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Well stimulation is a broad term used to describe the various techniques and well interventions that can be used to restore or enhance the production of hydrocarbons from an oil well, or energy from a geothermal well.
Well stimulation can be performed on an oil or gas well located onshore or offshore, often with specialised ships. The glossary of technical terms provided by Schlumberger (the world's largest oil service company) defines stimulation as:
A treatment performed to restore or enhance the productivity of a well. Stimulation treatments fall into two main groups, hydraulic fracturing treatments and matrix treatments. Fracturing treatments are performed above the fracture pressure of the reservoir formation and create a highly conductive flow path between the reservoir and the wellbore. Matrix treatments are performed below the reservoir fracture pressure and generally are designed to restore the natural permeability of the reservoir following damage to the near-wellbore area.
Stimulation is usually part of the completion stage in the life cycle of a well. Matrix acidising operates in the near-wellbore environment, and is aimed at restoring the natural permeability of the reservoir rock. But hydraulic fracking aims to increase the permeability of a far larger volume of reservoir rock. In addition to matrix acidising there is fracture acidising, which is a variety of hydraulic fracking.
The Society of Petroleum Engineers (SPE) points out that these two kinds of acid treatment often lead to confusion.
The flow chart here helps to clarify the definitions. Under stimulation, non-hydraulic methods include: the use of explosives underground - a technique which dates back to the mid nineteenth century,[1] and electrical methods.[2]
Fracking, using either hydraulic pressure or acid, is the most common method for well stimulation. Well stimulation techniques help create pathways for oil, gas or water to flow more easily, ultimately increasing the overall production of the well.[3] Both methods of fracking are classed as unconventional, because they aim to permanently enhance (increase) the permeability of the formation. So the traditional division of hydrocarbon-bearing rocks into source and reservoir no longer holds; the source rock becomes the reservoir after the treatment.
Hydraulic fracking is more familiar to the general public, and is the predominant method used in hydrocarbon exploitation, but acid fracking has a much longer history.[1][4][5][6] Although the hydrocarbon industry tends to use fracturing rather than the word fracking, which now dominates in popular media, an industry patent application[7] dating from 2014 explicitly uses the term acid fracking in its title.
- ^ a b Van Dyke JW. 1896. Increasing the flow of oil-wells. Patent No. US 556,651.
- ^ Melton and Cross 1969. Fracturing oil shale with electricity. J. Petroleum. Tech.20, 37-41, https://doi.org/10.2118/1969-PA
- ^ Nolan, Dennis P. (2019), "Overview of Oil, Gas, and Petrochemical Facilities", Handbook of Fire and Explosion Protection Engineering Principles for Oil, Gas, Chemical, and Related Facilities, Elsevier, pp. 33–50, doi:10.1016/B978-0-12-816002-2.00002-7, ISBN 978-0-12-816002-2, retrieved 2024-10-17
- ^ Grebe JJ and Stoesser SM 1935, Treatment of deep wells. Patent no. US 1,998,756,
- ^ Montgomery CT and Smith MB 2010, Hydraulic fracturing History of an enduring technology. J. Petrol. Tech.December 2010, pp. 26-41,
- ^ Barbati AC et al. 2016, Complex fluids and hydraulic fracturing.Annu. Rev. Chem. Biomol. Eng.
- ^ Dean RH and Schmidt JH 2017, Method of cryogenic acid fracking. Patent no. US 9,644,137 B2.
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