Steel casing is used in a well to provide protection for the wellbore and to provide an avenue for fluids or gas to reach the surface. Placing cement behind the casing was originally designed solely to protect the producing formation from fluids from formations closer to the surface. Operators soon realized that properly casing and cementing a well protected the well from high pressure formations and also protected groundwater aquifers.
West Virginia wells from about 1950 to the present generally consist of a conductor string of casing that goes only 20 or so feet into the ground and used to help stabilize the hole and support equipment. The surface string (in West Virginia law also called the fresh water protection casing) should go to below the lowest fresh water aquifers. This casing by current law must be cemented to the surface. The intermediate string (in West Virginia also called the coal protection casing) is still fairly shallow, though in deeper wells can pass through formations such as the Big Lime and Salt Sands. There are special cementing requirements in West Virginia for wells which pass through mines or workable coal. Generally this string should be cemented to the surface or at least well above the base of the surface string of casing.
The production string of casing in old wells descends to about 100 feet above the producing formation which is "shot." In newer wells the production string can extend almost to the total depth of the well. Generally the production string is not cemented to the surface. Instead cement is placed through the production zone and some distance above. This leaves an open annulus above the cement to the surface. Before a well is hydraulically fractured the casing is "perforated" with explosive charges which pierce the casing and cement, extending into the formation. This begins the fracturing process. Hydraulic fracturing uses fluid under high pressure to extend the fractures quite a distance from the well bore.
After the well has been fractured by explosives or by high pressure fluid injection relatively narrow diameter tubing is installed for production of oil or gas. This tubing is not cemented and is retrievable when repairs or modifications need to be made to a well.
A special type of casing, called a liner, is when casing is installed that does not ascend to the surface, only a relatively short section of casing remains in the well.
Sometimes it is necessary to repair leaking production casing in a well. A cement squeeze job is performed by perforating the casing at the leak and squeezing cement through the perforations into the annulus. Squeeze cement jobs don't have the same success rate as normal cementing while constructing a well.
A detailed schematic of a UIC class 2 disposal well shows the strings of casing and locations of cement for well that injected wasted into the Marcellus. There are descriptions of the types of cement used as well as grade and weights of the casing used. The position of the tubing and packer is made clear in the diagram. More information about this well can be found here.
Gas Well Site Visits
Gas Well Study is the examination of natural gas wells in West Virginia.
Underground Injection Control Class 2 Wells
These wells are used either for the disposal of oil and gas liquid waste or for the enhanced recovery of oil or natural gas.
Gas Well Study Site Visits
Annual reports, environmental assessments, and individual well information.
Select videos from the Gas Well Study YouTube channel.
What Happened at Fernow
An investigation into what caused the vegetation death in the land application area after landspraying hydraulic fracture flowback waste.
The Spill at Buckeye Creek
An investigation into a spill from a Marcellus well site into Buckeye Creek in Doddridge county.