

geophysical characteristics of the shale formation are unknown; (2) the average total carbon content is less than 

2 percent; (3) the vertical depth is less than 1,000 meters (3,300 feet) or greater than 5,000 meters (16,500 

feet), or (4) relatively large undeveloped oil or natural gas resources. 

The consultant relied on publicly available data from technical literature and studies on each of the selected 

international shale gas formations to first provide an estimate of the “risked oil and natural gas in-place,” and 

then to estimate the unproved technically recoverable oil and natural gas resource for that shale formation. This 

methodology is intended to make the best use of sometimes scant data in order to perform initial assessments 

of this type.

The risked oil and natural gas in-place estimates are derived by first estimating the volume of in-place resources 

for a prospective formation within a basin, and then factoring in the formation’s success factor and recovery 

factor. The success factor represents the probability that a portion of the formation is expected to have 

attractive oil and natural gas flow rates. The recovery factor takes into consideration the capability of current 

technology to produce oil and natural gas from formations with similar geophysical characteristics. Foreign 

shale oil recovery rates are developed by matching a shale formation’s geophysical characteristics to U.S. shale 

oil analogs. The resulting estimate is referred to as both the risked oil and natural gas in-place and the 

technically recoverable resource. The specific tasks carried out to implement the assessment include:

1. Conduct a preliminary review of the basin and select the shale formations to be assessed.
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U.S. Energy Information Administration | Technically Recoverable Shale Oil and Shale Gas Resources 6

2. Determine the areal extent of the shale formations within the basin and estimate its overall thickness, in 

addition to other parameters.

3. Determine the prospective area deemed likely to be suitable for development based on depth, rock quality, 

and application of expert judgment.

4. Estimate the natural gas in-place as a combination of free gas1 and adsorbed gas2 that is contained within 

the prospective area. Estimate the oil in-place based on pore space oil volumes. 

5. Establish and apply a composite success factor made up of two parts. The first part is a formation success 

probability factor that takes into account the results from current shale oil and shale gas activity as an 

indicator of how much is known or unknown about the shale formation. The second part is a prospective 

area success factor that takes into account a set of factors (e.g., geologic complexity and lack of access) that 

could limit portions of the prospective area from development.

6. For shale oil, identify those U.S. shales that best match the geophysical characteristics of the foreign shale 

oil formation to estimate the oil in-place recovery factor.3

 For shale gas, determine the recovery factor 

based on geologic complexity, pore size, formation pressure, and clay content, the latter of which 

determines a formation’s ability to be hydraulically fractured. The gas phase of each formation includes dry 

natural gas, associated natural gas, or wet natural gas. Therefore, estimates of shale gas resources in this 

report implicitly include the light wet hydrocarbons that are typically coproduced with natural gas.

7. Technically recoverable resources4 represent the volumes of oil and natural gas that could be produced with 

current technology, regardless of oil and natural gas prices and production costs. Technically recoverable 

resources are determined by multiplying the risked in-place oil or natural gas by a recovery factor.

Based on U.S. shale production experience, the recovery factors used in this supplement as in the previous 

report for shale gas generally ranged from 20 percent to 30 percent, with values as low as 15 percent and as 

high as 35 percent being applied in exceptional cases. Because of oil’s viscosity and capillary forces, oil does not 

flow through rock fractures as easily as natural gas. Consequently, the recovery factors for shale oil are typically 

lower than they are for shale gas, ranging from 3 percent to 7 percent of the oil in-place with exceptional cases 

being as high as 10 percent or as low as 1 percent. The consultant selected the recovery factor based on U.S. 

shale production recovery rates, given a range of factors including mineralogy, geologic complexity, and a 

number of other factors that affect the response of the geologic formation to the application of best practice 

shale gas recovery technology. Because most shale oil and shale gas wells are only a few years old, there is still 

considerable uncertainty as to the expected life of U.S. shale wells and their ultimate recovery. The recovery 

rates used in this analysis are based on an extrapolation of shale well production over 30 years. Because a 

shale’s geophysical characteristics vary significantly throughout the formation and analog matching is never 

exact, a shale formation’s resource potential cannot be fully determined until extensive well production tests 

are conducted across the formation.

Key exclusions

In addition to the key distinction between technically recoverable resources and economically recoverable 

resources that has been already discussed at some length, there are a number of additional factors outside of 

the scope of this report that must be considered in using its findings as a basis for projections of future 

 1 Free gas is natural gas that is trapped in the pore spaces of the shale. Free gas can be the dominant source of natural gas 

for the deeper shales.

2 Adsorbed gas is natural gas that adheres to the surface of the shale, primarily the organic matter of the shale, due to the 

forces of the chemical bonds in both the substrate and the natural gas that cause them to attract. Adsorbed gas can be the 

dominant source of natural gas for the shallower and higher organically rich shales.

3 The recovery factor pertains to percent of the original oil or natural gas in-place that is produced over the life of a production well. 4 Referred to as risked recoverable resources in the consultant report.
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U.S. Energy Information Administration | Technically Recoverable Shale Oil and Shale Gas Resources 7

production. In addition, several other exclusions were made for this supplement as in the previous report to 

simplify how the assessments were made and to keep the work to a level consistent with the available funding.

Some of the key exclusions for this supplement as in the previous report include:

1. Tight oil produced from low permeability sandstone and carbonate formations that can often be found 

adjacent to shale oil formations. Assessing those formations was beyond the scope of this supplement as in 

the previous report.

2. Coalbed methane and tight natural gas and other natural gas resources that may exist within these 

countries were also excluded from the assessment.

3. Assessed formations without a resource estimate, which resulted when data were judged to be inadequate 

to provide a useful estimate. Including additional shale formations would likely increase the estimated 

resource.

4. Countries outside the scope of the report, the inclusion of which would likely add to estimated resources in 

shale formations. It is acknowledged that potentially productive shales exist in most of the countries in the 

Middle East and the Caspian region, including those holding substantial non-shale oil and natural gas 

resources.

