During the drilling process, Chesapeake’s cementing and casing program is used to protect water aquifers from drilling activities. The vertical portion of the wellbore is normally drilled with air (through the freshwater aquifers) thus minimizing any risk of contamination. On the rare occasions when fluid is required, freshwater and mud are used instead of air. Steel casing and surrounding layers of concrete are then installed to isolate the well from the drinking water aquifers through which the wellbore penetrates. The depth at which the surface casing must extend is mandated by the applicable state regulatory agencies. In East Texas, the surface casing is typically set to a depth of approximately 1,850 feet. Then intermediate casing is set inside the surface casing to a depth of usually more than 11,200 feet below the freshwater aquifer1.
After it is determined that the well can produce natural gas, additional strings of casing and tubing are set to provide additional layers of separation between the gas stream and the freshwater aquifer. The multiple layers of steel and cement that go into the construction of a natural gas well virtually eliminate the possibility of contamination to any freshwater zones2.
The state regulatory agencies require documentation of drinking water aquifer intervals, the design and installation of surface casing relative to those intervals and the reporting of characteristics of the wellbore along with completion and production data.
Sourcing Reference:
1 USGS Estimated Use of Water in US, County Level Data for 2000
2 US Department of Energy - “Modern Shale Gas Development in the United States. A Primer” – Page 76