The Fracking Process
Hydraulic fracturing, commonly called fracking, is a drilling technique used for extracting oil or natural gas from deep underground.
Fracking is a hotly debated environmental and political issue. Advocates insist it is a safe and economical source of clean energy; critics, however, claim fracking can destroy drinking water supplies, pollute the air, contribute to the greenhouse gases that cause global warming, and trigger earthquakes.
HOW FRACKING WORKS
The oil and gas industry claim that hydraulic fracturing has been around since the 1940s. So if the technique has been around so long why is it controversial?
The answer is 3 recent technological developments which have enabled fracking to be used in so-called “unconventional” or “tight” geology such as shale. Prior to the 1990s, the oil and gas industry used to view shale as one of the useless layers of rock you had to drill through to get to a sandstone or limestone oil or gas reservoir. A single vertical well could drain one such reservoir; any oil or gas in the shale layer, however, simply does not want to flow. It has to be forced out
So what are the 3 technologies which have enabled the exploitation of shale oil and gas?
1) Deviated well bores / directional drilling, which was developed during the 1980s. The well bore needs to be in contact with as much as the shale layer as possible – a vertical well would only have access to a thin vertical section of rock.
2) Slickwater, developed in the mid 1990s. This is basically water with, amongst other things, friction-reducing chemical additives, enabling huge volumes of water to be pumped down the deviated well bores to create the network of fractures. (Hydro-fracturing into conventional geology typically uses less than 100,000 gallons of fluid; 2,000,000 – 6,000,000 gallons is required for for shale.)
3) Multi-well pads, first seen during the early part of the 21st century. A single deviated well bore would still only reach a small part of the shale layer. Drilling multiple wells from the same pad makes the process of extracting the oil and gas more economical.
In simplified terms, the fracking process starts with a well that is drilled vertically or at an angle from the surface to a depth of 1 to 2 miles or more. The vertical well is then encased in steel and cement.
Once the vertical well reaches the deep layer of rock where natural gas or oil exists, the well curves and begins drilling horizontally along that rock layer. Horizontal drilling can extend more than 1 mile from the vertical well bore.
After the fracking well is fully drilled and encased, fracking fluid is pumped down into the well at extremely high pressure, in some cases exceeding 9,000 pounds per square inch (62,050 kilopascals). The pressure is powerful enough to fracture the surrounding rock, creating fissures and cracks through which oil and gas can flow.
The fluid that is pumped into the well to fracture the rock is called slickwater. It is mostly water, though it also can contain a wide range of additives and chemicals that serve an engineering purpose. Additives can include detergents, salts, acids, alcohols, lubricants and disinfectants. These chemical additives usually make up 0.5 to 2 percent of the slickwater, with the remaining 98 to 99.5 percent consisting of plain water.
In addition to the water and chemical additives, "proppants" such as sand and ceramic particles are also pumped into the fracking well. These proppants are added to prop open the fractures that form under pressure, thereby ensuring that gas and oil can continue to flow freely out of rock fractures even after pumping pressure is released.
Once the underground rock is shattered and proppants are pumped into place, trapped reservoirs of gas and oil are released and pumped back to the surface, along with millions of gallons of "flowback" liquid.
The flowback liquid contains water and a number of contaminants, including radioactive material, heavy metals, hydrocarbons and other toxins. Flowback water can be treated, but there are large volumes of it and so dealing with it is expensive. Faults in the casing, well design or cement bond are typical causes of flowback water contamination experienced in fracking areas. Earthquakes have also been linked to the reinjection of flowback water into disposal wells.