Study On Composite Bit For Siliceous Dolomite Stratum

The siliceous dolomite strata of the Cambrian-Ordovician in the Tarim Basin are highly abrasive and hard strata with serious heterogeneity.Drill bits for efficiently drilling into siliceous dolomite formations should have strong aggressiveness,strong impact resistance and high wear resistance.Conventional polycrystalline diamond compact(PDC)bits,roller cone bits,and impregnated bits cannot meet the above requirements,either the drilling speed is slow or the wear is fast.The development and application of non-planar drill bits and hybrid drill bits have improved the performance of the drill bit to a certain extent,but it is still unsatisfactory.Therefore,it is of great significance to study new high-efficiency drill bits to further improve the drilling efficiency of siliceous dolomite formations.In this paper,numerical simulation analysis and laboratory experiment research are used to carry out research on the cutting and crushing mechanism of siliceous dolomite,the optimization of high-performance PDC types,the optimization of the optimal PDC size and back rake angle,and the design of composite cutting structure.The following results and understandings are obtained.Discrete element method software PFC is used to establish a numerical model of PDC cutting siliceous dolomite.Through numerical simulation,the cutting failure mechanism of siliceous dolomite and the changing law of force on PDC are analyzed.The analysis shows that the poor penetration ability and stick slip oscillation caused by large force fluctuations,bit whirl and impact damage of cutters are the fundamental reasons for the low drilling efficiency of conventional PDC bits.Through the comparison of the rock breaking test and the impact resistance test of the cutters,the attack and impact resistance of the Ridge Diamond Element(RDE),the TripleRidge Diamond Element(T-RDE)and the conventional PDC are analyzed.The test results show that RDE are the most aggressive,and T-RDE are the most impact-resistant.Based on the requirements of the siliceous dolomite formation on the performance of PDC,RDE are preferably used for the design of the drill.The numerical model of rock breaking with RDE was established using finite software ABAQUS,and the influence of back rake angle,blade angle and diameter on the efficiency of rock-breaking with axe teeth was studied.The results of the study show that the RDE with a diameter of 16 mm and blade angle of 110 has the highest rock breaking efficiency when cutting the rock with a back rake angle of 15.Aiming at the characteristics of high strength and strong abrasiveness of siliceous dolomite,a new combined cutting structure of ‘RDE + DIC’ is designed.Combining the characteristics of the siliceous dolomite formation in the Tarim Basin,a new type of combined PDC bit is designed.