First, the concept and phenomenon of pressure
Pressure support is the phenomenon that weight on bit cannot be effectively transferred to the bit due to excessive bore reduction or friction resistance during drilling. The results showed that weight on bit continued to increase but no penetration, pump pressure was stable and torque did not increase significantly. At this time, the speed should be reduced and gradually pressurized until the torque surges and the weight on bit rebounds, indicating that the bit breaks through the reducing section. The hole should be crossed repeatedly after each job to ensure that the hole is smooth. Improper operation may lead to the risk of holding the pump or sticking.
Second, the harm and causes of pressure
Poor wellbore trajectory: In directional or horizontal Wells, trajectory deviation or multiple reverse connections can increase friction between the drilling tool and the wellbore wall, especially in Wells with high production slope.
Cuttings accumulation: It is difficult to carry cuttings in highly inclined Wells, forming a cuttings bed and increasing sliding friction. Hard strata such as Shahejie are more likely to be supported by cuttings bed.
Poor mud performance: thick mud cake or high friction coefficient will increase the contact resistance between the drilling tool and the wall. When the mud cake is too thick, the pressure may suddenly suppress the pump, and the lifting force even exceeds the lower pressure load.
Third, the solution
Optimize wellbore trajectory and drilling tools: Use steering technology to control trajectory, reduce the number of drill collars, and use heavy drill pipe to reduce rigidity and avoid local support of the wellbore wall.
Enhanced borehole purification: Increase the flow rate (e.g. Φ311 > 3.4m³/min), adjust the mud dynamic plastic ratio to 0.42~0.50, maintain the viscosity for more than 48 seconds, and enhance the sand carrying capacity. The old hole is cycled to remove the cuttings bed during orientation.
Improve mud lubricity:
Mix 3 to 5 tons of crude oil (content < 10%) and use with water-based lubricant to avoid the collapse of mud cake.
Adding sulfonated asphalt or phenolic resin to improve the quality of mud cake, hard formation can be added 200~300kg expanded graphite to reduce friction.
Conclusion
The problem of pressure support should be dealt with comprehensively from three aspects: engineering control, borehole cleaning and mud optimization. Through fine operation and material adjustment, the risk of pressure support can be effectively reduced to ensure drilling efficiency and safety.