| Chinese oil and gas exploration and development work gradually to the deep well,ultra-deep well development,and large diameter wells increased,the traditional cone bit and PDC drill bit in the drilling process,broken rock low efficiency,slow drilling and short life,can not meet the drilling Speed increase efficiency requirements,and improve the deep well,large diameter section of the drilling rate has become the current domestic and foreign oil and gas drilling an urgent need to solve the main problem.Single-cone-PDC double-stage drill bit as a new type of drill takes the way to break the rock,in order to achieve rapid hardening drilling efficiency to provide a new idea.Based on the theory of elasto-plastic mechanics,rock mechanics and simulation study,the interaction law and rock breaking characteristics of single-cone-PDC double-stage drill bits and rock are studied.Rock characteristics to guide its structural design,to speed up its application has important engineering significance.The main contents and achievements of this thesis are as follows:(1)Carry out a two-stage drill bit rock breaking mechanism and cutting tooth force analysis.Based on the theory of elasto-plastic mechanics and rock mechanics,the rock breaking mechanism and the force of cutting teeth are analyzed.The mechanical mechanism of the double-stage drill bit to improve the drilling speed is obtained from the angle of rock breaking mechanism.The subsequent chapters of the simulation analysis laid the theoretical foundation.(2)Carry out the study of the stress field at the bottom of the ladder.The stress state of the bottom of the ladder is analyzed by using the method of numerical simulation.The stress ratio of the drill floor and the relative height of the two-stage rock breaking structure to the stress field of the bottom of the ladder are analyzed and compared.The bottom of the ladder bottom hole collar wall stress release significantly,drillability is strong,collar hole bottom stress release significantly,easy to break the rock;drilling expansion ratio is smaller,collar hole wall stress release more fully,the rock can drill stronger,And the smaller the drilling expansion ratio is,the larger stress release area of the collar hole is.The smaller the relative height of the two-stage rock breaking structure is,the more fully the stress release of the borehole wall rock is.When the relative height exceeds the certain value,the stress release area will extend to the periphery of the wellbore.It is not conducive to the stability of the borehole wall,and make the drill rock during the process of excessive energy dissipation.(3)Carry out a single cone-PDC two-stage drill with conventional PDC bit,two-stage PDC bit rock breaking simulation comparison.The results show that the stress level of the rock under the action of the single-cone-PDC double-stage drill bit is lower than that of the conventional PDC bit,and the stress level of the rock is lower than that of the conventional PDC bit.The two-stage drill torsional vibration is lower than the conventional PDC bit and the two-stage PDC bit,which is about 75%lower than that of the conventional PDC bit,about 30%lower than the two-stage PDC bit,and the torque average Both of which are reduced by about 65%and 56%.The axial impact of the two-stage drill bit on the rock is higher than that of the conventional PDC bit and the double-stage PDC bit,and has higher rock breaking efficiency.(4)The effects of drilling expansion ratio and relative height of two-stage rock breaking structures on the rock breaking characteristics of double-stage drill bits were studied.The rock breaking model of two-stage drill bits and three kinds of relatively high-grade double-bit bit rock breaking model are established.The results show that under the condition that the relative height of the two-stage rock breaking structure is constant.The smaller the drilling expansion ratio is,the greater the impact of the double-stage drill bit is on the rock.The higher the efficiency of the rock breaking is,the faster the drilling speed is,but the greater the torque is required to rock the rock.The smaller the relative height is,the stronger the interlocking effect of the two-stage rock-breaking structure is,and the greater the impact on the rock in the direction of drilling is,and the higher the efficiency of rock breaking is,and the faster the drilling speed is,while the greater the torque required to break the rock is. |
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