Reza Rostamzadeh - Sahand University of Technology Faculty of Chemical Engineering
Saeed Parvizi Ghale - Sahand University of Technology Faculty of Chemical Engineering
Masood Banafi - Sahand University of Technology Faculty of Chemical Engineering

Rotary drilling, as we know it today, replaced percussion or cable tool drilling in the 1930’s. Since that time, wells have been drilled using a drill string consisting of drill pipe, drill collars, a bit and varying downhole tools known as a bottom hole assembly (BHA). When the bit wears out or the BHA has to be changed, the process of tripping is commenced. Tripping consists of hoisting the drill string out of thewell in lengths of 30, 60, or 90 feet. This process is labor, equipment and energy intensive and takes up to 35% of the total time to drill a well.The casing-drilling system (CDS) provides an alternative to conventional drilling systems by use of ordinary casing for the drill string. This enables the well to be cased as it is drilled, which reduces well costs. The main reasons to use this technique are to reduce trip time, eliminate well conditioning time before running casing into the well, overcome troublesome formations with well instability and loss circulation problems, and improve well control. Actually, in this study we want to investigate the different methods of casing while drilling and their procedure. Furthermore we talk about advantages and disadvantages of this new technique and also we will study some case study that uses from casing while drilling technique to drill the well.

conventional drilling, rotary drilling, casing-drilling, bottom hole assembly