Fluid Mechanics Analysis Of Cause With Regard To Erosive Groove On The Drill Pipe

The drilling pipe will always be damaged in the course of drilling, especially the thicken part of the drilling string. The main destroyed characters involve the abrasive erosion grooves and failure completely. Therefore, it is remarkable significant to analysis the causes why the erosive grooves come into being and study the erosion process deeply. Erosion of fluid under well brings, shock between solid particles in the drilling and interior wall of drilling pipe and change of flow style the structural size of the thickening area of the drilling pipe connectors brings are the main causes of the groove inner wall of drilling pipe.There are some conclusions that will be obtained from the material comparison experiments. The flow rate and viscosity of the drilling fluid will lead to the erosion of new drilling pipe, old drilling pipe and aluminum specimen under the solid-free condition. Notwithstanding, these increments are extremely small. If the experimental conditions are identical, the weight eroded of new drilling pipe and old drilling pipe are basically equal, too. However, the weight eroded of aluminum specimen is relatively greater. Secondly, the thinner solid particles are and the higher the density of solid particle in the drilling fluid is, the stronger block between the solid particles and wall of the drilling pipe and erosion drilling fluid will bring about are. When the diameter of the solid particle is about 0.05～0.1mm, the effect of the shock and the erosion will be more considerable. Moreover, if the flow rate is alike and rank the order according to the weight eroded, the aluminum specimen is the most serious, the new material is the least, and the old material is moderate. There are also some reasons that lead to the increases for the weight eroded, such as the augment of viscosity and confining pressure. Also, the erosive media is also noticeable factor bringing about the weight eroded. From the structural comparison experiments, the conclusions are as follows. Fist of all, the effect of density of drilling fluid can be ignored compared the viscosity of drilling fluid, because the viscosity are critical for the erosion. Secondly, the solid particle in the drilling fluid is also main reason to account for the erosion of drilling pipe connector. The most serious part of the drilling pipe connector which has erosion groove is at the bottleneck after the seam of male connector, joint between male connector and female connector and the interior thicken area of male connector which has relatively small diameter. The structural size of transitional area inner drilling pipe can have influence on the weight eroded to some extent. After the experiment which last for two hundreds hours of shock and erosion, the original male connector give birth to the remarkable erosive groove.Conclusions can be easily achieved after the numerical simulation. When fluid comes into the male connector, the flow field changes extremely owing to the geometry structure interior drilling pipe, for example, at the position that are where the interior diameters change considerably and joints. The results of numerical simulation are basically coincide with the experimental results, such as the influences flow rate, viscosity, density and size of solid particle and length of thicken area have on the erosion rate inner wall of the drilling pipe. This paper can be persuasively theory evidence for improving the design of the drilling pipe and avoiding the erosion groove by method which combines with the theory analysis, in-house experiment and the numerical simulation and studying systematically the process and rules of erosion groove of the drilling pipe.