Well Stimulation Treatment

​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​Well Stimulation Treatment (WST) refers to processes performed on oil and gas wells to increase production. The various types of WST enhance the permeability of the geologic formation containing oil and gas.

The Geologic Energy Management Division (CalGEM) oversees WST in California. CalGEM is responsible for safeguarding public health and the environment while working to reach state climate and carbon-neutral objectives. WST regulations increase operational transparency; reporting requirements, including disclosure of WST fluid chemicals; and neighbor notification with the opportunity for neighbors to seek baseline water quality testing. They require an extensive engineering review and well integrity evaluation for groundwater protection and seismic monitoring. This includes a stoppage ​for evaluation should any earthquake greater than magnitude 2.7 near a stimulation operation occur. The State Water Resources Control Board also must review all proposed projects to determine whether groundwater monitoring is required.


Effective December 11, 2020, the public can use WellS​TAR to find information about well stimulation treatment permits, well stimulation disclosures, well maintenance data, well records, and underground injection control (UIC) projects.​

WellSTAR User Informati​on

For technical assistance with WellSTAR, please download and use this Service Desk Email Template and email your request to  WellSTAR@conservation.ca.gov.

For assistance or questions regarding well stimulation and well maintenance data, please email WST@conservation.ca.gov​.​​​

In November 2019, CalGEM requested a third-party scientific review of pending well stimulation permit applications to ensure the state’s technical standards and legal requirements for public health, safety, and environmental protection are met prior to approval of each permit. The Department of Conservation asked experts at the Lawrence Livermore National Laboratory (LLNL) to assess CalGEM’s permit review process. LLNL also evaluated the completeness of operators’ application materials and CalGEM’s engineering and geologic analyses. Review Process Update.

Inland District Well Stimulation Treatment Operation
Well Stimulation Treatment

WST Permit and Disclosure Data

WST Application​ Data prior to WellSTAR

Neighbor Notification and Water Sampling

WST Glossary​  

Hydraulic fracturing (also known as fracking, hydrofracturing, or fracing) is a type of WST. Oil and gas operators sometimes use hydraulic fracturing when 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.​

The hydraulic fracturing process involves a mix of fluids and substances called “proppants” injected at high pressure into an oil or gas reservoir. The mix and the force with which it is injected causes reservoir rock to fracture. When the fluids are removed, the proppants keep the cracks open. Natural gas or oil flow into the cracks and into the well.

Acid fracturing and acid matrix are other types of well stimulation.

Well Stimulation Permit Review Process

The following flowchart and documents provide the steps involved in the review process to issue well stimulation permits.

Related Information

WST Annual Reports

WST Final Environmental Impact Report (FEIR)

California Council on Science and Technology study "Advanced Well Stimulation Technologies in California"

For Operators