The Canadian, or rod, system differs from the American system principally in the use of slender wooden or metal rods in place of the cable, a sim ple auger, like a carpenter's auger on a large scale, instead of drills, and a different transmission of power. This system was developed to meet the conditions of the Petrolia oil regions in Ontario, where boring in the greasy clays was done with an open clay auger turned by a horse traveling in a circle. Rods of tough, long-grained, white ash, two inches in diameter, were used originally, but in some of the places where the Canadian system was introduced later it was necessary to use iron rods. The rod system is best in many places for moderate depths and where inclined strata make it extremely difficult, often impossible, to keep the drill hole straight, if the cable system is tried. An improve ment on the Canadian system is the modern method of diamond drilling, as it is called, in which the drill consists of a hollow rod with a diamond or steel crown, a continuous supply of water being forced through the rod to keep the crown cool and to carry off the debris. It is a more rapid method than either of the others, and in deep drilling is regarded as cheaper in the end.
The condition of the strata in many places pre sents serious difficulties to all drilling operations. In the California fields, for example, slipping and caving of the highly inclined layers is a constant source of trouble, so that it becomes necessary to insert iron casing pipes as fast as the drill pene trates the rock. Under these conditions it some times takes a year to complete a well, and the cost of the casing alone is much greater than that of a completed well in Pennsylvania. Single wells in the Coalinga field, California, where the conditions are particularly bad, have cost upward of $30,000. Similar trouble is encountered in the Russian dis tricts, often to such an extent that wells have to be started with a drill two or more feet in diameter at the surface, in order to have the necessary room for the tools, as successively smaller casings are in serted with increasing depth.
Oil wells, in general, when completed, may be regarded as consisting of three sections: first, the surface portion in the deposits of loose gravels and clays ; second, the middle portion through the dif ferent strata which usually contain more or less water; and third, the lower portion in the oil sands. The conductor or drive pipe passes through the first section. Iron casing pipe is used in the middle section to keep ground water from becom ing mixed with the oil, and making the well "roiley," as the oilmen say. Originally, the so called "seed bag" was used to close the end of this casing, the device consisting of a simple leather bag filled with dry flaxseed, slipped over the cas ing, and pressed down to the top of the first oil sand. The swelling of the flaxseed, as soon as it
was wet, quickly filled the space between the pipe and the sides of the drill hole, effectively shutting out all water from above.
The general practice in latter years, however, has been to sink a large steel-shod, iron drive pipe down to bed rock. Drilling begins with a hole from eight inches to a foot in diameter, extending from the bottom of the drive pipe to the bottom of the lowest water-bearing stratum. Then, by reduc ing the size of the bore, a beveled shoulder is made in the rock, and a casing pipe, having a collar de signed to fit water-tight on the beveled surface, shuts off all the water before the lower portion of the well is drilled. Thus, the ground water is posi tively excluded from the oil and at the same time its interference with drilling operations in the lower part of the well is lessened.
As regards depth, time to drill, cost of comple tion, and yield when finished, different wells, even in the same region, vary greatly. Drake's well was seventy feet deep, took a long time for completion, and yielded only a few barrels a day when done. Since then deeper drilling has been generally re sorted to, in order to secure as large supplies as possible. In the Bakt district, for example, it has been a common custom to continue boring, even after oil is actually struck, until the oil flows from the mouth of the well; there, wells side by side vary by hundreds of feet in depth. Recent opera tions in this country have extended wells to depths of more than 4,000 feet, although, in such cases, the difficulties of drilling are very great, and the cost increases rapidly. Where the drilling is easy, and the depth not great, profitable wells may be com pleted easily in two or three weeks, at a total cost of only a few hundred dollars, as in some of the Ohio districts. In the face of natural difficulties, accidents, or the necessity of penetrating to greater depths, the cost mounts upward rapidly to as high as $30,000 or $40,000.
No less variable is the yield of different wells, ranging from the non-productive "dry" holes or "dusters" to the gigantic spouters pouring forth millions of gallons a day. On the basis of the general character of the yield, wells are divided into two classes, the flowing, spouting, or gushing wells, and the pumping wells. The character of the yields, however, does not necessarily indicate whether the venture is a profitable one. In some cases the cost of drilling is so great that a well flowing less than a hundred barrels a day would be regarded as a financial failure, while another well, much less expensive to drill, might be profitable if only a pumping well at twenty barrels a day.