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Well stimulation is a well intervention performed on an oil or gas well to increase production by improving the flow of hydrocarbons from the reservoir into the well bore. It may be done using a well stimulator structure or using off shore ships / drilling vessels, also known as "Well stimulation vessels". [1] [2]
The assortment of drilling fluid pumped down the well during drilling and completion can often cause damage to the surrounding formation by entering the reservoir rock and blocking the pore throats (the channels in the rock throughout which the reservoir fluids flow). Similarly, the act of perforating can have a similar effect by jetting debris into the perforation channels. Both these situations reduce the permeability in the near well bore area and so reduce the flow of fluids into the well bore.
A simple and safe solution is to pump diluted acid mixtures from surface into the well to dissolve the offending material. [3] [4] Once dissolved, permeability should be restored and the reservoir fluids will flow into the well bore, cleaning up what is left of the damaging material. After initial completion, it is common to use minimal amounts of formic acid to clean up any mud and skin damage. In this situation, the process is loosely referred to as "well stimulation." Oftentimes, groups that oppose oil and gas production refer to the process as "acidization," which is actually the use of acids in high volume and high pressure to stimulate oil production.
In more serious cases, pumping from surface is insufficient as it does not target any particular location downhole and reduces the chances of the chemical retaining its effectiveness when it gets there. In these cases, it is necessary to spot the chemical directly at its target through the use of coiled tubing. Coiled tubing is run in hole with a jetting tool on the end. When the tool is at its target, the chemical is pumping through the pipe and is jetted directly onto the damaged area. This can be more effective than pumping from surface, though it is much more expensive, and accuracy is dependent on knowing the location of the damage.
In cased hole completions, perforations are intended to create a hole through the steel casing so that the reservoir can be produced. The holes are typically formed by shaped explosives that perforate the casing and create a fractured hole into the reservoir rock for a short distance. In many cases, the tunnels created by the perforation guns do not provide enough surface area and it becomes desirable to create more area in contact with the wellbore.
In some cases, more area is needed if the reservoir is of low permeability. In other cases, damage caused by drilling and completion operations can be severe enough that the perforation tunnel does not effectively penetrate through the damaged volume near the bore. This means that the ability of fluids to flow into the existing perforation tunnels is too limited. One method to achieve more stimulation is by carrying out a hydraulic fracture treatment through the perforations.
If permeability is naturally low, then as fluid is drained from the immediate area, replacement fluid may not flow into the void sufficiently quickly to make up for the voidage and so the pressure drops. The well cannot then flow at a rate sufficient to make production economic. In this case, extending a hydraulic fracture deeper into the reservoir will allow higher production rates to be achieved.
Propellant stimulations can be a very economical way to clean up nearbore damage. Propellants are a low-explosive material that generate large amounts of gas downhole very rapidly. The gas pressure builds in the wellbore, increasing tension in the rock until it becomes greater than the breakdown pressure of the formation. Fracture length and fracture pattern are highly dependent on the type of propellant stimulation tool that is used.
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Fracking (also known as hydraulic fracturing, fracing, hydrofracturing, or hydrofracking) 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" (primarily water, containing sand or other proppants suspended with the aid of thickening agents) 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 (either sand or aluminium oxide) hold the fractures open. [5]
Hydraulic fracturing began as an experiment in 1947, [6] and the first commercially successful application followed in 1950. As of 2012, 2.5 million "frac jobs" had been performed worldwide on oil and gas wells, over one million of those within the U.S. [7] [8] Such treatment is generally necessary to achieve adequate flow rates in shale gas, tight gas, tight oil, and coal seam gas wells. [9] Some hydraulic fractures can form naturally in certain veins or dikes. [10] Drilling and hydraulic fracturing have made the United States a major crude oil exporter as of 2019, [11] but leakage of methane, a powerful greenhouse gas, has dramatically increased. [12] [13] Increased oil and gas production from the decade-long fracking boom has led to lower prices for consumers, with near-record lows of the share of household income going to energy expenditures. [14] [15]
Hydraulic fracturing is highly controversial. [16] Its proponents advocate the economic benefits of more extensively accessible hydrocarbons, [17] [18] as well as replacing coal with natural gas, which burns more cleanly and emits less carbon dioxide (CO2), [19] [20] and energy independence. [21] Opponents of fracking argue that these are outweighed by the environmental impacts, which include groundwater and surface water contamination, [22] noise and air pollution, and the triggering of earthquakes, along with the resulting hazards to public health and the environment. [23] [24] Research has found adverse health effects in populations living near hydraulic fracturing sites, [25] [26] including confirmation of chemical, physical, and psychosocial hazards such as pregnancy and birth outcomes, migraine headaches, chronic rhinosinusitis, severe fatigue, asthma exacerbations and psychological stress. [27] Adherence to regulation and safety procedures are required to avoid further negative impacts. [28]
The scale of methane leakage associated with hydraulic fracturing is uncertain, and there is some evidence that leakage may cancel out any greenhouse gas emissions benefit of natural gas relative to other fossil fuels. [29] [30]
Some stimulation techniques do not necessarily mean altering the permeability outside the well bore. Sometimes they involve making it easier for fluids to flow up the well bore having already entered. Gas lift is sometimes considered a form of stimulation, particularly when it is only used for starting up the well and shut off during steady state operation. More commonly though, lifting as a stimulation refers to trying to lift out heavy liquids that have accumulated at the bottom, either through water entry from the formation or through chemicals injected from surface such as scale inhibitors and methanol (hydrate inhibitor). These liquids sit at the bottom of the well as can act as a weight holding back the flow of reservoir fluids, essentially acting to kill the well. They can be removed by circulating nitrogen using coiled tubing.
