Motor de fondo

Páginas: 24 (5887 palabras) Publicado: 15 de noviembre de 2011
Downhole Mud Motors 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 thePDM is the main workhorse for directional drilling.   * Motor SelectionFour configurations of drilling motors provide the broad range of bit speeds and torque outputs required satisfying a multitude of drilling applications. These configurations include:High Speed / Low Torque Medium Speed / Medium Torque Low Speed / High Torque Low Speed / High Torque -Gear Reduced The high speed drilling motorutilizes a 1:2 lobe power section to produce high speeds and low torque outputs. They are popular choices when drilling with a diamond bit, tri-cone bit drilling in soft formations and directional applications where single shot orientations are being used. The medium speed drilling motor typically utilizes a 4:5 lobe power section to produce medium speeds and medium torque outputs. They arecommonly used in most conventional directional and horizontal wells, in diamond bit and coring applications, as well as sidetracking. The low speed drilling motor typically utilizes a 7:8 lobe power section to produce low speeds and high torque outputs. They are used in directional and horizontal wells, medium to hard formation drilling, and PDC bit drilling applications. The gear reduced drilling motorcombines a patented gear reduction system with a 1:2 lobe high speed power section. This system reduces the output speed of the 1:2 lobe power section by a factor of three, and increases the output torque by a factor of three. The result is a drilling motor with similar performance outputs as a low speed drilling motor, but with some significant benefits. The 1:2 lobe power section is moreefficient at converting hydraulic power to mechanical power than a multi-lobe power section and also maintains more consistent bit speed as weight on bit is applied. This motor can be used in directional and horizontal wells, hard formation drilling, and PDC bit drilling applications. Some other motor selections are also available including a tandem and modified motor. These variations are describedbelow. Tandem Drilling Motor - The drilling motor utilizes two linked power sections for increased torque capacity. Modified Drilling Motor - The bearing section of the drilling motor has been modified to provide different drilling characteristics (ie. change bit to bend distance, etc.). * Components All drilling motors consist of five major assemblies: 1. Dump Sub Assembly 2. PowerSection      3. Drive Assembly 4. Adjustable Assembly 5. Sealed or Mud Lubricated Bearing Section. The gear reduced drilling motor contains an additional section, the gear reducer assembly located within the sealed bearing section. Some other motor manufacturers have bearing sections that are lubricated by the drilling fluid. * Dump Sub Assembly As a result of the power section (described below),the drilling motor will seal off the drill string ID from the annulus. In order to prevent wet trips and pressure problems, a dump sub assembly is utilized. The dump sub assembly is a hydraulically actuated valve located at the top of the drilling motor that allows the drill string to fill when running in hole, and drain when tripping out of hole. When the pumps are engaged, the valve automaticallycloses and directs all drilling fluid flow through the motor. In the event that the dump sub assembly is not required, such as in underbalanced drilling using nitrogen gas or air, it’s effect can be negated by simply replacing the discharge plugs with blank plugs. This allows the motor to be adjusted as necessary, even in the field. Drilling motors 95 mm (3 3/4”) and smaller require the dump...
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