Geological Results of Petroleum Exploration in Britain, 1945-1957 (Geological Society Memoir No. 2)

GEOLOGICAL SOCIETY M E M O I R No. 2 Falcon & K e n t : Geological results of petroleum exploration in Britain 1945-1957

Corrigenda P a g e 1 O, F i g . 4. The Purbeck Cinder Bed at Brightling No. 1 borehole should be shown as 5 feet thick at depth 100 to 105 feet. P l a t e V.

Depth given at Kelham borehole should read --1470 feet.

T a b l e II. Plungar No. 1 borehole : Top of Millstone Grit should read 2864 feet, as in Fig. 23, p. 41. Ruskington No. 1 borehole : Delete the figure 3277 quoted for top of Millstone Grit; insert 3277 in Carboniferous Limestone column. Widmerpool No. 1 borehole : Figure for top of Lower Carboniferous should read 4550 feet, as in Fig. 9, p. 19. T a b l e I I I . Kirkleatham No. 1 and No. 2 boreholes should be shown as reaching Millstone Grit and Carboniferous Limestone (Yoredale Series) respectively beneath the Permian, as in Fig. 15. Kirkleatham No. 1 borehole : Delete ? 3154 in Coal Measures column ; insert ? 3154 in Millstone Grit column. Kirkleatham No. 2 borehole : Delete ? 2897 in Coal Measures column; insert ? 2897 in Carboniferous Limestone column. In last column (' completed in '), for ' Carboniferous ' read ' Carboniferous Limestone (Yoredale Series) '

GEOLOGICAL SOCIETY OF L O N D O N MEMOIR No. 2

GEOLOGICAL RESULTS OF PETROLEUM EXPLORATION IN BRITAIN I 9 4 5 - I 9 5 7

BY N O R M A N LESLIE FALCON, M.A.F.1K.S. (CHIEF GEOLOGIST, THE BRITISH PETROLEUM COMPANY LIMITED)

AND

PERCY E D W A R D KENT,

D.Sc.,

Ph.D.

(GEOLOGICAL ADVISER, BP EXPLORATXON [CANADA])

LONDON 4- AUGUST, I960

LIST PLATE

I, FIG. 1. 2.

II.

OF

PLATES

H y p o t h e t i c a l section through Kingsclere a n d Faringdon borings.

(By R. G. W. BRU~STRO~)

I n t e r p r e t a t i v e section t h r o u g h Fordon No. 1. Based on seismic reflection a n d drilling results, taking into account the probability of faulting of the t y p e exposed in the H o w a r d i a n Hills Jurassic outcrop. Borehole sections in West Yorkshire.

(By A. P. TERRIS)

III.

Borehole sections in the Carboniferous rocks of Scotland.

IV.

Type column of the Upper Carboniferous succession in the E a k r i n g area, showing lithological marker beds. (By M. W. STI~O~C)

V.

Structure contour m a p of the Top H a r d (Barnsley) Seam in the Nottinghamshire a n d Derbyshire Coalfield. Scale : 1 inch to 2 miles.

LIST OF TABLES D a t a from exploration wells, 1945-1957, m - TABLE I. II.

Southern E n g l a n d a n d the South Midlands The E a s t Midlands

III.

E a s t a n d West Yorkshire

IV.

Lancashire and t h e West Midlands

V.

Scotland

LIST

OF

FIGURES

IN

THE

TEXT

Page Fig. 1. 2.

General m a p of areas explored to t h e end of 1957

6

A r r e t o n : g r a v i t y residuals a n d reflection contours .

8

A s h d o w n : seismic i n t e r p r e t a t i o n of s t r u c t u r e after drilling. sea,level

Depths shown are of Great Oolite below 9

4.

Mesozoic borehole sections in s o u t h e r n E n g l a n d

10

5.

F a r i n g d o n area : g r a v i t y residuals a n d seismic refraction s t r u c t u r e

14

6.

Stratigraphical columns of F a r i n g d o n , Kingsclere a n d Willesden borings

15

7.

E a s t Midlands borehole localities, showing variation in t h e Millstone Grit sands

17

8.

Limits of t h e W i d m e r p o o l Lower Carboniferous gulf

18

9,

Stratigraphical columns in t he W i d m e r p o o l gulf, South N o t t i n g h a m s h i r e

.

.

.

.

19

10.

Millstone Grit correlation b e t w e e n t h e Huddersfleld area a n d boreholes a t Trumfleet, Belton a n d Corringham

21

11.

Igneous rock distribution in the E a s t Midlands Carboniferous rocks .

22

12.

Location m a p of igneous rocks in K e l h a m Hills oilfleld

23

13.

A. Sections t h r o u g h c o n t e m p o r a n e o u s igneous lenses, K e l h a m Hills oilfield, showing non-displacive relationships. B. Sections t h r o u g h intrusive igneous lenses, showing displacement of Coal Measures a n d P e r m i a n rocks .

24

14. 15.

H y p o t h e t i c a l m a p of t h e s u b - P e r m i a n floor in E a s t Yorkshire .

27 28

16.

Mesozoic sections in E a s t Yorkshire

29

17.

Permo-Triassic sections in E a s t Yorkshire

30

18.

Borehole sections in t h e F o r m b y area

33

19.

Comparative sections t h r o u g h t h e F o r m b y a n d Clitheroe areas

35

20.

Geological m a p of t h e F o r m b y area, showing post-Triassic faults. (By R. G. W. BRVNSTROM)

36

21.

S t r u c t u r a l section t h r o u g h U p h o l l a n d No. 1 boring

37

22.

Borehole sections in t h e Carboniferous rocks of Lancashire. (By A. P. TERRIS)

38

23.

Millstone Grit succession at P l u n g a r

41

24.

S t ru c t ure contour m a p of t h e P l u n g a r oilfield .

42

25.

