Tool String & Joints

Tool String & Joints

While the machine imparts the lifting and dropping action to the tool string, the string is the equipment which does the work in the hole. It has four basic components whose combined weight provides the force needed to drill the well. These are the rope socket, the drilling jars, the drill stem, and the drill bit itself. They are connected (from top to bottom in that order) to each other by means of tool joints.

Cable tool joints consist of a tapered threaded pin and its conforming box, the dimensions of which are critical for many phases of drilling. The chief measurements of interest to the driller are the dimensions of the threaded areas, the diameters of the pin collar and of the box collar, and the size of the wrench squares. See Figure 3-1 for identification of these parts of the tool joint as well as of tool string components.

As its name implies, the rope socket is the tool which holds the string on the cable, or wire rope. Its body diameter will be the same as the box collar diameter of the cable tool joint selected. To the rope socket is connected the drilling jar — when used. Drilling jars go in the tool string as a precaution against the bit sticking and always are positioned between the rope socket and the drill stem. When starting the hole, however, the drilling tool string should not include jars.

The drill stem furnishes most of the weight needed to perform the drilling operation and also guides the rest of the tools as they rise and fall in the hole. It is basically a round bar of steel with a pin joint at its upper end and a box joint below. The body of the stem will not exceed the pin collar diameter, although the box collar may be a size or two larger.

At the business end of the tool string is the drill bit. This is the tool which does the actual cutting. The bottom is flared out beyond the body to the diameter of the hole to be drilled. Length determines bit weight, and water well bits usually are four to five feet long.