Abstract:

This paper introduces One type of PDC drill bit repair technique.

First of all, confirm the steel body PDC bit which has been already used can be repaired.

After pretreated the drill bit that meets the repair conditions, heat it at a speed of 8-10 ° C / min, and heat to about 620 ° C, and the solder of welding cutters begins to melt, then take down PDC cuts, put them to 620 ° C solder flux to keep warm for use.

Finally, repair the bits by resurfacing welding technique. The on-the-spot test proved that there is no obvious difference between the quality of the drill after repair and the new one.

For an example of repairing a 121/4 in steel body PDC bit, it can save at least RMB 41,400, and the economic benefits are obvious.

In oil drilling, PDC drill bits feature long life, high mechanical drilling speed and large footage in soft-medium hard formations, which are favored by drilling companies, and their user accounts for more than 60% of total bit consumption. Although the overall cost of drilling with PDC bits is lower than that of rock bits, the unit price is higher.

For example, the price of 121/4 in steel body PDC is usually about RMB240,000. How to reduce the cost of the PDC bit itself has become the goal pursued by the drilling companies. This paper points out a drill repair technique that reduces the cost of PDC bits.

There are steel body and matrix PDC bits. This paper introduces the repair technology of steel body PDC drill bits.

 1.Confirmation of steel body PDC bit that can repair

The form of damage for steel body PDC bit is the wear of the cutter and the shrink in the outer diameter of the drill bit.

In the design of the PDC drill bit, the arrangement of the cutter usually applies the minimum distance distribution cutter, equal cutting volume distribution cutter, equal cutting power distribution cutter, equal wear distribution cutter, and etc. but no matter what kind of distribution cutter method is used, it is affected by the distribution space and the model error.

It is impossible that make the wear of cutter of the drill bit consistent. Because there are machining errors in the production of the PDC bit, as well as the factors in the actual use such as formation, operation, equipment.

In the condition of the outer ring cutter of used drill bits have been severely worn, and the inner ring cutters are only slightly worn out. This feature takes value to the repair of PDC bits. Whether the used steel body PDC bit can be repaired again should meet the following conditions:

• The number of the reusable cutter on the used PDC bit is not less than 1/4 of the total number of the cutter of the drill. The inner ring cutters of the drill bit usually wear little, and most drills meet this requirement in the actual use. According to Table 1, judge whether the cutters can be reused.

 

Table 1 Reusable Cutters Evaluation Table

 

 

• The maximum wear of all cutters on the drill to be repaired shall not exceed 50% of the diameter of the cutter. If the wear of the cutter is over than 50%, the inlaid cutters have been greatly damaged, and the repair quality is not obtained.
• The outer diameter of the PDC bit to be repaired shall not exceed 8 mm.

2.Drill repair auxiliary heating equipment

In the repair process of the steel body PDC bit, use the medium frequency induction heating method to heat the bit body. The reasons are the following:

• The height of the drill to be repaired is high and the stability is poor. The medium frequency induction heating method can fix the drill bit on the lifting platform to make the operation safer.
• Frequent pick-and-place of the cutter and closed heating method cannot meet the requirement during the repair process of the drill bit.
• The intermediate frequency heating can move up and down the induction loop, determine the ideal heating part.

3. Select of repair materials

Use tungsten carbide surfacing material to repair the drill bit by oxy-acetylene surfacing technique.

4. Steel body PDC drill bit repair process

        Pre-preparation of PDC drill bit repair

First, put the steel body PDC bit to be repaired in the container filled with water, and clean up the cuttings, dirt on the bit body. Place the cleaned drill bit on the lifting frame and heat it with an intermediate frequency heating device.

In order to reduce the thermal stress of the bit body, the heating speed is usually controlled at 8-10 ° C / min, while the silver solder flux is placed in the crucible, heated to  600 ° C in an electric furnace and keep in the molten state for use.

When the bit body temperature is heated to 620 ° C, the silver solder material of the welded PDC begins to melt. At this time, remove the cutter, put the cutter that meets the reuse conditions in the prepared crucible filled with the solder flux. After the cutters are completely removed, the drill bit is placed in the insulating material to be insulated and for cooling.

• PDC drill bit body repair

Put the cooled bit body in the sandblasting machine for sandblasting treatment. Inlay the graphite substitute block into the tooth cavity, and then place it in the heating furnace for preheating.