S t ru c t ure contour maps of the E g m a n t o n oilfield, showing contrasting s t r u c t u r e at different horizons

44

26.

Cross-section of t h e E g m a n t o n oflfield. (By K. H. ROBERTS)

45

F o r d o n : seismic reflection contours on P e r m i a n limestone, a n d shallow borehole locations .

GEOLOGICAL RESULTS OF PETROLEUM EXPLORATION IN BRITAIN 1945-1957 CONTENTS Page

I.

INTRODUCTION

5

.

i i . GE~ER.~ EX~01CATION (a) Southern. England (i) Dorset and the" Hampshire basra (ii) The Isle of Wight (Arreton) (iii) The Wealden area (b) South Midlands 9 . (c) East Midlands . (i) Outline of operations (ii) Stratigraphy . (iii) Igneous rocks in the" Upper Carboniferous (d) East Yorkshire . (i) Fordon and Lockton (ii) Eskdale, Robin Hood's Bay a f l ( i Redear (e) West Yorkshire (f) Lancashire (i) Formby area . (ii) Upholland (g) The Midland Valley of Scotland

III.

ESTABLISHED

(a) General (b) The Plungar oilfield, Leicestershire (c) The Egmanton oilfield

7 7 7 8 9 14 16 16 20 23 26 26 28 32 34 34 37 39

OILFIELDS

IV. POSTSCRIPT :NOTE (dated 5 January, 1959): More recent borings in southern England .

Page 40 40 40 43

46

V. APPENDIX: Lithological and faunal markers useful for well correlation in the Upper Carboniferous of the East]Midlands, summarized from unpublished reports by T. M. W. STRONG

50

.

VI. LIST OF REFEREI~CES

55

SUMMARY

The main geological results of exploration by the British Petroleum Company Limited since 1945 are outlined, and the general basis of operations described. In the south of England new data emphasize the progressive development of the Wealden area as a Jurassic depositional basin, on a surface of mainly Devonian and Carboniferous rocks. In the East Midlands and West Yorkshire more information on the relation of Carboniferous basins is now available, and extensive occurrences of contemporary and intrusive basic igneous rocks are described. In East Yorkshire a south-easterly extension of the Permian potash basin has been proved. Post-Permian formations tend to thicken eastwards from outcrop and also inland (westwards) from the coast. The Permo-Triassic rocks of the Formby area (Lancashire) have been found to lie in a deep valley cut into Carboniferous rocks, and stratigraphic thickness variations demonstrate intra-Triassic fault movements. Further oilfields have been developed at Plungar and Egrnanton in the East Midlands, and three additional discoveries await evaluation. I. INTRODUCTION I n 1937 t h e Geological S o c i e t y r e c e i v e d f r o m G. M. Lees a n d P. T. Cox a d e s c r i p t i o n of t h e b a s i s o f t h e s e a r c h for oil i n B r i t a i n , a n d i n 1945 t h i s was followed b y a r e p o r t o f t h e d i s c o v e r y o f f o u r oilfields, w i t h geological i n f o r m a t i o n of g r e a t r e g i o n a l s i g n i f i c a n c e (Lees & T a i t t 1946). T h e s u c c e e d i n g t w e l v e y e a r s h a v e seen t h e s e a r c h c o n t i n u e d b y t h e B r i t i s h P e t r o l e u m C o m p a n y L i m i t e d w i t h t h e d i s c o v e r y of two m o r e fields.

T h e a c c o u n t w h i c h follows s u m m a r i z e s t h e m o r e i m p o r t a n t i n f o r m a t i o n o b t a i n e d i n t h i s

t h i r d stage. D u r i n g t h e p e r i o d i n q u e s t i o n t h e b a s i s o f e x p l o r a t i o n h a s b e e n b r o a d e n e d to i n c l u d e s e a r c h for n a t u r a l gas on b e h a l f of t h e Gas C o u n c i l a n d i n c o n j u n c t i o n w i t h I m p e r i a l C h e m i c a l I n d u s t r i e s .

These organiza-

t i o n s h a v e p e r m i t t e d t h e i n c l u s i o n h e r e of i n f o r m a t i o n f r o m t h e j o i n t o p e r a t i o n s . The only significant changes in exploration techniques during the last twelve years have been an i n c r e a s i n g use o f m o d e r n r e f l e c t i o n s e i s m i c w o r k a n d of t h e v a r i o u s m e t h o d s o f electric logging.

The

GEOLOGICAL RESULTS OF PETROLEUM EXPLORATION IN BRITAIN 1945-1957 CONTENTS Page

I.

INTRODUCTION

5

.

i i . GE~ER.~ EX~01CATION (a) Southern. England (i) Dorset and the" Hampshire basra (ii) The Isle of Wight (Arreton) (iii) The Wealden area (b) South Midlands 9 . (c) East Midlands . (i) Outline of operations (ii) Stratigraphy . (iii) Igneous rocks in the" Upper Carboniferous (d) East Yorkshire . (i) Fordon and Lockton (ii) Eskdale, Robin Hood's Bay a f l ( i Redear (e) West Yorkshire (f) Lancashire (i) Formby area . (ii) Upholland (g) The Midland Valley of Scotland

III.

ESTABLISHED

(a) General (b) The Plungar oilfield, Leicestershire (c) The Egmanton oilfield

7 7 7 8 9 14 16 16 20 23 26 26 28 32 34 34 37 39

OILFIELDS

IV. POSTSCRIPT :NOTE (dated 5 January, 1959): More recent borings in southern England .

Page 40 40 40 43

46

V. APPENDIX: Lithological and faunal markers useful for well correlation in the Upper Carboniferous of the East]Midlands, summarized from unpublished reports by T. M. W. STRONG

50

.