5. Offshore portions of assessed shale oil and shale gas formations were excluded, as were shale oil and shale 

gas formations situated entirely offshore.
XI. United Kingdom EIA/ARI World Shale Gas and Shale Oil Resource Assessment

 

May 17, 2013 XI-1 

XI. UNITED KINGDOM

SUMMARY

The United Kingdom has substantial volumes of prospective shale gas and shale oil 

resources within Carboniferous- and Jurassic-age shale formations distributed broadly in the 

northern, central and southern portions of the country. 

Figure XI-1 : Shale Basins in the United Kingdom

Source: ARI 2013.
XI. United Kingdom EIA/ARI World Shale Gas and Shale Oil Resource Assessment

 

May 17, 2013 XI-2 

The risked, technically recoverable shale resources of the U.K. are estimated at 26 Tcf 

of shale gas and 0.7 billion barrels of shale oil and condensate in two assessed regions, Tables 

XI-1 and XI-2. This is based on the much larger unrisked estimates of 623 Tcf of shale gas inplace (134 Tcf, risked) and 54 Bbbl of shale oil in-place (17 billion barrels, risked). These 

estimates reflect only the higher-TOC portions of the Carboniferous and Jurassic shale 

intervals.

Table XI-1. Shale Gas Reservoir Properties and Resources of the United Kingdom

Source: ARI, 2013

Table XI-2. Shale Oil Reservoir Properties and Resources of the United Kingdom

Source: ARI, 2013

North UK

Carboniferous Shale Region

(10,200 mi2)

South UK

Jurassic Shale Region

(3,470 mi2

)

Carboniferous Shale Lias Shale

Carboniferous L. Jurassic

Marine Marine

5,100 1,735

Organically Rich 820 165

Net 410 149

Interval 5,000 - 13,000 4,000 - 6,000

Average 8,500 5,000

Normal Normal

3.0% 3.0%

1.30% 0.85%

Medium Medium

Dry Gas Assoc. Gas

117.3 14.5

125.6 8.0

25.1 0.6

Reservoir 

Properties

Reservoir Pressure

Average TOC (wt. %)

Thermal Maturity (% Ro)

Clay Content

Resource

Gas Phase

GIP Concentration (Bcf/mi2

)

Risked GIP (Tcf)

Risked Recoverable (Tcf)

Physical Extent

Prospective Area (mi2

)

Thickness (ft)

Depth (ft)

Basic Data

Basin/Gross Area

Shale Formation

Geologic Age

Depositional Environment

South UK

Jurassic Shale Region

(3,470 mi2

)

Lias Shale

L. Jurassic

Marine

1,735

Organically Rich 165

Net 149

Interval 4,000 - 6,000

Average 5,000

Normal

3.0%

0.85%

Medium

Oil

30.9

17.1

0.69

Reservoir 

Properties

Reservoir Pressure

Average TOC (wt. %)

Thermal Maturity (% Ro)

Clay Content

Resource

Oil Phase

OIP Concentration (MMbbl/mi2)

Risked OIP (B bbl)

Risked Recoverable (B bbl)

Physical Extent

Prospective Area (mi2

)

Thickness (ft)

Depth (ft)

Basic Data

Basin/Gross Area

Shale Formation

Geologic Age

Depositional Environment
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May 17, 2013 XI-3 

Initial exploration drilling has confirmed the presence of thick, gas-bearing shale deposits 

in the Bowland Sub-basin in the west portion of the Pennine Basin of northwest England. 

However, production testing has not yet occurred and the other shale regions remain undrilled. 

EIA/ARI’s current estimate of the UK’s shale gas resources is about 10% higher than our initial

2011 assessment, while new shale oil potential has been added. 

Compared with North America, the shale geology of the UK is considerably more 

complex, while drilling and completion costs for shale wells are substantially higher. The 

Pennine Basin, one of the country’s most prospective areas, has been tested with five vertical 

wells which cored the Carboniferous Bowland Shale. Other prospective areas include the rest 

of the North UK Carboniferous Shale region and the liquids-rich Jurassic Shale region of 

southern England in the Wessex and Weald basins, Figure XI-1.

Shale testing is still at an early phase in the UK – flow testing and horizontal shale 

drilling have not even been attempted. In a temporary setback, the first shale well to be 

hydraulically stimulated triggered a series of minor earthquakes related to a nearby fault. 

Following an 18-month moratorium, the government concluded that the environmental risks of 

shale exploration are small and manageable. Shale drilling was allowed to resume in 

December 2012, albeit with stricter monitoring controls. Current shale operators include 

Cuadrilla Resources, IGAS, Dart Energy, and others. 

INTRODUCTION

Within Europe, the United Kingdom stands next after Poland in pursuing its shale gas 

and shale oil potential. However, with a small existing onshore conventional oil and gas 

industry, the UK has limited domestic service sector capability for shale exploration. Natural 

gas prices are high (~$9/MMBtu) in the UK compared with North America, but geologic 

conditions are much more complex. Faults are numerous, geologic data control is weak, and 

shale wells are more costly to drill. While the UK’s shale resource base appears substantial, 

commercial levels of shale production are yet to be established. 

Political opposition to shale development is greater in the UK than in Poland but less 

than in France or Germany. Hydraulic fracturing got off to an abysmal start. The UK’s first 

shale production test well triggered small local earthquakes during fracture stimulation and the 

vertical wellbore was deformed. This is perhaps unsurprising given the highly faulted nature of 

shale deposits in the UK (and generally in Europe). The government banned onshore hydraulic 

fracturing for a period of eighteen months to better evaluate the risks. 
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May 17, 2013 XI-4 

In January 2012 the British Geological Survey noted that the risks of shale development 

to groundwater and earthquakes had been exaggerated. Minor earthquakes caused by the 

Preese Hall-1 well were “comparable in size to the frequent minor quakes caused by coal 

mining. What's more, they originate much deeper in the crust so have all but dissipated by the 

time they reach the surface.”1 In December 2012 the UK government finally granted conditional 

approval for shale exploration, albeit with strict monitoring conditions. Cuadrilla recently 

delayed its plan to resume fracture stimulation until 2014 at the earliest.

