Circulating System. When passing through running-sands or caving-shales with the standard tools, it often becomes necessary to 'mud up' the walls in the same way as is done with a rotary in order to keep the casing free and make progress. Two pumps are set on the derrick-floor with hose connections as in the rotary method, the flush-boxes and pit being also used. The swivel, however, is not necessary, as the casing is not turned or rotated but set upon the spider as in the cable-system. A circulating head (Fig. 126) with 2-in. side-openings is screwed into the top couplings of the casing and the hose connected to one of the openings. A long hollow-steel plunger is previously placed above the rope-socket and works through a stuffing-box in the top of the circulating-head. When drilling, the tools are lowered to bottom, the .plunger raised with the wire line-clamps and there tightened with a set-screw, allowing space for the plunger to work without striking the circulator-head. Drilling is thus carried on simultaneously with the working of the pumps, the latter carrying much of the cutting from the well in a form of sediment and depositing it in the trench where it can be removed. It is not necessary to bail as frequently as with the ordinary cable system, 25 to 30 ft. often being made before the mud accumulates and prevents the free fall of the tools. Constant circulation of muddy water prevents the .walls from caving, and keeps the casing free. The latter may be raised or lowered while pumping and a joint is added by removing the circulating-head whenever suf ficient hole has been made.
After the territory becomes familiar to the operator it is often found that continuous circulation is not necessary. The pumps are run at intervals while the driller is absent for meals and the well shut down, while in other cases the well is circulated four or five times a day. If the pipe becomes 'logy,' pumping can be repeated at shorter intervals. Complete circulation is not always
necessary, the important thing being to keep the walls of the hole completely 'mudded up.' In using the combined rotary and cable-tool system, the bull wheel and calf-wheels are installed, while on the right-hand side of the derrick are placed the line-shaft and draw-works with an extra engine. The pumps are placed on the left side and the rotary, when not in use, can be removed from over the hole. It will be seen that one system can be changed to the other without much difficulty. For instance, if the cable-tools are in use and a change to the rotary is desired, the calf-line is trans ferred to the draw-works, the rotary table installed and, with a few minor changes, drilling progresses with the rotary.
In the Parsons and Barrett combination-method, provision is made for continuous drilling without any changes. A cellar 20 ft. deep is sunk and the rotary placed at bottom. The return water is carried off through a tunnel at the level of the cellar floor to a well, from whence it is drawn by a small pump and carried back to the pit. The casing is suspended by a bridle with two long, heavy wire-line reins which are fastened to the spider below and the casing hook above the walking-beam. These reins are wide enough to permit the beam running between them and are long enough to give sufficient freedom for lowering a length of casing without interfering with drilling operations. The rotary is applied direct to the casing and is run by a separate engine, while a special rotary shoe is attached to the casing. A with plunger is used and the drilling is carried on at the same time that the casing is being rotated. The under reamer or other cable tools can be used the same as in ordinary work. Some operators use the long reins without rotating the casing, thus eliminating the rotary table and extra engine. The casing can be moved at short intervals while drilling is being carried on.