pressure gate valve to the top. If, however, the casing has not been cemented or is not securely set with a packer, there is always danger of the gas escaping around the casing. It is always best to tube a gas well of average volume and use a packer at the top of the gas sand. This confines the gas to the stratum in which it is found and in the tubing. There are two methods of anchoring the tubing. When the volume of gas is not large, and in shallow wells where the pressures are low, the tubing is usually anchored with clamps to the casing or drive pipe (refer to Fig. 216). For deep wells with a large volume of gas at greater pressure (the gas pressure usually corresponds to water pressure at depth, 0.434 pounds per foot) it is safe to anchor the tubing to the casing, provided there is a long and heavy string of casing in the well that will serve as an anchoring medium. Where there may be no such long string of casing, it is safer to anchor the tubing in a big "gasser" to sills bolted to dead men buried in the ground, using long anchor bolts extending from the tubing clamps down through the sills. Another effective method is to dig two trenches four to six feet deep, extending about 20 feet from either side of the well, each trench to be widened near the well sufficiently to provide a space about six feet square. A joint of casing is set in each trench and anchor bolts with an eye that will slip over the casing are engaged with the tubing clamps. Concrete is then mixed and poured over the casing and around the bolts in the enlarged part of the trench and the earth replaced in the trench. The shutting in of gas wells of large volume and high pressure drilled in hard rock formations, or in soft formations where the casing has been set and cemented, is not a difficult matter. When a heavy volume of gas is struck in a well drilled by the rotary system before casing has been set, the result is sometimes a disastrous blow-out. Such wells have created veritable craters that have swallowed the rig and machinery. The remedy is to mud off the gas, if possible, until casing can be set and cemented, when the well is cleared of mud fluid by methods elsewhere described, gate valves are screwed to the top of the casing and the casing anchored so the gas may be confined. Interesting accounts of the capping of big gas wells and the extinguishing of burning wells accompanied by illustrations will be found in "Hand Book of Natural Gas" by Henry P. Westcott.* Illustration (Fig. 218) is of a gas well in the Louisiana field closed in with stuffing box casing head, otherwise known as a “Bradenhead," master gate valve, outlet gate valves and anchor clamps. * "Hand Book of Natural Gas," published by Metric Metal Works, Erie, Pa. CHAPTER XIII COST OF DRILLING WELLS IN VARIOUS LOCALITIES Many factors enter into well drilling costs, such as the local competition or the lack of it among rig and drilling contractors, the distance of the field from railway facilities with consequent high or moderate teaming expense, the character of the formations to be drilled, etc. The following cost estimates for several fields were compiled during a period of high prices and of active development work (the year 1920) and they may appear high as compared with the costs of a few years previous and the costs that may prevail in the future. They are, however, the costs that were current at the time this was written and are believed to be reliable as a basis for estimates. Some cost figures of previous years are given for the purpose of comparison. COMPARISON OF COST OF COMPLETED DERRICKS AS OF THE YEARS 1914 AND 1920 74-foot Derrick with 42-in. Rig Irons in Penn sylvania, West Virginia and Ohio...... 74-foot Derrick with 42-in. Rig Irons in Okla homa .... 950.00 2,150.00 82-foot Derrick with 5-in. Rig and Calf Irons in Oklahoma 84-foot Heavy Derrick with 6-in. Ideal Chain Driven Rig and Calf Irons in North Texas. 84-foot Heavy Derrick with 6-in. Ideal Chain Driven Rig and Calf Irons in California. Weight, 100,000 lbs..... |