When the bit body is preheated to about 450 ° C, the H01-20 type suction type welding torch is used to modulate the slight carbonization flame for heating the part of the bit body that needs to be repaired.

When heating, the distance between the tip of the flame core and the resurfacing welding surface is kept about 3mm until the surface of resurfacing welding slightly sweating, and the tip is slightly raised, and the distance between the flame core and the surface of the resurface welding is far, and the end of the wire around the inner flame is close to the tip of the flame core.

The molten alloy drops onto the resurfacing welding surface that has been in the sweating state, while spreading it evenly, and then moving the flame forward by a certain distance, and repeat the above operation.

After the repair work of the bit body is completed, the bit body is again placed in the heat insulating material to be insulated and cooled.

• PDC drill bit cutter welding

The cutter silver brazing is a combination of intermediate frequency induction heating and oxy-acetylene heating. When welding, the bit body is placed in the induction coil, and the parts to be welded are covered with solder flux, and then heat and turn on.

The heating power is usually controlled at 10-15KW, and pay attention to the moving of the drill bit up and down to make the heating uniform. When the overall temperature of the drill bit rises to about 600 ° C, fire the torch, put the solder into each hole, and the cutters are placed one by one with tweezers.

When welding, use the welding gun aim at the welding holes to assist heating, making the solder melted, and the cutter and the holes should be completely matched, and fully rotate to ensure that the cylindrical and end surface of PDC is evenly covered with solder, and finally apply a certain pressure in the molten state, and quickly withdraws the torch. Cooling the PDC and position it. It should be noted that the wear portion of the reusable cutter is rotated to the side of the cutter cavity.

• PDC drill bit truing

After repairing the outer diameter of the drill bit, fix the repaired drill bit clamp on the grinding machine, and the outer diameter of drills should be used for processing by the large-diameter resin bond diamond grinding wheel.（If the actual grinding process requires the removal of steel and iron materials, then consider mixed abrasive of diamond and CBN grinding wheel）.

Remove the excess materials on the drill bit during the repair process by the portable grinding wheel and pneumatic grinding wheel. (Vitrified bond diamond grinding wheel of φ200 can greatly improve the production efficiency.), the regular shape and size will be obtained.

5. Pay attention to several key issues of PDC drill bit repair

5.1 Carefully confirm the drill bit that can be repaired. Only repair the drill bit that meets the repair conditions to ensure the repair quality of the drill bit.

5.2 Do the detailed inspection for the joints of the repair bit to ensure downhole safety.

5.3 Keep the proper heating and cooling speed to avoid the stress and affect the repair quality of the bit during the heating and holding process of the bit body.

5.4 Place the recycled qualified cutters in the preheated solder flux to prevent oxidation and affect the cutter quality.

5.5 In the truing process of the drill bit, choose special superhard grinding wheel for PDC drill bit truing which not only has good grinding surface quality but also has high grinding efficiency, saving labor cost and grinding wheel cost.

6 On-the-spot test

We repaired a 121/4 in BTM605 steel body PDC bit recovered from the spot. The repaired drill bit was tested in the 6-11 well of Shengli oil filed in China. The drill bit was drilled form the well depth of 300m and drilled to 1798m. The footage was 1498m, and the pure drilling time was 33.4h, and the mechanical drilling speed was 44.55m/h. After the drill bit is raised, there is no erosion on the surface of the bit body, and there is no tooth loss on the cutter. The wear is normal, and the new degree is 80%. There is no significant difference compared with the newly processed drill bit.

7 Cost analysis

The processing cost of the drill bit is usually composed of the material cost of the drill bit, the depreciation of fixed assets, the charge of water and electricity, the management fee and the salary of the staff. For example, a 121/4 steel body PDC bit with a number of the cutter of φ 19.05 mm × 50pcs and

φ 13.44 × 12pcs. Table 2 shows the cost of the new and repaired drill bits. It can be seen from Table 2 that the repair of a 121/4 in steel body PDC bit can save at least RMB41,400, the PDC bit repair technology has obvious economic benefits.

Table 2 121/4 in new and repaired drill bit cost table

After repairing the products, on-the-spot trials and cost analysis, the following conclusions can be drawn:
8 Conclusions:

8.1 There is a significant difference between the quality of the drill bit repaired by the steel body PDC drill bit repair technique and the new ones.

8.2 The steel body PDC bit repair technique can greatly reduce the cost of the drill bit and has obvious economic benefits.