Structure And Dynamic Analysis Of Miniature Vibrating Screen For Sampling In Drilling Mud

During the exploration and exploitation phase of oil field, the first tasks of field geological work is to figure out the geological formation and draw the geological well log. By determining the strata sequence, burial depth, stratigraphic thickness and the rocks' characteristics of the drilled strata formed in different geological era, we can gain knowledge of the formation and reserves of oil and gas, the constitution and position of cap rock, the lithologic character and the gas-oil conditions and so on in order to provide fundamental information for the calculation of oil reserves, the adjustment of well grid in the oil zone as well as for the drilling fluid configuration, the use of the drill bit, pressure test on oil layer, acidification and other projects carried out during the drilling process. In the course of drilling, we usually call those rock fragments which are borne on the earth by the mud debris. Rock fragments of large uniformly sized solids will be used to analyze rock sample in the engineering practice.In the paper we use small vibratory screen for mud screening. Meanwhile, water will be sprayed onto the screen surface to wash out the mud and the fine materials so as to clear the debris and obtain the desired rock sample. Therefore, a reasonable design for the vibrating screen is the key to get the desired rock sample. In terms of designing a vibrating screen, the screen should first screen out the given material according the vibration requirement; Second, the screen should be of certain rigidity and hardness in order to meet the basic requirements such as long working life, high reliability; last but not the least, the designed vibrating screen should be of simple structure, small volume, light weight and easy displacement, because it needs to be transported to new oil wells for sampling.On the basis of these demands, the content of this study includes the following aspects when the structure and the dynamics of the vibrating screen are analyzed.(1)Optimize dynamic parameter of vibrating screen.The relationship between the motion parameters can be obtained based on the analysis of the displacement of particles on the screen, and a mathematical model between the motion parameters will be established. Then an optimizing programme will be composed to optimize all motion parameters in order to obtain a group of motion parameters that make the vibrating screen the most efficient and meet the required handling capacity.(2)Structure design and dynamic analysisi of vibrating screen.A proper electric machine will be chosen for the vibrating screen and the damping system will be designed based on the optimized motion parameters. Then an initial overall structure of the vibrating screen is achieved, which provides a basis for the establishment of its mechanical model. In light of the mechanical model, a dynamic analysis will be carried out to calculate the natural frequency and the system response of the vibrating screen and to determine preliminarily whether its structure is reasonable. The structure of the vibrating screen will be improved otherwise.(3)Construction of screen box finite element model. A finite element model of screen box will be established to run finite element analysis according to its initially determined structure. First, create a three dimensional model of the screen box; second, import the three-dimensional model in to ANSYS to mesh. During the meshing process, the screen box will be simplified first so as to ignore some unnecessary constraint holes and process holes. However, the mass of the screen plates cannot be ignored due to the fact that the vibrating screen analyzed in this paper is small-scaled. Since excessive screening meshes make the mesh complicated, the screen plates are simplified as the first-quality flat plates. Then the middle plane will be selected from the overall screen box, and is meshed by shell element, the value of which is set to the thickness of the plate.(4)Finite element analysis of screen box. The main operation in the finite element analysis is to conduct modal analysis and harmonic response analysis of the screen box. In modal analysis, the first 15 natural frequency and the corresponding array graph will be established to determine whether the working frequency falls within the proximity of the natural frequency of vibrating screen. In harmonic response analysis, a displacement nephogram and stress nephogram will be obtained to improve undesired parts.The conclusions arrived in this paper provide guidance for the structure design, the optimization of the dynamic parameters as well as the finite element analysis and the structure of the screen box, and theoretical and factual basis for small-scaled vibrating screen for sampling in drilling mud.