Useless Casing Drilling
Useless casing drilling is a process wherein a hole is created by cylinders, which are cased in steel and directly filled with drilling mud. This allows for a relatively precise control of downhole pressures and also helps to insulate against lost circulation. It is an important part of any exploration process as it gives an indication of the physical properties of the formations being drilled.
The process of useless casing drilling involves the entry of the drillstring into the well bore and its penetration through the steel casing. The casing is usually composed of very thick steel pipe, with the purpose of providing support and stability to the walls of the borehole. As the drillstring penetrates the casing, mud is forced into the casing to fill it, creating a continuous column of pressurized mud.
Once the casing is in place, a drilling bit is attached to the end of the drillstring, which is then slowly lowered through the wellbore. As the bit is lowered, it is continuously cutting through the formation, reaching deeper and deeper until the desired depth is reached. The mud that was forced into the casing helps stabilize the drillstring, as well as creating a channel that the cuttings can be carried away in.
The mud used in useless casing drilling is usually made up of a combination of bentonite, hydroxyethyl cellulose, and other materials. Bentonite is able to form a gel around the drillstring, which helps provide additional support and helps to prevent lost circulation of the drilling mud, while still allowing it to flow freely through the wellbore.
Once the desired depth has been reached, the drillstring is then slowly withdrawn as the mud is removed. This helps to remove any cuttings, keeping them out of the wellbore, and also helps ensure that nothing is left behind. The last step of the process is to remove the steel casing, although in some cases, it may be left in place if there are further drilling operations planned.
Useless casing drilling may not be the most glamorous of oil and gas operations, but it serves an important purpose, and can help to reduce the risk of lost circulation, as well as helping to provide information on the formation being drilled. As with all oil and gas operations, proper planning and execution is key to a successful operation.
