A drillability classification of geologic formations
Head, Albert Lee
Master of Science
This thesis has been written because of the need in the oil well drilling industry for a system by which different types of bits can be classified with respect to different types of geological formations. As background material, a discussion of the factors which affect the rate of penetration of rock bits has been presented. These factors are: (1) formation, (2) type of bit, (3) weight on bit, (4) rotational speed, (5) hydraulic action, (6) size of hole, and (7) personnel and equipment. A classification of geological formations based entirely upon the relative efficiency with which these formations can be drilled with a small rolling-cutter type of test bit has been established. This classification has been shown to be consistent with actual field drilling practices. A method of classifying different types of actual bits with respect to the classified formations has been illustrated. This method provides a means of determining a sphere of application for each type of bit; that is, the formations which each type drills most economically with respect to all the other types can be determined. This means that most of the guesswork concerning the selection of a bit for a particular formation can be eliminated. Limited tests have been conducted to determine if there is any relationship between the drillability of a formation and the hardness. Based on the results of these tests, no relationship could be established.