• Finding Oil at Eakring and Dukes Wood

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. 

• 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.

  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.

  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
  Sand	Eakring	Dukes Wood Dome
  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	Caunton	Kelham Hills
  Upper Grit Group	0.880	0.892
  Middle Grit Group	0.870	0.880

   

• 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 4½ 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 6¾inch 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 6½ 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 8¾inch hole from the surface to the top of the oilsand, then run a 6¾inch 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.