California Senate Bill 4 (2013) was signed into law on September 20, 2013 and was incorporated into statute as Public Resources Code (PRC) Article 3 (Sections 3150 through 3161). SB 4 was first implemented as an interim regulation (California Code of Regulations [CCR] Title 14) beginning on January 1, 2014 and continued through June 30, 2015. During the interim period, well stimulation treatment (WST) projects were approved as complete under an Interim WST Notice, and operators disclosed WST information that was displayed on the Division of Oil, Gas, and Geothermal Resources (Division) website.
Since July 1, 2015, SB 4 has been implemented under the permanent version of the WST regulations. The statutes and regulations can be found on the Division “Well Stimulation Program Requirements” webpage located at
Back to top
Well stimulation treatment is defined in regulation as “a treatment of a well designed to enhance oil and gas production or recovery by increasing the permeability of the formation.” (14 CCR § 1761(a).)
Hydraulic fracturing, (also known as hydrofracturing, “fracking”, or “fracing”) is the process of creating small cracks, or fractures, in underground geological formations to allow oil or natural gas to flow into the wellbore and thereby increase production. Prior to initiating hydraulic fracturing, engineers and geologists study and model the physical characteristics of the hydrocarbon bearing rock formations, including the formation
porosity, and thickness. Using this information, the well operator designs the process to keep the resulting fractures within the target formation.
To fracture the formation, fracturing fluids are injected down the wellbore and into the formation. These fluids typically consist of water, sand (proppant), and chemical additives. The pressure created by injecting the fluid opens the fractures. In some applications, sand (proppant) is transported into the fractures by a gel-based fluid that keeps the fractures open to increase the flow of oil or natural gas to the wellbore. The chemical additives serve a variety of purposes, including increasing viscosity, reducing friction, controlling bacteria, and decreasing corrosion.
During 2014, 652, or 97.46%, of the well stimulation treatments in California were conducted using hydraulic fracturing.
More information about hydraulic fracturing in California is available on the Division’s website located at:
Acid fracturing is a hydraulic fracturing technique that replaces sand with acid in order to “etch” pathways into an acid soluble rock (such as limestone or dolomite) or partial acid soluble rock (such as sedimentary rock with calcite cement or rock with calcite veining). Acid matrix stimulation treatment is conducted at pressures lower than the pressure necessary to fracture the underground geologic formation. In 2014, only 17 wells, or 2.54% of the well stimulation treatments were conducted using the acid matrix process.
No WST projects using acid fracturing were reported during 2014. Commonly 15% hydrochloric acid (HCl) is used for acid matrix stimulation treatments, although HCl is sometimes mixed with acetic and formic acid. In other areas of the United States, hydrofluoric acid is sometimes mixed with HCl to stimulate wells in sandstone; however, the use of hydrofluoric acid in stimulating carbonate rocks such as limestone or dolomite is typically not practiced since doing so can form precipitates that would defeat the purpose of well stimulation. No hydrofluoric acid was reported as having been used during acid matrix stimulation treatments during 2014. In March 2015, one acid fracturing WST was conducted using hydrofluoric acid, with hydrofluoric acid comprising 15% of the well stimulation fluid.
In 2014, 669 WST projects were reported to the Division. Of these, 665, or 99.4%, were located in western Kern County. 545, or 81.46%, were located within the Belridge oilfields.
Based on 2014 reported data, well stimulation treatment in California was conducted between the depths of 600 and 12,000 feet below the ground surface. The average reported depth of well stimulation is between 1,700 and 2,300 feet below the ground surface. On July 1, 2015, the California State Water Resources Control Board (SWRCB) adopted Model Criteria for Groundwater Monitoring in areas of Oil and Gas Well Stimulation (Model Criteria). Further information concerning monitoring groundwater quality with respect to well stimulation can be found at the SWRCB’s website:
Directional drilling is a technique in which drilling tools are used to drill a wellbore. A directionally drilled well that drills down vertically and then turns to become near parallel with the ground surface is considered a horizontal well. Of the wells stimulated in 2014, 15, or 2.2%, were reported as horizontally drilled.
In other regions of the United States, such the Midwest or the Great Plains, target formations for well stimulation are organic-rich shales that are horizontally layered and extend over a large area. These “oil shales” are low in both porosity and permeability. Porosity is the amount of void space within a rock where oil can accumulate. Permeability is the ability of fluids to flow through the rock. Horizontal drilling is used to expose the wellbore to a longer interval of the geologic formation (up to 6,500 feet lateral to the wellbore), and well stimulation provides a process to enhance oil recovery.
In California, the geologic conditions are more complex; geologic formations are not typically layered horizontally and are not as continuous. As a result, well stimulation intervals are typically less than 800 feet, and typically occur along vertical, rather than horizontal, wellbores.
