The severity of the dust-disposal problem varies from location to location 

 and depends on whether the well is being drilled near habitations. In some areas, 

 no attempt is made to control the air, except to prevent its blowing back onto 

 the rig. The methods of dust control most commonly used consist of either 

 separating the air from the dust in a cyclone-type separator or taking the dust 

 out of the air with water sprays. There are almost as many variations of these 

 two methods as there are air-drilling rigs. In many instances, improvisations or 

 refinements are made on the job. To maintain good public relations and to 

 avoid damage suits, some method or combination of methods must be develop- 

 ed to fit the circumstances. 



Fishing operations in air-drilled holes are more simple than those in a 

 fluid-drilled hole because air-drilled holes can easily be cleaned of all cuttings, 

 thus reducing the possibility of the "fish" being stuck or of the cuttings pre- 

 venting the fishing tool from reaching its target. 



Diamond coring is quite satisfactory with air if the proper type of bit is 

 used and if there is no core contamination. Fluid loss from the core because 

 of decrease in pressure is no more serious than contamination by water or mud 

 infiltration into a conventional core. The increase in penetration rate with a 

 diamond-core head is equivalent to the increase with a drilling bit. 



AERATED MUD OR WATER Drilling with mud and drilling with air have 



been discussed. Between these two are in 

 infinite number of combinations of fluid and air. Aerated fluid is used to combat 

 one or more of the disadvantages of air drilling. 



If water is present in the hole and creates a condition that causes sticking 

 of the drill pipe, water then may be added to the system to thin the slurry in 

 the hole so that it may be blown out. In general, the lowest ratio of fluid to air 

 that will successfully accomplish the purpose is the most desirable. 



When aerated fluid is used, it is important that the fluid be saturated with 

 lime to prevent rapid corrosion of the drill pipe. If an appreciable quantity of 

 water enters the hole, it becomes difficult to maintain the lime saturation, and 

 corrosion may still result. 



There are no hard and fast rules as to the most appropriate ratio of fluid 

 to air for any particular situation; therefore, this ratio must be determined in 

 the field at the time of the operation. The ratio of fluid to air should be governed 

 by the hole conditions. If low-pressure zones are present, the water should be 

 decreased. Conversely, if water flows are present, the ratio of water to air 

 should be increased to give a head that minimizes the flow of formation water 

 into the hole. 



The mud-pumping equipment on a conventional drilling rig is not suitable 

 for aerating because it is extremely difficult to control with sufficient accuracy 

 the amount of fluid used at the lower range of fluid volumes. 



739 



