Electric drills. Their advantages and disadvantages.

The electric motor is controlled directly by the operator as commands are sent through the surface gear and computer whereas a PDM (turbodrill) is controlled indirectly via variations in the mudflow. The electric motor allows complete, and direct, control of the motor. Speed may be increased or decreased with a joystick or set through a keyboard instruction. Hydraulic power is required solely for cuttings clearance. This provides for better control of the drilling process while allowing circulation flexibility. Another advantage of the electric drilling motor is the bottom hole assembly (BHA) is insensitive to aerated or energized drilling mediums. There are a number of difficulties associated with electric motors. One problem associated with electrical motors is a low starting torque. There have also been difficulties associated with plugging of the pump used for pumping production fluids out of the well and the inability to restart afterwards. Another difficulty is both motor and electrical shorts (замыкание) during operation. Rotating seals provide the primary protection for motor electrical wiring. Recent attempts to integrate electric motors into a rotary drilling assembly have had limited success, mainly due to the difficulties of providing a high capacity electric link to the downhole drilling assembly.

(забойная буровая машина с погружным электродвигателем, предназначенная для бурения глубоких скважин. При бурении электробур, присоединённый к низу бурильной колонны, передаёт вращение буровому долоту. Электроэнергия подводится к электробуру по кабелю, смонтированному отрезками в бурильных трубах. При свинчивании труб отрезки кабеля сращиваются специальными контактными соединениями. К кабелю электроэнергия подводится через токоприёмник, скользящие контакты которого позволяют проворачивать колонну бурильных труб. Для непрерывного контроля пространственного положения ствола скважины и технологических параметров бурения при проходке наклонно направленных и разветвлённо-горизонтальных скважин используется специальная погружная аппаратура (в том числе телеметрическая). При бурении электробуром очистка забоя осуществляется буровым раствором, воздухом или газом.)

13. The concept of drilling regime.

 

Drilling regime is a combination of special parameters of drilling: (1) WOB - Pbit – weight on bit, (2) n - rotation rate of bit, (3) flowrate Q of drilling fluid, (4) drilling fluid parameters (density, viscosity, filtration rate, plastic viscosity). By changing these parameters speed of penetration into the formation (rate of drilling process) can be regulated.

Rational regime of drilling means the combination of above parameters which provide the most effective work.

 

14. Principles of selection and justification for a well construction.

 

Well construction defines the sizes and location of casings, the height of cement column and drill bit sizes should be used. Casings are placed to prevent rock fall in a well (stabilize well walls) and isolate formation waters.

It means, well construction should be selected so, that it will meet all the given requirements – provide stability and isolation. Also, it should be work properly for a long time.

Well construction is planned according to the available geological data, information on formation fluids.

Also, when selecting production casing, future production rates, pressures should be taken into account.

 

15. Fundamentals of depth choice for casing settings.

 

The depth to which casing will be settled and number of casing tubings depend on:

(1) Purpose of drilling

(2) Depth of oil-bearing formation, diameter of production casing

(3) Formation pressures

(4) Type of well completion and production technology that will be used

(5) Well profile

(6) Rock properties

 

16. Fundamentals of drilling method selection.

 

Some of the methods – rotary drilling, downhole motor, drilling with depression on bottomhole, coiled tubing drilling.

(1) Purpose of drilling

(2) Depth of oil-bearing formation, diameter of production casing

(3) Formation pressures

(4) Type of well completion and production technology that will be used

(5) Well profile

(6) Rock properties

В принципе то же, что и в предыдущем вопросе можно пихнуть и развить.

 

17. The principles of calculating the parameters for the drilling mode.

 

(1) Calculating drilling fluid parameters. First of all, drilling fluid should be able perform all of its functions effectively. Secondly, there is a relationship between pressure drop (between hydrostatic pressure of drilling fluid and formation pressure) and rate of penetration. Above certain value ROP is stable (do not fluctuate). Also, if hydrostatic pressure is too high ROP can be decreased. All of these should be concerned when designing drilling fluid.

(2) Calculating flowrate of drilling fluid. Qd.f = 007*Abh, where Abh – area of bottom hole. This relationship gives the most effectiveness.

(3) Calculating rate of rotation. Higher the rotation rate higher ROP is. But after certain critical value, ROP starts decreasing. This critical value is different for different types of drilling bits. Should be noted also, that increasing rotation speed fastens the bit damage.

(4) WOB. Bigger weight on bit leads to an increase in ROP.

 

18. Features of rotary drilling mode.

 

In this mode drilling parameter are independent from each other. Changing one parameter do affect another parameters.