Definition(s)
Zone Of Critical Cement
For surface casing strings shall be the bottom 20% of the casing string, but shall be no more than 1,000 feet nor less than 300 feet. The zone of critical cement extends to the land surface for surface casing strings of 300 feet or less.
Source: Oil and Gas Division, Texas Administrative Code, Title 16, Chapter 3, February 2013. Regulations