Well stimulation

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The well stimulation ship Bigorange XVIII being repaired in Frederikshavn, Denmark Keld Gydum-IMG 3522 Bigorange XVIII IMO 8311314.JPG
The well stimulation ship Bigorange XVIII being repaired in Frederikshavn, Denmark

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.

Contents

Hydraulic fracturing (fracking) and acidizing are two of the most common methods for well stimulation. These well stimulation techniques help create pathways for oil or gas to flow more easily, ultimately increasing the overall production of the well. [1]

Well stimulation can be performed on an oil or gas well located onshore or offshore.

Cleaning the formation

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. [2] [3] 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.

Extending the perforation tunnels and fractures

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.

Acidization

Acidizing is a well stimulation technique that injects an acid solution into the well. Acidization process cleans out debris clogging the well and increases the permeability of the reservoir rock, allowing oil or gas to flow more freely. [4]

Hydraulic fracturing

This section is an excerpt from Fracking.[ edit ]
Fracking
Shale gas drilling rig near Alvarado, Texas BarnettShaleDrilling-9323.jpg
Shale gas drilling rig near Alvarado, Texas
Shale gas drilling rig near Alvarado, Texas
By country
Environmental impact
Regulation
Technology
Politics

Hydraulic fracturing [a] 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 1949. 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 potent 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 highlight the economic benefits of more extensively accessible hydrocarbons (such as petroleum and natural gas), [17] [18] the benefits of replacing coal with natural gas, which burns more cleanly and emits less carbon dioxide (CO2), [19] [20] and the benefits of 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, the triggering of earthquakes, and 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]

Diagram of Hydraulic Fracking Machinery and Process Diagram of Hydraulic Fracking.jpg
Diagram of Hydraulic Fracking Machinery and Process
Increases in seismic activity following hydraulic fracturing along dormant or previously unknown faults are sometimes caused by the deep-injection disposal of hydraulic fracturing flowback (a byproduct of hydraulically fractured wells), [31] and produced formation brine (a byproduct of both fractured and non-fractured oil and gas wells). [32] For these reasons, hydraulic fracturing is under international scrutiny, restricted in some countries, and banned altogether in others. [33] [34] [35] The European Union is drafting regulations that would permit the controlled application of hydraulic fracturing. [36]

Lifting the well

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.

Well stimulation vessels

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. [39] Also known as "Multipurpose drilling vessels", these ships replace the conventional drilling oil rig, thus resulting in considerable savings in cost. [40] 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. [41] [42]

See also

Notes

  1. ↑ also known as hydraulic fracturing, fracing, hydrofracturing, or hydrofracking

Related Research Articles

<span class="mw-page-title-main">Natural gas</span> Gaseous fossil fuel

Natural gas is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane (95%) in addition to various smaller amounts of other higher alkanes. Traces of 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.

<span class="mw-page-title-main">Oil well</span> Well drilled to extract crude oil and/or gas

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 and if necessary equipped with extraction devices such as pumpjacks. Creating the wells can be an expensive process, costing at least hundreds of thousands of dollars, and costing much more when in difficult-to-access locations, e.g., offshore. The process of modern drilling for wells first started in the 19th century but was made more efficient with advances to oil drilling rigs and technology during the 20th century.

<span class="mw-page-title-main">Barnett Shale</span> Geological formation in Texas, United States

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.

<span class="mw-page-title-main">Drilling fluid</span> Aid for drilling boreholes into the ground

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.

<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">Shale gas</span> Natural gas trapped in shale formations

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.

<span class="mw-page-title-main">Monterey Formation</span> Miocene geological sedimentary formation in California

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.

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

Shale gas in the United States is an available source of unconventional natural gas. Led by new applications of hydraulic fracturing technology and horizontal drilling, development of new sources of shale gas has offset declines in production from conventional gas reservoirs, and has led to major increases in reserves of U.S. natural gas. Largely due to shale gas discoveries, estimated reserves of natural gas in the United States in 2008 were 35% higher than in 2006.

<span class="mw-page-title-main">Tight gas</span> Natural gas produced from reservoir rocks

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".

<span class="mw-page-title-main">Tight oil</span> Light crude oil in petroleum-bearing formations

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".

<span class="mw-page-title-main">Fracking</span> Fracturing bedrock by pressurized liquid

Hydraulic fracturing 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 proppants</span> Fracking materials

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.

<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 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>

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.

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

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.

<span class="mw-page-title-main">Exemptions for fracking under United States federal law</span>

There are many exemptions for fracking under United States federal law: the oil and gas industries are exempt or excluded from certain sections of a number of the major federal environmental laws. These laws range from protecting clean water and air, to preventing the release of toxic substances and chemicals into the environment: the Clean Air Act, Clean Water Act, Safe Drinking Water Act, National Environmental Policy Act, Resource Conservation and Recovery Act, Emergency Planning and Community Right-to-Know Act, and the Comprehensive Environmental Response, Compensation, and Liability Act, commonly known as Superfund.

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.

<span class="mw-page-title-main">Marcellus natural gas trend</span> Natural gas extraction area in the United States

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.

<span class="mw-page-title-main">Fracking in Canada</span>

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.

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

Unconventional reservoirs, or unconventional resources are accumulations where oil and gas phases are tightly bound to the rock fabric by strong capillary forces, requiring specialized measures for evaluation and extraction.

References

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