A PDC-roller hybrid bit with an independent buffer structure
In the process of oil and gas exploration and development,low drilling efficiency and short bit lifespan in hard-to-be-drilled strata are the bottleneck problems impacting the drilling cycles and costs of deep and ultra-deep wells.The polygonal effect generated by the alternating contact between the cutting structure and the wellbore in the operation process of the drill bit is the main factor leading to the unstable operation of the drill bit and the impact failure of the cutting teeth.To improve the operation stability of drill bit,this paper proposes a new type of PDC-roller hybrid bit with an independent buffer structure.In response to the serious impact failure of conventional PDC drill bits in the Ø311.2 mm well section of Maokou Formation in the Sichuan Basin,a 3+3+3 type(3 main blades,3 roller-cones,and 3 independent buffer blades)hybrid bit with an independent buffer structure is designed.Then,laboratory full-scale bit drilling comparison experiments are conducted.In addition,it is applied to the actual drilling in the Maokou Formation-Qixia Formation of Sichuan-Chongqing shale gas block.And the following research results are obtained.First,superior to conventional hybrid bits,the one with an independent buffer structure has an additional independent buffer blade in the clearance between the roller cutting structure and the fixed cutting structure,which effectively alleviate the polygon effect to provide the buffering protection for PDC cutters while sharing the excessive weight on bit(WOB)to restrict the cutting depth of cutting teeth,so as to prevent the stick-slip vibration of drill bit.Second,the WOB and torque of the hybrid bit fluctuate in a small range,and its torque is 1/5 of that of the PDC bit.Third,the hybrid bit has set up a new record of drilling footage of 170 m with one single drill bit,which is 73.5%greater than the maximum drilling footage of one single PDC bit in the same layer of the adjacent well.In conclusion,the independent buffer blade plays a key role in improving the stability of the drill bit,which not only prolongs its service life,but effectively improves the composite drilling efficiency in complex and difficult-to-be-drilled strata and complex-structure wells and reduces oil and gas exploration and development costs.
Hybrid bitIndependent buffer structurePolygon effectDrill bit stabilityROP improvementHard-to-be-drilled strata
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