The cellar, when stove-pipe is being used, demonstrates its value, for a 20-ft. length can he inserted and drilled over without interfering with the operations of the temper-serew. Nearly all casing is inserted in the day by the combined crew, and when bot tom has been readied, each driller and helper runs his shift or 'tower' of twelve hours.
In sonic localities, where the formation is solid, the stove-pipe is often held suspended on a friction-block, the walls of the well creating enough resistance to hold the string together. However, when a sufficient strain, by reason of the weight of the casing, has been attained to cause the joints to open, the pipe should be set on bottom. The reason for holding the casing up is to enable the bit to swing freely below the shoe, thereby cutting a larger hole than if the string were following. In drilling through any casing, it is always well, wherever possible, to keep the bit working from 15 to 30 ft. ahead of the shoe for this reason, Should it be found necessary to drive the stove-pipe, because of the caving mud or 'friction' behind it, damping at the surface is not. necessary. Stove-pipe is designed, primarily, to ease out running sands, which would fall around the projecting couplings of a screw-easing and freeze or stick the string, but to reach the sands, beds of clay, shale, shells and boulders are nearly always encountered, Ns the clay is usually tough and resistant, the bit bores a small hole, leaving the stove-pipe shoe to cut its way through the walls, necessitating hard driving with the stein to force the string down. For this reason, many operators prefer the turnback starter-joint which has no shoe, as it follows the bit more readily by reason of its smaller clearance. For drilling through blue clay, a short stem 8 to 10 ft. long, called a sinker-bar, is used above the jars to knock the tools loose when they stick or become fast, as often happens. The jars in such cases are loosened sufficiently to deliver a short, upward blow keeping the tools loose and saving considerable time which would otherwise be spent in 'switching.' This term is used to designate the high rate speed at which the engine is run to jar the bit loose when no sinker-bar is carried. Short pieces of wire-line, when thrown into the well, are helpful in holding up the tools and enlarging the hole.
Gray or blue shale is usually easily drilled and ordinarily gives no trouble to stove-pipe, while hard strata of limestone, sandstone, etc.,
if carefully reamed with a sidehill bit and enlarged with small pieces of cast iron or short lengths of wire-line, should not interfere with the passage of the casing. Boulders are often troublesome, both to stove-pipe and screw-casing, particularly when small enough to roll behind the pipe and dent or mash it. Running sands are best handled by letting the stove-pipe follow through, or driving it ahead and bailing as little as possible. It will be found that the shoe of the stove-pipe is often several feet ahead of actual bottom until the sand stratum has been penetrated.
Aside from any fishing jobs that might occur from the use of stove-pipe, the principal troubles encountered are parting, collapsing, or freezing. Parting is caused by drilling out a sand plug or bridge near the bottom when the upper portion is frozen, suspending the whole column from the surface when the pipe may part from excessive weight, neglect of the driller to properly join the sections, tearing out an inside section with the bit when drilling, starting the walls to caving to such an extent that the in-rushing material forces the string apart, and driving the column together at some point. If the part comes near the surface, the hole can be continued by hand from the cellar down outside the column and the pipe properly connected. Should the part be deep, however, a swage can be run to bottom on a string of 6 or 8-in. screw-casing and slips or wedges lowered by the sand-line over the top of the swage when the smaller casing can pulled, with the result that the swage pulls up against the slips and engages with the stove-pipe. A stem and fishing-jars are used above the swage and are coupled to the casing by a substitute con nection, the latter having a mandrel at the top. When the stove pipe cannot be loosened by an ordinary pull, a string of tools with a socket attached can be _lowered inside the screw-casing and a hold taken on the mandrel. Jarring then proceeds, a strain being kept on the inside string. Instead of using a second string of tools, the dead-line is often taken from the casing-block and attached to the back-sill of the derrick, the spudding-shoe and jerk-line are put on and an upward blow delivered by the inside column of casing to the stove-pipe. The latter, when freed, is withdrawn to the point where it parted and lowered again after repairs.