VI. LIST OF REFEREI~CES

55

SUMMARY

The main geological results of exploration by the British Petroleum Company Limited since 1945 are outlined, and the general basis of operations described. In the south of England new data emphasize the progressive development of the Wealden area as a Jurassic depositional basin, on a surface of mainly Devonian and Carboniferous rocks. In the East Midlands and West Yorkshire more information on the relation of Carboniferous basins is now available, and extensive occurrences of contemporary and intrusive basic igneous rocks are described. In East Yorkshire a south-easterly extension of the Permian potash basin has been proved. Post-Permian formations tend to thicken eastwards from outcrop and also inland (westwards) from the coast. The Permo-Triassic rocks of the Formby area (Lancashire) have been found to lie in a deep valley cut into Carboniferous rocks, and stratigraphic thickness variations demonstrate intra-Triassic fault movements. Further oilfields have been developed at Plungar and Egrnanton in the East Midlands, and three additional discoveries await evaluation. I. INTRODUCTION I n 1937 t h e Geological S o c i e t y r e c e i v e d f r o m G. M. Lees a n d P. T. Cox a d e s c r i p t i o n of t h e b a s i s o f t h e s e a r c h for oil i n B r i t a i n , a n d i n 1945 t h i s was followed b y a r e p o r t o f t h e d i s c o v e r y o f f o u r oilfields, w i t h geological i n f o r m a t i o n of g r e a t r e g i o n a l s i g n i f i c a n c e (Lees & T a i t t 1946). T h e s u c c e e d i n g t w e l v e y e a r s h a v e seen t h e s e a r c h c o n t i n u e d b y t h e B r i t i s h P e t r o l e u m C o m p a n y L i m i t e d w i t h t h e d i s c o v e r y of two m o r e fields.

T h e a c c o u n t w h i c h follows s u m m a r i z e s t h e m o r e i m p o r t a n t i n f o r m a t i o n o b t a i n e d i n t h i s

t h i r d stage. D u r i n g t h e p e r i o d i n q u e s t i o n t h e b a s i s o f e x p l o r a t i o n h a s b e e n b r o a d e n e d to i n c l u d e s e a r c h for n a t u r a l gas on b e h a l f of t h e Gas C o u n c i l a n d i n c o n j u n c t i o n w i t h I m p e r i a l C h e m i c a l I n d u s t r i e s .

These organiza-

t i o n s h a v e p e r m i t t e d t h e i n c l u s i o n h e r e of i n f o r m a t i o n f r o m t h e j o i n t o p e r a t i o n s . The only significant changes in exploration techniques during the last twelve years have been an i n c r e a s i n g use o f m o d e r n r e f l e c t i o n s e i s m i c w o r k a n d of t h e v a r i o u s m e t h o d s o f electric logging.

The

6

FALCON

AND

KENT

CARBONIFEROUS PROSPECTS ScoTLAND Oil & Gas shows in outcropping rocks & in workings & borings of oil shale field. Oil show in D'Arcy ~ 1 drilled after f914-1918 war & in N°-I & N.°5 at Cousland. N° of Test Boreholes : 8. Total footage:20,270 feet. Small 9asfield in Lower Carboniferous at Cousland.

GLASGOW •

\ CARBONIFEROUS //

PROSPECTS

N. E. FNG,LAND

//

Oil or Gas accumulations possible in Carboniferous & older rocks. C)ccasional gas in coal-mines & some oil reported in a borehole near Richmond. No wells drilled to date f o r oif or gas.

/ CARLISLE

Kirkteatham Robin Hoods Bay

CARBONIFEROUS

~PROSPECTS

N.W. ENGLANO

Strong Oil seepages in Peat. near Formby. Small oilfield in Tries rocks near surface. N9 of shallow Boreholes; 75. Total footage; 26,964 feet.(including producing wells.) N° of Deep Boreholes; 8.Total footage 35,790 feet. ~ _ Ftea

~

PERMIAN PROSPECTS

Evidence of Oil 8, Gas in boreholes & outcropping rocks. Oil & Gas fields in Germany, N9 of Boreholes: 11. Total footage 36,504 feet. Eskdale N° 2 Gas in Upper Permian Limestone N°10 - " Lower " " N9 of shallow Boreholes; 3. Total footage; 2,873 feet. CARBONIFEROUS

PROSPECTS

MIDLANDS

Oil in Carboniferous rocks, in outcrop, boreholes & mines - . Limestone in Hardstoft N91 • Plunger N°2 ;~)~/) OIL F IELD$ IN EAKRING AREA .on//J 60iifields. N9 of Borehotes: 412. Total footageiI,034,613 feet. ~'t/o/n f Producing Horizon is the Millstone Grit Series. -~' o ~ N'.O of Shallow Bar.holes: 14. Total

~,

Stoke

21,367Feet,

_ f~;~C'~'k?'~footaqe:

BIRMINGHAM

PALAEOZOIC PROSPECTS Oil accumulationspossiblein Car~)oniferous & older rocks Occasional shows of gas in boreholes. NOof boreholes;2. Total footage: 5,8ti feet

/

__

A.s.hdo.wj, .m.

Bri~

Herr&n(

-~'ceo~"r) Down MESOZOIC PROSPECTS Oil impregnated sandstones, etc., of Jurassic & Cretaceous age outcropping along coast. Gas at Heathf/e/d (Sussex). N9 of Deep Boreholes:14. Total footage;48.221 feet. N9 of Shallow Information Boreholes; 30. Total 8,508 feet SCALE " Scale ~ Mites 0 5 I i i i i I i i ~ $ J

Fla. l.--General

map

of areas explored

to the end of 1957.

former has been particularly useful in the exploration of the East Midlands concealed coalfield area, and the latter in the development drilling of the newly discovered oilfields. In particular, the use of gamma-ray logging has been of considerable help in the correlation of marine bands in the East Midlands area. Other Publications.--Since the publication by Lees & Taitt (1946) the British Petroleum Company has released a considerable amount of data on additional wells. Summary accounts have been published

