استخدامات الموتور وادوات الحفر الاتجاهي-Bent Sub And Mud Motor In Directional Drilling
The most generally used fashion for changing the line of the wellbore uses a piece of outfit known as a “ fraudulent sub, ” which is used only in directional well-conditioned drilling( Figure 1) with a Positive relegation( slush) motor..webp "استخدامات الموتور وادوات الحفر الاتجاهي-Bent Sub And Mud Motor In Directional Drilling")
What's The Bent Sub In Directional Drilling
A fraudulent sub( Drilling Subs) is a short length of pipe with a periphery roughly the same as the collars and threaded connections on either end. It's manufactured in such a way that the axis of the lower connection is slightly neutralize( lower than 3 degrees) from the axis of the upper connection. When made up into the Bottom Hole Assembly BHA, it introduces a “ cock angle ” to the rudiments of the BHA below it and, thus, to the axis of the drilling bit..webp "استخدامات الموتور وادوات الحفر الاتجاهي-Bent Sub And Mud Motor In Directional Drilling")
still, the preface of a fraudulent sub into the Directional BHA means that the center of the bit is also neutralize from the center line of the drill string( Check Drill String Design computation) above the fraudulent sub, and it isn't possible, thus to rotate the drill bit by rotating the drill string from face. Indeed if this were possible, the effect of the cock angle would be excluded since there would be no preferential direction for the bit to drill by. thus, the fraudulent sub must be used with a Positive Displacement Motor, PDM, or a Turbine.
How To Use Bent Sub With Directional Mud Motor
The PDM is frequently called a slush motor and is used in far further wells than the turbine. The slush motor is made up into the Driling BHA of the drill string below the fraudulent sub, between the fraudulent sub and the bit. When drilling fluid is circulated through the drill string, the inner shaft of the slush motor, which is connected to the bit, rotates, and thus the bit rotates. It is, thus, not necessary to rotate the entire drill string from the face if a slush motor is included in the BHA.slush motors and turbines are infrequently used when not drilling directionally because they're precious pieces of outfit and do wear out.
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A scribe line is marked on the inside of the bend of the fraudulent sub, and this indicates the direction in which the bit will drill( this direction is known as the “ tool face ”). A directional surveying tool( frequently an MWD tool) is generally run as part of the BHA( check our check computation companion) just above the fraudulent sub so that the well-conditioned line of the well can be checked periodically as the well is swinging.
The Major Disadvantage Of The Bent Sub
The fraudulent sub and PDM can, of course, only be used in the figure- up or drop- off portion of the well since the bit will continue to drill in the direction of the cock angle as long as the fraudulent sub is in the assembly and the slush motor is being used to rotate the bit. This leads to the significant disadvantage of using a fraudulent sub and PDM to change the line of the well.When drilling a well, the “ conventional ” assembly( without a fraudulent sub and slush motor) used to drill the straight portion of the well must be pulled from the hole, and the fraudulent sub and PDM assembly run in the hole before the well-conditioned line can be changed.
The fraudulent sub and motor will also drill off in a particular direction. When the well is drilling in the needed direction( inclination and azimuth), the fraudulent sub and PDM must also be pulled and the conventional assemblyre-run. else, the drill bit would continue to change direction. This is a veritably time- consuming operation( taking roughly 8 hrs at 10,00 ft depth for each trip out of and into the hole). Flash back, still, that the figure-up section of a well can be 1- 2000 ft long depending on the figure- up rate( generally 1- 3 degrees/ 100ft) and the needed inclination. thus, depending on the penetration rate, the fraudulent sub and slush motor will be, depending on the rate of penetration, in the well for quite a long time.
originally, check the motor and also test using standard procedures.
- Before drilling can begin with a motor and fraudulentsub-assembly, acquaint the fraudulent sub( tool face) in the asked direction.
- Work the pipe until string necklace is excluded. The stylish results are attained by using a relatively gormandize up- and- down pipe movement. It's recommended that the bit be kept at least 5 bases from the bottom of the hole.
- Make a reference mark on the kelly bushings, lock the rotary table, and take a check to determine tool face exposure.
- Turn the drill pipe to achieve the asked tool face exposure. This exposure should include an allowance for the anticipated left wing- hand reactive necklace.
- When orientating, turn the pipe to the right unless the turn is lower than 90 ° left wing of the present setting.
- Work the string up and down so that the turn reaches the bottom hole assembly.
- Lock the rotary table before beginning to drill.
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