Application of downhole motors

When selecting the downhole motor and its combination, you should work out drilling program, fully consider hole size, hole trace, bit type, specification, formation structure and hydraulic calculation.

1. Surface Checking Before Tripping in

1.1 Except lifting the connections between nipple and by-pass valve, other connections on shell of downhole motor shall be coated with locking agent.

1.2 Assembly bit on the handling device, counter clockwise rotate the drive shaft ends only with chain wrench to protect the inside threads from loosening.

1.3 Hoist lifting sub and put downhole motor into turntable and by-pass valve into the center in easy watch position. And then clamp tightly downhole motor with slips, and disassembly lifting sub.

1.4 Check by-pass valve: Press downward the valve stem with hammer handle or wood stick. Fill water from the top into the valve, there shoud be no leakage from the valve and no great drop of water level. And then loosen the stick, the valve stem is springed up to its original position. The filled water shall flow out evenly from the side holes. This is normal.

1.5 Connect and low down the kelly. Put by-pass valve under the kelly in easy watch position. Start pump, and gradually increase flow rate till by-pass valve is closed. Lift the downhole motor to watch bit rotating. Now by-pass valve is in "close" position.

There should be no fluid flowing out of by-pass hole. To do this is only for checking bit rotation. It should not last longer. In the operation, it should prevent the bit from touching wellhead blowout preventer and flow line. After pump stops, check by-pass valve in open position or not, and fluid flowing out of by-pass valve or not. Do not lift the valve over turntable until pump completely stops as to protect the platform from pollution.

1.6 Disassembly kelly and combine the downhole motor in accordance with the program. Connect bent sub, non-magnetic collar and stabilizer etc. separately. If you make deflection with muleshoe, before twisting bent sub into by-pass valve, you should examine deflecting key to ensure muleshoe sitting in normal working position, and align the scale line of connector and bent sub.

During the period of downhole motor combination and drill pipe connection, pay attention to avoiding thread gluing and alternation.

In order to prevent thread from moving in the operation, it is advised to keep in mind: Rotary direction of bit sub opposite the shell is counter clockwise. lf you rotate turntable or clamp motor with turntable in wrong direction, thread loosening and thread off will occur on parts inside the downhole motor. This is caution for the customers.

2. Trip in the combined downhole motor into borehole

Even though the outside of downhole motor looks simple and it has enough rigidity, it still needs controlling trip-in speed, when drillers are stripping in downhole motor. Otherwise, the downhole motor may be damaged by san bridge, hole shoulder or casing shoe in the hole. When this happens, it is usually required to start pump, slowly to extend the hole for its passing.

If it is a bent sub or bent shell, it is easily for bit side to touch the hard rock status and casing shoe etc. on the bore wall. So periodically rotate downhole motor combination to eliminate the influence of lateral drilling.

As to deep and hi-temperature well, it is advised periodically to conduct middle way recycling while stripping in the downhole motor. Thus, this can protect the bit from plugging or protect stator from damaging due to high temperature.

In case the fluid can not rapidly flow through the holes of by-pass valve in the borehole, the strip-in speed should be slowed down or suspended regularly for mud filling. Again in stripping in, take care, there occurs no percussion or direct strip-in.

3. Start Downhole Motor

lf downhole motor is located at the hole bottom, you must lift it for 0.3-0.6m. Then start the pump and record the readings of riser pressure. As compared with the calculated pressure value, it is also normal if it is over the pressure of hydraulic calculation. This is caused from lateral drilling. Clear the hole bottom. In particular, for slant hole, the hole bottom must be very "clean" since the cuttings packed and deposited in the bottom affect the torque or deflection. lt is best to clean it with normal recycling. While cleaning, slowly turn the downhole motor or turn it by times(turning 30°- 40° each time), gradually to clean up the bottom. Then lift downhole motor for 0.3-0.6m, calibrate and record the pressure value.

Gradually enhance drilling weight when tripping into the bottom again. Meanwhile motor torque increase, riser pressure on gauge increases, too. The pressure value should conform with the motor pressure loss specified for any type of downhole motor. The increased value on the gauge indicates motor load is normal or not, and also shows the added weight is appropriate or not. Therefore, motor torque and drilling weight shall be kept stable only by limiting the riser gauge reading to the recommended range. This makes drillers know downhole motor operation timely.

When the bit is not at the bottom, if recycling pressure is lower than the calculated value, it is possible that by-pass valve locates in "open" position, or it is caused by drill pipe damage or well leakage etc.

If recycling pressure is higher than the calculated value, and the factor of pressure rise caused in re-entry is eliminated, but it is still over the calculated value, possibly the bit nozzle is plugged or drive shaft is sticked. Now recycling pressure is much higher than the calculated value.

4. Trip Out

Downhole motor tripping out is similar to the conventional trip-out. By-pass valve is in open position in stripping out. The fluid in string is allowed to be drained into annular space. But downhole motor can not rapidly discharge the fluid by itself. Usually a section of heavy fluid is added into the top of string before stripping out, to press the fluid in the pipe smoothly to drain.

4.1 After downhole motor is stripped out to the location of by-pass valve, disassembly the parts on the top of valve holes, Firstly wash it from the valve top with clean water, and then press down the valve stem with hammer handle or wood stick, loosen it for free movement. As soon as cleaning is completed, twist lifting nipple and trip out the downhole motor.

4.2 Install the bit assembly and disassembly device to clamp the shell of downhole motor. Turn the bit in counter rotation to drain the residual mud from by-pass valve, and then disassembly bit.

4.3 Disassembly downhole motor. Wash it from the holes of drive shaft, to clean the cap of drive shaft and bearing. Then handle the downhole motor onto a flat place. lt is standby after repair and maintenance. lt is advised to inject small quantity of mineral oil (not allow adding diesel) into downhole motor against rusting, if it is not used temporally or if it is stored for a longer time.

5. Troubleshooting

As mentioned above, the change of fluid recycling pressure is indicated from the pressure gauge of riser. This may help site operators identify what is happening in the bottom. In fact, correct identification can save tripping time and cut down the costs.

Complex trouble shooting is shown in Table-3 for customers reference.