ON PETROLEUM

EXPLORATION

IN

BRITAIN

1945-1957

of several borings in Nottinghamshire (Edwards 1951), of three borings in the Market Drayton area of Staffordshire (Wills 1956) and of borings in Dorset at Chaldon Down and Broadbench (Arkell 1947B). More detailed accounts have been published of the Permo-Triassic and Carboniferous sequence of Forn~lby, Lancashire, of the Mesozoic rocks down to basement at North Creake, Norfolk (Kent 1947, 1948) and of the Whittington (Derbyshire), H a y t o n (Yorkshire), Farleys Wood (Nottinghamshire) and Spital (Lincolnshire) borings marginal to the Yorkshire Coalfield (Wilcockson 1950). This information is not repeated in the description below. The Gun Hill (Staffordshire) boring briefly described by Lees & Taitt has been discussed in detail by Hudson & Cotton (1944) and the Kingsclere (Berkshire) boring described more fully by Arkell (1947A). F. H. Stewart has published a series of papers on the Permian evaporites of the Eskdale area (1954) ; F. W. Anderson (1939) has worked on the ostracod faunas of sections in southern England, and M. W. Strong (1956) has described iron-precipitating bacteria in the Permian salt from several borings in Yorkshire. More recently (1958) the British Petroleum Company has issued for limited distribution an account by Taitt & K e n t of the Portsdown and Henfield borings, which provide standard reference sections in the south. II. GENERAL EXPLORATION (a) Southern England (Table I) (i) Dorset and the Hampshire Basin The extent of oil shows at outcrop in Dorset marginal to the Hampshire basin has continued to a t t r a c t our interest. The borehole at Poxwell originally proved the complexity of the movements in pre-Albian times (Taitt & Kent 1939), and holes drilled through the Chalk at Chaldon Down, north of Lulworth, passed directly from Albian to Kimmeridge Clay, showing t h a t strong local pre-Albian uplift continued eastwards from outcrop (Arkell 1947B). Telluric surveys carried out over this area showed a number of anomalies but their interpretation was uncertain, and seismic and gravity surveys south of the Tertiary syncline of Wareham failed to give clear-cut results beneath the Chalk blanket. The next stage, in progress at the time of writing, has included further investigation of outcropping structures in Dorset and seismic work in the less strongly disturbed area north of the Ballard Down fault in Dorset and in the T e r t i a r y basin in Hampshire. The first of the outcropping structures to be drilled was the fold at Chaldon Herring, which had a superficial appearance of simplicity (Arkell 1947B). Four boreholes in a N.-S. line across the culmination proved it to be a structure of Poxwell type, flanked by a fault with a large pre-Albian throw, with the additional complication t h a t the fault plane had been sharply distorted by the final phase of folding. An account by M. R. House is in the press. F u r t h e r operations on outcropping structures are planned on the Weymouth anticline near Langton Herring (see Postscript Note, p. 49) and also at Broadbench, where an earlier hole found a minor oil show in the Corallian. Within the Tertiary outcrop two areas have received detailed attention by seismic reflection survey. The first is near Wareham, where gravity and seismic refraction survey had proved an anomaly. The second is the l%ingwood gravity high in Hampshire (White 1949), where reflection survey has detailed a subcircular crest maximum in the Jurassic ; the shape and size of this structure suggest t h a t it could be an uplift caused by a local intrusion of Triassic salt at depth, analogous to the domal uplift of Compton Valence (Falcon & K e n t 1950) 1. 1 Since this account was prepared, drilling of Fordingbridge No. 1 has shown that this structure is pre-Albian, like those of Dorset, for Gault rests directly on Kimmeridge Clay, with elimination of the thick Portland, Purbeck, Wealden and Lower Greensand (see Postscript :Note). Also, a test well drilling near Bere Regis, north-west of Wareham, at the time of going to press, located on ~, seismic reflection high, has proved Oxford Clay immediately below the Gault.

ON PETROLEUM

EXPLORATION

IN

BRITAIN

1945-1957

of several borings in Nottinghamshire (Edwards 1951), of three borings in the Market Drayton area of Staffordshire (Wills 1956) and of borings in Dorset at Chaldon Down and Broadbench (Arkell 1947B). More detailed accounts have been published of the Permo-Triassic and Carboniferous sequence of Forn~lby, Lancashire, of the Mesozoic rocks down to basement at North Creake, Norfolk (Kent 1947, 1948) and of the Whittington (Derbyshire), H a y t o n (Yorkshire), Farleys Wood (Nottinghamshire) and Spital (Lincolnshire) borings marginal to the Yorkshire Coalfield (Wilcockson 1950). This information is not repeated in the description below. The Gun Hill (Staffordshire) boring briefly described by Lees & Taitt has been discussed in detail by Hudson & Cotton (1944) and the Kingsclere (Berkshire) boring described more fully by Arkell (1947A). F. H. Stewart has published a series of papers on the Permian evaporites of the Eskdale area (1954) ; F. W. Anderson (1939) has worked on the ostracod faunas of sections in southern England, and M. W. Strong (1956) has described iron-precipitating bacteria in the Permian salt from several borings in Yorkshire. More recently (1958) the British Petroleum Company has issued for limited distribution an account by Taitt & K e n t of the Portsdown and Henfield borings, which provide standard reference sections in the south. II. GENERAL EXPLORATION (a) Southern England (Table I) (i) Dorset and the Hampshire Basin The extent of oil shows at outcrop in Dorset marginal to the Hampshire basin has continued to a t t r a c t our interest. The borehole at Poxwell originally proved the complexity of the movements in pre-Albian times (Taitt & Kent 1939), and holes drilled through the Chalk at Chaldon Down, north of Lulworth, passed directly from Albian to Kimmeridge Clay, showing t h a t strong local pre-Albian uplift continued eastwards from outcrop (Arkell 1947B). Telluric surveys carried out over this area showed a number of anomalies but their interpretation was uncertain, and seismic and gravity surveys south of the Tertiary syncline of Wareham failed to give clear-cut results beneath the Chalk blanket. The next stage, in progress at the time of writing, has included further investigation of outcropping structures in Dorset and seismic work in the less strongly disturbed area north of the Ballard Down fault in Dorset and in the T e r t i a r y basin in Hampshire. The first of the outcropping structures to be drilled was the fold at Chaldon Herring, which had a superficial appearance of simplicity (Arkell 1947B). Four boreholes in a N.-S. line across the culmination proved it to be a structure of Poxwell type, flanked by a fault with a large pre-Albian throw, with the additional complication t h a t the fault plane had been sharply distorted by the final phase of folding. An account by M. R. House is in the press. F u r t h e r operations on outcropping structures are planned on the Weymouth anticline near Langton Herring (see Postscript Note, p. 49) and also at Broadbench, where an earlier hole found a minor oil show in the Corallian. Within the Tertiary outcrop two areas have received detailed attention by seismic reflection survey. The first is near Wareham, where gravity and seismic refraction survey had proved an anomaly. The second is the l%ingwood gravity high in Hampshire (White 1949), where reflection survey has detailed a subcircular crest maximum in the Jurassic ; the shape and size of this structure suggest t h a t it could be an uplift caused by a local intrusion of Triassic salt at depth, analogous to the domal uplift of Compton Valence (Falcon & K e n t 1950) 1. 1 Since this account was prepared, drilling of Fordingbridge No. 1 has shown that this structure is pre-Albian, like those of Dorset, for Gault rests directly on Kimmeridge Clay, with elimination of the thick Portland, Purbeck, Wealden and Lower Greensand (see Postscript :Note). Also, a test well drilling near Bere Regis, north-west of Wareham, at the time of going to press, located on ~, seismic reflection high, has proved Oxford Clay immediately below the Gault.

