How Casing Protects Groundwater
Why are casing and cementing important in the hydraulic fracturing process?
Casing strings are an important element of well completion with respect to the protection of groundwater resources because they provide for the isolation of fresh water zones and groundwater from the inside of the well. Casing is also used to transmit flowback fluids from well treatment. In this regard, surface casing is the first line of defense and production casing provides a second layer of protection for groundwater. As important as casing is, it is the cementation of the casing that adds the most value to the process of groundwater protection.
State Regulation of Well Construction
In a review of the regulations of twenty-seven state oil and gas agency regulations conducted in 2009 by the GWPC, the following percentage of states had the listed requirement for casing and cementing:
Although some states require complete circulation of cement from the bottom to the top of the production casing, most states require only an amount of cement calculated to raise the cement top behind the casing to a certain level above the producing formation. For example, in Arkansas, production casing must be cemented to two-hundred-fifty feet above all producing intervals.
There are a number of reasons why cement circulation from bottom to top on production casing is not always required including the fact that in very deep wells, the circulation of cement may be unnecessary due to the differences in depth between the production zone and fresh groundwater zones. Also, under certain circumstances, cementing must be handled in multiple stages which can result in a poor cement job or damage to the casing if not done properly. Finally, the circulation of cement on production casing prevents the monitoring of the space between the casing strings for changes in pressure which could indicate leakage through the casing or cement sheath.
For more information about the regulatory requirements of each oil and gas producing state, go to the Regulations By State page or the report State Oil and Natural Gas Regulations Designed to Protect Water Resources.