The line passing through the two coincident angular markings give us bent sub tool face, i.e. the orientation of our bent sub or mud motor.

Transcription

1 The line passing through the two coincident angular markings give us bent sub tool face, i.e. the orientation of our bent sub or mud motor.

2 Now our next job is orient our MWD/LWD tool in the direction of bent. Below is a typical BHA arrangement for a 8 1/2" Hole Section :

3 After we are done with adjusting the bent sub to a desired angle, we make up the string stabilizer, the float sub, the UBHO sub and 1 (one in number) NMDC (also called Monel). To know more about Stabilizer, Float Sub and UBHO sub refer my blog post : Stabilizer, Float Sub, UBHO Sub. Now out job is to lower the MWD tool assembly into the NMDC. The MWD tool is run inside the NMDC (Monel). It gets seated in the mule shoe sub (UBHO Sub) which is at the bottom of NMDC. The tool face of MWD usually doesnot remain aligned with the toolface of downhole motor. So as to align the MWD toolface with the toolface of downhole mud motor we practise any one of the following procedure : 1 In this procedure, we get back to the time when we have made up the UBHO sub and the MWD tool has not yet been lowered. The mule shoe sub has an adjustable key. The sleeve with the key can be rotated.

4 The set screw is loosened and the key is alligned with the bent of the downhole mud motor. Once the key is aligned with the bent of the motor, the set screw is tightened. This keeps the key always aligned with the bend provided to the motor. Now the orientation of mule shoe is same as that of the motor bend. The MWD tool is run into the NMDC. The tool has a mule shoe stinger on it. The stinger has a slot and the mule shoe sleeve has a key. When the mule shoe stinger enters the mule shoe sub, it is rotated until it gets lined up with the orientation of the mule shoe sub and the motor. This happens when the slot of the stinger gets seated in key of the UBHO sub. Note : The survey tool can easily be manually rotated until the tool is aligned with the key. Thus now the tool face shown by the MWD tool is also the tool face of the bend of the down hole motor.

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6 2 In this procedure, we are at the situation when we have lowered the MWD tool in the NMDC and the stinger's slot has got seated in the UBHO sleeve's key. The scribe line at the mule shoe key indicates the tool face of the MWD tool. The scribe line at bend of the downhole motor indicates the toolface of the bent of the motor. Now we check that the two scribe lines (one of the motor and other of the surveying tool i.e. MWD here) are aligned or not. At present condition, we have the following arrangement hanging fron the elevator from top to bottom: NMDC - UBHO Sub - String Stab - Mud Motor - Bit. We lower the present made assembly until UBHO Sub is on man height. At the key of the UBHO sub (i.e. on the scribe line), we make any marking like placing a chalk piece or any pointed visible object which shows us the position of the scribe line/ the UBHO key. Some people tape a laser pointing downwards. Now we lift the made assembly upwards using elevator until we have our bent sub at the man height. We apply slip to make the assembly stationary.

7 Now we look up at our placed marking on the UBHO sub and find its position relative to the bend sub scribe line. (For this, the operator stands closer to the bent sub, looks upward to the made marking and tries to make an imaginary line from the marking to the bent. Magnetic Tool Face It is the direction, in the horizontal plane, the bent sub scribe line is pointing with regard to the north reference (Grid, Mag, or True). Magnetic orientation is used when the inclination of the well bore is less than 5. When the inclination is below this amount, the survey instrument cannot accurately determine the highside of the instrument for orientation purposes. The toolface will be presented in azimuth or quadrant form, referenced to magnetic north. The magnetic toolface reading is whatever magnetic direction the toolface is pointed. Gravity Tool Face It is the angular distance that a bent sub scribe line is turned, about the tool axis, relative to the high side of the hole.

8 If the inclination of the well bore is above 5 to 8, then the gravity toolface can be used. The toolface will be referenced to the highside of the survey instrument, no matter what the hole direction of the survey instrument is at the time. The toolface will be presented in a number of degrees either right or left of the highside. GTF orientation is represented by figure below :

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