Development of Services and Equipment for Small Holes

The New Proven Small-Hole Completion As a result of slim-hole development, small holes can now be drilled and completed with 4½-in. OD casing at a savings up to 35 per cent over conventional well sizes. This economical completion is illustrated as the "1954" completion in Fig. 1. Important advances in drilling tools and techniques have resulted in drilling rates for these small holes which are comparable to rates for larger holes. Savings from employing smaller and more economical drilling equipment and reductions in casing tonnage, coupled with advances in completion technology, are effecting a size reduction such that 4½-in. OD casing set in holes from 5 5/8 in. to 6 1/8 in. in diameter and completed with 2-in. tubing is growing in acceptance. Although certain calculated risks are taken, experience has indicated that the incidence of fishing operations should not exceed that experienced in holes of conventional size, provided the usual precautions are taken. Furthermore, fishing for such items as drill collars and bits should be limited in light of the economics of sidetracking and redrilling the inexpensive small hole. Savings in exploration and development costs adequately compensate for the slight risk involved. These holes for 4½-in. casing may be drilled, fished, logged, completed, produced, and reworked without undue difficulty. Equipment for Drilling and Completing Wells with 4½-in. OD Casing Recently, important improvements have been made in drilling tools and techniques for these small holes. Bearings in 5 5/8-in. and slightly larger rock bit sizes have been improved. This, coupled with the introduction of long-tooth, soft formation bits, has resulted in drilling rates for these holes being comparable to larger holes. In addition, diamond or similar type drilling and full-hole coring become increasingly effective with reduction in hole size. Several good rig designs for this small-hole work are offered by manufacturers, but such rigs are not widely available for contract drilling. The universal rig design is as unattainable here as for larger holes; but in most cases, a unitized trailer-mounted slim-hole rig which does not require guy wires is very desirable because of portability and speed. In some areas available lightweight, large-hole rigs may be profitably used in slimhole drilling to greater depths; and in other areas, special design considerations for restricted highway loading may be desirable.