FALCON AND K E N T

(ii) The Isle of Wight (Arreton) The results of the pre-war deep test borings in the Wealden region indicated that most of the folds were Tertiary structures, developed too late to act as traps for oil migrating towards the edge of the Wessex basin. Interest therefore moved to the marginal parts, and discovery of a regional gravity rise from the mainland across the Isle of Wight (White 1949) led to a search for a suitable structural target in the southern part of the island on the hypothesis that the gravity rise indicated the flank of the Jurassic basin. Both the Sandown and Brighstone folds have their culminations off-shore and were therefore impracticable for drilling, but a third dome was found between them at Arreton, nearly in the centre of the island, at a locality indicated by surface geology and a local gravity high subsequently detailed by reflection survey (Fig. 2).

k )~,' NEWPORT

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refraction

structure.

(b) South Midlands (Table I) M. Lees advanced the view that foreland folds in advance of the Variscan front could provide oil prospects in the southern Midlands, and extensive magnetic and gravity surveys and more limited seismic surveys were carried out to investigate underground conditions. The main results of the magnetic and gravity work have already been presented to this Society (FMcon & Tarrant 1951). Two borings have been made, the first at Willesden, North London, to investigate the circumstances of an oil and gas show reported in an earlier water well ; the second at Faringdon, Berkshire, to check underground stratigraphical conditions on a seismic high with a NW.-SE. trend before undertaking more detailed seismic surveys (Fig. 5). Paringdon

and

Willesden.--G.

ON P E T R O L E U M

EXPLORATION

1945-1957

IN BRITAIN

15

The Willesden boring started in London Clay, reached the Chalk at 196, Upper Greensand at 800 and the Palaeozoic at 1010 feet. As in the original water well, the Palaeozoic rocks proved to be Upper Devonian, dipping at about 15 ~ but although they were predominantly red mudstone and marl with very occasional thin limestones they yielded a rich marine fauna. Dr. Stubblefield (1947) commented briefly on the lithology and on the fossils collected by the late A. G. Davis and by Geological Survey officers from the ~mBR ~

.

j

Willesden

,STOC.... ~oo~ ~,.. I

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,,

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2000i

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/

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U DEVONIAN

DEVONIAN

Bottom of Ho~e

,,

3131'

Bottom of Hole z68o'

Fro.

6.--Stratigraphical columns of Faringdon, Kingsclere and Willesden borings.

cored sections between 1020 and 1176 feet, also between 1400 and 1611 feet. He subsequently reported

Productella subaculeata (Murchison), Schizophoria striatula (Schlotheim) and Cyrtospirifer verneuili (Murchison) from limestones at 1624 feet and Camarotoechia ferquensis (Gosselet) from similar sediments at 1630 feet.

Below this depth coring was intermittent. The late Stanley Smith named the corals Alveolites suborbicularis? Lamarck, Thamnopora cervicornis (de Blainville) and a stromatoporoid from a short limestone core at 1719 feet. The hole was continued to 2680 feet in beds becoming generally greyer