In more recent times, due to the temporary nature of well stimulation, specialized drilling ships known as "well stimulation vessels" have been used for deep sea well stimulation. [37] [38] Offshore companies such as Norshore and Schlumberger operate a fleet of such specialized ships. [1] Also known as "Multipurpose drilling vessels", these ships replace the conventional drilling oil rig, thus resulting in considerable savings in cost. [39] Some WSV's such as the "Norshore Atlantic" are able to perform multiple tasks including riserless operation in the shallow- and mid-water segments, drilling complete oil wells and performing complete subsea decommissioning (P&A). They are also able to perform pre-drilling of the top hole sections in deep water and well intervention operations with workover risers. [40] [41]
Natural gas is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane (97%) in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbon dioxide, nitrogen, hydrogen sulfide, and helium are also usually present. Methane is colorless and odorless, and the second largest greenhouse gas contributor to global climate change after carbon dioxide. Because natural gas is odorless, odorizers such as mercaptan are commonly added to it for safety so that leaks can be readily detected.
An oil well is a drillhole boring in Earth that is designed to bring petroleum oil hydrocarbons to the surface. Usually some natural gas is released as associated petroleum gas along with the oil. A well that is designed to produce only gas may be termed a gas well. Wells are created by drilling down into an oil or gas reserve that is then mounted with an extraction device such as a pumpjack which allows extraction from the reserve. Creating the wells can be an expensive process, costing at least hundreds of thousands of dollars, and costing much more when in hard to reach areas, e.g., when creating offshore oil platforms. The process of modern drilling for wells first started in the 19th century, but was made more efficient with advances to oil drilling rigs during the 20th century.
The Barnett Shale is a geological formation located in the Bend Arch-Fort Worth Basin. It consists of sedimentary rocks dating from the Mississippian period in Texas. The formation underlies the city of Fort Worth and underlies 5,000 mi² (13,000 km²) and at least 17 counties.
In geotechnical engineering, drilling fluid, also known as drilling mud, is used to aid the drilling of boreholes into the earth. Used while drilling oil and natural gas wells and on exploration drilling rigs, drilling fluids are also used for much simpler boreholes, such as water wells.
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.
Shale gas is an unconventional natural gas that is found trapped within shale formations. Since the 1990s a combination of horizontal drilling and hydraulic fracturing has made large volumes of shale gas more economical to produce, and some analysts expect that shale gas will greatly expand worldwide energy supply.
The Monterey Formation is an extensive Miocene oil-rich geological sedimentary formation in California, with outcrops of the formation in parts of the California Coast Ranges, Peninsular Ranges, and on some of California's off-shore islands. The type locality is near the city of Monterey, California. The Monterey Formation is the major source-rock for 37 to 38 billion barrels of oil in conventional traps such as sandstones. This is most of California's known oil resources. The Monterey has been extensively investigated and mapped for petroleum potential, and is of major importance for understanding the complex geological history of California. Its rocks are mostly highly siliceous strata that vary greatly in composition, stratigraphy, and tectono-stratigraphic history.
