Casing Drilling Plastering Effec

During drilling operations, many problems are encountered. Among them, lost circulation and wellbore stability are two of the severest. These problems affect the drilling operation in terms of economic, environmental and safety aspects. Based on the field experience, it has been reported that casing drilling has an impact on reducing lost circulation and improving wellbore stability. One of the proposed reasons for that observation is the plastering (smearing) effect of the casing string.;To minimize problems related with lost circulation, an understanding of plastering effect is crucial. This study focuses to investigate this phenomena both theoretically and experimentally. For the experimental part, core samples collected from a sandstone sample were used to mimic the plastering effect by using a benchtop setup designed specifically for this purpose. Three different cuttings concentrations, four different numbers of contacts between the core sample and the drill string were simulated while applying low contact force. Also, for mimicking the high contact force case, three different cuttings concentration and three different number of contacts were applied. The permeability of the samples was tested on a permeameter after conducting these smearing experiments. It was observed that all of the different conditions listed above have an impact on permeability mitigation. A simplified one-dimensional mathematical model was used to show the change in permeability, fluid velocity and location of the lost fluid in the porous media. Comparison between the model results and experimental data was conducted. The results show that the proposed models has a good agreement with the experimental data. Finally, a case study is presented for potential field applications, and corresponding recommendations are proposed for further investigation.