| Horizontal directional drilling(HDD)is a trenchless construction method typically used for pipeline construction in petroleum and natural gas industries.It has lower economic costs,takes less time to complete,is environmentally friendly and has a high efficiency compared with other construction methods.However,cone reamer drilling in hard rock formation often has occurred roller shedding,tooth wear and tooth breakage,which seriously affect the construction efficiency and safety.At present,the researches on reamer used in rock formations are mostly stagnant in the structural improvement of cone reamer,and the new reamer has not been studied from the mechanism of rock fragmentation.For the above problems,a new type of PDC reamer is systematically analyzed in this paper.Based on the elastic-plastic mechanics and rock mechanics,and using the Drucker-Prager criterion as the rock constitutive relation,the rock-breaking efficiency of the PDC reamer and its cutting teeth are systematically analyzed by the finite element method.On this basis,a two-stage PDC reamer is proposed,and the structural parameters that affect rock-breaking efficiency are analyzed.The main points of this paper are listed as follows:(1)The literature on the development of the reamer and PDC cutting theory at home and abroad has been studied in a more comprehensive and detailed way.And the research content,purpose and methods are confirmed.(2)Based on the geometric theory of PDC bit,the geometry of PDC reamer is analyzed,and the cutting tooth-rock interaction model is established.The relationship between the cutting force of rock and the mechanical properties of rock and the parameters of cutting teeth is determined.Finally,the working load relation of the reamer is obtained.(3)The finite element software is used to establish the nonlinear three-dimensional numerical simulation model of the cutter of PDC reamer cutting section rock.The influence of cutting depth,back-rake angle and side-rake angle on rock-breaking efficiency of two typical cutting sections under different rock lithology is compared.(4)A three-dimensional numerical simulation model of reamer breaking rock is established,and the differences between PDC reamer and cone reamer are analyzed.The influence of reaming parameters and formation lithology on PDC reamer breaking rock is studied.(5)Using excavation ideas,a three-dimensional finite element model of rock bottomhole stress field of two-stage PDC reamer is established,the rock bottom stress state of routine wellbore and stepped borehole is analyzed.And the influence of the structural parameters of two-stage PDC reamer on rock-breaking is mainly considered.The results of this paper can provide guidance for the structural design of PDC reamer and the selection of parameters in the construction process.And the new two-stage PDC reamer can provide new ideas for high-efficiency rock breaking in reaming operation. |
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