Torque and Drag Analysis Considering Drilling Fluid Circulation

With the development of extended-reach drilling (ERD) and horizontal wells, the ultimate limits of ERD wells are continually being extended, and the lengths of horizontal sections in horizontal wells are also gradually increasing. This has led to higher accurate demands for the analysis of tubular torque and torque. In previous analyses, the influence of fluid circulation on the axial force distribution of the tubular string was not considered, and only the buoyancy of stationary fluid was taken into account. Therefore, there is a certain deviation from the actual situation. Based on the conservation of fluid momentum and energy, this paper derives the forces exerted on the tubular string during fluid circulation. Combining this with the soft-string model, the distribution formula for the axial tensile force of the tubular string is obtained. The study finds that the magnitude of the forces exerted on the tubular string during fluid circulation is related to the outer diameter of the tubular string and the pressure drop in the annular fluid, but not to the inner diameter of the tubular string or the pressure drop inside the tubular string. Fluid circulation in the wellbore will reduce the surface hookload during normal circulation, while reverse circulation will increase the hookload. The accuracy of the model proposed in this paper is also verified through practical examples. Based on the model proposed in this paper, the extension limits of ERD wells and the length limits of horizontal sections in horizontal wells can be accurately analyzed.