Companies which have been granted a Petroleum Exploration and Development license 

(PEDL) by the UK government are permitted to explore and develop shale gas, as well as other 

types of petroleum resources (conventional, coalbed methane, tight gas, etc.). Field 

development is subject to necessary national and local consent and planning permission. 

Currently there are about 334 onshore PEDLs, of which several dozen have recognized shale 

potential. Proprietary shale data typically are kept confidential for a four-year period from the 

date of well completion. 

At least six oil and gas companies are targeting shale gas exploration in the UK but only 

two have actually drilled shale wells. All wells have been vertical. UK-based Cuadrilla 

Resources, partly (43%) owned by Australian drilling company AJ Lucas, is the most active, 

drilling and coring four shale exploration wells in the West Bowland Sub-basin that confirmed 

the presence of up to 2-km of gas-bearing organic-rich shale. However, at least one well 

encountered active faults and high-stress conditions. IGAS Energy has drilled a shale well

nearby, coring the 1,600-ft thick Bowland Shale. Horizontal shale wells have not yet been 

attempted in the UK, nor have flow tests been reported. Coastal Oil and Gas Ltd., Celtique 

Energie, Dart Energy, and Eden Energy also are evaluating their UK shale resource potential 

but haven’t yet drilled.
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May 17, 2013 XI-5 

GEOLOGIC OVERVIEW

As early as the late 1980s researchers at Imperial College, London had identified the 

main stratigraphic targets for shale gas exploration in the UK, the marine-deposited black shales 

of Carboniferous and Jurassic age.2,3 More recently in 2003, a study conducted by the British 

Geological Survey (BGS) and published by the UK Department of Trade and Industry (DTI) 

presented an integrated review of the geology of Britain’s onshore conventional oil and gas 

fields and source rock shales, although it was not asked to consider shale as a productive 

reservoir.4 In 2010 BGS published a compilation of shale-specific geologic data collected from 

outcrops and conventional petroleum wells.5 

BGS published its preliminary evaluation of UK shale gas resources later in 2010,

conducted on behalf of the Department of Energy and Climate Change (DECC).6 BGS’ initial 

estimate was 5.3 Tcf (150 Bcm) of recoverable shale gas resources. BGS, in association with 

DECC, plans to release an updated evaluation of shale gas potential of northwest England later 

in 2013, followed eventually by a more complete national estimate.7

The main onshore sedimentary basins in the UK that produce oil and gas or have 

conventional or shale exploration potential are shown in Figure XI-1. The current EIA/ARI 

resource assessment groups these numerous, typically fault-bounded basins into two main 

shale exploration regions:

• North UK Carboniferous Shale Region. A complex assemblage of isolated structural 

basins and troughs is present across northern England and southern Scotland. These 

contain prospective organic-rich shales of Carboniferous age, including notably the 

Bowland Shale. Within the greater Pennine Basin, individual sub-basins include the 

Bowland, Cleveland, Cheshire, West Lancashire, Northumberland, East Midlands, 

Gainsborough, Midland Valley, as well as others. The Bowland Sub-basin is the only 

area to undergo shale exploration drilling to date.

• South UK Jurassic Shale Region. In southern England the Wessex and Weald basins 

extend offshore into the English Channel. They contain Jurassic-age shales that are oilprone. While no shale drilling has occurred here yet, the region includes Britain’s 

largest onshore oil field and appears highly prospective for shale oil development. 
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May 17, 2013 XI-6 

It is important to note that the UK shale basins generally are not simple continuous 

structures, such as found in many North America shale regions, but rather typically comprise a 

series of small fault-bounded sub-basins. Figure XI-2 shows a regional cross-section from the 

Wessex Basin in the south to the Bowland Sub-basin in the north, highlighting the 

Carboniferous-Namurian and Jurassic shale targets. Even the interior of the sub-basins may be 

significantly faulted, to an extent generally not displayed on schematic cross-sections. The 

structural complexity, coupled with the relatively small data base of onshore petroleum wells in 

the UK (particularly in the troughs), makes resource assessment more difficult. It also could 

slow the pace of shale exploration, de-risking, and commercial development in the UK.

Figure XI-2 : Regional Cross-Section from Wessex Basin Through Bowland Sub-basin

Highlighting Carboniferous-Namurian and Jurassic Shale Targets

Source: British Geological Survey, 2012

The main stratigraphic targets for shale exploration in the UK are the Carboniferous 

Mississippian (Lower Namurian)8 and the Lower Jurassic Lias formations, both of which contain 

organic-rich, marine-deposited shales, Figure XI-3. Other potential shale targets include the U. 

Cambrian and the U. Jurassic Oxford and Kimmeridge Clays, but these were excluded from our 

study due to their low thermal maturity, lower organic content, and/or extreme structural 

complexity. In particular, organic-rich shales found within the Carboniferous Coal Measures 

were excluded because these non-marine shales are coaly, high in clay, and unlikely to be 

sufficiently brittle. However, further data collection and mapping may reveal these or other 

shale formations to be prospective in places.
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May 17, 2013 XI-7 

Figure XI-3: Stratigraphic Column Showing UK Formations That Contain Organic-Rich Shales.

The Lower Jurassic Lias And Carboniferous Shales Appear Most Prospective.

Source: Smith et al., 2010

The BGS has cited the Middle Cambrian Conasauga Shale in Alabama as the closest 

North American geologic analog for Cambrian shale deposits in the UK, given their similar age 

and degree of structural complexity. However, shale gas development in the Conasauga Shale 

has not been successful to date. The Cambrian-age shale deposits in the UK were not 

assessed in the EIA/ARI study due to their structural complexity and lack of geologic data.
XI. United Kingdom EIA/ARI World Shale Gas and Shale Oil Resource Assessment

 

May 17, 2013 XI-8 

SEISMIC HAZARDS

The UK shale industry experienced a serious setback in 2011, when the first hydraulic 

fracturing operation of a shale well unexpectedly generated a series of very small earthquakes. 