16

FALCON

AND

KENT

and more sandy below but with a similar fauna ; dips decreased to about 10 ~ in the neighbourhood of 2000 feet. Dr. Stubblefield noted t h a t Tentaculites, plentiful in the limestone bands between 1410 and 1595 feet, was also recognized in thin limestones at 2230 feet. Cyrtospirifer verneuili found at 1410 feet, 1496 feet, 1624 feet and elsewhere was also recorded from 2446 feet associated with Atrypa. From the nature of the fossils the facies was deemed to be marine throughout, though the uppermost 160 feet appeared to be shallower water with deposits rich in Lingula with few associated lamellibranchs and fishes. No indications of oil were found. The Faringdon (Shellingford) test well in Berkshire started at the top of the Corallian limestones, and proved a Jurassic sequence intermediate between the South Cotswolds and Kingsclere (Fig. 6). The Oxford Clay measures 418 feet, the Kellaways 30 feet (both reduced as compared with the Swindon boring) ; the Great Oolite Series (180 feet) is in the Oxfordshire facies with a thin (10 feet) representative of the Fuller's E a r t h at the base. Sixty-five feet of limestones are ascribed to the Inferior Oolite, but this may include some early Bathonian (Chipping Norton Limestone) above. The Lias measures 655 feet, with typical green oolitic "Marlstone " 75 to 95 feet down from the top (the base of the Middle Lias is arbitrarily placed 30 feet below this in the absence of cores), and includes 20 feet of " H y d r a u l i c Limestones " close to the base. The Rhaetic totals 60 feet, with 20 feet o f " White Lias " at the top separated by 30 feet of green and brown shales and limestones (Cotham Beds) from 10 feet of Black Shales ; at 1525 feet it rests on normal Keuper Marl which extends to 2080 feet. This sequence is very markedly thinner t h a n the Jurassic of Kingsclere (Fig. 6), and Arkell (1947A) has suggested t h a t a sudden thinning over a fault or monocline immediately north of the Kingsclere fold may be the feature controlling sedimentation on the edge of the shelf. The Keuper Marl at Faringdon is separated from the Palaeozoic floor by 70 feet of conglomerates, the upper 40 feet with a red shale matrix, comparable with the " conglomeratic g r i t " of the basal Keuper in the Burford borings, the remainder with a red and purple fine sandstone matrix. A dip-meter survey later showed both groups to be practically horizontal ; hence they are probably post-Variscan, but may be either Keuper or Upper Coal Measures, or both. Beneath this level 981 feet of steeply dipping Palaeozoic rocks were penetrated (Falcon 1955). The sequence is one of indurated sandstones, shales and bedded siltstones forming a uniform series. Grey silts with plant fragments yielded Pachytheca to Dr. Stubblefield, the only evidence of date. Pachytheca ranges from the Silurian to Middle Old Red Sandstone, and a Downtonian age is considered most likely for this series. Dips varied from 45 ~ to vertical, and the locality must be either within the Variscan front or in a sharp fold in the foreland. A section by R. G. W. Brunstrom is appended (P1. I, fig. 1). The tectonic and stratigraphical facies of this Palaeozoic sequence are too unpromising for oil exploration, and further geophysical work in the region is considered unjustified. The structural foreland to the north, however, still has prospects, and a boring at Noke on the Islip anticline has been projected as a further step (see Postscript Note).

(c) East Midlands (Table II) (i) Outline of Operations.--A series of wells has been drilled in a search for homologues of the Millstone Grit reservoirs of the Eakring group of structures, and also to follow up oil shows encountered in coal exploration borings (Fig. 7). This work has produced four successes, the E g m a n t o n and Plungar oilfields described below, and the Langar and Bothamsall discoveries, which are now being followed up. Several of the holes were designed to trace the Eakring anticlinal trend, rerlethorpe No. 1, l o c a t e d down-pitch on the line of the north-western nose, did not find the dip reversal which general indications from colliery workings had suggested, but application of modern seismic reflection techniques to this

ON PETROLEUM EXPLORATION I N BRITAIN

1945-1957

17

area led to a test at Bothamsall, one mile north-east of Perlethorpe, and this has recently proved a commercial off accumulation in the Rough Rock 6 apparently of the same order of size as the E g m a n t o n field. Two wells were drilled at Hockerton on the south-western flank of the Duke's Wood field, where wedging of the beds offered a possibility of closure at depth, and one at Kirklington on the southern plunge, where a coal boring had encountered gas and where seismic work indicated a small subsidiary dome. None of these was successful, apparently through lack of closure in each case. Two wells were drilled at Farndon, near Newark, to intersect sands pinching out up-dip towards the crest of the Rolleston structure, but the structure proved too complex and too much invaded by igneous rocks in the Coal Measures and Millstone Grit to be productive. Igneous rocks were found in quantity also in borings on a seismic high at Screveton and at Harlequin (Radcliffe-on-Trent), east of Nottingham ; at Screveton sills and flows appear to have invaded or replaced both Coal Measures and the higher Millstone Grit sands, while at Harlequin a thick jointed sill in the basal Coal Measures flowed oil briefly but failed to give sustained production.

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Fro. 15.--Hypothetical map of the sub-Permian floor in East Yorkshire. separated by the Carnallitic Marl and Upper Magnesian Limestone, resting on a very anhydritic development of the Lower Magnesian Limestone. From 7135 to 7559 feet (final depth) Fordon No. 1 penetrated Millstone Grit (to about 7245 feet) and "Yoredales", developed as pyritic siltstones, sandy shales and sandstones. Cravenoceratoides (E z age) was identified by the Geological Survey 50 feet below the Permian, and beds at 7175 to 7183 feet are considered to represent the Colsterdale Marine Beds of the West Yorkshire outcrop. (ii) Eskdale, Robin Hood's Bay and Redcar.--The first deep test in the centre of the Permian basin o f north-eastern Yorkshire was drilled from analogy with conditions in the potash basin of South Germany (Lees & Cox 1937); the discoveries made at that time have been followed by twelve more exploratory borings, of which ten were put down to define the thickness and value of the potash deposits by Imperial Chemical Industries Ltd. (Fleck 1950) and Messrs. Fisons Ltd., and two more sunk in continuation of the search for gas. One of the potash borings, made at Robin Hood's Bay by Fisons Ltd.,

1945-1957

ON PETROLEUM EXPLORATION I N BRITAIN

29

has also been deepened to explore for hydrocarbons, and two tests (one on behalf of Imperial Chemical Industries) have been made in the Kirkleatham area near the Tees (Fig. 17). The stratigraphy and mineralogy of the evaporite deposits have been described at length by Stewart (1954), Dunham (1948), Hollingworth & others (1948), and this aspect of the subject will not be included here. Surprisingly sharp changes in thickness have been discovered in the evaporites, and in consequence the positions of crests at depth in the two Permian limestone reservoirs are considerably displaced from the surface culminations. LOCATION

MAP

\

FORDON

CHALK

II !

