Fracking proppants

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A proppant is a solid material, typically sand, treated sand or man-made ceramic materials, designed to keep an induced hydraulic fracture open, during or following a fracturing treatment, most commonly for unconventional reservoirs. It is added to a fracking fluid which may vary in composition depending on the type of fracturing used, and can be gel, foam or slickwater–based. In addition, there may be unconventional fracking fluids. Fluids make tradeoffs in such material properties as viscosity, where more viscous fluids can carry more concentrated proppant; the energy or pressure demands to maintain a certain flux pump rate (flow velocity) that will conduct the proppant appropriately; pH, various rheological factors, among others. In addition, fluids may be used in low-volume well stimulation of high-permeability sandstone wells (20 to 80 thousand US gallons (76 to 303 kl) per well) to the high-volume operations such as shale gas and tight gas that use millions of gallons of water per well.

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Conventional wisdom has often vacillated about the relative superiority of gel, foam and slickwater fluids with respect to each other, which is in turn related to proppant choice. For example, Zuber, Kuskraa and Sawyer (1988) found that gel-based fluids seemed to achieve the best results for coalbed methane operations, [1] but as of 2012, slickwater treatments are more popular.

Other than proppant, slickwater fracturing fluids are mostly water, generally 99% or more by volume, but gel-based fluids can see polymers and surfactants comprising as much as 7 vol%, ignoring other additives. Other common additives include hydrochloric acid (low pH can etch certain rocks, dissolving limestone for instance), friction reducers, guar gum, biocides, emulsion breakers, emulsifiers, 2-butoxyethanol, and radioactive tracer isotopes.

Proppants have greater permeability than small mesh proppants at low closure stresses, but will mechanically fail (i.e. get crushed) and produce very fine particulates ("fines") at high closure stresses such that smaller-mesh proppants overtake large-mesh proppants in permeability after a certain threshold stress. [2]

Though sand is a common proppant, untreated sand is prone to significant fines generation; fines generation is often measured in wt% of initial feed. One manufacturer has claimed untreated sand fines production to be 23.9% compared with 8.2% for lightweight ceramic and 0.5% for their product. [3] One way to maintain an ideal mesh size (i.e. permeability) while having sufficient strength is to choose proppants of sufficient strength; sand might be coated with resin, to form curable resin coated sand or pre-cured resin coated sands. In certain situations a different proppant material might be chosen altogether—popular alternatives include ceramics and sintered bauxite.

Proppant weight and strength

Increased strength often comes at a cost of increased density, which in turn demands higher flow rates, viscosities or pressures during fracturing, which translates to increased fracturing costs, both environmentally and economically. [4] Lightweight proppants conversely are designed toals can break the strength-density trend, or even afford greater gas permeability. Proppant geometry is also important; certain shapes or forms amplify stress on proppant particles making them especially vulnerable to crushing (a sharp discontinuity can classically allow infinite stresses in linear elastic materials). [5]

Proppant deposition and post-treatment behaviours

Proppant mesh size also affects fracture length: proppants can be "bridged out" if the fracture width decreases to less than twice the size of the diameter of the proppant. [2] As proppants are deposited in a fracture, proppants can resist further fluid flow or the flow of other proppants, inhibiting further growth of the fracture. In addition, closure stresses (once external fluid pressure is released) may cause proppants to reorganise or "squeeze out" proppants, even if no fines are generated, resulting in smaller effective width of the fracture and decreased permeability. Some companies try to cause weak bonding at rest between proppant particles in order to prevent such reorganisation. The modelling of fluid dynamics and rheology of fracturing fluid and its carried proppants is a subject of active research by the industry.

Proppant costs

Though good proppant choice positively impacts output rate and overall ultimate recovery of a well, commercial proppants are also constrained by cost. Transport costs from supplier to site form a significant component of the cost of proppants.

Other components of fracturing fluids

Other than proppant, slickwater fracturing fluids are mostly water, generally 99% or more by volume, but gel-based fluids can see polymers and surfactants comprising as much as 7 vol%, ignoring other additives. [6] Other common additives include hydrochloric acid (low pH can etch certain rocks, dissolving limestone for instance), friction reducers, guar gum, [7] biocides, emulsion breakers, emulsifiers, and 2-Butoxyethanol.

Radioactive tracer isotopes are sometimes included in the hydrofracturing fluid to determine the injection profile and location of fractures created by hydraulic fracturing. [8] Patents describe in detail how several tracers are typically used in the same well. Wells are hydraulically fractured in different stages. [9] Tracers with different half-lives are used for each stage. [9] [10] Their half-lives range from 40.2 hours (lanthanum-140) to 5.27 years (cobalt-60). [11] Amounts per injection of radionuclide are listed in The US Nuclear Regulatory Commission (NRC) guidelines. [12] The NRC guidelines also list a wide range of radioactive materials in solid, liquid and gaseous forms that are used as field flood or enhanced oil and gas recovery study applications tracers used in single and multiple wells. [12]

In the US, except for diesel-based additive fracturing fluids, noted by the American Environmental Protection Agency to have a higher proportion of volatile organic compounds and carcinogenic BTEX, use of fracturing fluids in hydraulic fracturing operations was explicitly excluded from regulation under the American Clean Water Act in 2005, a legislative move that has since attracted controversy for being the product of special interests lobbying.[ citation needed ]

See also

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<span class="mw-page-title-main">Fracking in the United States</span>

Fracking in the United States began in 1949. According to the Department of Energy (DOE), by 2013 at least two million oil and gas wells in the US had been hydraulically fractured, and that of new wells being drilled, up to 95% are hydraulically fractured. The output from these wells makes up 43% of the oil production and 67% of the natural gas production in the United States. Environmental safety and health concerns about hydraulic fracturing emerged in the 1980s, and are still being debated at the state and federal levels.

