DETERMINATION OF DRILLING METHOD The determination of the drilling method is dependent on natural conditions. The two main systems are: 1. The Standard Cable-Tool or percussion system.
2. The Rotary system.
The Circulator system is a modification of the Standard Cable Tool system. The Combination system is a combination of Standard Cable-Tool and the Rotary systems.
The Standard Cable-Tool system is best employed in hard strata like sandstones, limestones, and hard shales. Holes in these formations "stand up" or do not cave readily, and can be drilled "dry," a preferable system for the proper testing of sands. Such a system is best used in the Carboniferous and earlier rocks of West Virginia, Pennsylvania, Kentucky, Ohio, Illinois, Oklahoma, Kansas, and North-Central Texas. It has also been successfully used in the Cretaceous beds of the Wyoming fields, and in the Sespe region of California, where the rocks of Oligocene and Eocene age are compact and "stand up." The Rotary system of drilling is best employed in the soft, unconsolidated sediments of the Gulf Coast areas of Louisiana, and Texas, in the soft Miocene beds of California, and in the Per mian Red Beds of Oklahoma and Texas.
The Hydraulic Circulating system has had far better success in California than Standard Cable Tools, and with the Rotary system forms the two main systems employed in California at present. Recently the Circulator system has been success fully introduced at Blackwell in western Oklahoma where the handling of gas sands has been a difficult problem.
Combination System.—The combination system of drilling is used to good advantage in several fields. Where the upper beds are soft, unconsolidated sediments, say 2500 ft. thick, with hard beds below, the Rotary system may be used to a depth of 2500 ft., after which cable tools are employed. On the other hand, in fields where there is a series of sandstones underlaid by a thick series of caving shales, the cable tools may be used through, the hard sandstone beds, and then rotary tools below in the shale.
Figure 2, page 38, shows the arrangement of the derrick for the combination system.