Reverse drilling is only one of the many methods of mud drilling. It’s best used in large-diameter unconsolidated formations.
In the ’50s, George E. Failing Company manufactured a reverse circulation drill called the JED-A. JED stood for “Jet Eduction Device.” If I remember right the “A” stood for the first version. This drill was first tested on George E. Failing’s private plantation and later sent to Nebraska to drill several 60-inch-by-400-foot wells for irrigation.
My dad, “Porky Senior,” was working with research and development on the project and was seriously burned when a salamander heater backfired and caught his clothes on fire. He returned to the Enid hospital where he recovered after several weeks.
The jet eduction device worked with some success, but most owners eventually went to straight suction. This meant connecting the pump suction to the swivel, and all fluids and cuttings went straight through the pump and into the mud pit. This worked pretty well except the kelly had to be less than 10 feet long, and each time a connection was made it was hard to re-prime the pump because of the air in the suction from the return flow fluid level and the weight of the drilling fluid and cuttings up to the pump intake, which caused the pump to lose its prime.
Reverse air drilling is similar to air developing a well. An air line is run through the gooseneck of the swivel and extends some distance through the kelly into the drill stem. The drilled hole is kept full of drilling fluids and all fluids and cuttings then return to the surface through the drill stem and out the swivel hose and into the mud pit. No pump is required, only compressed air. Since the lift is very low it doesn’t require high pressure-150 psi is OK. The cubic feet per minute is not important, however I found that 150 cfm or more works best.
Reverse circulation is achieved by blowing compressed air down through an air line inside of the drill stem. The differential pressure creates air lift for the drilling fluid and cuttings, bringing them up inside the drill stem and out through the swivel hose returning to the mud pit. The swivel hose must be firmly secured above the mud pit because when the air is turned on, the swivel hose can become dangerous and will attempt to swing violently. Be prepared to run and duck!
When using reverse air drilling, the longer the air line inside the drill stem, the better it works. After making a connection, open the air line slowly until the fluid in the hole clears and then turn it on all the way.
Some advantages of using reverse air/mud drilling include:
• The potential for larger holes.
• No promotion of differential pressures in the hole.
• The prevention of washouts (pot bellies).
• Less loss of drilling fluids into formations.
• Fewer problems with boots in the hole.
I can’t think of any disadvantages except large gravel or boulders. But no methods of drilling-except for cable tool drilling-handle large gravels and boulders well.
If I was drilling large diameter deep holes in unconsolidated formations, reverse air drilling would be my preference!
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