<span class="mw-page-title-main">Well stimulation</span>

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The Fracturing Responsibility and Awareness of Chemicals Act was a 2009 legislative proposal in the United States Congress to define hydraulic fracturing as a federally regulated activity under the Safe Drinking Water Act. The proposed act would have required the energy industry to disclose the chemical additives used in the hydraulic fracturing fluid. The gas industry opposed the legislation.

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Fracking is a well stimulation technique involving the fracturing of formations in bedrock by a pressurized liquid. The process involves the high-pressure injection of "fracking fluid" into a wellbore to create cracks in the deep-rock formations through which natural gas, petroleum, and brine will flow more freely. When the hydraulic pressure is removed from the well, small grains of hydraulic fracturing proppants hold the fractures open.

<span class="mw-page-title-main">Fracking in the United Kingdom</span>

Fracking in the United Kingdom started in the late 1970s with fracturing of the conventional oil and gas fields near the North Sea. It was used in about 200 British onshore oil and gas wells from the early 1980s. The technique attracted attention after licences use were awarded for onshore shale gas exploration in 2008. The topic received considerable public debate on environmental grounds, with a 2019 high court ruling ultimately banning the process. The two remaining high-volume fracturing wells were supposed to be plugged and decommissioned in 2022.

<span class="mw-page-title-main">Fracking by country</span> Hydraulic fracturing by country

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<span class="mw-page-title-main">Environmental impact of fracking</span>

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<span class="mw-page-title-main">Uses of radioactivity in oil and gas wells</span>

Radioactive sources are used for logging formation parameters. Radioactive tracers, along with the other substances in hydraulic-fracturing fluid, are sometimes used to determine the injection profile and location of fractures created by hydraulic fracturing.

Hydraulic fracturing is the propagation of fractures in a rock layer by pressurized fluid. Induced hydraulic fracturing or hydrofracking, commonly known as fracking, is a technique used to release petroleum, natural gas, or other substances for extraction, particularly from unconventional reservoirs. Radionuclides are associated with fracking in two main ways. Injection of man-made radioactive tracers, along with the other substances in hydraulic-fracturing fluid, is often used to determine the injection profile and location of fractures created by fracking. In addition, fracking releases naturally occurring heavy metals and radioactive materials from shale deposits, and these substances return to the surface with flowback, also referred to as wastewater.

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<span class="mw-page-title-main">Unconventional (oil and gas) reservoir</span> Type of hydrocarbon reservoir

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References

  1. ↑ Mader, Detlef (1989). Hydraulic proppant fracturing and gravel packing. Amsterdam: Elsevier. p. 473. ISBN   0-444-87352-X.
  2. 1 2 "Physical Properties of Proppants". CarboCeramics Topical Reference. CarboCeramics. Archived from the original on 18 January 2013. Retrieved 24 January 2012.
  3. ↑ "Critical Proppant Selection Factors". Fracline. Hexion. Archived from the original on 11 October 2012. Retrieved 25 January 2012.
  4. ↑ Rickards, Allan; et al. (May 2006). "High Strength, Ultralightweight Proppant Lends New Dimensions to Hydraulic Fracturing Applications". SPE Production & Operations. 21 (2): 212–221. doi:10.2118/84308-PA.
  5. ↑ Guimaraes, M. S.; et al. (2007). "Aggregate production: Fines generation during rock crushing" (PDF). Journal of Mineral Processing. 81 (4): 237–247. doi:10.1016/j.minpro.2006.08.004.
  6. ↑ Hodge, Richard. "Crosslinked and Linear Gel Comparison" (PDF). EPA HF Study Technical Workshop. Environmental Protection Agency . Retrieved 8 February 2012.
  7. ↑ Ram Narayan (8 August 2012). "From Food to Fracking: Guar Gum and International Regulation". RegBlog. University of Pennsylvania Law School . Retrieved 15 August 2012.
  8. ↑ Reis, John C. (1976). Environmental Control in Petroleum Engineering. Gulf Professional Publishers.
  9. 1 2 Scott III, George L. (3 June 1997) US Patent No. 5635712: Method for monitoring the hydraulic fracturing of a subterranean formation. US Patent Publications.
  10. ↑ Scott III, George L. (15-Aug-1995) US Patent No. US5441110: System and method for monitoring fracture growth during hydraulic fracture treatment. US Patent Publications.
  11. ↑ Gadeken, Larry L., Halliburton Company (08-Nov-1989). Radioactive well logging method.
  12. 1 2 Jack E. Whitten, Steven R. Courtemanche, Andrea R. Jones, Richard E. Penrod, and David B. Fogl (Division of Industrial and Medical Nuclear Safety, Office of Nuclear Material Safety and Safeguards (June 2000). "Consolidated Guidance About Materials Licenses: Program-Specific Guidance About Well Logging, Tracer, and Field Flood Study Licenses (NUREG-1556, Volume 14)". US Nuclear Regulatory Commission. Retrieved 19 April 2012. labeled Frac Sand...Sc-46, Br-82, Ag-110m, Sb-124, Ir-192{{cite web}}: CS1 maint: multiple names: authors list (link)
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