Aimed at studying the casing wear in the highly deviated well drilling, the experimental study on the casing wear was carried out in the first place. According to the test data and the linear wear model based on the energy dissipation proposed by White and Dawson, the tool joint-casing wear coefficient was obtained. The finite element model for casing wear mechanism research was established using ABAQUS. The nodal movement of the contact surface was employed to simulate the evolution of the wear depth, exploiting the Umeshmotion user subroutine. In addition, the timedependent geometry of the contact surfaces between the tool joint and casing was being updated continuously. Consequently, the contact area and contact pressure were changed continuously during the casing wear process, which gives a more realistic simulation. Based on the shapes of worn casing, the numerical simulation research was carried out to determine the remaining collapse strength. Then the change curve of the maximum casing wear depth with time was obtained. Besides, the relationship between the maximum wear depth and remaining collapse strength was established to predict the maximum wear depth and the remaining strength of the casing after a period of accumulative wear, providing a theoretical basis for the safety assessment of worn casing.
In this paper, a novel fractal model for the invasion depth of fluid through the tortuous capillary bundle with roughened surfaces in porous media is proposed. The capillary pressure effect is considered in the proposed model. The proposed model is expressed as a function of structure parameters of porous media, including the relative roughness, the fractal dimension for pore size distribution, the contact angle, the density, the gravitational acceleration, the tortuosity and porosity. The invasion depth can be quantitatively characterized by the proposed model. By using the fractal theory, the effect of relative roughness on the invasion depth is discussed. It is observed that the invasion depth decreases with increasing the relative roughness of the tortuous capillary bundle with roughened surfaces. In addition, it is found that the invasion depth increases with the increase of the invasion time. The proposed model predictions are in good agreement with the available experimental data. Each parameter in our model has clear a distinct physical meaning, which may contribute to comprehend the better understanding of seepage mechanisms.
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