Read and translate the text. The mechanical factors of bit weight and rotary speed must be coordinated with bit selection in order to achieve optimal drilling rates

The mechanical factors of bit weight and rotary speed must be coordinated with bit selection in order to achieve optimal drilling rates. Generally speaking, an increase in either bit weight or rotary speed will increase the rate of penetration, provided that bottomhole cleaning (bit hydraulics) is attended to properly. But weight on bit and rotary rpm should not be increased indiscriminately. Overworking the bit wears the bit's bearings and cutting structures. Such drilling practices can also cause hole devia­tion. When these added costs are considered, the intended benefits of such high-energy drill­ing are lost. And since least-cost drilling is the objective, bit weight and rotary speed are usu­ally applied in inverse proportion to each other.

Most soft, shaly formations respond to varia­tions in rotary speed, and bit weights are light (3,000-7,000 psi bit diameter). The shearing action of soft-formation bits is well-suited for rotary speeds of up to 250 or even 300 rpm. Although increases in weight may increase the rate of penetration, the chances for hole devia­tion also increase, especially as the bit becomes dull.

In hard formations, heavy weights (5,000-10,000 psi bit diameter) are required for the bit's crushing-chipping action to overcome the compressive strength of the rock. Because a certain amount of finite time is required for the bit cutting structure to fracture the rock, the rate of increase in the drilling rate does not cor­respond directly with rotary speed increases. Excessive rotary speed can result in shock loads that can shatter bit teeth and cause drill string connections to fail. Rotary speed may vary between 30 and 80 rpm.

In calculating the appropriate bit weight and rotary speed, the capability of the rig must be considered. Additional weight requirements call for additional drill collars, which are expensive to buy and maintain and require extra handling time on round trips. Drill collars are heavy and hard to handle in the derrick and at the rotary, where lifting subs and safety clamps have to be used. Ten stands (thirty collars) or more are sometimes used, and several hours may be required to break out and make up the collars during a round trip.

Increased weight and rpm increase rotary torque, or resistance to turning. Higher torque means that more horsepower is required to operate the rotary. Here again, the rig's power system may impose limitations. Long-tooth bits require more horsepower than do short-tooth bits for the same formations. Slanted holes and wells with sharp doglegs also require more rotary power because of the greater friction between the drill string and the wall of the well.

The combined factors of high rotary speed, rotary torque, and extreme weight on bit can create great stress on the drill string. Smooth running is important. Since the drill string is a flexible shaft, a certain amount of irregularity is to be expected. But if centrifugal forces are severely unbalanced, hole friction will increase and the bit may wear unevenly. In such instances, joint failure, twistoffs, tooth breakage, and bit bearing failure may result.

The level of energy (weight and rpm) imposed on insert bits is generally lower that that required on steel-tooth bits to avoid insert chippage and breakage. Improvements in insert grades and shapes have allowed for higher rotary speeds in soft formations and higher weights in hard forma­tions than were previously possible.

Diamond bits are best operated under much lower weights than roller cone bits; rotary speeds are relatively high. Weights usually range from 350-750 psi of hole area, but even greater weight may be used, depending on the drilling situation. The value of diamond bits and the nature of their cutting action require the use of the lowest weight at which good penetration can be achieved. Rotary speeds are usually in the 100-rpm range, but when downhole motors are used, speeds from 200 up to 1,000 rpm are feasible. With smooth running, proper hydraulics, and optimum weight, diamond bit drilling rates usually increase in direct proportion to rotary speed.

5. Give the adequate Russian variants for the following word combinations:

Rotary rpm; the intended benefits of high-energy drill­ing; least-cost drilling; to apply in inverse proportion; to cause drill string connections to fail; additional weight requirements; to require extra handling time on round trips; to break out and make up the collars; to increase rotary torque; wells with sharp doglegs; to be severely unbalanced; to avoid insert chippage and breakage.

6. Find the English equivalents for the following words and word combinations:

Достичь оптимальной скорости бурения; увеличить скорость проходки; нагрузка на долото; количество оборотов ротора в минуту; перенапряжение долота; вызывать искривление скважины; намеченная прибыль; цель; хорошо подходить для чего-то; преодолеть; ограниченное время; разбить зубья долота; бурильная колонна.

7. Find the synonyms:

- choice

- limited time

- to break, to crack

- roughly

- worn bit

8. Match the words with their definitions and give their Russian equivalents:

9. Look through the texts and give your definitions of the following words:

- Overworking the bit

- Shock load

- Round trip

- Horsepower

- Rig

10. Agree or disagree with the following statements:

1. An increase in either bit weight or rotary speed will increase the rate of penetration.

2. Bit weight and rotary speed are usu­ally applied in direct proportion to each other.

3. Most soft, shaly formations don’t respond to varia­tions in rotary speed.

4. In hard formations, heavy weights (5,000-10,000 psi bit diameter) are required for the bit's crushing-chipping action.

5. Additional drill collars are heavy and hard to handle in the derrick and at the rotary, they require extra handling time on round trips but they are cost effective.

6. Long-tooth bits require less horsepower than do short-tooth bits for the same formations.

7. If centrifugal forces are severely unbalanced, hole friction will increase and the bit may wear unevenly.

8. The level of energy (weight and rpm) imposed on insert bits is generally higher that that required on steel-tooth bits to avoid insert chippage and breakage.

9. With smooth running, proper hydraulics, and optimum weight, diamond bit drilling rates usually increase in inverse proportion to rotary speed.

11. Complete the following sentences:

1. The mechanical factors of bit weight and rotary speed must be ...

2. And since least-cost drilling is the objective ...

3. The shearing action of soft-formation bits ...

4. The capability of the rig must be considered in ...

5. Increased weight and rpm increase rotary torque which means that ...

6. The combined factors of high rotary speed, rotary torque, and extreme weight on bit can create ...

7. Improvements in insert grades and shapes have allowed for ...

8. The value of diamond bits and the nature of their cutting action require ...