DRILLING OF OIL WELLS The drilling of oil wells is a branch of skilled labor which, like all other trades, can be learned only by the actual doing. The tools for carrying on drilling work are supplied by manufacturing concerns who are alive to the necessity of providing improved devices based upon the inventive genius of many well drillers. Our purpose is not to recount the duties of a skilled driller, nor to summarize the information contained in the many complete and excellent catalogs of oil well machinery, but rather to present general principles conducive to most efficient operations.
The most effective use of skilled workmen and good tools re quires planning, and inspection. This procedure applies to all construction work, whether it be that of a tall building or of a deep oil well. This chapter aims to present the general features involved in planning and inspecting the drilling of oil wells.
Geological and Physical Conditions Affecting a Well.—The two general conditions which govern the productiveness and value of an oil well are the natural or geological conditions of the locality, and the artificial or physical conditions of the well in question and its neighbors. It would be impractical to enumer ate all of the various combinations of conditions here; however, the following sketches illustrate some conditions which are fre quently encountered.
The sketches herewith presented particularly emphasize the flooding of oil wells by water, which is a great problem in many fields. The first five sketches (Figs. 4-8) illustrate the damage resulting from physical conditions in the wells themselves while the remaining sketches (Figs. 9-13) illustrate the damage due to failure of development work to conform to geological conditions.
It will be seen, from the foregoing sketches, that the number of separate strings of casing to be used in a well will depend upon the number of strata which are to be kept separated. The cas ing program is in fact one of the first things which must be defi nitely decided upon before drilling begins.
Log of Well.—In order that some knowledge may be gained as to geological conditions near a well, it is necessary, so far as possible, to identify and record the thickness, composition and content of the various strata which the drill penetrates. This
is sometimes a simple matter owing to great differences in the nature of the strata. In other cases all the strata penetrated are so similar that it is difficult, if not impossible, to distinguish between them during the process of drilling. Identification of the various strata usually must be made from the comparatively small samples of drill cuttings which are brought to the surface. The action of the drilling tools, in the hands of an experienced and competent driller, frequently will indicate the nature of the rock encountered.
After a well is completed little or no evidence as to underground conditions will be available, except that which has been recorded from observation while drilling was in progress. Therefore, in order to obtain the necessary evidence in the form of a correct and complete record or log of a well, it is absolutely necessary that the drillers shall be thoroughly informed as to the nature and value of the information which is to be collected. The col lection of this evidence involves the installation of a system which will provide for the collection of samples of drill cuttings and for the regular recording of all pertinent information.
Daily Drilling Reports.—The complete operations of the drill ing crew should be written at the well every day. In fact the daily record should be so divided as to provide for recording the operations of each crew or shift of men.
One of the best methods for keeping daily drilling reports is to provide the necessary blanks in book form, with a page for each shift or tour. A carbon copy of each page should be made, which should be promptly removed from the book and filed in a safe place, because the original book easily becomes soiled and illegi ble or may be lost. The daily drilling report should show the depth of the well at the beginning and at the end of the tour; also what sort of work the crew was engaged in, the size, weight and amount of casing put in or taken out. It should also show the depths at which changes of formation occurred, describe or name the formations, and state any evidence indicating the pres ence of oil, gas or water in the well.