Study On ROP Increasing Mechanism And Tool Development Of Compound Percussive Drilling

Deep oil and gas reservoirs are rich in China and are the key areas for future oil and gas exploration and development.However,the high strength,strong abrasiveness,and poor drillability of the rock in deep formation can lead to severe stick-slip vibration of drill string and low rock breaking efficiency of PDC bit during drilling,which brings great challenges to safe and efficient drilling in deep formation.Compound percussive drilling technology is a new technology proposed in recent years to solve the above problems in drilling operations,which has broad application prospects.This new technology uses impact tools to apply axial impact and torsional impact loads to the bit or drill string at the same time to form a compound percussive effect.However,the vibration law and rock breaking mechanism of PDC bit are not clear,the application effects in different formations vary greatly during compound percussive drilling,and the design of impact tool lacks theoretical guidance,resulting in the slow popularization and application of this technology.Therefore,the following research on the speed-increasing mechanism and impact tool structure optimization of compound percussive drilling has been carried out:Ⅰ.Based on the bit-rock interaction model,an integrated dynamic model of drill string system is established.Considering the regenerative cutting effect,the axial and torsional dynamic of drill string system is coupled.The drill string structure is spatially discretized by using the finite-element method.The vibration of the drill string system with compound percussive drilling tool is numerically studied,and the effects of axial and torsional impact load on bit motion are explored.The results show that the compound impact load can effectively alleviate the stick-slip vibration of bit and improve the stress condition of bit in the process of drilling in hard rock formation.However,the compound impact load will cause the axial and torsional vibration of the bit and has no speedincreasing effect on soft rock formation.Ⅱ.A numerical model of rock breaking with a single PDC cutter is established using the cohesive element method.The mechanical parameters such as elastic modulus and compressive strength of rock are obtained through the split Hopkinson impact bar(SHPB)test.Then,the dynamic rock breaking process under compound impact load is simulated,and the effects of different impact parameters on rock breaking performance are analyzed.The research shows that a stereoscopic rock-breaking effect can be formed under the action of compound impact load.The crack propagation in the rock below the cutter leads to the formation of a rock crushing pit,and the rock in front of the cutter is crushed owing to the shear crack in the rock extending from the tip of the cutter to the upper free surface.The impact load amplitude,impact angle,and impact duration have a significant influence on rock fragmentation.As the impact load amplitude increases,more severe rock breakage is induced.However,both the impact angle and impact duration have an optimal value.Under cyclic loading,as the number of impacts increases,the degree of broken rock increases significantly,and the crushed volume of rock presents a periodic jump.Cyclic loading is beneficial for reducing the impact load threshold,which achieves the stereoscopic crushing effect.The rock breaking performance is the best under sine wave loading under the same impact energy,indicating that the energy transfer efficiency of sine wave is the highest under rectangular wave,triangular wave,and sine wave loading.Ⅲ.Based on the research of axial-torsional coupling vibration and the rock breaking mechanism of bit under compound impact load,a novel pulsating compound percussive tool without impact hammer is designed to produce axial and torsional impact load at the same time.Then,the calculation model of tool impact performance parameters is established based on the analysis of tool working principle,the influence law of drilling parameters on tool impact load and impact energy is studied,and the tool structure parameters are optimized.The field application shows that the ROP increases by 105%compared with the same formation section without an impact tool in the adjacent well.The developed pulsating compound percussive tool can effectively improve the ROP and protect the bit.Through the research of this paper,the drill bit vibration rules and the rock breaking mechanism under compound impact load are clarified,and the pulsating compound percussive tool is designed,which can provide theoretical guidance for the application and promotion of compound percussive drilling technology,and has important theoretical and engineering significance for improving the ROP in hard formation.