In most of the United States, hydraulic fracturing or other forms of WST are performed in oil shale formations where the hydrocarbon bearing formations have low
permeability. In California, 86% of WST occurs in a rock called diatomite, which consists of the same material used as filtering medium for swimming pools (diatomaceous earth). Diatomite contains a high porosity, but a low permeability. WST provides fracture pathways through the diatomite formation that increase permeability. Economically feasible quantities of hydrocarbons could not be produced from the diatomite without hydraulic fracturing. As of June 2015, California was ranked third in oil production, behind only Texas and North Dakota.
Based on 2014 data, on average, well stimulation fluid consists of 77% water, 20% proppant (e.g., sand) and less than 2% of other additives.
The WST regulations require rigorous testing and evaluation before, during, and after stimulation operations to ensure that wells and geologic formations remain competent and that drinking water is not contaminated. The WST regulations require operators to evaluate the casing, tubing, and cement lining of the wellbore borehole to ensure that the well’s construction is more than adequate to withstand operations that are intended to increase the permeability of the hydrocarbon producing formation. In addition, operators are required to analyze the faults, natural fracture zones, and other wells in the area to ensure that they will not cause the migration of fluid to other zones. If there is potential for induced fractures to extend beyond the treated hydrocarbon zone, the regulations impose requirements to help prevent groundwater contamination. The regulations also require operators to monitor and test the well during and after well stimulation treatment to verify that well failure has not occurred.
Yes, the regulations require the following:
1. Operators performing well stimulation treatment must comply with the SWRCB’s Model Criteria for Groundwater Monitoring in areas of oil and gas well stimulation and
2. As part of their WST permit application, operators must develop a water management plan that addresses the source, disposition, and anticipated water use.
The Air Resources Board (ARB) has played a significant role in the implementation of SB 4 (2013) which calls for a study to assess various aspects of well stimulation treatments, including air quality impacts. The Division consulted with ARB and other California regulatory agencies to determine appropriate approaches to protecting air and water quality, and the safe handling of chemicals used in well stimulation. The resulting inter-agency cooperation over the regulation of well stimulation treatment is the subject of several memorandums of agreement between the Division and these other agencies.
In 2011, in response to Assembly Bill (AB) 1960, the Division promulgated and implemented regulations to ensure that oilfield fluids are safely managed. As of January 29, 2011, the AB 1960 regulations require secondary containment features around fluid containers, regular testing and maintenance of tanks and pipelines, and operator implementation of a detailed spill contingency plan. In addition to these existing requirements, the WST regulations prohibit the storage of well stimulation fluids in unlined sumps or pits.
Various state and federal laws already require remediation and reporting of spills or releases of hazardous substances. A matrix of reporting requirements can be found on the CalOES website here:
WST regulations also require operators to specifically include well stimulation treatment fluids in their spill contingency plans. The implementing regulations include this requirement as well as the requirement to cleanup spills in accordance with all applicable statutes and regulations.
The WST regulations require operators to report to the Division if an earthquake of magnitude 2.7 or greater occurs in the area of a recent well stimulation treatment. Tracking of seismic activity during and after well stimulation treatment will incorporate use of the California Integrated Seismic Network, and additional evaluations will be required if an earthquake larger than magnitude 2.7 occurs within the vicinity of a well stimulation treatment.
After the well stimulation operations are complete, much of the fluid comes back out of the well along with the oil, gas, and brackish water produced in the operation. In California, 80-90% of the water produced from oil wells is brackish water associated with the oil and gas in the geologic formation. The well stimulation fluid flowback is commingled with the other produced fluids. Most produced fluids in California are re-injected into oil and gas bearing zones to increase production. Other produced fluids may be injected into deep disposal wells or processed for alternative disposal.
Wells used for sustained injection of oil and gas fluids, either for increased production or disposal, are separately regulated by the Division. Applicable requirements include permitting, inspection, mechanical integrity testing, and plugging and abandonment provisions.
Yes. SB 4 (2013) required the Division to prepare an EIR to evaluate and inform decision-makers and the public of potential environmental impacts of well stimulation in California. The Division and Department of Conservation began the process of “scoping” the EIR in late November 2013. The scoping process defined the extent of coverage of the EIR within the parameters established under SB 4 and CEQA. The EIR was completed and certified by July 1, 2015 per regulatory deadline.
Information about the SB 4 Final EIR is available on the Division website at:
As of July 1, 2015 all WST performed in California must be permitted on an individual treatment-by-treatment basis. Prior to performing WST, the operator must submit a permit application for the Division’s review and possible approval. WST cannot be performed on any well without a valid WST permit issued by the Division. Well stimulation treatment permits will be posted within 5 business days of issuing the permit.
