Hydraulic Fracturing (Fracking) for the extraction of gas and oil

A Talk by Ken Wilkinson 8th April 2015

Ken Wilkinson is a graduate of Manchester University in Aeronautical Engineering. His hobby is active, even extreme sports. His early career was in the oil industry working first for Schlumberger and then Halliburton Oil. Later he became a Physics teacher. Ken's experience leads him to believe that there is a lot of misinformation around concerning Hydraulic Fracturing (commonly called fracking) for the creation of gas and oil wells and he tried to allay fears of some of the common concerns.

Leakage from vertical wells

The drill hole is lined with a steel tube. To protect the tube from rusting, liquid cement is forced down the tube under pressure and rises in the cavity on the outside of the tube. This operation may be repeated several times as the well is extended downwards. In the highest layers where leakage might contaminate soils, water aquifers, or ocean, two or more concentric steel or cement barriers may be installed. To check the integrity of these measures, various kinds of instrumentation are lowered into the well, including radioactive neutron generators. The statistics of the Department of Environment and Climate Change (DECC) show that there are well over 2000 wells in Britain (mostly in the North Sea, some of them quite old) and none of them are leaking.

Horizontal gas/oil collection bores

To maximise the area from which gas/oil can be extracted it is normal, to drill away from the well bottom in various directions for several kilometres. This minimises the number of vertical wells to be drilled and the number of well head installations. Temporary plugs are introduced to define the area to be fractured next, starting at the remote end. Fracturing fluid is introduced to the defined area at high but controlled pressure to make the fractures. The fluid will contain sand or other material to prop fractures open, and may contain chemicals to assist the process. For example dilute hydrochloric acid may be used to widen the fractures.

By introducing microphones into the bore it is possible to make a 3 dimensional model of the direction and length of the fractures. The risk of extended fractures extending upwards into aquifers can be avoided. Although considerable quantities of fracturing fluid are required, this is only a tiny fraction of the rock being fractured. Extraction of the fluid is most unlikely to result in subsidence.

Disposal of fracturing fluid

The extracted fluid it may be reconditioned for reuse but eventually it has to be made safe and disposed of. The DECC has set down stringent regulations for these operations, so there are unlikely to be reoccurrences of the occasional unfortunate incidents that there have been in the United States.

Typical well RPEC is pleased to acknowledge the use of Mike Norton's excellent drawing taken from Wikipedia.

John Coneybeare 9th April 2015

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