5/31/2020  Brian Douglas
                                                                  What Is Fracking Used For?

Definition of hydraulic fracturing:

Fracking as it is more commonly known can otherwise be called hydraulic fracturing. It can be defined as a well stimulation technique that involves the fracturing of subsurface bedrock formations by the use of liquid under great pressure.

The process involves the high-pressure injection of 'fracking fluid' into a wellbore in the earth surface to create cracks in the subsurface rock formations through which natural gas, petroleum, and brine will flow more freely.

A typical example of a fracking fluid is water containing sand or other proppants suspended with thickening agents. When the hydraulic pressure is removed from the well, Pore space formed by dissolution or fracturing of grains is called secondary porosity.


What is fracking used for:

  1. Hydraulic fracturing or fracking is mostly used to improve the migration and recovery of formation fluids, such as petroleum, water, or natural gas.

  2. Hydraulic fracturing is also used for the stimulation groundwater wells.

  3. To precondition or induce rock cave-ins mining of solid minerals due to the formation of fractures in subsurface rock that leads to instability.

  4. This process is applied as a method of enhancing waste remediation caused by hydrocarbon exploitation, usually hydrocarbon waste or spills

  5. Hydraulic fracturing is a process of hydraulic injection and this can be applied in the disposition of waste by injecting deep into sub surface rocks.

  6. To increase injection rates for geologic sequestration of CO2

Rock examples where fracking is applied:

Examples of formation rocks where hydraulic fracturing has improved the recovery of formation fluids.

Carbonate muds rocks are characterized by it very fine-grained particles and so do not have high enough primary porosity and permeability to form reservoir rocks for trapping fluids, but may gain porosity and permeability by fracturing and become fractured reservoirs.

Figure 1fracture in reservoir sandstone (Tilje Fm, Smorbukk Field)

Some source rocks may have enough permeability to serve as reservoir rocks too. The Miocene Monterey Formation in California is an organic-rich diatomaceous source rock, which is also a reservoir rock. Oil can in this case be produced and extracted from source rock by the method of hydraulic fracturing.


Methods of hydraulic fracturing

hydraulic fracturing is a process formed by pumping fracking fluids into a wellbore at a high rate sufficient to increase pressure at the targeted depth which would be estimated to exceed that of the formation rock fracture gradient (pressure gradient).

The targeted formation rock cracks and the pressurized fracture fluid permeates the rock extending the crack further.

Bore well operators then try to maintain the "fracture width" that has been created to prevent it from closing up, or slow its decline by introducing a proppant into the injected fluid.

Proppants consist of material such as sand grains, ceramic, or other particulate, which will fill-up the fractures thus preventing the fractures from closing when injection is stopped and pressure removed. Consideration of proppant strength and prevention of proppant failure becomes more important at greater depths where pressure and stresses on fractures are higher.

During the process of fracture stabilization, fracturing fluid leaks off into the surrounding permeable rocks. If this phenomenon is not controlled, 70% or more of the injected fluid volume may be lost. Which may further result in damage of formation matrix, adverse formation fluid interaction, and altered fracture geometry, this condition can however decrease efficiency of the fractures.


Examples of Fracking fluids

Fluid mixtures used in fracking is consist of the mixture of water, sand and chemicals to create hydraulic fracturing fluid. Approximately 40,000 gallons of chemicals are used per fracturing.

Important material properties of the fluid include viscosity, pH, temperature.

A typical chemical additive can include one or more of the following

  1. Acids: examples are hydrochloric acid (HCl), acetic acid is used in the pre-fracturing stage for cleaning the perforations and initiating fissure in the near-wellbore rock.

  2. Sodium chloride (NaCl): this helps to delay the breakdown of gel polymer chains.

  3. Polyacrylamide: A friction reducer that decreases turbulence in fluid flow and pipe friction, thus allowing a higher rate of fluid pumping without having greater pressure on the surface.

  4. Ethylene glycol: helps to prevents the formation of scale deposits in the bore pipe.

  5. Borate salts: used for maintaining fluid viscosity during the temperature increase.

Environmental Impacts Hydraulic fracturing

The potential effect caused by hydraulic fracturing on the environment may include but not limited to air pollutant emissions and climate change, high volume of water consumption, underground water contamination, massive land use, increases risk of artificially induced earthquakes, noise pollution from trucks and pumps, and effect on human health.

Air emissions consists primarily of methane gas that seeps out from wells, along with industrial emissions from equipment used in the extraction process.

Surface water bodies including nearby rivers, streams, lakes, ponds etc., may be contaminated through spillage and improperly built disposal mechanism.

Also, ground water contamination arises when fluid in the well bore is able to escape out of the formation being fractured.

Hydraulic fracturing has been evident to be a major cause of induced seismic activities or earthquakes. The magnitude of these events is usually too small to be detected at the surface.


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