At the height of the oil boom, 8,000 three-pole derricks dotted the countryside around Petrolia. Each derrick indicated the location of a working well. So many wells were sunk because the oil was not found in one large pocket beneath the ground, but in thousands of smaller formations. The surface of the oil field was divided accordingly into small parcels of land, each containing many wells.
These three-pole derricks, made of the black ash so prevalent in the Enniskillen swamp, were used for servicing a well which was being pumped. The pump's valve, located at the bottom of the well, had to be cleaned and repaired regularly. In order to do this work, the entire pump mechanism had to be removed from the well. This was accomplished with the three-pole derrick which had a block hung directly over the well hole. A line was run from the top of the well hole, up through the block, back down to another block at the foot of one of the poles and from these to a team of horses. The team walked forward about 10.5 metres, this being the distance from the top of the well to the first block. The lifting action provided by the horses pulled up the tubing from the well in 10.5-metre sections until the valve mechanism reached the surface. The hole was then cleaned, the valve repaired and the tubing replaced.
