The controversial documentary film “Gasland”, released in 2010 and nominated for an Academy Award, focuses on the effects of the process of hydraulic fracturing on ground water and the people who rely on that ground water. But those who are not familiar with processes used in oil and natural gas production may not understand the methodology of hydraulic fracturing, sometimes contracted “frac’ing”.
What is Hydraulic Fracturing?
Hydraulic fracturing is a process that uses a hydraulic medium, usually water, to introduce fractures in rock. In the case of oil and natural gas wells, the process of hydraulic fracturing allows oil and natural gas to flow up through the cracks to the drill bore, where it can be collected. This process can also be applied to ground water reservoirs to facilitate flow, or in mining operations to pre-condition rock to make it easier to be removed. Hydraulic fracturing is most often used in the United States to facilitate the production of natural gas from coal bed and shale rock formations.
Hydraulic fracturing can be used in an existing oil well where the initial internal pressure has equalized and oil is no longer flowing on its own. This process can also be applied to open up new areas of a oil or natural gas reservoir that were previously inaccessible.
While hydraulic fracturing can occur naturally, such as when water within small cracks freezes and expands, these effects usually happen at ground level, while man-made hydraulic fractures are made at depth in proximity to an oil or natural gas reservoir.
How is Hydraulic Fracturing Performed?
To perform hydraulic fracturing, a fracturing fluid is pumped into the well at a high pressure. This fluid pressure causes rock formations to crack, facilitating flow of the fluid further into the formation, facilitating further cracking, and so on. A fracturing fluid is mostly water and sand, but can often contain gels, foams, or gasses such as carbon dioxide to facilitate cracking. Occasionally, radioactive sand is used to enable traceability of the flow. Also, seismic monitoring is performed to track cracking locations by using geophones to record seismic events.
Fracturing can be performed at intervals along a borehole by inserting plugs above and below the fracturing region to localize the fracturing fluid. The assembly is then indexed down the borehole to maximize flow of the oil or gas into the well bore. This process is called “plug and perf”.
Controversies with Hydraulic Fracturing
While the process of hydraulic fracturing allows oil and gas companies to extract more product from each well and reservoir in a cost-effective manner, the process does have some controversies associated with it. The primary controversy concerns the migration of hydraulic fracturing fluid into ground water reservoirs. Hydraulic fracturing for ground water access only uses water and a disinfectant as a medium, but the fluid for gas and oil wells can contain a variety of chemicals. Opponents of hydraulic fracturing have evidence that these chemicals have shown up in ground water, including potable water wells, and that the chemicals include toxins, known carcinogens and heavy metals. A 2004 EPA study designated the process of hydraulic fracturing as safe, but noted uncertainties in its study.
Hydraulic fracturing is an efficient way to improve the flow of oil or gas through wells by injecting a pressurized fluid to crack the rock formations within a reservoir. However, the effects of this process are hard to quantify due to the difficulty of monitoring the flow of liquid thousands of feet below the surface.
Susan Kristoff - Susan Kristoff is mechanical engineer by trade, but has a diverse set of professional and personal interests. The glue that binds all of ...
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