However, it is noteworthy that none of the approximately 50,000 horizontal shale wells drilled in 

North America during the past decade have generated significant earthquakes, although a few 

suspected seismic events are under review. 

In August 2010 Cuadrilla drilled the UK’s first shale gas exploration well, spudding the 

Preese Hall-1 vertical well in the Bowland Sub-basin near Blackpool, Lancashire. The well was 

fracture stimulated during early 2011, inducing several dozen small earthquakes close to the 

downhole injection zone. The timing of the earthquakes corresponded with fluid injection and 

continued for several hours after injection ceased. Fortunately, the largest earthquakes were 

relatively small, measuring magnitudes of 2.3 and 1.5 on the Richter scale. No surface damage 

was reported. However, the UK government shut down shale testing in the country for 18 

months to determine the cause of the seismic events and to develop mitigation rules.

An evaluation of seismicity from these earthquakes generated by the Preese Hall-1 well 

and the fault geometry of the basin indicated that movement was strike-slip along a sub-vertical 

fault plane. The suspected fault was located on the well’s image log as well as on detailed 

seismic, Figure XI-4.9 Separately, bedding plane slip -- already noted in core cut prior to 

running casing in the well -- induced wellbore damage, with oval deformation noted across 

several hundred feet of the 5.5-inch casing.

The maximum horizontal stress gradient, based on mini-frac and borehole breakout 

data, was determined to be relatively high at 1.25 psi/ft. The stress differential within the 

Bowland Shale -- about 4,000 psi -- was found to be an order of magnitude higher than in North 

American shale plays, which typically have stress differentials of only several hundred psi. It is 

unclear whether the high stress differential is local or widely prevalent across the UK. 

Cuadrilla’s consultants concluded that excess fluid pressure exerted on the fault during

the hydraulic stimulation overcame the rock friction containing this stress, which enabled the 

fault to slip and generate small earthquakes. Simultaneously, bedding plane slip up the hole 

caused the well’s casing string to deform. Based on fault size and geometry, the maximum 

earthquake in the Bowland Sub-basin was estimated to be approximately magnitude 3.0, still 

considered too small to cause significant damage to surface structures in this region. 
XI. United Kingdom EIA/ARI World Shale Gas and Shale Oil Resource Assessment

 

May 17, 2013 XI-9 

Figure XI-4: Seismic Reflection Line Showing Suspected Active Faults

Near The Preese Hall-1 Well In The Bowland Sub-basin

Source: de Pater and Baisch, 2011

The consultants also inferred that the injected frac fluid remained contained within the 

induced fracture system and did not leak into the shallow freshwater aquifer system, because of 

the thick and impermeable Bowland Shale and overlying Permian anhydrites. A subsequent 

report recommended monitoring during hydraulic fracturing operations to help mitigate induced 

seismicity.10 

As a result of the earthquakes the government halted shale operations in the UK from 

May 2011 until December 2012. The Royal Society and Royal Academy of Engineering 

conducted a review of the risks, recommending the following three primary steps for ensuring 

health and safety during shale development:11

• Groundwater Monitoring. The BGS should conduct regional baseline surveys of 

groundwater ahead of shale development, while operators conduct site-specific surveys 

to identify possible natural methane concentrations in groundwater. Abandoned wells 

should be monitored and remediated to prevent fracture fluids from entering freshwater 

aquifers.
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May 17, 2013 XI-10

• Well Integrity. Well design, construction, and integrity testing should ensure that 

multiple layers of steel and cement are present to preclude leakage of fluids into 

freshwater aquifers.

• Mitigating Seismicity. The BGS should survey the regional distribution of faults, 

stresses, and seismic hazards ahead of shale development, while operators conduct 

site-specific surveys. Seismicity should be monitored before, during, and after hydraulic 

stimulation, which should be shut down if seismic risks become unacceptable.

After considering these and other views, DECC put in place a new regulatory regime for 

shale development starting December 2012. The regime requires operators to evaluate 

potential seismic hazards posed by hydraulic fracturing, implement seismic monitoring of each 

individual well site area, and propose mitigation steps to minimize the chance of future 

earthquakes due to hydraulic fracturing. A real-time trigger is to be installed to cut off injection 

should significant earthquake risks arise. These rules are expected to add significant cost and 

time to drill shale wells in the UK. Cuadrilla’s Anna’s Road-1 well is the first to be spud under 

the new shale rules. Hydraulic stimulation of this well -- which Cuadrilla recently announced 

would be delayed until 2014 at the soonest -- would require further specific approvals.

1. NORTH UK CARBONIFEROUS SHALE REGION

1.1 Introduction and Geologic Setting

Northern England and southern Scotland are characterized by a complex assemblage of 

isolated basins and troughs which contain thick, organic-rich Carboniferous shales, Figure XI-1. 

These shale-prospective lows are separated by structural highs where Carboniferous was not 

deposited or has been eroded. Based on mapping of Carboniferous basins conducted by the 

BGS, these troughs cover a total area of approximately 10,000 mi2

. 

The Bowland Sub-basin of Lancashire, where shale drilling has been concentrated thus 

far, is one such trough, representing the onshore margin of the petroliferous East Irish Sea 

Basin. Further to the east the Cleveland Basin is considered the onshore extension of the 

Southern North Sea gas basin. In between lay the Cheshire, West Lancashire, 

Northumberland, East Midlands, Pennine, Gainsborough, Midland Valley, and other basins and 

troughs containing Carboniferous-age shales. Our study grouped these isolated basins into a 

single region for shale resource assessment.

