"Freezing casing is stuck tight by mud or shale settling around the pipe it is said to be "frozen." Where a pipe is frozen it may be very difficult to free it. Freezing is 'avoided by maintaining circulation with the rotary or the circu lator systems. Where the mud pumps are not used the pipe must be lifted from time to time to keep it free.
Shooting off is sometimes found that a string of casing cannot be pulled from the hole, as the casing is "frozen" tight. Shooting is employed to save part of the casing.
A torpedo is prepared and lowered on a sand line to a depth just above the frozen part, preferably at the last collar, which is located by a collar finder. The casing is now put under strain by being pulled taut. The shot is fired; the collar expands a trifle, and the tension on the casing is sufficient to free it. Shoot ing this way is very satisfactory. Firing is generally done by a battery although a jack squib may be used.
Fishing subject of fishing is directly connected with the drilling of oil wells, and also with the handling of production.
Accidents may happen to drilling tools, to casing, or to tubing in a hole which may result in the loss of the tools or of the casing. If the tools are dropped or lost they must be "fished out" if possible.
Fishing methods are by no means simple. Different methods and tools must be employed for varying conditions.
The underlying principle of all fishing tools is to furnish a grab or hold on the broken or lost parts. This hold may be obtained by tools which take a direct hold or grab or by a fric tion hold, or by both combined.
Auxiliary tools are used to prepare the way for the grabbing operation.
Fishing troubles are due mainly to the following causes: On drilling (Standard Cable-Tools) wells 1. Cable breaks 2. Breaking of pins at tool joints (jumped pins) 3. Unscrewing of pins 4. Casing troubles (1) Collapsing (2) Slipping of threads (3) Corkscrewing due to dropping (4) Freezing of casing Rotary—drilling wells 1. Loss of bits 2. Twisting off of drill pipe 3. Freezing of drill pipe or casing Finding the Trouble.—When an accident has occurred the first consideration is to determine the trouble, and then to plan the remedy.
The best procedure is first to run an impression block in the hole to determine the position of the lost part.
The impression block is made by putting a covering of asphalt or tightly packed soap upon the bottom of a block of wood which is fastened on the end of a joint of pipe, or of tubing. The block is made just small enough in diameter to enter the hole.
Photographic devices have been tried, but their use is expen sive and questionable.
The impression block is let into the hole on the sand line. It is lowered firmly on the top of the lost tool, or the top of the lost casing. This leaves an impression in the gum on the block.
When the block is withdrawn the impression shows the relative position of the lost tool or the casing to the sides of the hole and the impression of the broken parts. This furnishes a guide for later procedure.
Where the threads in the box of a tool joint or where the threads of a casing collar are stripped, it may be possible to screw on a new box or to put in a fresh joint of casing.
Such cases are simple. However, if the tops of the tools are battered other methods must be tried.
Fishing.—Fishing " jobs " are of two types: (A) Fishing for lost drilling tools or parts of tools (B) Fishing for lost casing, rotary-drill pipe or tubing The most general cases of Class A are (1) lost bits, lost strings of tools, lost bailers, lost cable and tools.
Fishing for lost tools is difficult work. A lost tool may be re covered quickly by fishing or may require months of hard work. The procedures fol lowed in disposing of lost tools are: (a) Fishing tools out, (b) Sidetracking tools, and (c) Drilling them up.
Fishing String.—When fishing for a string of tools, fishing jars are used. These jars are much longer than ordinary drilling jars so that a long upstroke may be obtained. The arrangement of the string is also differ ent (see Fig. 33). The stem is placed above the jars to give a heavy upstroke and the fishing tool is, of course, below the jars which is the opposite arrangement to the drilling string. When a grip has been secured and a good pull on the lost tool fails to budge it, an upstroke is attempted, and a series of these strokes may "jar loose" the lost casing or lost tools.
Fishing Procedure.—If a drilling cable has parted and the tools have dropped, the procedure is to "run into the hole" with a rope-spear, or grab (see Fig. 34, page 90) and pull out the cable and tools. If a string of tools is lost and there is only a small amount of cable above it insufficient to secure a hold, then it is necessary to use a slip socket (see Fig. 34) and attempt a hold. The same will apply with a "jumped pin" (one broken off at the joint).
A bailer, if the bail is still intact, is caught by a latch jack (see Fig. 34) which is simply a that catches the bail. If the bail is broken, a casing spear with slips may be run into the hole to grab the bailer.
If the tools are merely unscrewed and a pin is sticking up, then it may be possible to screw on again and pull out, but this is not easy to accomplish in a large hole.
Fishing for casing, tubing or drill pipe requires one of three types of tools : (A) Die Couplings. s (B) Casing Spears. steel die nipples.
(C) Overshot. steel die collars.
If the casing or tubing has unscrewed and has not dropped far it may be possible to screw it on again. This procedure is possi ble with casing or tubing more often than with the tools. How ever, if the loss is due to stripped threads a new collar on the casing or a new joint of pipe may secure results.
Die die nipple (see Fig. 35), is used where it is possible to cut new threads in a collar that has been stripped. The nipple is used on the bottom of the string of fishing casing. The die collar is used on a casing where the collar has been strip ped and it is possible to cut new threads.
If die nipples fail and the casing is open at the top a casing spear (see Fig. 36, page 92) is used. This tool enters the casing and when pulled upward the slips take a good grip. The casing may be readily pulled if no cavings have settled around the pipe. If so jarring may be necessary.