Analysis Of Crown Profile Geometry And Borehole Trajectory Of PDC Bit In Directional Wells

With the gradual decrease of oil and gas resources,the directional well,horizontal well and other directional drilling technology are widely used in the exploitation of complex buried and deeper oil and gas resources,so the well structure becomes increasingly complex.But the oblique section is used as the change direction part of the directional well during drilling process,its control accuracy of oriented process has important influence on the downhole accident and drilling cost.At the same time,compared with the design trajectory,the widespread offset phenomenon of actual well trajectory has also brought greater difficulties to the drilling operation of directional well,and how to real-time and effectively control the well trajectory has long been a key issue which field engineers and drilling workers manage to study and solve.The PDC bit as the vanguard for drilling engineering,its cutting teeth directly break the rock,the drill bit whipstocking ability has the crucial impact on directional well quality,risk,cost and so on.To improve the deflection capability and drilling efficiency of the PDC bit under the action of the guiding tool,this paper explores the influence of PDC drill bit's heart contour,the radius of the transition arc,transition arc position and other key geometric parameters on its guiding performance and drilling efficiency based on the existing well trajectory geometry,the design theory and the research status of the PDC bit used in directional well.According to the existing well trajectory geometry,design theory and well trajectory analysis method,this paper has qualitatively analyzed the key geometric factors that affect the PDC bit drilling performance and deflection performance by adopting the research method of extermal contour geometry based on the study of the problem that the wellbore curvature is too large and irregular and so on.Meanwhile,based on the analysis of geometrical characteristics of PDC bit crown curve,the conical contour of the ordinary PDC bit is replaced by the circular curve to enhance the deflection performance of the PDC bit under the action of the guidance tool.In order to study the stress state of PDC bit in oblique section,on the basis of the analysis model of single-tooth rock-breaking mechanics and the rock force model under the action of shear force,and combing the drill bit biasing force which is given by the flexible drilling pipe of the drilling tool.According to the static limit equilibrium principle of space force,the mechanical analysis model for PDC drill bit on increased inclined section,downhill section and horizontal section is established.At the same time,the bottomhole pattern drilled by different types of drill bits is analyzed,and the forming characteristics of PDC bit bottomhole pattern and the process of cutting rock are discussed.A simulation cutting method of PDC drill bit bottomhole pattern is proposed.The method uses the three-dimensional software to simulate the extermal contour of the PDC bit and the height of protrusion of the cutting teeth,and then carries on the simulation cutting,which has a certain reference value to the structural design of the external contour of the PDC bit and the arrangement of the cutting teeth.Through the bench test and the oblique drilling experiment in a cement pier,we found that the new drill bit "vertical heart" phenomenon was obviously reduced;In the process of guided drilling,the actual well trajectory of new PDC bit has a better matching degree with the design trajectory compared with the ordinary PDC bit,and it also exhibits better whipstocking controllability under the action of guiding tool.