The western portion of the Bowland Sub-basin has been the site of all UK shale 
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May 17, 2013 XI-11

exploration drilling to date. The Carboniferous Bowland Shale is the main target, ranging from 

about 2.0 to 2.5 km deep across the moderately faulted Bowland Sub-basin, Figures XI-5 and

XI-6. Cuadrilla’s Preese Hall-1 well encountered the top of the target Lower Carboniferous 

Bowland Shale at a measured depth of 6,854 ft and penetrated a total 2,411 ft of organic-rich 

shale, Figure XI-7. The BGS has mapped the thickness of the Upper Bowland Shale Formation, 

as well as its organic-rich (high-gamma) section, across northern England, Figure XI-8. The 

organic-rich shale ranges up to 120 m thick but more typically is recorded as 20 to 40 m thick. 

Note, however, that petroleum wells are preferentially drilled on structural highs, where shale 

tends to be thinner than in the troughs. 

The eastern Bowland Shale play extension in the Gainsborough Basin has less geologic 

control than the west. Here the shale ranges up to 300 m thick in the Dinantian half-graben 

basins, Figure XI-9. Dart Energy reported that the most organic-rich portion defined by highgamma shales ranges up to 110 m thick. In the Cheshire Basin the Carboniferous (Namurian) 

Bowland and Holywell shales with TOC up to 5% occur at depths of 1 to 5 km, Figure XI-10. 

Elsewhere in the region, the Namurian Holywell Shale, source rock for conventional oil 

fields in the southern East Irish Sea as well as the Formby oil field, is reported to have an 

overall average TOC of 2.1% (range 0.7% to 5%) and averages 3.0% TOC in its lower, more 

organic-rich portion. Clay content is uncertain, although public data indicate that Carboniferous 

mudstones in the UK generally average around 25% Al2O3 (range 12-38%), mostly from clay.

The Pennine Basin has relatively good geologic control from past petroleum exploration. 

The Craven Group (Mississippian) ranges from about 1.5 km thick in the Craven sub-basin to 

over 5 km thick in the Widmerpool Gulf. These mudstones were deposited in distal slope 

turbidite and hemipelagic environments in relatively narrow, deep depocenters. The early 

Namurian shale units (local names Bowland, Edale, Holywell shales, top part of Craven Group) 

of the Pennine Basin have high TOC and are known to have sourced hydrocarbons. These 

Namurian marine shales generally have rich TOC in excess of 4%. 
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Figure XI-5: Structural Cross-Section in the Bowland Sub-basin Region, Northwest UK

Showing Numerous Faults Across the Cuadrilla and IGas Energy Licenses.

Source: Source: IGAS Energy, 2012

Figure XI-6: Structural Cross-Section In The Bowland Sub-basin Region Showing The Highly Faulted

Bowland Shale At 2 To 3 Km Depth. Additional Faults Penetrated By The Ince Marshes Well

Suggest That Many Additional Faults Are Present But Unrecognized.

Source: IGAS Energy, 2012; modified from BGS Map 96_Liverpool
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Figure XI-7: Stratigraphic Column and Composite Log for the Cuadrilla 

Preese Hall-1 well in the Bowland Sub-Basin

Figure XI-8: Thickness of the Upper Bowland Shale Formation in Northern

England, as Well as the High-Gamma Thickness. Note That Petroleum 

Wells Tend to be Drilled on Structural Highs Where the Shale May be 

Thinner Than in the Troughs. 

Source: de Pater and Baisch, 2011 Source: Smith et al., 2010
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Figure XI-9: Schematic Cross-Section Across The Gainsborough Trough Showing Thick Bowland Shale. 

Additional Faults Are Likely To Be Present But Not Shown.

Source: Dart Energy, 2013

Figure XI-10: Geologic Map and Generalized Structural Cross-Section of the Cheshire Basin. Carboniferous 

(Namurian) Bowland and Holywell Shales with TOC Up to 5% Occur at Depths of 1 to 5 km.

Source: DECC, 2012
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May 17, 2013 XI-15

The North UK Carboniferous Shale region is mainly in the dry gas window. For 

example, the Normanby-1 and Grove-3 conventional petroleum wells reportedly recorded highgamma sections within the Bowland Shale, while the Scaftworth-B2 well measured 2.07% to 

3.63% TOC with 1.26% Ro at a depth of 2,246 m.12 In addition, most of the Cleveland Basin is 

known to be within the dry gas window. Oil and wet gas thermal maturity windows may be 

present locally but could not be defined with the limited data available. 

No porosity data are available for Namurian shales in the Pennine Basin. Based on

boreholes drilled by the BGS in the southern Midlands, relatively shallow (900 m deep) Upper 

Paleozoic shales retained high porosities (5-10%). However, porosity is likely to be 

considerably lower (perhaps 3-5%) at typical target shale depth of 2-4 km.

The Midland Valley Basin (MVB), a large east-northeast trending graben complex that 

stretches across southern Scotland, is bounded by the Highland Boundary Fault to the 

northwest and the Southern Upland Fault to the southeast. The MVB comprises a complex 

series of small faulted sub-basins, such as the Kinkardine Basin where Dart Energy is 

evaluating shale gas resources. This structural complexity was over-printed by extensive 

igneous intrusion during late Carboniferous to early Permian time. 

The MVB contains a relatively complete sequence of Carboniferous deposits up to 6 km 

thick, Figure XI-11.13 Namurian strata range from 450 m to 1,400 m thick at outcrop. The 

depositional sequence reflects mixed marine shelf carbonate and deltaic successions, 

comprising upward-coarsening cycles of marine limestone, mudstone, siltstone and

sandstone.14 Lower Carboniferous (Dinantian) oil-shale source rocks, such as the Mid-Lothian 

Oil shale, buried deeply in the Midlothian-Leven Syncline generated waxy crude oil that sourced

clastic reservoirs of similar age in the adjacent anticlines.
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Figure XI-11: Geologic Map of the Midland Valley Basin. Carboniferous (Namurian)

Shales Crop Out at the Surface but May Reach Prospective Depth.