Gasland is a 2010 American documentary film written and directed by Josh Fox. It focuses on communities in the United States where natural gas drilling activity was a concern and, specifically, on hydraulic fracturing ("fracking"), a method of stimulating production in otherwise impermeable rock. The film was a key mobilizer for the anti-fracking movement, and "brought the term 'hydraulic fracturing' into the nation's living rooms" according to The New York Times.
Tight gas is commonly used to refer to natural gas produced from reservoir rocks with such low permeability that massive hydraulic fracturing is necessary to produce the well at economic rates. The gas is sealed in very impermeable and hard rocks, making their formation "tight". These impermeable reservoirs which produce dry natural gas are also called "Tight Sand".
Tight oil is light crude oil contained in unconventional petroleum-bearing formations of low permeability, often shale or tight sandstone. Economic production from tight oil formations requires the same hydraulic fracturing and often uses the same horizontal well technology used in the production of shale gas. While sometimes called "shale oil", tight oil should not be confused with oil shale or shale oil. Therefore, the International Energy Agency recommends using the term "light tight oil" for oil produced from shales or other very low permeability formations, while the World Energy Resources 2013 report by the World Energy Council uses the terms "tight oil" and "shale-hosted oil".
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.
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 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 to the high-volume operations such as shale gas and tight gas that use millions of gallons of water per well.
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.
Fracking has become a contentious environmental and health issue with Tunisia and France banning the practice and a de facto moratorium in place in Quebec (Canada), and some of the states of the US.
Environmental impact of fracking in the United States has been an issue of public concern, and includes the contamination of ground and surface water, methane emissions, air pollution, migration of gases and fracking chemicals and radionuclides to the surface, the potential mishandling of solid waste, drill cuttings, increased seismicity and associated effects on human and ecosystem health. Research has determined that human health is affected. A number of instances with groundwater contamination have been documented due to well casing failures and illegal disposal practices, including confirmation of chemical, physical, and psychosocial hazards such as pregnancy and birth outcomes, migraine headaches, chronic rhinosinusitis, severe fatigue, asthma exacerbations, and psychological stress. While opponents of water safety regulation claim fracking has never caused any drinking water contamination, adherence to regulation and safety procedures is required to avoid further negative impacts.
The environmental impact of fracking is related to land use and water consumption, air emissions, including methane emissions, brine and fracturing fluid leakage, water contamination, noise pollution, and health. Water and air pollution are the biggest risks to human health from fracking. Research has determined that fracking negatively affects human health and drives climate change.
Shale gas in the United Kingdom has attracted increasing attention since 2007, when unconventional onshore shale gas production was proposed. The first shale gas well in England was drilled in 1875. As of 2013 a number of wells had been drilled, and favourable tax treatment had been offered to shale gas producers.
The Marcellus natural gas trend is a large geographic area of prolific shale gas extraction from the Marcellus Shale or Marcellus Formation, of Devonian age, in the eastern United States. The shale play encompasses 104,000 square miles and stretches across Pennsylvania and West Virginia, and into eastern Ohio and western New York. In 2012, it was the largest source of natural gas in the United States, and production was still growing rapidly in 2013. The natural gas is trapped in low-permeability shale, and requires the well completion method of hydraulic fracturing to allow the gas to flow to the well bore. The surge in drilling activity in the Marcellus Shale since 2008 has generated both economic benefits and considerable controversy.
Fracking in Canada was first used in Alberta in 1953 to extract hydrocarbons from the giant Pembina oil field, the biggest conventional oil field in Alberta, which would have produced very little oil without fracturing. Since then, over 170,000 oil and gas wells have been fractured in Western Canada. Fracking is a process that stimulates natural gas or oil in wellbores to flow more easily by subjecting hydrocarbon reservoirs to pressure through the injection of fluids or gas at depth causing the rock to fracture or to widen existing cracks.
Unconventional reservoirs, or unconventional resources are accumulations where oil & gas phases are tightly bound to the rock fabric by strong capillary forces, requiring specialised measures for evaluation and extraction.
{{cite book}}: |journal= ignored (help)The shale-drilling frenzy in the Permian has enabled the United States not only to reduce crude-oil imports, but even to become a major exporter [...] New technologies for drilling and hydraulic fracturing helped bring the break-even price
During much of the fracking boom, the US economy grew and emissions declined. One study found that between 2005 and 2012, fracking created 725,000 jobs. That's largely due to natural gas from fracking displacing coal in electricity production.
... hydraulic fracturing techniques spurred a historic U.S. production boom during the decade that has driven down consumer prices, buoyed the national economy and reshaped geopolitics.