| Due to the extremely complex underground geological structure in China,oil reservoirs are very deep.In order to increase the exposed area of oil and gas reservoirs,in recent years,the drilling of large-slope wells and long horizontal wells has become an important tool in oil exploration and development,but in the process of drilling large-slope wells and horizontal wells,rock chips are very likely to accumulate to the bottom of the wellbore annulus due to their own gravity,forming a rock chip bed,which in turn leads to high friction,high torque and jamming of drilling tools,greatly reducing the efficiency of drilling and increasing the drilling This greatly reduces drilling efficiency and increases drilling costs.Therefore,in this paper,a study on the mechanism of chip transport was carried out to analyse the law of different factors affecting chip transport.This paper firstly investigates the mechanism of rock chip particle deposition,the mechanism of rock chip particle suspension and diffusion,the analysis of the collision mechanism between the particles and the drill pipe and well wall,as well as the transient numerical analysis simulation to provide a theoretical basis for the finite element simulation.Secondly,a three-dimensional simulation model is established based on the mass conservation equation and the momentum conservation equation,and the mesh irrelevance is verified to ensure more accurate calculation results.The reliability of this 3D simulation model was verified by Han et al.’s experiments on liquid-solid flow in the annulus of a wellbore,and the effects of drilling rod rotation,drilling fluid discharge and drilling fluid rheology on the rock chip transport were analysed to fully understand the amount of rock chip transients in the annulus of a large displacement well section.Again,a directional pulse jet type chip-breaking tool was designed to analyse its working principle.The strength calibration and modal analysis of the tool are completed by the finite element method to ensure the safety of the tool.Finally,a three-dimensional model of the directional pulse jet tool was established based on the theoretical foundation of the previous three chapters to analyse the effects of nozzle flow rate,nozzle size,drill pipe rotation,drilling fluid discharge,drilling fluid rheology and other factors on the rock chip transport under the use of the directional pulse jet tool,and the two types of rock chip transport efficiency were compared to obtain the following conclusions:(1)Increasing the drilling rod speed and increasing the drilling fluid displacement and density can improve the chip transport efficiency and reduce the deposition of chips in the annulus.(2)The quality of chip deposition with the directional pulse jet tool is always lower than that with conventional steel drill pipe,indicating that the tool can effectively improve the chip transport efficiency.(3)Increasing the nozzle flow rate and nozzle size of the directional pulse jet tool can increase the rock-carrying efficiency of the drilling fluid,destroy the formed rock chip bed and facilitate borehole cleaning. |
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