Source: Underhill et al., 2009

1.2 Reservoir Properties (Prospective Area)

The total mapped deep Carboniferous area in the North UK Carboniferous Shale region 

is approximately 10,200 mi2

. Because of structural complexity and poor depth control was poor, 

only half of the total area was assumed to be in the prospective depth window and relatively 

unfaulted (4,635 mi2

). The target lower organic-rich portion of the Bowland and Holywell shales 

(and local equivalents) averages about 300 ft thick and 8,000 ft deep in the Bowland Sub-basin 

region, with 3.0% average TOC. Porosity is estimated to be about 4% at target depths of 3 km, 

much lower than the 5-10% measured at shallow <1 km depth. Thermal maturity is mainly in 

the dry gas window (Ro 1.3%), although less mature pockets in the wet gas window may exist.
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1.3 Resource Assessment

Risked, technically recoverable shale gas resources in the North UK Carboniferous 

Shale region are estimated to be 25 Tcf, out of a risked shale gas in-place of 126 Tcf, Table XI1. The play has a favorable net resource concentration of about 117 Bcf/mi2

, reflecting the 

significant thickness of organic-rich shale.

For comparison, in September 2011 Cuadrilla Resources estimated the total shale gas 

in-place within its Bowland Sub-basin licenses to be approximately 200 Tcf, based on logs and 

core from two shale and three conventional petroleum wells.15 The company has estimated the 

total shale gas resource-in-place concentration at its Preese Hall-1 well to be 539 Bcf/mi2. 

Cuadrilla’s estimate is that 10% or about 20 Tcf may be recoverable. It appears that Cuadrilla’s 

estimate is based on the entire shale section, whereas EIA/ARI considers only the lower, most 

organic-rich section as the prospective interval.

Separately, IGAS Energy’s independent consultant identified a 1,195-km2 prospective 

area within an average 250-m thick organic-rich interval, constrained by geophysical logs from 

eight conventional petroleum wells that penetrated the Bowland Shale. After drilling its first 

shale appraisal well last year, IGAS estimated the shale gas in-place (GIP) resources within its 

licenses to be about 9.2 Tcf. 

Dart Energy’s third-party consultant NSAI has estimated that Dart’s licenses have some 

32.46 Tcf of GIP in unspecified shale formations in the Gainsborough Trough of East Midlands, 

as well as 30.55 Tcf of shale gas GIP in the Cheshire Basin (gross, Best Estimate). No 

recovery estimate was reported.16 Finally, in Scotland’s Midland Valley Basin, Dart Energy 

reported that the company’s PEDL 133 license has an estimated 2.5 Tcf of shale gas GIP based 

on a third-party consultant report. Recoverable prospective shale gas resources were 

estimated at 115 Bcf in the Carboniferous Black Metal Shale and 255 Bcf in the LothianBroxburn Shale (Best Estimates; net to Dart). 

1.4 Recent Activity

The Bowland Sub-basin, the only active shale drilling region in the UK, has had five 

shale exploration wells drilled to date. The main operators are Cuadrilla Resources (4 licenses 

totaling 1185 km2

; 4 wells), IGAS Resources (14 licenses; 1363 km2; 1 well), and Dart Energy 

(11 licenses; 1041 km2

). 
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In August 2010 Cuadrilla drilled the first shale gas exploration well in the UK, spudding 

the Preese Hall-1 vertical well in the Bowland Sub-basin near Blackpool, Lancashire. The top 

of the target Lower Carboniferous Bowland Shale was encountered at a measured depth of 

6,854 ft. The well penetrated a total 2,411 ft of organic-rich shale. Naturally fractured, the 

Bowland is within the dry gas thermal maturity window. 

After drilling was completed on the Preese Hall-1, Cuadrilla completed and fracture 

stimulated the well in early 2011. This operation represented the UK’s first and only concerted 

attempt to produce shale gas. As previously discussed, small earthquakes were induced near 

the well by the hydraulic fracture stimulation. Operations at the well were halted in May 2011 

with no gas production reported.

In completing the well, Cuadrilla perforated shale formations within the Bowland Shale, 

Worston Shale, and Hodder Mudstone at depths ranging from 7,670 to 8,949 ft. Five shale

zones, out of 12 originally planned, were individually stimulated with a sand/water slurry, 

separated by bridge plugs. The total stimulation size, over 50,000 bbl of water and 400 t of 

sand proppant, was relatively large for a vertical shale well but still considerably smaller than the 

typical stimulation of a horizontal shale well in North America (about half the water volume and 

10% of the sand volume).

Cuadrilla drilled and cored two other vertical wells in the Bowland Basin. During 2H 

2010 the nearby Grange Hill-1 vertical well logged over 2 km of Carboniferous shale across the 

depth interval of 1,200 m to 3,300 m, the total depth of the well. In 2011 the Becconshall-1

well logged shale from depths of 2,450 m to 3,100 m, the total depth of the well. 

Cuadrilla’s most recent shale well in the Bowland Sub-basin, the Anna’s Road-1, was 

abandoned at a depth of 2,000 ft due to drilling problems. The well was expected to be re-spud 

in January 2013 and completed in about four weeks, with the top Bowland Shale predicted at a 

depth of about 3100 m.

IGAS Energy Plc, 24.5% owned by Nexen and the UK’s largest onshore operator of oil

and gas fields, is evaluating the shale gas potential of its blocks. IGAS had acquired Nexen’s 

portfolio of UK coalbed methane licenses in March 2011. The company reported that at its 

Point of Ayr acreage has shale extending over the entire block with an expected average 

thickness of more than 800 ft. IGAS Energy noted that a significant proportion of its acreage in 
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May 17, 2013 XI-19

the northwest England—from Ellesmere Port in the west in PEDL 190 to the Trafford Centre in 

the east within PEDL 193—is considered to have shale potential.