No.1.

I--41 I

I

I

i'"(''("i RED CHALK SPEETON

? SCALE ?

?,,,,

614'

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LOCKTON No.1.

ESKDALE No.2.

1060'

/

KIMMERIDGE

CLAY

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2000 =

2190;

F r o . 1 6 . - - M e s o z o i c sections in E a s t Yorkshire.

The structural and stratigraphic knowledge gained by the potash exploration drilling suggested that the divergences between surface Jurassic structure and Permian sub-surface structure were great enough to warrant seismic investigation, in spite of the unfavourable topography. Seismic reflection work was consequently carried out over the area of the Eskdale anticline, with extension lines to the Robin Hood's Bay anticline ; the opportunity of some seismic ship trials also allowed some marine reflection work to be carried out in Robin Hood's Bay. This work confirmed the divergences and also depicted the PermianCarboniferous junction.

FALCON AND KENT

30

The major thickness changes in the Permian proved by drilling in this area (see Raymond 1953) occur in the evaporite group between the two Magnesian Limestones. It is not yet known how much of this change is due to relative upward movements during Permian deposition, or how much is regional due to the sinking of the Permian basin as a whole. Some stratigraphio anomalies in well records suggest that more faulting is present at depth than is known at surface, this being an additional hazard in seismic work. HAYTON

NO 1

FORDON

NO 1

ROBIN HOOD'S

BAY N ~ !

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KEUPs

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] '

, 33"135'

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xf ? 3663'

:'::::: 884'

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SALIFEROUS MARLS

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ON PETROLEUM

EXPLORATION

IN

BRITAIN

1945-1957

39

likely that the margin of the Pendle gulf runs between Upholland and Croxteth, and possibly across the Rossendale area (Fig. 22). A considerable thickness of Lower Carboniferous rocks in a relatively un. attractive facies is thus to be expected beneath, and drilling depths to massive reservoir limestone would be relatively great. (g) The Midland Valley of Scotland (Table V) The basis of exploration in the Midland Valley of Scotland has been given in G. M. Lees's previous communications (Lees & Cox 1937, Lees & Taitt 1946). The Calciferous Sandstone Series has throughout been the principal objective, as containing good reservoir sandstones plus oil shales as possible source beds, and attention has been mainly given to those structures marginal to the basin where early migration conditions were favourable. In 1938 gas with a little oil had been found in the Cousland anticline, Midlothian, and three additional structures were drilled in 1944-46: Salsburgh (near Airdrie), Easter Pardovan and Blackness (near the Firth of Forth). Dr. W. Q. Kennedy gave valuable advice during these operations. Further exploration of Cousland has more recently been carried out for gas production, and an exhaustive study of the gas prospects of the region has been made under the direction of A. H. Taitt. Since resumption of operations is envisaged in the future the following account is limited to the specific objectives drilled since the last report. The Salsburgh structure is a broad, gentle, well-defined anticline, with closure of 200 feet in the coalfield east of Glasgow, which brings Millstone Grit up to 146 feet from surface. The boring therefore proved the whole sequence from the basal Coal Measures downwards, ending in probable Lower Old Red Sandstone lavas (P1. III). The Millstone Grit measured 306 feet, the Carboniferous Limestone Series 1613 feet and the Calciferous Sandstone Series 1925 feet, the basal part being overlapped against a southerly shoreline. These measurements are much thinner than in the basins to east and west, and confirm expectation of a transverse ridge (or swell) which controlled sedimentation. Sandstones were not well developed, but at 2739 to 2884 feet a sandy facies of the Upper Limestone Group (below the Houston Marls) yielded gas at the rate of 330,000 cubic feet a day. Apart from this show, hydrocarbons were represented only by slight traces of oil. Volcanic ash was reached at 3657 feet and red and purple tufts at 3990 feet. At 4041 feet the boring entered homogeneous white trachyte with feldspar phenocrysts. This was compared by Dr. W. Q. Kennedy with the acid lavas of the Lower Old Red Sandstone, the junction probably corresponding with lateritic beds at 3990 feet. The Easter Pardovan boring was located on the northern culmination of a faulted dome half a mile south-west of Philipstoun. It started in the Upper Oil Shale Group (Champfleurie-Dunnet horizon) of the Calciferous Sandstone Series and was taken into the Lower Oil Shale Group. The Dunnet Sandstone was proved at 292 to 402 feet and yielded gas at the rate of 13,000 cubic feet a day. Seven other horizons yielded a little gas with water, but on the whole reservoir conditions were poor. Structural control of the shallower horizons is good, and failure is to be ascribed mainly to lack of good sands at depth, with the possibility also that sharp thickness changes may displace the underground crest relatively to the surface. TheBlackness dome, on the southern shore of the Firth of Forth, is a symmetrical structure with closure exceeding 300 feet located near the northern margin of the main Calciferous Sandstone basinm a locality which should have been favourable both for reservoir conditions and for early migration. Drilling began in the Calciferous Sandstone Series 750 feet above the Burdiehouse Limestone, and a normal development of the Lower Oil Shale Group, unfortunately with few and indifferent sands, was drilled to 2085 feet. At this depth the well entered lavas (albitized basalt or rhyolite) which continued to the final depth of 2455 feet. These were considered unlikely to be the Arthur's Seat volcanic group but

