Simulation And Application Of Multi - Phase Flow Field In PDC Drill

PDC drill bit, as an efficient drilling tool, has been widely used in petroleum and natural gas drilling and exploitation. PDC drill bit’s Hydraulic structure has a very important influence on the drilling performance, and the main purpose of the study is to improve the migration effect on bottom hole cuttings, cleaning and cooling effect of bit cutting teeth to ensure that PDC bit is always in the most good drilling performance. In actual drilling operations, bottom hole flow field is multiphase flow field formed by the mix of drilling fluid and cuttings, whose flow characteristics is complex three-dimensional turbulent flow. Therefore, judging and simulating the bottom hole flow field are not accurate enough through the single-phase flow field analysis in the existing literatures.In this paper, PDC bit’s the structure and fluid flow characteristics has been comprehended sufficiently, then the liquid-solid two phase flow field for PDC bits is simulated. The main research works in this paper are as follows:(1) Based on the multiphase flowr basic theory, the basic theory about PDC drill bit bottom hole multiphase flow field and mathematic model of numerical simulation are established.(2)The quantitative analysis on cuttings volume generated by the blades and discharged by each flow channel are carried out, involved in the evaluation of bottom hole flow field of PDC bit, which improved the existing evaluation optimize methods of PDC bit bottom hole flow field and provided theoretical basis for the hydraulic structure optimization.(3)Modeling theory and method of PDC drill bit liquid-solid two phase fluid simulation are studied, by means of CAD software to set up the PDC drill bit bottom hole flow model and calculate the volume of cuttings generated every single cutting teeth, the initial velocity of cuttings and initial direction; Generated unstructured tetrahedral grid domain, the simulation of PDC drill bit’s bottom hole liquid-solid two phase flow field is carried out using CFD software; according to the simulation results, the deficiencies of the PDC bit hydraulic structure are found and the structure is adjusted.(4) Numerical simulation of liquid-solid two-phase flow field for a specific PDC bit is implemented. Also the remaining cuttings volume in PDC drill flow field, the volume of cuttings, mud discharged through each flow channel, each cutting tooth surface flow velocity, bottom velocity distribution and surface erosion are analyzed. According to the analysis, the original hydraulic structures of PDC drill bit still have some flaws. Based on PDC bit hydraulic structure modeling methods, the nozzle location and the spray angle of the original drill bit model are optimized. When compared the bottom hole flow field after the PDC drill bit optimization with the original model, the results show that the drill bit bottom hole flow field has been significantly improved.The above research results enrich and develop simulation methods of PDC drill bit in bottom hole flow field. Furthermore, it guides PDC bit hydraulic structure optimization design and improves PDC bits performance, which will have important academic value and engineering significance.