In 2011-12 IGAS drilled the Ince Marshes-1 well to a total depth of 5,714 ft in the 

Bowland Sub-basin. Originally intended as a shallow coalbed methane test, the well was 

deepened and encountered the upper two-thirds of the Bowland Shale at depths of 4,200 to 

5,200 ft. The Bowland Shale, estimated at 1,600-ft total thickness, had gas shows and TOC 

ranging from 1.2% to 6.9% (average 2.7%). Thermal maturity appeared to be in the wet gas 

window (Ro 1.0-1.1%).17

Dart Energy, based in Australia and Singapore, holds a significant shale position in the 

UK, including the western Pennine Basin, but has not yet drilled for shale there or elsewhere in 

the country. Dart’s 14 PEDL’s with shale potential, part of its acquisitions of coalbed methane 

operators Composite and Greenpark Energy, total about 3,700 km2 in gross area. Third-party 

consultant NSAI has estimated these blocks hold approximately 65 Tcf of total shale GIP, of 

which approximately 30.5 Tcf is located in the western Pennine Basin (gross, Best Estimate). 

No shale drilling has occurred yet on the eastern side of the Bowland Shale 

Region. Dart Energy holds the largest land position, a total of 13 licenses covering about 1,235 

km2

. NSAI has estimated that Dart’s blocks hold about 47.6 Tcf of shale GIP (gross, Best 

Estimate). Houston-based eCORP International, LLC has committed to drilling and coring a 

horizontal well by 2014 to farm into one of Dart’s blocks. Separately, IGAS estimates it holds 

388 km2 of shale-prospective area in 9 licenses in this region. 

Dart Energy, the only active shale operator in the Midland Valley Basin, has not 

announced firm plans for shale drilling. BG Group remains a joint-venture partner on Dart’s 

Lothian Shale interval in this region. 

Much further to the south, Australia-based Eden Energy and UK-based Coastal Oil and 

Gas Ltd. jointly control 2100 km2 of shale gas and coalbed methane potential in South Wales, 

Bristol, and Kent. Prospective recoverable shale gas resources were estimated by Eden’s thirdparty consultant to be 18.3 Tcf out of a total 49.8 Tcf of GIP (gross; Best Estimate). This 

includes 806 km2 within 7 PEDLs in South Wales with potential in the Namurian Measures. 

However, this region was not assessed by EIA/ARI because of limited publicly available data.
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2. SOUTH UK JURASSIC SHALE REGION

2.1 Introduction and Geologic Setting

The Wessex and Weald basins region of southern England is the UK’s principal onshore 

oil-producing area. Both basins produce oil and some natural gas from conventional Jurassic 

and Triassic clastic and carbonate reservoirs which were sourced by Jurassic marine shales. 

The Wessex Basin hosts the 500 million bbl Wytch Farm oil field, by far the country’s largest 

onshore field, whereas the Weald Basin has several much smaller oil fields.

The Wessex Basin comprises a series of post-Variscan extensional sedimentary troughs

and intra-basinal highs, located mainly in Hampshire and Dorset and extending into adjacent 

offshore areas. The Weald Basin is a better defined and structurally simpler syncline located in 

Sussex, Surrey, and Kent. The basins are separated by the Hampshire-Dieppe High, but the 

boundary is indistinct and the two basins were intermittently connected during Mesozoic 

deposition. They contain repeating cycles of Jurassic shallow-water marine mudrocks, 

sandstones, and limestones which are overlain by largely non-marine sediments of the Lower 

Cretaceous Wealden Group. 

For the purpose of this study, the Wessex and Weald basins are considered a single 

Jurassic oil-prone shale resource region. Additional Jurassic shale areas with affinity to the 

Wessex Basin may exist further to the west (e.g., Bristol Channel Basin), but these were not 

assessed.18

The structural geology of the Wessex and Weald basins is somewhat simpler than most 

other UK shale regions, although still more complex and faulted than North American shale 

plays. While not intensively deformed, these basins comprise a series of individual sub-basins 

separated by normal faults. For example, the Wessex Basin comprises four smaller halfgrabens (Pewsey, Mere-Portsdown, Dorset and Channel).

 Figure XI-12 shows that roughly 10,000-ft thick of Lower Carboniferous to Tertiary 

sedimentary rocks is present in the Weald Basin. Lower Jurassic organic-rich shales reach 

depths of about 7,000 ft or more along the basin axis. Interior faults appear to be relatively few, 

spaced about 5 to 10 km apart, and seemingly allow ample room for shale development. The 

strata dip quite gently, only a few degrees.
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Figure XI-12: Geologic Map and Generalized Structural Cross-Section of the

Weald Basin. Lower Jurassic Shales Occur at a Depth of about 7,000 ft.

Source: DTI, 2003

However, close-spaced drilling often reveals the presence of additional faults. Indeed, a 

detailed cross-section of the southern portion of the Wessex Basin, constrained by multiple 

wells, shows a series of closely spaced faults, Figure XI-13. The depth to the Lias (JB) in this 

offshore setting south of Wytch oil field ranges from 4,000 to 5,000 ft. Note how each well is 

located in a separate fault block. Further drilling is likely to discover additional faults.

The Jurassic section comprises an alternating sequence of organic-rich mudstones and 

carbonates with subordinate sandstones. The main source rocks and potential shale targets in 

this region are several Jurassic-age shale formations, which are mainly oil-prone in deeper 

settings (immature elsewhere), in contrast with the mostly dry-gas prone Carboniferous shales 

of northern England and Scotland.
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Figure XI-13: Structural Cross-Section of a 9-Mile Long Portion of the Wessex Basin, Located Offshore Just 

South of Wytch Oil Field, Showing Depth to the Lias (JB) Ranging from 4,000 to 5,000 ft. Note How Each 

Well is Located in a Separate Fault Block and Further Drilling is Likely to Discover Additional Faults.

Source: Underhill and Paterson, 1998

The Lias, Kimmeridge, and Oxford clays contain Types II (algal sapropelic), III (terrestrial 

plant), and II/III (mixed or degraded) kerogen sources. Thermal maturity is highly variable, 

dependent upon the complex structural evolution of the basins. In general, thermal maturity 

increases towards the centers of the Wessex and Weald basins, where it reaches adequate 

rank for shale oil exploration.