40

FALCON AND KENT

were regarded as very early Carboniferous or possibly Devonian, and as deeper prospects were unpromising the well was abandoned. A small oil show was obtained by testing thin sands just above the lavas, and negligible quantities of gas were obtained at higher levels. Lack of success is due mainly to poor reservoir conditions, although, as at Easter Pardovan, divergence between surface and underground structure cannot be excluded. I I I . ESTABLISHED OILFIELDS (a) General At the time of the last review five oilfields had been discovered--four in Nottinghamshire and a very small one at Formby, Lancashire. Exploitation of each of these has continued and up to the end of 1957 had produced the following cumulative quantities : F o r m b y (1939) 9500 tons, Eakring (1939) 256,000 tons, Duke's Wood (1941) 473,000 tons, K e l h a m Hills (1941) 241,000 tons, and Caunton (1943) 32,000 tons. s The new fields at Plungar (North Leicestershire) and E g m a n t o n (near Tuxford, Nottinghamshire), both geophysical discoveries, have now come on production, with the following figures to date : Plungar (1953) 11,800 tons, E g m a n t o n (1955) 36,000 tons. I n the older felds there has been little new development (production from the thin Kinderscout Grit at E a k r i n g is a minor exception) and attention has been mainly concentrated on secondary recovery operations by peripheral repressuring of the sands--particularly of the R o u g h Rock, which is markedly lenticular and has poor natural water-drive characteristics. This has involved drilling a n u m b e r of new holes for water injection around the field margins at Eakring, Duke's Wood and K e l h a m Hills, b u t the additional structural and stratigraphical data obtained show no divergences from the interpretation of Lees & Taitt. Operation of the secondary recovery scheme has been described by Dickie & Adcock (1954), and the practical results have more recently been illustrated by W a r m a n & others (1956). Only the two recently developed fields are therefore described here. Of the additional discoveries of the last few months Bothamsall, on the Eakring nose, has an oil-sand development in excess of 85 feet and appears to have reserves of the same order as E g m a n t o n , although its areal extent is likely to be less. Corringham, near Gainsborough, m a y be somewhat smaller t h a n this.

(b) The Plungar Oilfield, Leicestershire The consensus of evidence up to 1952 suggested t h a t there was a higher probability of finding commercial oil accumulations in the zone of sharpest thinning of the Millstone Grit t h a n either to east or west. Plungar, situated in this zone in N o r t h Leicestershire between Barkestone No. 1 (with almost no sand) and Long Clawson No. 1 in the Widmerpool gulf (with thick sandy Millstone Grit), was believed to be on the western flank of a Carboniferous Limestone high defined by seismic refraction work and to offer the possibility of stratigraphic oil traps in lensing sands. This general expectation was fulfilled in 1953, although the structure as subsequently detailed independently by seismic reflection work and by drilling proved to be rather more complex, consisting of an irregular flattened subsidiary dome about one mile across with a steep southern flank on the edge of the Widmerpool gulf (Fig. 24). Three sandstone groups have been proved, one in the basal Coal Measures and two in the Millstone 8 The cumulative crude oil production figures to 31 December 1959 are as follows :-Formby . . . . . . . . . . . . . . . . . . . . 9,6{~8tons Bothamsall (1958) . . . . . . . . . . . . 8,066 tons Eakring . . . . . . . . . . . . . . . . . . 267,928 ,, Corringham (1958) . . . . . . . . . . . 2,485 ,, Duke's Wood . . . . . . . . . . . . 511,780 ,, Gainsborough (1958) . . . . . . . . . 1,211 ,, Kelham Hills . . . . . . . . . . . . . 259,151 ,, Kimmeridge (1958) . . . . . . . . . . 2,366 ,, Caunton . . . . . . . . . . . . . . . . . . 34,595 ,, Plungar . . . . . . . . . . . . . . . . . . . 18,650 ,, Egmanton . . . . . . . . . . . . . . . . 106,842 ,, [Note added 23 February 1960]

ON

PETROLEUM

EXPLORATION

IN

BRITAIN

41

1945--1957

Grit. Sand conditions in this marginal zone have, however, proved highly variable, and less than half of the wells drilled (21 by the end of 1957) have yielded commercial production, so that Plungar has remained one of the smallest fields of the United Kingdom. Its discovery and development are to be regarded as a stage in the exploration of a favourable belt adjoining the thick deposits of source-rock type in the Carboniferous gulf, a belt which may in the long run provide a number of fields.

17

15

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LIMESTONES VOLCANICS

FIG. 23.---Millstone Grit succession at Plungar. Physical characteristics of the sands with specimens of the electric and gamma logs obtained at Plungar have been published by Warman & others (1956, p. 342). Plungar is situated on the Lower Lias, and the wells penetrate the earlier part of this formation, the Rhaetic, Keuper, Bunter and Carboniferous in downward sequence (the locality lies south of the limit of the Permian). The great development of igneous rocks in the Coal Measures has already been described ; the following paragraphs briefly outline the stratigraphy of the pre-Permian rocks. Carboniferous Limestone.--The top of the Carboniferous Limestone has been cored without finding diagnostic fossils, but a shelly horizon 464 feet below the top in No. 8 well yielded Gigantoproductus,

4~

FALCON

AND

KENT

Zygopleura cf. rugosa (de Koninck) and corals which are referred to D r This is the deepest penetration so far ; it encountered continuous massive "block facies " limestone with n o shale partings or igneous rock.

Millstone Grit.~Goniatite bands have been found in the Upper Carboniferous with sufficient frequency to give a fair idea of absolute dating. Identifications listed are by Dr. W. H, C. Ramsbottom of the Geological Survey. The first is the G. subcrenatum band (Pot Clay Marine Band) marking the base of the Coal Measures, which yielded the zonal goniatite in No. 8 and less distinctive faunas in other wells, in each case at the top of the middle group of sandstones. About 25 feet lower is a bed with G. cf. cancellatum Bisat, and 50 feet below this the R,. stage is indicated by Reticuloceras reticulatum mut. 7. Seventy feet lower is a group of shelly brachiopod shales with Productus carbonarius de Koninck and Punctospirifer cf. northi Muir-Wood, which may be a condensed deposit. Near the top it has yielded Reticuloceras j~

9 Iot.UNGAR"~/ ~/J

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