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Hydraulic Fracturing in California

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Also see U.S. Geological Survey hydraulic fracturing information page here


Public concern over hydraulic fracturing currently is high.  This information page is intended to describe the current approach of the California Department of Conservation’s Division of Oil, Gas and Geothermal Resources (“Division”) to the practice and regulation of hydraulic fracturing.  Viewers are encouraged to visit this page periodically as the content may change as new information becomes available to the Division.  Feel free to contact the Division via email at with comments regarding any of this information, or to provide independent information.  The Division recognizes that other members of the public may have differing views about the practice of hydraulic fracturing in our State.

Overview of Hydraulic Fracturing

Hydraulic fracturing (also known as hydrofracturing, “fracking”, or “fracing”) is the high-pressure injection of a mix of fluids and substances called “proppants” into an oil or gas reservoir.  The mix, injected under pressure, fractures the reservoir rock. When the fluids are removed, the proppants keep open the cracks left by the fracturing, allowing oil or natural gas to flow back to the well.  Fracturing the rock is necessary to extract oil or natural gas from formations in which the pore space in the rock making up the oil or natural gas reservoir is too tight to allow the flow of fluids or gasses to the well.  Without a man-made fracture, the oil or gas cannot be recovered.
Hydraulic fracturing was first used in 1947 in a well in Kansas.  Since then, hydraulic fracturing has become a regular practice to tap into previously unrecoverable reserves, or to stimulate increased production from existing oil or gas wells in the United States.  In California, hydraulic fracturing has been used as a production stimulation method for more than 30 years with no reported damage to the environment.

With the increase in the development of horizontal shale gas wells in various regions of the United States, hydraulic fracturing has become the focus of significant attention.  Some have questions about the safety of continued use of this technology.  Congress and the U.S. Environmental Protection Agency are examining whether the practice is likely to contribute to the contamination of surface or groundwater, and whether it poses risks to public health or safety. 

Just as oil and gas production operations differ from region to region nationwide, so too do regional methods of hydraulic fracturing.  To date, the Division is aware of very little, if any, fracturing of horizontal shale gas wells in California of the type performed in other parts of the United States.  Most of California’s oil and gas production to date has been from vertical wells into traditional oil and natural gas reservoirs.  

How Does Hydraulic Fracturing Typically Occur in California?

In California, most oil and natural gas reservoirs are “conventional.”  That is, the reservoirs are found in layers of underground rock (“reservoir rock”) beneath a layer of less permeable rock (“cap rock”). Over millennia, this less permeable cap rock trapped the oil and natural gas in the reservoir rock; without the cap rock, the oil and natural gas likely would have seeped to the surface long ago.  These conventional reservoirs typically were under pressure.  When they were first tapped, many would have had a natural “artesian” flow to the surface through the wells.  Some would even have appeared as “gushers.”  Today, after recovery of some of the reservoirs’ hydrocarbons, most of California’s oil and gas reservoirs require some form of stimulation to flow.
One way to stimulate flow is to fracture the rocks in the reservoir, creating channels through which the oil and/or natural gas can reach the well. The fluids are injected into the reservoir at high enough pressures to cause breaks in the reservoir rock.  This type of hydraulic fracturing is conducted below the pressure at which the cap rock would fracture.  This practice not only complies with Division regulations to protect groundwater and public health and safety, but is also common-sense practice for the oil producer.  No producer wants to take a chance on breaking the cap rock because doing so can cause a loss of production capacity from the reservoir.

In some other parts of the United States, natural gas is trapped not in a reservoir protected by cap rock, but inside uncapped rock formations.  In these “unconventional” cases, hydraulic fracturing is necessary to free the resource for production.  Unconventional natural gas resources are common in places like the East Coast’s Marcellus Shale gas deposits.  The Marcellus Shale covers parts of New York, Pennsylvania, Ohio, Maryland, Virginia and West Virginia.  In California, by contrast, hydraulic fracturing is principally a means of ensuring that individual, conventional wells attain maximum production, often a preferable alternative to drilling additional wells to produce the same resources.

There are other differences between the typical use of hydraulic fracturing in California and elsewhere.  For instance, in other states the extraction of unconventional natural gas resources requires lengthy fracturing periods along lengthy stretches of horizontally-drilled production wells.  Millions of gallons of water are injected under constant pressure, a process that may take days or weeks in order to effectively open the reservoir rock.  In California, much less water is used and the period of pressurizing the reservoir rock is much shorter.  In other states, the extent of fracturing in unconventional rock stretches for hundreds of yards along the horizontal well and the fractures stretch farther away from the well.  In California, fracturing projects tend to use far less fluid to fracture within a narrow vertical band along a well, generally starting at a point several thousand feet underground, with the fractures extending only tens to hundreds of feet away from the well.


California’s Well Construction Standards

All oil and gas wells drilled and constructed in California must adhere to strict requirements.  These requirements include general laws and regulations regarding the protection of underground and surface water, and specific regulations regarding the integrity of the well casing, the cement used to secure the well casing inside the bore hole, and the cement and equipment used to seal off the well from underground zones bearing fresh water and other hydrocarbon resources.  (See California Public Resources Code sections 3106, 3203, 3211, 3220, 3222, 3224, 3255; Title 14 of the California Code of Regulations, sections 1722.2, 1722.3, 1722.4, etc.)

For more information about oil and gas well drilling and well completion techniques, please refer to, “California’s Oil, Gas, and Geothermal Resources, An Introduction,” Chapters 6 and 7, pp. 35-43.   The basic drilling techniques and environmental precautions – well casing integrity, blow-out preventer use, etc. – described there have not changed substantially since that report’s publication.

Next Steps

California’s requirements for the protection of underground resources and well construction standards provide a first line of protection from potential damage caused by hydraulic fracturing.  However, California’s regulations do not require notification to the Division when hydraulic fracturing occurs.  There is a gap between the requirements placed on oil and gas operators to safely construct and maintain their wells, and the information they provide to the Division about hydraulic fracturing operations and steps taken to protect resources and the environment.  The Department’s pending regulatory process is intended to close that gap.

Division of Oil, Gas & Geothermal Resources 

Division of Oil Gas and Geothermal Resources