The Settlement Drag Coefficient of Gulong Shale Cuttings in Power-Law Fluids in Daqing Oilfield

Horizontal wells with long horizontal sections are mostly adopted in developing the Gulong shale oil in Daqing Oilfield. However, during the drilling process of the horizontal wells with long horizontal sections, the broken cuttings in the borehole annulus easily settle freely in wellbore drilling fluids to form cuttings beds. In order to avoid downhole failures such as sand sinking and sticking caused by cuttings deposition, it is necessary to study the settlement law of cuttings particles and predict the final velocity of cuttings settlement. In this paper, the settlement behavior of particles in power-law fluids was systematically recorded by visual devices and high-speed cameras during experiments. The experimental data from the free settlement of 196 groups of spherical particles and 224 groups of irregularly shaped cuttings in the power-law fluids were obtained. A mechanical model dependent on the force balance of settling particles was adopted, and the experimental data were analyzed in detail. A model for predicting the drag coefficient of spherical particles in the power-law fluids was established. On this basis, a two-dimensional shape description parameter was introduced to establish a model for predicting the drag coefficient of irregularly shaped cuttings in the power-law fluids. The prediction model showed high accuracy, and the average relative error was only 6.93%. Therefore, the model can meet the need of predicting cuttings settling velocity in drilling engineering.