Back to top
Prior to performing well stimulation treatment on an oil or gas well, well operators are required to hire an independent third party to identify property owners or tenants of property located within a 1500 foot radius of the wellhead or within 500 feet of the surface representation of the horizontal path of the subsurface parts of the well. The third party agency then sends the identified owners and tenants a Well Stimulation Treatment Neighbor Notification Form, which indicates, among other things, the earliest date upon which the well stimulation treatment may be performed. Well stimulation treatment cannot commence until at least 30 days after all required notices have been provided.
This advance notice provides an opportunity for certain neighboring property owners or tenants whose property contains an existing water well or surface water suitable for drinking or irrigation purposes to obtain water quality testing.
Property owners or tenants of property located within a 1500 foot radius of the wellhead or within 500 feet of the surface representation of the horizontal path of the subsurface parts of the well.
SB 4 (2013) requires that operators notify certain nearby property owners and tenants in advance of commencing stimulation operations. Additionally, within five days of issuing a permit, the Division will post on its public website information submitted as part of the operator’s WST permit application, including the location of the well. The Division’s website is at:
http://www.conservation.ca.gov/dog. The results of the stimulation operation, including identification of chemicals used and their concentrations, will be posted on a Division-maintained public disclosure website currently under development. The Division website is anticipated to be available to the public by January 1, 2016.
More information concerning neighbor notification is available on the Division website at:
Property owners have the option of requesting that the operator of the oil or gas well arrange and pay for water quality testing, while tenants may arrange for such testing at their own expense. Property owners may alternatively elect to arrange for their own water quality testing and will be reimbursed for all reasonable costs by the well operator, provided that the testing is performed by a Designated Contractor for Water Sampling approved by the State Water Resources Control Board.
Operators are required to work through an independent third party contractor to notify owners and tenants of certain nearby real property prior to conducting well stimulation treatment. (See 14 CCR § 1783.2.) Property owners with surface waters or wells suitable for drinking or irrigation purposes may request water quality testing to be performed before and after the well stimulation treatment. (See 14 CCR § 1783.3.) The test results will be provided to the requesting party, well operator, the Division, and the State Water Resources Control Board.
In accordance with regulation, any operator conducting a WST must report or “disclose” all details of the project within 60 days after the cessation of a WST. The disclosure information includes, but is not limited to well identification, stimulation location, volume and source of water used, composition and disposition of recovered fluids, and chemical additives used. In addition, operators are required to employ the FracFocus website (https://fracfocus.org) to make the information about the chemical composition of the well stimulation fluids available to the public. On January 1, 2016, the disclosure reporting (and public access to reported data) will transition to a Division-maintained public disclosure website.
The disclosure data is used by the Division to inform the public about the details of WST conducted in California. SB 4 (2013) requires the Division to prepare a comprehensive annual report on WST. The first annual report is due on or before January 1, 2016. The report will be publically available and an electronic version will be posted on the Division’s website. In addition to the annual report, disclosure data will be posted on the Division’s public disclosure website at:
The Division’s public disclosure website (http://www.conservation.ca.gov/dog/Pages/WST.aspx) contains information reported to the Division pursuant to regulation. The Division’s website will list similar information as the FracFocus website (https://fracfocus.org) however, the WST regulations provide for public disclosure of additional information not accessible through FracFocus. The Division’s public disclosure website provides the opportunity to search disclosure data that has undergone a rigorous validation process to ensure high quality data is posted on the Division’s website.
Yes, under very limited circumstances. SB 4 (2013) imposes significant limitations on trade secret protection for well stimulation fluids, and provides a process for evaluating the validity of trade secret claims. And even if the information is legitimately withheld as a trade secret, certain government agencies and health professionals may gain access to the information.
A very small subset of wells may be exempt from disclosure if they are classified as confidential wells pursuant to statute. Confidential status allows operators an opportunity to utilize information obtained from a well without having to publicly disclose the information. Confidential status applies to onshore wells for two years, subject to six month extensions, but in no case may confidential status apply to onshore wells for longer than a total of four years. SB 4 (2013) includes a provision that requires disclosure of a proposed or completed stimulation treatment on a confidential well, but not the chemical constituents used.
In 2014, 1,772,760 barrels (or 74,455,920 gallons) of water were used for well stimulation, of which 15% (265,952 barrels or 11,169,984 gallons) was not suitable for use as drinking water or for agriculture. The average water used per well was 2,650 barrels (or 111,300 gallons). Information on reporting of water produced and used in oil field operations can be found here:
Disclosure data is updated nightly and uploaded to the Division website.
If you have comments on the public disclosure website, please contact:
The disclosure data set is available on the Division website at: