WorldWide Drilling Resource

Air & Mud Rotary: An Overview by Scott Cosby This month’s article will focus on air and mud rotary drilling, including a basic overview and the advantages and disadvantages of both methods. As a drill crew member, I’ve experienced both; and the agency drill rigs are capable of both methods. This article is meant for informational purposes. I’m not advocat- ing one method over the other. The firm/ agency’s budget, rig cost, and material (i.e. soil and rock) types in a particular locale are the factors to consider before deciding on the best rotary method. In air rotary drilling, high-pressure air is pumped down the drill pipe and escapes into the borehole through holes in the bit. As the bit turns, it grinds the cuttings into small pieces, which the compressed air carries to the top of the borehole. If drilling below the water table, copious amounts of water are also ejected. The primary air rotary advantage is the improved drill speed, as well as the time factor in the operation. The disadvantages: air rotary is not suitable for all material types, initial cost (which will depend on the size of the operation), and maintenance costs as well. With the mud rotary method, the bit is attached to the drill rod being rotated and advanced into the borehole while pumping a drill mud consisting of ben- tonite or polymer slurry into the borehole. The drilling mud is circulated into a mud pit where the cuttings from the bore- hole drop out and the mud is reused. Mud rotary is often used in soft materi- als which may or may not be saturated with groundwa- ter. The mud rotary advan- tage: the drilling fluid and circu- lation stabilizes the boreho l e through hydro- static pressure so the depth is not a big factor in the incremental cost of drilling. The mud rotary disadvantages are similar to air rotary: high maintenance costs, and operation during freezing con- ditions can be difficult to almost imprac- tical. Each method has its place. There are numerous online sources on this topic, and there are many quality rig manufacturers in the market. Docu- ment your drilling needs and consult with these manufacturers. Ask many questions before making a final deci- sion concerning the best rotary method for drilling operations. Scott Scott Cosby may be contacted via e-mail at admin@ worldwidedrillingresource.com Air/Mud rotary rig. Mud rotary in action. 12 AUGUST 2014 WorldWide Drilling Resource ® " ; # 511-,(2 0) 20'5&43 %9 4+(3( ,/( $/5)$&452(23 ; 08 029'0/ # ! : : $8 $,- 3$-(3 *,6(/3,/4(2/$4,0/$- &0. "(% ,4( 777 *,6(/3,/4(2/$4,0/$- &0.