SWAGE If the casing has been crushed and its inside diameter reduced to a size that tools or a bailer will not enter readily, a swage (see Fig. 38) is generally employed. The swage is put on the bottom of a string of tools in place of a bit, and is driven through the collapsed place in the pipe. This brings the casing back to its normal diameter. Jars are used with the swage so if the swage sticks it can be jarred loose.
A small swage may be used at the start, and as the inside of the casing is opened a larger swage may be employed.
Sidetracking Tools or has been found in drilling operations in areas of soft unconsolidated formations, like those occurring in California and Louisiana, that a whole string of lost tools, or several hundred feet of lost casing may be drilled by or "sidetracked." This is done only after every effort has been made to recover the lost tools or casing. Sidetracking appears strange to those operators trained in hard rock areas where the hard formations do not permit the passing of a string of tools and the pushing of the lost string into the soft wall of the hole. In some drilling operations it is not unusual to sidetrack as much as 400 ft. of casing and proceed with opera tions as if no loss had occurred.
This method cannot be employed , with hard rocks like those in the Eastern States.
"Drilling Up" Bits, Casing or Other Lost Material.—In cases where lost parts cannot be recovered it may be possible to "drill up" the parts.
Cast-iron breaks up readily. Iron and steel pipe cannot withstand the drilling action of a hard-steel bit, but tempered tools and parts cannot be "drilled up" readily.
In rotary drilling, milling tools have been used to drill a hole through the bit left on the bottom of a string of drill pipe.
Lee Hager, of Houston, Texas, drilled such a hole which was reduced to a 4-in. diameter. The 4-in. drill pipe was "frozen tight" at a depth of 2000-ft. The oil sand was expected within 20 ft. The case appeared a hopeless one. The difficulty was overcome by using 2-in. drill pipe and a milling tool that was rotated through the rotary bit. A flowing well making several hundred barrels was successfully obtained in this way.
The casing splitter (see Fig. 38) is used when a hole is about to be abandoned. The casing is ripped at a joint and the weakened threads will not hold against a strong pull on the pipe.
Rock Classification.—The importance of keeping good logs of wells cannot be over-estimated. Rocks are given various names by different drillers. Table 9, after Arthur Knapp, taken from his interesting paper "Rock Classification from the Oil Driller's Standpoint," presented at the New York Meeting of the A. M. M. E., February, 1920, summarizes the various names and gives their usages. This is a valuable table for the inter pretation of formation names used in drilling.