Structural Design And Rock-breaking Performance Of Two-stage Two-speed Composite Drilling Tools

With the exploitation of petroleum moving from shallow wells to deep wells and ultra-deep wells,the problem of drilling costs increasing is becoming increasingly serious.Low rate of penetration and long drilling cycle are common problems of deep and ultra-deep wells.In allusion to these problems,a combined drilling tool characterized by dual-stage and dual-speed is presented.Its' working performances are studied by means of simulation and experiment after the structure design.The key developments and results of the thesis are as follows:(1)A new combined drilling tool with dual-rotation is presented based on the investigation and analysis of the structure design,optimization of materials and property prediction of positive displacement motors and the developments,characteristics and applications of reaming while drilling tools.The structure design and working principle of the tool which can both improve the rate of penetration and ensure the diameter of the well are completed.(2)The stress field of concave well bottom caused by the dual-rotation bit is studied by means of the ABAQUS software.The stress states of both normal well bottom and concave well bottom are compared on the basis of simulation results.The results indicate that the concave shapes contribute to stress relief,which makes the concave well bottom more easily to break compared to normal well bottom.The higher the diameter ratio of the pilot and reamer is,the more serious the stress concentration at the pilot zone becomes,and the weaker the stress concentration at the reamer zone behaves.It is determined that the preferred diameter ratio of the pilot bit and the reaming bit is 0.5.(3)A comparative study on rock breaking simulation of the new drilling tool and conventional PDC bit is carried out.Based on ABAQUS software,the finite element models of dual-rotation drill bit and conventional PDC bit are established.The rock breaking simulations are completed.After comparison,the following results are obtained:the new drilling tool has the lower stress level at well bottom,the higher rate of penetration,the weaker axial vibration and the more stable torque of bit than the conventional PDC bit(4)The research on the influence of the rotate speed of the pilot bit on rock breaking performance of the dual-rotation drill bit is carried out.The rock breaking performance of the dual-rotation bit of composite drilling tool is compared when the pilot bit is rotating at low speed,medium speed and high speed respectively.The results show that the increase in the rotate speed of the pilot bit can increase the rate of penetration,but at the same time increase the axial vibration of the dual-rotation drill bit and the torque of the bit.(5)The bench test and field test of the composite drilling tool with dual-rotation drill bit are performed.It is verified that the composite drilling tool with dual-rotation drill bit can achieve the expected function.The influence of drilling fluid displacement and reaming bit nozzle type on the rotate speed of the pilot bit is analyzed in order to guide the adjustment of drilling fluid displacement during tool using.According to the data and effect analysis of the tool field test,the composite drilling tool with dual-rotation drill bit can effectively improve the rate of penetration.To sum up,in this paper,based on the structural characteristics and working principle of the composite drilling tool with dual-rotation bit,the finite element simulation of static concave well bottom and dual-rotation bit dynamic rock breaking are carried out.Analyze the rock breaking performance of the tool.Through bench test and field test,the tool has the potential to improve the rate of penetration.It provides a reference for the research about dual-stage drilling tools and reaming while drilling tools.