1. Flow Passage Erosion, Perforation, and Nozzle Drop-off
The primary causes of flow passage erosion and perforation are as follows:
– Use of dual nozzle combinations;
– Excessive inlet flow velocity in the nozzle;
– High-density mud with high solid-phase content;
– Use of pulse nozzle structures incompatible with our tricone drill bits.
Due to unique geological conditions in some oilfields and the drilling processes used, iron ore powder is added to the mud system. Using dual nozzle combinations and pulse nozzle structures increases hydraulic impact, which significantly damages the tricone drill bit flow passages. This situation also reveals that our tricone drill bit flow passages may not fully meet users’ specialized requirements.
Reusing old nozzles or using non-standard nozzles that don’t align with our company’s specifications can enlarge the gap at the nozzle shoulder, creating eddy currents that lead to perforation of the nozzle seat. This is also one of the primary causes of nozzle failure.
Nozzle drop-off incidents are concentrated mainly in North America and Shengli Oilfield. The main reasons include improper installation methods during nozzle mounting or the presence of foreign materials that cause mud leakage. Once the sealing ring or retaining ring is eroded and falls, the nozzle becomes unrestrained and may fall into the well.
2. Cone or Cone Tip Dropping into the Well
There have been 21 cases of cones or cone tips dropping into wells, mainly in Sichuan, Shengli, and Karamay oilfields.
The cause of cone tip failure is eccentric rotation of the drill bit, or severe wear on cone teeth and grooves, leading to tip breakage and subsequent mud ingress into the bearings, causing failure. Eccentric rotation of the drill bit can be caused by:
– Abrasive formations or formation changes that cause inner row teeth wear or breakage;
– Incorrect bit selection, an unclean bottom hole, or an irregular borehole;
– High lateral forces when composite drilling with a mud motor.
Cone drop failures are caused by:
– Tip breakage with delayed tripping, resulting in bearing journal wear and lock groove damage, leading to steel ball release and cone drop;
– Aggressive drilling with mud motors, resulting in bearing seal failure or adhesive wear, which leads to cone drop;
– Abnormal working conditions of the drill bit downhole.
3. Tooth Breakage, Tooth Drop, and Flat Teeth
Main causes of tooth breakage include:
– Debris at the bottom of the well;
– Inappropriate bit selection or hard formations;
– Bit bounce or unclean bottom hole.
Tooth drop mainly occurs due to excessive wear on the cone shell, reducing the holding force of the teeth. Tooth flattening has been observed in geothermal wells in Dalian and Tianjin, mainly due to hard and abrasive formations.
4. Bearing Failure
Causes of adhesive wear failure due to excessive localized bearing load include:
– High WN values, use of a single-bend motor, resulting in high lateral forces on the drill bit;
– Formation conditions or foreign materials at the bottom hole, causing bit bounce and impact loads;
– Eccentric rotation of the bit, leading to uneven bearing load.
Early failure of bearing seals is due to high downhole temperatures or bit usage in deviated wells. Frictional heat is generated by contact between the cone back and wellbore, causing rubber seals to heat and degrade prematurely.
5. Thread Connection Fracture and Leg Breakage
Drill bits with fractured thread connections generally experience this due to misaligned makeup or excessive torque, which creates stress concentrations that initiate and propagate cracks, ultimately causing thread connection failure.
Leg breakage typically occurs at the stress concentration near the bearing journal root, primarily due to:
– Improper or incompatible bit box makeup, which stresses the cone and applies excessive torque;
– Formation conditions that cause severe diameter wear, reducing journal strength;
– Abnormal stress on the drill bit.
Media Contact
Company Name: TIANJIN GRAND CONSTRUCTION MACHINERY TECHNOLOGY CO., LTD.
Email: Send Email
Phone: +86 13920330362
Address:NO. 1 YANMEN ROAD
City: TIANJIN
Country: China
Website: https://www.grandebit.com/