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Research on PDC Bits for Directional Wells

Research on PDC Bits for Directional Wells

1. Model analysis of interaction between PDC rock bit and formation in directional wells


There are many factors that affect the interaction between the PDC rock bit and the formation in directional wells. In order to express the quantitative parameters of the formation rock, the parameters of the formation rock should be quantitatively analyzed first. The formation anisotropy parameter is one of the main parameters of the formation rock.


Sedimentary rock formations generally have anisotropy due to different depositional conditions. In the process of oil drilling, sedimentary rock formations are often encountered.


Due to the existence of formation anisotropy, in the process of directional well drilling, it is easy to cause the phenomenon that the downhole drill bit deviates from the predetermined trajectory, which affects the quality and efficiency of directional well drilling.


During the drilling process of the PDC rock bit, not only the axial drilling trend of the PDC rock bit will exist, but also the lateral drilling trend of the bit will exist, that is, the different performance of the PDC rock bit axial drilling.


In the actual PDC drilling process, the design of the bit generally focuses on the axial drilling of the bit to avoid the phenomenon of lateral drilling of the bit.


When designing the hydraulic structure of the drill bit, it is also designed to facilitate the axial drilling of the drill bit. The sidetracking performance of different types of drill bits is also different.


In order to obtain the sidetracking performance parameters between a specific stratum and the PDC rock bit, the theoretical calculation method is usually used according to the actual parameters of the stratum, and sometimes the corresponding sidetracking parameters are obtained through indoor rock breaking experiments. 


Under normal circumstances, most of the strata encountered in the actual drilling process are heterogeneous, regardless of the homogeneity of the stratum. Moreover, even if the bit axis sidetracking index is the same, the direction of the resultant force generated by the directional drilling bit cannot be completely consistent with the displacement direction of the bit.


During the mechanical analysis, the force on the formation is only in the form of force, not the real force, which is quite different from the actual mechanical force. When the formation is subjected to force analysis, the characteristic parameters of the formation are converted into the expression of force form for easy analysis.


2. Research and analysis of factors affecting the drilling trend of PDC rock bits in directional wells


In the process of directional well drilling, there are many factors that affect the drilling trend of PDC rock bits, including the drilling tool assembly on the upper part of the bit, the shape parameters of the bit, the properties of formation rocks, and the parameters of actual drilling.


Various factors have different action mechanisms and various manifestations that affect the drilling of the drill bit. When the diameter of the centralizer in the downhole BHA increases, it will have a certain impact on the well deflection force of the drill bit, but it will not cause a large influence.


In terms of PDC rock bit structure, when the length of the gage teeth of the PDC rock bit is lengthened, the well deviation force of the drill bit is always upward, and the magnitude of the value gradually decreases, so the lengthening of the gage teeth can achieve the purpose of reducing the well deviation.


Therefore, when drilling directional wells with PDC rock bits, the method of reducing the length of the gauge teeth can be used to achieve the purpose of stabilizing the inclination and orientation of the wellbore.


In terms of drilling parameters of directional wells, when the WOB of drilling increases, the well deviation force of the drill bit is always downward, and the value is gradually increasing, so the increase of WOB will increase the well deviation, and the magnitude of increase increases with the increase of WOB.


However, the azimuth force of the PDC rock bit is zero, so in the drilling of highly deviated wells, the increase of the WOB can increase the slope of the wellbore and stabilize the orientation of the wellbore trajectory.


When the rotational speed of the drill bit increases, the inclination of the wellbore decreases, which can achieve the purpose of well inclination. During the deviating process of the PDC rock bit in directional wells, when the bit moves from a harder formation to a softer formation, the The advancing direction will be offset by a certain distance to the soft formation.


The quality and speed of directional well drilling can be improved by studying the factors affecting the drilling trend of the PDC rock bit in directional wells.


PDC rock bits are widely used in directional well drilling. With the continuous development of the theory and technology of directional well PDC rock bits, the use of PDC rock bits will continuously improve the accuracy and efficiency of directional well drilling.


Due to the existence of formation anisotropy, it is easy to cause the phenomenon that the downhole drill bit deviates from the predetermined trajectory in directional well drilling. There are three types of lateral forces when the directional well PDC rock bit works.


Through the research on the factors of the PDC rock bit drilling trend, the PDC rock bit manufacturer has obtained the influence rule of each factor on the PDC rock bit drilling trend, which can better improve the quality and speed of directional well drilling.

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