DRILLING
There are many ways of discovering the underground oil, but the only way to get it is to make a deep hole called a borehole, or a well, through the rock, earth and sand. The steel framework over the well is called a derrick. From this the machinery that drills the hole is raised and lowered.
The technique of well drilling goes far back into history. It is first mentioned in ancient Chinese manuscripts, which describe wells drilled as early as the third century A.D. to tap underground strata for brine. The wells were drilled with a heavy bit, which hung from a rope and was raised up and down by several of men jumping on a spring board.
The petroleum industry is traditionally considered to have been born in 1859 near Titusville, Pennsylvania where Drake drilled the first well. In Russia the first oil well was drilled in 1856 by a Russian engineer A.F. Semenov. At around the same time oil wells were also being drilled in other places, notably at Oil Springs, Ontario, Canada and Wietze near Hanover, Germany and there is some doubt as to which country should be credited with having drilled the first commercial oil well. All these wells were drilled by the cable tool methods.
The cable tool system was essentially a method of making a hole by repeated blows with a bit attached to a “drill stem”, a heavy length of steel suspended from a wire rope. The hole was kept empty except for a little water at the bottom. After drilling a few feet, the bit was pulled out and the cutting removed with a “bailer”, an open tube with a valve at the bottom. Steel pipes known as casing, of progressively smaller diameter, were run from time to time to prevent the hole from caving and to keep back any water flow.
Cable tool drilling was cheap, simple and effective for shallow wells, but progress was slow and no means was provided for stemming the flow of oil and gas when encountered under pressure. In such cases the wells blew out and spewed quantities of oil and gas over the countryside. The “gushers” of these early days were spectacular but wasted a lot of oil and gas, and were a serious fire hazard.
The present-day method of drilling, known as the “rotary method” was introduced at around the turn of the century. With this method, the bit, instead of moving up and down, is attached to the bottom of a string of steel pipes and rotated by means of a rotary table which turns the uppermost pipe or “kelly”. “Drilling fluid” or “drilling mud” is continuously circulated down through the hollow drilling string, through the bit and back up to the surface through the annular space between drilling string and borehole wall. The drilling fluid flushes the cuttings out of the hole and, by the weight of its column, holds the fluids under pressure in formations penetrated by the bit, thus greatly reducing the risk of blowout.
A variant of rotary drilling is known as “turbo-drilling”. With this method the pipe is not rotated but is kept stationary and the bit is rotated on bottom by means of a fluid motor or turbine powered by the mud stream. Although the rate of penetration of the bit can be faster with this method than with conventional rotary drilling the bit wears out much faster, so that the overall efficiency is lower. However, the method has some application where high-grade steel is difficult to obtain, and where rapid bit wear is unimportant.
17. Ответьте на следующие вопросы:
1. What is the only way to get the underground oil? 2. When was well drilling mentioned for the first time? 3. How were the wells drilled then? 4. Which country should be credited with having drilled the first commercial oil well? 5. What is the cable tool system? 6. What advantages and disadvantages of cable tool drilling do you know? 7. What’s the difference between cable tool drilling and rotary method of drilling? 8. What variant of rotary drilling do you know? 9. Where is turbo-drilling applied?
18. Перескажите текст “Drilling” по следующему плану:
1. The appearance and development of well drilling technique.
2. Cable tool method of drilling.
3. Rotary method of drilling.
4. Turbo-drilling.
19. Прочтите текст: