The Establishment and Correction of a Prediction Model for the Repose Angle of a Cuttings Bed in Highly Deviated Well Interval

The cuttings bed in the highly-deviated well interval of a horizontal well can easily cause instability or overall sliding and successive rapid sand plug accumulation, while the instability section of cuttings bed is difficult to predict. In order to solve this problem, the force balance of the cuttings bed in a highly-deviated well interval was analyzed, and the prediction method for the repose angle of cuttings bed was studied. Based on the wedging accumulation model in sedimentology, the prediction model for the repose angle of cuttings bed was established by analyzing the force conditions of particle rolling and sliding of the average cuttings bed surface and combining it with the bulk density concept. At the same time, the prediction model was corrected accordingly by measuring the repose angle of cuttings bed in polyacrylamide polymer (PAM) solutions with various concentrations. The test values of the repose angles in those polyacrylamide polymer solutions were 26.9°, 27.5°, 29.7° and 30.2°, respectively, and the theoretical values obtained from the sliding repose angle prediction model were 24.2°, 25.8°, 27.1° and 28.5°, respectively. The theoretical value is more conservative compared with the tested one, whereas the theoretical value can ensure safe drilling. According to this research, the established and corrected prediction model for the repose angle of cuttings bed in a highly-deviated well interval can render reliable prediction results, and it could be applied and provide references in determining the effective section of the wellbore cleaning tools and the location of downhole failures.