MechChem Africa March 2017

⎪ Petrochemical industries, oil and gas ⎪

How hydraulic fracturing works: Edited from an OilPatch CopyWriter article by Cyndee Davis.

is pumped into the well, opening up tiny fractures deep into the shale. Once the water is removed, the sand remains, holding the fractures open. This makes it possible for gas or oil to travel from the shale out into the well. Bridge plugs are inserted, allowing the fracturing process to continue across the whole length of the horizontal well. After the fracturing process is completed, all the bridge plugs are removed, allowing the gas or oil to flow freely to the surface. On average it takes four to eight weeks to prepare a site for drilling and a further four to five weeks during which the casing and cementing occurs. Hydraulic fractur- ing, itself, only takes between two to five days, making the entire process fracking from start to finish, a total of seventy to a hundred days. Following the establishment of a well by fracking, the facility can typically produce energy for 20 to 50 years. Trucks, pumps and equipment are removed, leaving only a production valve and collection equipment on the land surface. q

Awellbore is drilledusing a drill pipe andbit. Mud is pumped down to the drill to cool and lubricate the drill pipe and bit. This helps to stabilize the wellbore and helps carry rock fragments to the surface. Drilling continues way past groundwa- ter levels and typically, over 500 m of rock separatestheshalereservesfromthelowest groundwater reservoirs. The drill pipe and bit are removed and a steel tube called surface casing is set inside the well. The tube stabilises the sides of the well, creating a protective barrier between the well stream and any underground fresh water reservoirs. Cement is then pumped into the well, through and out of the casing, displacingremainingdrillingfluidsandsecur- ingthecasinginplacepermanently.Fillingthe gapbetweenthecasingandwellborecement creates a protective seal, keeping outside materials from entering the well flow. The casing is pressure-tested to make

sure hydrocarbons and other fluids do not seep out as they are brought to the surface. Drilling continues and another layer of casing and cement are set in place to cre- ate a second permanent protective barrier. These multiple layers of casing and cement are critical for safewell construction and to protect drinking water. At about 150 m above the hydrocarbon shale formation a specific drilling motor with sophisticated measuring instruments begins drilling at an angle to create a hori- zontal path into the targeted layer of gas or oil bearing shale. The casing and cementing process continues through the entire length of the now horizontal wellbore. A perforating tool is inserted into the well, creating holes in shale layers to allow the hydrocarbons to enter the well stream. Once the perforating tool is removed, a fracturing fluid made up of water, sand and small percentages of a chemical solution,

The establishment of a shale oil or gas well by fracking typically takes only eight to 12 weeks, with the hydraulic fracturing only taking two to five days. After this time, a well can produce oil or gas for 20 to 50 years.

March 2017 • MechChem Africa ¦ 21