Design and Field Application of a Micro-Coring PDC Bit

During coring, the cuttings obtained by an ordinary PDC bit are broken into small bits and cannot meet the minimum necessary conditions for logging cuttings.Further, the cone bit has small footage, low ROP and there are high risks of cone breakage.In order to overcome these challenges, a micro-coring PDC bit was designed.This paper describes the overall structural design and also describes the best method for optimizing structural parameters for the micro-coring PDC bit.Aligning with the results of mechanical analysis, a small-size bit was designed and manufactured, and laboratory coring experiments and acceleration experiments were carried out.Using specifications developmed from the formation lithology from Well Jie 403 in Linpan Oilfield and Well Tuo 202 in Shengtuo Oilfield, a ϕ215.9 mm micro-coring PDC bit was designed and manufactured.The bit was then sent to the field where it was put into use in order to verify the design.Both the results of laboratory experiments and the field tests showed that the cuttings obtained by this bit were relatively large and the size was equivalent to that drilled by a cone bit, which could meet the requirements of cuttings logging.In addition, the bit footage and ROP were similar to that of ordinary PDC bit, and the efficiency was significantly improved compared to the cone bit.The results showed that the micro-core PDC bit could replace the cone bit in the interval for logging the cuttings, and could improve the efficiency due to its higher ROP.