Method of drilling with downhole motors. Advantages and disadvantages of this method.

Downhole drilling motors can be configured to answer specific downhole conditions or well designs. Such as, Conventional directional drilling,Steerable and horizontal drilling,Air/foam and underbalanced drilling,Harsh environment,Shale drilling,Coiled tubing drilling,Coring,Slimhole drilling,Casing drilling,Vertical drilling

Downhole motor is positive-displacement motor, widely used in drilling, kick-of, azimuth control, coring, reaming, work over for directional wells, horizontal wells, of oilfields and coal mines.

Dowhole motor is made up of 4 parts which are driving assembly, motor assembly, connecting assembly, dump assembly. The mud stream from the outlet of mud pump flows into the motor by transit the pump valve. This stream produces pressure loss between the inlet of motor to the outlet of motor that can push the rotor of motor into rotating, and to transmit the torque an rotate speed onto the bit used by connecting assembly and driving assembly. In fact the downhole motor is a kind of energy transformation machine which transform the pressure of liquid to the energy of engine. ((погружная машина, преобразующая гидравлическую, пневматическую или электрическую энергию, подводимую с поверхности, в механическую работу породоразрушающего инструмента (долота) при бурении скважин.))

There are two major types of downhole motors powered by mud flow. 1) The turbine, which is basically a centrifugal or axial pump and 2) The positive displacement mud motor (PDM). The principles of operation are shown in Figure and the design of the tool are totally different. Turbines were in wide use a number of years ago and are seeing some increased use lately but the PDM is the main workhorse for directional drilling. (Наиболее существенно отличаются по устройству и принципу действия забойные двигатели вращательного (турбобур, винтовой забойный двигатель и электробур) и ударного типов (гидро- и пневмоударник).)

Advantages:

· Increased rate of penetration

· Better hole deviation control

· Reduction in drill string failure rate

· Reduction in casing and drill pipe wear

· Reduction in wear and tear of the swivel, Kelly, and rotary drives

· Reduction in fuel cost, since compared to rotary drilling, less energy is required to power a Downhole Motor