This paper was prepared for the SPE Symposium on Mechanical Engineering Aspects of Drilling and Production to be held in Fort Worth, Tex., March 5–7, 1967. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon requested to the Editor of the appropriate journal, provided agreement to give proper credit is made.

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Abstract

Big hole drilling techniques have been significantly improved during the past few years. it has been amply demonstrated that none technique applies to all drilling conditions, but workable methods have been evolved for most drilling environments. At present, drilling technology has considerably outstripped the industry's capability to line the hole economically, once drilled, particularly in the larger hole sizes.

The mining industry's most pressing need is for shafts of diameters that are presently near or beyond the capability of rotary tools driven from the surface. Thus, it appears to the writer that the current investigations into down-the-hole rotary tools, capable of drilling holes to 20 or more feet diameter, and a satisfactory solution to economical casing or lining of such holes, must bear fruit if drilled mine shafts are to become the preferred method of underground mine access.

Drilling TECHNIQUES

The progressive development of big hole drilling techniques over the past few years has been the subject of a number of papers and magazine articles, and consequently will not be dealt with in detail here. It should be noted that a number of these techniques were born of desperation and have since been refined to work somewhat more smoothly than the jury-rig prototypes, but do not necessarily represent the optimum combination of equipment and engineering for the particular technique. More on this later.

To review briefly some of the major technological advances of the recent past, the development of the big drill pipe and ancillary equipment is probably the greatest single step. However, the high volume-low pressure centrifugal pumps initially coupled with these big hole tools have not, in my opinion, proven particularly useful or desirable. It was originally believed, with justification, that very high mud volume flows must be provided to lift cuttings. This led to the use of centrifugal pumps, with capacities of 6,000 or more gal/min each, and two or more in operation. It occurred to some people, however, that to provide adequate rising velocities in the annulus as the holes continued to increase in diameters and depth might be hard to accomplish, despite these huge volumes. For example, in a 6-ft-diameter hole a 10,000 gal/min mud flow should provide a rising velocity of about 47 to 48 ft/ min—barely adequate by oilfield standards. Increase the hole diameter to 10 ft and the same mud volume provides an annular velocity of about 17 ft/min. Luckily, the large drill pipe made it possible to employ reverse mud circulation usually by means of an air lift.

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