Method for evaluating downhole working condition of a PDC bit

A method for evaluating downhole working condition of a polycrystalline diamond compact (PDC) bit, the method comprising:

• performing an indoor test, comprising performing a drilling test in different full-sized cores by using the PDC bit with different degrees of abrasion and balling under conditions of given weight on bit (WOB) and rotational speed to acquire change characteristics of a WOB, a rotational speed, a torque, a rate of penetration (ROP), and a vibration severity of the PDC bit in different time domains when the PDC bit drills in different cores under different drilling parameters;
• improving and perfecting an existing prediction model and evaluation method for the downhole working condition through data obtained by the test to obtain a method for evaluating the downhole working condition of the PDC bit;
• reading parameters of the WOB, the rotational speed, the torque and the ROP in real time during drilling;
• and
• determining the downhole working condition of the PDC bit by using the method obtained in the improving and perfecting;
• wherein, a test device and a test instrument required in the performing the indoor test comprise an acceleration acquisition system fixed on a drill pipe nipple;
• a first end of a WOB-torque-displacement acquisition system are mounted beneath the drill pipe nipple, and a second end of the WOB-torque-displacement acquisition system is connected to the PDC bit, the PDC bit is connected with a hydraulic system, and the core is provided below the PDC bit and fixed on a rotary table;
• and
• wherein a manner for processing data of the WOB, the torque and a displacement obtained in the performing the indoor test is as follows:
• intercepting a WOB data, a torque data and a displacement data in a time domain during which the WOB is stable, and obtaining average values of all intercepted data as the WOB data, the torque data and the displacement data of the test;
• a manner for processing acceleration data is as follows:
• obtaining absolute values of tangential acceleration data and radial acceleration data, and obtaining a first root mean squares value and a first maximum value based on the absolute values of the tangential acceleration data and a second root mean squares value and a second maximum value based on the absolute values of the radial acceleration data, obtaining absolute values of axial acceleration data after adjusting a baseline to 0, adding 1 to the absolute values of the axial acceleration data, and obtaining a third root mean square value and a third maximum value based on the absolute values added of the axial acceleration data.