TUBING
As long as the casings must remain in a well for a long time and their repair or replacement would be costly, another string of pipe is placed in the well through which the oil is produced. This is called tubing. During the later life of the well, the same tubing may be used to support a submersible pump or for other means of artificial lift. The tubing is suspended from the wellhead (surface) and usually reaches to within a few feet of the bottom of the well. Tubing is used as the flow string because casing is usually too large to permit the well to flow efficiently, or (in some cases) to maintain continuous flow.
Tubing packers are sometimes used in the tubing string to seal off the space between the tubing and the oil string of casing. This is done particularly in wells where there are high reservoir pressures. By sealing off this space the casing is not exposed to high pressure, and the chances of a casing failure are reduced. Tubing packers also sup-port part of the weight of the tubing in the casing and prevent the tubing string from moving up and down.
Sometimes it is both practical and economical to drill a small diameter hole and use conventional tubing as casing in completing a well. This is called tubing less completion since no retrievable inner string of tubing is used to conduct fluids to the surface. The casing is cemented from bottom to the top and perforated opposite the pay zone. The equipment used is essentially the same as a conventional well, including a float collar, guide shoe with backpressure valve, and landing nipple. Tubing less completions provide for well control, well stimulation, work over and an artificial lift system.
EXERCISE 22 Answer questions about the text.
1. Why is another string of pipe placed in the wellhead?
2. What can be used for artificial lift?
3. How is this tubing installed?
4. Why is tubing used as the flow string?
5. What is the purpose of sealing off the space between the tubing and the oil string of casing?
EXERCISE 23 Connect the terms with their definitions.
| 1. The equipment | a) packers are sometimes used in the tubing string to seal off the space between the tubing and the oil string of casing. |
| 2. During | b) off this space the casing is not exposed to high pressure, and the chances of a casing failure are reduced. |
| 3. The casing | c) used is essentially the same as a conventional well, including a float collar, guide shoe with backpressure valve, and landing nipple. |
| 4. Tubing | d) the later life of the well, the same tubing may be used to support a submersible pump or for other means of artificial lift. |
| 5. By sealing | e) is cemented from bottom to the top and perforated opposite the pay zone. |
EXERCISE 24 Translate into English in written form.
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2. .
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4. .
5. , .
EXERCISE 25 Give the English equivalents to the following word combinations.
1.
2.
3.
4.
5.
6. -
7.
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9.
10.
EXERCISE 26 Open brackets and use active or passive form of the verb. Consult the text if necessary.
1. As long as the casings must remain in a well for a long time and their repair or replacement would be costly, another string of pipe (to place) __________ in the well through which the oil (to produce) __________.
2. Tubing (to use) __________ as the flow string because casing (to be) __________ usually too large to permit the well to flow efficiently, or to maintain continuous flow.
3. Tubing packers (to use) __________ sometimes in the tubing string to seal off the space between the tubing and the oil string of casing.
4. Tubing packers also (to support) __________ part of the weight of the tubing in the casing and (to prevent) __________ the tubing string from moving up and down.
5. Tubing less completions (to provide) __________ for well control, well stimulation, work over and an artificial lift system.
CHAPTER VI
