SEISMIC METHODS 885 



Drilling Crew Performance 



The drill crew consists of three men: a driller, a helper, and a water- 

 truck driver. When the truck driver is not actually hauling water, he assists 

 the other two members of the crew at the drill. The truck driver frequently 

 can have the water sump already dug and filled with water before the drill 

 arrives at the location of the next hole. 



In soft formations, such as clay and shale, it is often possible to drill a 

 60-foot hole in twenty or thirty minutes net drilling time. The time required 

 for moving from one hole location to the next varies with the distance 

 between holes, the topography of the country, the condition of the roads, 

 and the obstacles encountered, such as swamps, forests, fences and detours 

 around weak bridges. After the drill truck has reached the location, it takes 

 only five or ten minutes before drilling starts if the mud pit or sump has 

 been prepared and filled with water. 



The diameter of the hole required for seismic shooting varies from Z" 

 to 6". The size is determined by the hardness of the ground, the diameter of 

 the explosive being used, and whether or not casing is required. Under 

 average medium ground conditions it is not unusual for a crew to drill six 

 holes per day in one eight-hour shift. Exceptional daily performances of ten 

 to fourteen holes 60 feet in depth have been reported. Where deeper holes 

 are required and the drilling is more difficult, a performance of one hole per 

 day may be considered satisfactory. 



The drilling equipment in some cases is all owned and operated by the 

 organization making the seismograph survey. In other cases, the equipment 

 is supplied by an independent drilling contractor. These contractors are 

 usually employed on a per drill per month basis. On a one shift per day 

 operation where the contractor provides the drill unit and the water truck, 

 furnishes a three-man crew, and supplies gasoline, lubrication, insurance, 

 and supervision, the rate per drill per month varies from $1,700 to $2,200 

 (1949). 



The actual cost per foot of hole drilled varies between wide limits. It 

 depends upon the hardness and character of the ground, the distance be- 

 tween the hole locations, the size of the hole being drilled, the type of drill- 

 ing equipment being used, the morale, efficiency and experience of the drill 

 crew, and the supervision provided. Direct operating expenditures include 

 costs for labor, fuel, lubrication, bits, normal replacements and supplies, 

 and can average as low as 12 cents or 15 cents per foot under favorable 

 circumstances. On the other hand, these direct costs may average 60 to 75 

 cents per foot, if boulders or loose gravel are encountered, the holes are 

 sparsely spaced, the roads are bad, the water supply is inaccessible, or 

 casing is required to keep the hole open. 



The initial cost of the drilling machine, including the motor truck, the 

 complete drill assembly with mud pump, Kelly, drill rods, suction and 

 swivel hose, bits and small tools, will vary from $8,000 to $15,000, depend- 

 ing upon the size of the unit. The cost of the water truck will vary from 



