In the fields where the strata are steeply inclined, the direction of the holes is frequently thrown off from the vertical by reason of the constant deflection of the drilling-tools in the direction of the dip. Such a condition may result in one or two joints of pipe being broken off when the casing is lowered to where the hole swerves. The pieces are usually quite loose in the hole and may be recovered with a spear or a bell-socket. In fact, it is said that the latter was first used for jobs of this kind before its wider application for fishing bailers and broken tubing was developed.
Accidents to Producing Wells. The accidents that befall pro ducing-wells, while of rather frequent occurrence, are not liable to be of a serious nature, and the remedies are usually simple. Aside from the unscrewing of sucker-rods, parting of the. tubing is probably the most common mishap. This may result from carelessness while withdrawing or inserting it, from defective threads weakened by long wear, or from what is known as the `back lash' of sucker-rods, caused by the rods parting at the time a strain has been placed on them when trying to loosen a plunger that is 'sanded up' in the working barrel.
If the tubing drops only a short distance, it will usually remain intact and may be recovered with a bulldog tubing-spear (Fig. 205). In producing-wells, the fishing-tools are customarily run on tubing, instead of a drilling-line and string of fishing-tools, since the latter has usually been removed for use elsewhere. However, a precaution that should always be followed is that of inserting a set of jars between the tubing and the spear. The need for this arises from the fact that the lost tubing may be wedged so that in applying a direct pull on it sufficiently strong to pull up the lost material, there will be considerable danger of parting the tubing at a new point above the spear. With the jars placed between the tubing and the spear, a few upward bumps may be applied and the lost pipe dislodged.
When the size of the casing is enough greater than that of the lost tubing inside of it so that difficulty may be experienced in getting the spear to enter the tubing, a hood or bowl is attached to the spear for the purpose of guiding the tubing up over the latter, as in Fig. 206. This figure illustrates also another type of the same style of spear, found to be more convenient where several different sizes of tubing are in use on the same property.
Instead of a solid body throughout, it is so constructed that any one of the different bars or mandrels with slips for grasping the various sizes of tubing may be screwed into the body.
When the lost tubing cannot be pulled readily but must be jarred before it becomes free, the jarring of the spear often splits the tubing until the slips reach the end of the joint at which, if a collar has remained at the top of the lost pipe, the slips become lodged and take hold while it is pulled out. If collar is at the top of the uppermost joint in a lost string that is being split, a spear-mandrel about 25 ft. in length is used, permitting the slips to pass through the top joint and grasp the second joint below the collar that connects it with the first joint.
The behavior of tubing when dropped seems to be very erratic. At times it falls for a considerable distance without suffering any material injury, and in other cases, when dropped possibly only a few feet, assumes a spiral shape or breaks at a number of points. In such instances the upper portions become wedged with the lower, two or more pieces will be flattened against each other, and the difficulty of its recovery is greatly increased because the pipe is no longer in a single string and the flattened openings prevent the ready admission of the ordinary spears.
When such an accident has occurred, it is advisable to expedite the fishing by installing a drilling-line and string of tools, which may be run in and out of the hole faster than can be done with tubing and permit more effective jarring in the endeavor to loosen pieces of pipe that resist an ordinary pull. Deformation of the lost tubing renders it imperative in nearly all such cases that the attempts to fish it out be made with forms of overshot-tools, that grasp and hold the exterior of the pipe. The impression-block is also a very necessary help, as it must be run after each piece of pipe has been pulled in order to show the shape of the next piece that is to be caught. Much ingenuity is shown in designing special tools with which to recover such material, the bell-socket (Figs. 174 and 175), rotary over-shots (Figs. 212, 213 and 214) and casing-bowls all being called into requisition and adapted at one time or another for work of this class.