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Finding Oil at Eakring and Dukes Wood
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THE EAKRING OILFIELD GEOLOGICAL SECTION
A cross section of the anticline that made the Dukes Wood area a unique site for Oil
extraction.
Notice the coal seams at HIGH HAZEL, TOP HARD, DUNSIL,
WATERLOO, ELL, SILKSTONE, TUPTON LOW MAIN and KILBURN levels. Notice too
how relatively thin but wide spread these seams are.
The principal industry in Nottinghamshire up to the
early to mid 1980s was Coal Mining.
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There's Oil down there.
The known anticlines on the flanks of the Pennine
Uplift had rightly received priority in the rather disappointing
1918-1922 exploration programme, but more information became available
through colliery sinkings. A new programme took full advantage of this new
information and detailed contour maps were prepared.
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The new maps showed that Carboniferous
Rocks were folded into a large anticline with it's crest
peeking below the village of Eakring and Dukes Wood. A Coal
exploration borehole at Kelham had also showed a small quantity of oil
in the Carboniferous Sandstone near the top of the Millstone Grit.
A refraction survey was carried
out to define the position of this crest and a test well was dug in
1939. (Details of this test well can be found in
the Museum)
The well, Eakring Number 1, found oil
in three sands of basal Coal Measures and also in three horizons of
the Millstone Grit Sand, namely the Rough Rock, or top Millstone Grit
Sand, about 60ft thick, the Longshaw, about 25ft thick and lastly the
Chatsworth Grit, which though about 250ft thick is petroliferous
only in the upper part. Further drilling proved that the Kinderscout
lower grit contained oil only in some parts.
The limestone itself was subsequently
drilled through at Well 146, the deepest well to be drilled at Dukes
Wood, a depth of 7473 feet was achieved here. |
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Whilst the Eakring Dome was being drilled, surveys
continued working south and east from Eakring and established three other domes
at Dukes Wood, Caunton and Kelham Hills and all were found to contain
commercially important quantities of oil.
Specific gravities of Crude Oil from Eakring, Dukes Wood, Caunton
and Kelham
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Sand
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Eakring
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Dukes Wood Dome
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| Bunter Sandstone |
0.853 |
0.863 |
| Rough Rock |
0.848 |
0.861 |
| Dolomitic Sandstone |
0.828 |
- |
| Longshaw Grit |
- |
0.857 |
| Chatsworth Grit |
0.837 |
0.862 |
Sand
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Caunton
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Kelham Hills
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| Upper Grit Group |
0.880 |
0.892 |
| Middle Grit Group |
0.870 |
0.880 |
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The Exploration Technology
| In the early days elaborate
and costly deep well equipment and layout involved excessive use of
manpower and considerable loss of time. The outbreak of the second
world war caused shortages of both material supplies and labour and
this coincided with planning of intensive drilling operations.
As mentioned in the History
section the solution was to bring over an American drill crew and
their equipment. Opposite shows a 87ft Jack-Knife mast Rig they used.
The whole Rig being designed for maximum mobility and for drilling
depths of up to 5000ft. The drill pipe was 4˝ inches diameter. The
rigs were powered either by two semi-Diesel 169hp engines, running at
1300rpm or by two 150hp electric motors. A Mud pump with a 12in
stroke and 6žinch bore and working at 60 strokes per minute delivered
about 440gallons/min. The pump is set behind the motors and is driven
by multiple belts known as Vee belts, running in V-shaped groves. By
using one motor the pump can be run as separate unit from the drawworks
which eased transportation and assembly.
By replacing the old type of heavy exploration
outfits with these new units, the transfer time of drilling equipment
was cut from about two weeks to about 12 hours in good weather.
At Eakring a record time move of 6˝ hours was
achieved. |
Utilized Jack-Knife Drilling Rig at Eakring (date
unknown)
The village can be seen in the
background |
Where formation conditions are known the practice was to
drill with an 8žinch hole from the surface to the top of the oilsand, then
run a 6žinch string of casing to the bottom and cement it in that position.
This casing will contain the float collar or non-return valve about 30ft
from the bottom of the casing, to prevent cement leaking back into the
casing. The cement prevents waters from entering either the coal-bearing
formations or the oilsands beneath. The drilling
bits used were usually Hughes (Howard Hughes) and Reed rock bits of the
types suitable for the particular formation to be expected. Formerly when
viscous Muds were considered necessary the footage drilled by one bit
was low but the Americans brought with them a technique where they used
light Muds and high circulation speeds and this was found to reduce the bit
consumption from about thirteen to six for the average production
well. A more detailed description of Well conditions
and drilling and exploration techniques can be found at the Dukes Wood Oil
Museum. |
   
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