Drill mud bag problem and treatment

Causes of PDC bit balling 

1. Geological factors: the stratum to be drilled is soft mud that is not diagenetic in the upper part, which is very easy to stick to the surface of the drill bit and cause bit balling after compaction; although the mud shale in the stratum is diagenetic, it is easy to hydrate and disperse, making the wellbore The content of mud or solid phase in the mud increases greatly, which is adsorbed on the surface of the drill bit to cause mud balling; or the formation contains dispersed gypsum, which causes mud pollution, and the harmful solid phase in the mud is difficult to remove, which greatly increases the probability of the drill bit being mud bagged ;The formation has high permeability. Under the action of pressure difference, it absorbs harmful solid phase in the wellbore and cuttings that are not carried out in time, forming a thick mud cake, which accumulates under the PDC bit when tripping out to form a bit bag.

3.Engineering technology factors: the displacement during drilling is small, the bottom of the well and the drill bit cannot be cleaned effectively, and the speed of upward return is insufficient, and the cuttings stay in the well for a long time, adhering to the well wall to form a thick mud cake, especially in the middle and upper parts. It is more serious when the speed is high; in the soft mudstone formation, the drilling pressure is too large, the formation or drilling cuttings form direct contact with the drill bit surface, causing the bit balling;The scraped mud cake or cuttings will mud pack the drill bit.

4.Drill bit selection factors: the design of the water hole cannot meet the requirements of chip removal; the chip removal angle of the flow channel prevents the cuttings from leaving the bottom of the well smoothly.

5. Factors of operating level: the drilling speed is too fast, the drill bit is not sliding down the spiral track, but continuously scraping the mud cake or cuttings on the well wall, which can easily cause the bit bag; It is not to connect the kelly to flush the drill bit circularly, but to press down or punch down, and the mud cake or cuttings scraped from the well wall will pack the drill bit; the operation method is wrong when drilling to the bottom. , After starting the pump, it will also cause the drill bit to bag; when drilling in soft formations, the drill will be delivered unevenly.

Handling of PDC bit mud bag 

1. The first principle of dealing with drill bits is: don’t rush to drill, because the more packed the better;

2. Regardless of the prevention or treatment of mud balling, it is inevitable to adjust the mud performance. If there is any sign of mud balls on the drill bit, the drilling should be stopped immediately and a cleaning agent should be injected into the well to clean the drill bit at the first time;

3. Stop drilling, increase the displacement to enhance the hydraulic flushing effect, lift the drill bit up to leave the bottom of the well, increase the rotational speed and increase the centrifugal force to make the mud block easy to throw out, and move up and down a large number of times, and then press down until the bottom of the well without turning the turntable Cycle for 5-10 minutes, and repeat the above process; if it is invalid within 2 cycles, you should consider pulling out of the drill.

The solution is: control the addition of poorly dispersed white clay and juniper asphalt when converting and treating the mud, start the solid control equipment in time to remove the tiny harmful solid particles in the mud during drilling, and replace the PDC bit in the middle of drilling. Displacement circulation removes the mud sticking to the drill bit while drilling in time. After reaching the bottom, first circulate a large displacement for a few minutes before drilling. Grasping these key links can effectively prevent the PDC bit from bagging. It is worth noting that technicians must correctly understand that the pump pressure of the standpipe is composed of the circulation pressure and the pressure drop of the nozzle. As long as the pressure drop of the nozzle is zero, no matter how many water holes are installed, the standing pressure will not be affected. Therefore, by unloading the eye, not only the vertical pressure cannot be changed, but also the PDC drill bit is often easily caused to bag.

2. Explore and grasp the control rules of directional well trajectory in each block as soon as possible, optimize the drilling tool structure, and minimize the use of PDC caused by adjusting the azimuth and well deviation midway. If it is necessary to use compound drilling in the lower well section with poor drillability , Using high-end PDC bits with good wear resistance can improve the use effect of PDC bits and increase drilling speed.