ROTARY DRILLING METHOD The drilling bit with the rotary is attached to the bottom of a column of drill pipe which is given a rotary motion by a spe cial device on the floor of the derrick, called the rotary table. The drill pipe is first grasped by the rotary clamps. These clamps are locked in the rotary table and the table is turned or rotated by power transmitted from the engine by the chain drive. (See Fig. 15, Page 58.) The hollow pipe is suspended from the top of the derrick by drilling lines, similar to the casing lines of the Standard Cable Tool system. (See Fig. 15.) The drilling tools with the rotary consist of the bit, generally a fishtail (see Fig. 16), though several other types are used for special cases.
This bit is attached by a special tool-collar to the end of a string of pipe with upset ends called drill pipe, which is much heavier than casing and made to withstand hard twisting.
An important feature in rotary drilling is the use of water. A constant stream of water is pumped into the drill hole from the sump through the hollow drill pipe. This water leaves the drill pipe through small holes in the end of the bit. (See Fig. 15, page 58.) It tends to keep the bit clear of cuttings, and the steady stream also washes the cuttings from the hole as the water returns to the surface through the annular space between the drill pipe and the wall of the hole. The water has another important function. In soft beds the water acts as a jet and washes out the soft sediments. The bit in such cases has practi cally no cutting to perform, and the hole is washed down as rapidly as the drill pipe can be put in the hole. As high as 500 ft. per 24 hr. has been drilled in that way.
The Rotary method involves some of the same general pro cedure as with the cable tools.
In rotary drilling, however, the cutting action is obtained by rotating a sharpened steel bit shaped somewhat like a fish-tail. The action is a boring one, somewhat like an auger. The bit is attached to hollow drill pipe, which is turned at the top of the hole by a turning device called the rotary table. See Plate III.
The method of cleaning out the cut material differs also. Water is pumped down, the drill pipe and comes up outside the pipe bringing the cut material with it.
Casing is also used, but the head of mud-and-water in the hole is often sufficient to keep the walls intact so that less casing is needed in rotary than in standard test holes.
The drilling tools are suspended from the top of the derrick much the same as casing in the cable-tool method. However the drilling cable instead of being attached to a bull wheel is fastened to a drum (see Fig. 15, page 58) which is driven by a sprocket drive from the line shaft.
The "draw works," as the lifting machinery is designated, is much simpler than with Standard Cable Tools.
The motive power is generally steam. A sprocket and drive chain from the engine connect with a main sprocket on the drive shaft (see Fig. 17). To this main shaft are connected
the chain drives for the lifting drum, and for the rotary table (see Fig. 17).
In rotary drilling the various changes in speed and power are obtained by a system of sprockets.
A drive sprocket of small diameter connected to a big sprocket by chain drive gives low speed and high power. A large drive sprocket connected by a chain drive to a small sprocket means higher speed and less power. Figure 17, page 62, shows the relationship.
The middle sprocket M is driven from a sprocket on the engine. This sprocket turns the line shaft on which are two sprockets, D and R, and the cat heads at each end used for lifting material and pulling on the tongs in "tightening" or unscrewing pipe.
The small sprocket D drives the drum when the clutch is engaged.
The rotary drive sprocket R drives a chain which turns the rotary table. (See Plate III, p. 60.) That sprocket in turn drives the rotary table by means of a pinion (see Fig. 18, page 63), which meshes with cogs on the under face of the rotary table, Rotary Mud Pump.—In rotary drilling constant circulation of the water must be maintained.
"Circulation."—Circulation on a rotary or circulator, means that the water pumped downward, through the drill pipe or the casing, passes upward outside the drill pipe or casing to the surface. It literally circulates.
Heavy pumps are used to suck the water from the sump and drive it into the drill pipe. The big pumps have dimensions as follows: 12" X Or X 14".
Such pumps are generally placed in pairs, connected by a manifold. (See Fig. 19, page 64.) One pump is in constant use. If a pump requires any repairs, it is cut out and the good pump started.
Steel-wire hose is used to connect the lead pipe with the swivel arrangement which is an important factor in rotary drilling. The hose is attached to the gooseneck of the swivel. (See _ Fig. 20, page 65.) The water then enters the drill pipe. The lower .part of the swivel turns with the drill pipe, but the whole string of pipe hangs upon the bail which in turn hangs upon the C-hook and block, supported by the drilling lines.
The conical or ball bearings in the swivel permit the rotating of the lower part of the swivel and the string of pipe. A solid, non-rotating swivel would result in twisting of the drilling lines.
"Returns."—The drill cuttings or "returns" of the rotary come up between the drill pipe and the sides of the hole and flow into a ditch or box trough to the sump hole. A series of riffles in the ditch or box trough checks the flow of the. re turns, and as a result the cuttings deposit in the bottom of the trough, from which they are shoveled out. Some of the cuttings are carried into the sump which is also cleaned out at intervals.