The Lower Lias Clays (L. Jurassic), the most important source rock in the region as well 

as the main shale target, consists of interbedded shales, mudstones, marls and micritic 

limestones. Lower Lias shales contain 0.5% to 2.1% TOC, reaching as high as 7%. The 

isotopic character of conventional oils in the Weald Basin (35-42° API gravity) matches with that 

of the Lower Liassic, indicating close source rock genesis. Organic matter is predominantly 

sapropelic oil-prone kerogen derived from marine plankton.19 While vertical TOC variation is 

considerable, the eastern Weald Basin appears to have lower TOC.

The Arreton 2 well, a key data point located south of the Isle of Wight monocline, 

recorded oil-prone thermal maturity of 0.8% to 0.9% Ro in the Lias. Similar oil-prone maturity 

was noted at Penshurst in the central Weald Basin. Thermal maturity modeling indicates that 

the Lias is within the oil window across much of the Wessex-Channel Basin, perhaps becoming 

marginally gas-prone in the Pewsey Sub-Basin. 
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Secondary potential exists in the Oxford (up to 12% TOC) and Kimmeridge clays (up to 

20% TOC) in the Upper Jurassic. The Upper Jurassic Kimmeridge Clay consists of alternating 

shales (including oil shales), calcareous mudstones, interbedded micritic limestones, and thin 

sandstones and siltstones. The TOC of some thin black shales frequently reaches 10%, 

occasionally even 20%. Britain’s first natural gas well, drilled in 1895 at Heathfield in Sussex, 

produced 1,000 ft3

/d from an unstimulated Kimmeridge Clay section. However, the Kimmeridge 

Clay is considered thermally immature in the Wessex-Weald region, apart possibly from the 

northernmost axial part of the Wessex-Channel Basin. The Upper Jurassic Oxford Clay is 

organic-rich, reaching 10% TOC, but likewise is thermally immature. Consequently, the 

Kimmeridge and Oxford clays were excluded from our evaluation. 

Porosity and permeability of the Jurassic shales are likely to be higher than in the 

Carboniferous because they have not been subject to as much compaction. Jurassic 

mudstones encountered in shallow (<30 m) engineering boreholes have porosities in the range 

30-40%. However, Jurassic shales buried at depths of 1-5 km are likely to have much lower 

porosity, perhaps 7%.

2.2 Reservoir Properties (Prospective Area)

The Lias shales average about 600 thick (gross) in the Wessex and Weald basins. 

Organic-rich thickness of the most oil-saturated and brittle zones, based on analysis of the Lias 

in the Paris Basin,20 is estimated at approximately 165 ft, Figure XI-14. Depth to the Lias 

reaches 6,000 ft in the Weald Basin, averaging about 5,000 ft deep. TOC of the prospective 

zone is estimated to average 3% but could be considerably higher. Porosity, estimated at 7%, 

is likely to be higher than older Carboniferous shales, but lower than the 30-40% porosity 

measured at shallow locations near outcrop.21 The current average geothermal gradient is 

33°C/km.

Although not assessed, the Jurassic Kimmeridge Clay, another potential source rock in 

the Wessex and Weald basins, is notable for containing thin limestone stringers. These include

coccolithic carbonates which are somewhat similar to the lithology of the carbonate-rich MidBakken Shale in North Dakota.
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Figure XI-14: Log Suite Showing the Jurassic Lias In the Paris Basin, 

as a Proxy for the Wessex-Weald Shale Region in the UK

Source: M. Mullen, Realm Energy, 2011

2.3 Resource Assessment

The Wessex and Weald basins extend over an onshore area of approximately 3,500 mi2. 

The prospective area was estimated to be half of total area (1,740 mi2

), with the remaining area 

excluded due to potential faulting, shallow depth, erosion of the Lias, and surface access 

issues. Out of a risked shale oil in-place of 17 Bbbl and risked shale gas in-place of 8 Tcf, the 

risked, technically recoverable resources are estimated to be 0.7 billion barrels of shale oil and 

0.6 Tcf of associated shale gas, Tables XI-1 and XI-2.

Celtique Energie has reported that the Liassic Shale at their Weald Basin licenses 

ranges from 9,000 to 13,000 ft deep within a 467-km2 prospective area. The company 

estimated that the Liassic could have mean recoverable shale oil and shale gas resources of

125 million barrels of oil and 10 Tcf of shale gas. 
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2.4 Recent Activity

Privately held Celtique Energie holds licenses in three areas of the UK: the Cheshire 

Basin, East Midlands, and the Weald Basin. In the Weald Basin, Celtique has a 50% share in 

licenses covering 1,000 sq km. The company claims to have unconventional oil and gas 

potential in the Jurassic Liassic shales, as well as conventional potential in the Triassic. No 

shale drilling has been reported.

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4 UK Department of Trade and Industry, 2003. “The Hydrocarbon Prospectivity of Britain’s Onshore Basins.” Report prepared by 

British Geological Survey, 93 p.

5 Smith, N., Turner, P., and Williams, G.. 2010. “UK Data and Analysis for Shale Gas Prospectivity. In: Vining, B.A. Pickering,

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14 Waters, C.N., Browne, M.A.E., Jones, N.S., and Somerville, I.D., 2012. “Midland Valley of Scotland.” Chapter 14, 10 p.

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Key Structures along the Purbeck–Isle of Wight Disturbance.” Journal of the Geological Society, London, vol. 155, p. 975-992.
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 19 Stoneley, R. 1992. “Review of the Habitat of Petroleum in the Wessex Basin: Implications for Exploration.” Proceedings of the 

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20 Mullen, M., Realm Energy, 2011. “Shale Oil – The Next Big Play for Tight Oil?” January 30, 27 p.

21 Smith et al., 2010.