Well Stimulation Technologies

The Monterey shale is very complex, requring new well stimulation technologies to access its estimated resources.

The highly fractured Monterey Shale requires companies to use increasingly extreme well stimulation technologies to access California’s oil resources. (Source: AAPG)

While hydraulic fracking has received the most attention nationwide, there are a number of well stimulation technologies being used to extract California’s oil and gas reserves. Unconventional techniques, known broadly as ‘well stimulation,’ use different injection fluids such as petroleum, acid, or steam to release oil trapped underground.

Oil companies have faced a number of challenges in trying to extract oil from the Monterey Shale formation. The formation is characterized by low permeability, which makes traditional fracking less productive than it has been in other states.1  Other difficulties are the depth of the oil reservoirs, which geologists estimate range from 8,000-14,000 feet below the surface, and the highly fractured nature of the shale, which makes it more difficult for oil to flow to the surface.2

In May 2014, the Energy Information Administration (EIA) officially downgraded it’s estimates of technically recoverable oil contained within the Monterey Shale from 13.7 billion barrels to just 0.6 billion barrels of oil. Although large-scale fracking of the Monterey Shale seems unlikely, other forms of enhanced oil recovery throughout California continue to pose not fully-understood risks to the health and safety of Californians. This page summarizes some of the well stimulation technologies that oil companies are experimenting with in California. This list will be updated as information about new methods becomes available.

Overview of Well Stimulation Technologies

Acidization, one of many new well stimulation technologies, is popular in the Monterey Shale

A graphic explaining why acidization has proved popular as a way to access the oil in the Monterey Shale. (Credit: Steve Hargreaves/CNN Money)

Matrix Acidization uses high volumes of corrosive acid to access the oil and gas trapped beneath the earth. This technique uses chemicals rather than high-pressure fluid to break down rocks deep underground. Oil companies are using acid in oil fields across California. This includes the Elk Hills Oil Field in Kern County and wells located in highly urban areas around Los Angeles County.

Like traditional fracking, acidization uses water, sand and a variety of chemicals including gels, proppants, and high concentrations of hydrochloric or hydrofluoric acid. Hydrofluoric acid is one of the most dangerous industrial chemicals currently in commercial use and if spilled in transit may create a cloud of gas that can cause severe burns and respiratory problems.  Despite this, hydrofluoric acid has been used at concentrations of up to 30% in California, according to industry sources.

It is estimated that up to 80% of new well stimulation in the Monterey Shale uses some form of strong acid. However, detailed data about the use of acid is lacking as the practice was only regulated beginning in January, 2014. The use of acid is still exempt if used in concentrations under 7%. Read more about how well stimulation is regulated in California. 

Acid Fracking combines the techniques of hydraulic fracking and matrix acidization. While fracking uses high pressure to break through fractures in the earth and acidization uses acid to dissolve rocks, acid fracking does both. Hydraulic fracturing and acid fracking are similar in that they both use large volumes of water and chemicals. Further, they both produce large volumes of wastewater, and permanently change the underground geology of California.

Steam Injection is often used in conjunction with fracking to stimulate large oil reservoirs by injecting steam into multiple drill holes.  The amount of water used during steam injection can be reduced through a process known as cyclic injection, where steam and chemical additives are applied to a single well and left to soak in the shale for several days.  However, this technique is also imperfect. Producing steam may reduce the energy efficiency of oil extraction up to 50%3, and public data on the chemical additives used in steam injection is limited. 4

Carbon Dioxide Flooding, or ‘CO2 Enhanced Oil Recovery” injects CO2 into depleted oil reservoirs to release the remaining oil.5 Injection of CO2 gas has been linked to increased earthquakes.6

Diagrams of unconventiaonl well stimulation technologies

Diagrams of hydraulic fracturing and other unconventional well stimulation technologies being used to ‘unlock’ the Monterey Shale. (Source: The Wall Street Journal)

Dry or “waterless” fracking uses liquefied gasses such as butane or propane instead of water.  Waterless fracking is used in some water-stressed areas, but is considered less effective in deep formations because it requires a lot of liquefied gas to build up the necessary pressure. While dry fracking does not involve the injection of water, the chemicals used could still contaminate groundwater resources. Learn more about water contamination.

Offshore fracking uses traditional hydraulic fracking techniques to stimulate ocean wells.  While the process of offshore fracking is still rare in California, it has the potential to expand as technologies develop. Independent investigations recently revealed that oil company Venoco has been fracking off the coast of Santa Barbara since 2010 without notification or approval from state regulators. Half of the fracking operations in the Santa Barbara Channel are permitted to discharge their wastewater directly into the ocean. There have been no studies examining the potential threat of these chemicals to California’s shoreline.7

Off shore fracking is one of many new well stimulation technologies

Locations of offshore fracking near Long Beach. (Source: AP/Chris Carlson)

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