Since, the huge initial capital investment is involved once the type of formation characteristic, size and depth of bore hole to be drilled is known, you can always opt for the right rig to mitigate the requirement of your drilling programme.

For example, there is no fun in buying a heavy duty rig just for the construction of 4"-6" shallow test wells. This can

be drilled by a lighter capacity of rig with a suitable size of drill pipe and accessories, at much lesser cost. 

Selection of the best drilling method for an exploratory drilling required an understanding of the geological conditions and the physical limitation of drilling rig and equipment. Many of the drilling problems regarding the operation of drilling equipment as well as the problems of sub-surface condition has been in past and will be there in the future. The services of a skilled and experienced drilling engineer is most required thing who diagnose the troubles and keep the rig operative in a most efficient.

Manner with a minimum down time. To drill a well in a most economic and efficient manner it is always essential to maintain the proper drilling records and the samples as the drilling progresses. No doubt, the performance of drilling rigs reduces considerably with the passage of time in terms of rated capacity etc. Yet, it can construct a successful well of lesser depths and size irrespective of the age of drilling rig and accessories.

Considering the capital cost involvement, rate of drilling per meter and rate of penetration in various geological formations one can always select a most economical and efficient drilling to full fill the requirement as per table given below :