WANLONG
Pre-Drilling Preparation
1. Inspect the previous diamond core bit for any damage or missing cutting elements; ensure the wellbore bottom is clean and free of dropped objects.
2. Handle the diamond core bit with care, placing it on a rubber mat or wooden planks. Never place the diamond core bit directly onto a steel plate.
3. Inspect the cutting elements for damage, verify that there are no foreign objects inside the bit, and confirm that O-rings are installed within the nozzle ports; install nozzles as required.
Connecting the Diamond Core Bit
1. Clean the pin or box threads of the diamond core bit and apply thread compound.
2. Secure the handling tool (bit breaker) to the diamond core bit; lower the drill string to engage the threads.
3. Lower the diamond core bit and handling tool into the rotary table master bushing, then tighten the connection to the recommended makeup torque value.
Running the Bit
1. Lower the diamond core bit slowly, exercising extreme caution when passing through the rotary table, Blowout Preventer (BOP) stack, and casing hanger to protect the cutting elements.
2. Pay close attention to any tight spots or obstructions encountered during the previous trip out of the hole. When running in, proceed slowly through any sections of reduced diameter or doglegs.
3. When approximately 1 meter from the wellbore bottom, begin rotating the drill string at 50–60 RPM and start the mud pumps at their rated flow rate to flush the wellbore bottom.
4. Closely monitor the weight indicator and torque gauge to ensure the diamond core bit makes smooth contact with the wellbore bottom.
Wellbore Enlargement with Diamond Core Bits
1. It is not recommended to use a diamond core bit for wellbore enlargement (reaming) operations.
2. If hole-enlargement operations are deemed necessary, they should be performed while the mud pumps are operating at their rated displacement; simultaneously, the applied torque should be reduced gradually.
Bit Seating (Establishing Downhole Drilling Mode)
1. Maintain the mud pumps at their rated displacement and slowly lower the diamond coring bit to the bottom of the hole.
2. Drill at a slow rate for at least 1 meter to establish a stable downhole drilling pattern.
3. Gradually increase the Weight on Bit (WOB) in increments of 10 kN until the optimal value for normal drilling operations is reached. Applying excessive WOB is strictly prohibited, as this may lead to the premature failure of the diamond coring bit.
4. While maintaining a constant WOB, adjust the rotary speed to achieve the optimal combination of drilling parameters.
Normal Drilling Operations with Diamond Coring Bits
1. Reduce the rotary speed to extend the service life of the diamond coring bit.
2. Adjust both the rotary speed and the WOB simultaneously to maintain optimal drilling efficiency.
3. Observe the following points whenever adding a stand (or single joint) of drill pipe:
3.1 Restore the mud pump stroke rate and check the standpipe pressure.
3.2 Start the mud pumps before the diamond coring bit makes contact with the bottom of the hole; subsequently, slowly lower the bit to the bottom at a rotary speed of 50–60 RPM.
3.3 Slowly restore the WOB to its original operating level, and then restore the rotary speed to the original drilling speed.
Field application practices have demonstrated that diamond coring bits offer numerous advantages when drilling through both soft and hard formations. These advantages include high Rate of Penetration (ROP), high footage drilled per run, long service life, stable operation, a low incidence of downhole accidents, and excellent borehole quality. Furthermore, diamond coring bits not only possess a long service life but are also reusable. After being returned to the factory for refurbishment, the performance of these diamond coring bits is comparable to that of brand-new bits, thereby enabling significant savings in overall drilling costs.
