Casing Design with Flowing Fluids

Abstract

Summary Tubing forces and displacements have long been calculated for design purposes. Formulations, such as Lubinski's buckling model (Lubinski et al. 1962), have the underlying assumption that the fluids are static. Adding the effects of fluid dynamics to the pipe-force-equilibrium problem is not as straightforward as one might think. The key point is the loads generated by the fluid on the tubing. What information can we obtain from a simple balance of momentum of the fluid in bulk? For example, for flow inside a pipe, we can determine exactly the load exerted on the pipe by the flowing fluid in terms of only the fluid density, pressure, and momentum. What might be the effect of fluid dynamics? Most papers have dealt with static fluids, but how are these static effects modified for a flowing fluid? Do we need to add a pressure gradient to the pipe buoyancy? How is fluid friction included in the pipe loading? How does fluid momentum affect the pipe? For curved pipes, we might expect a centrifugal force term. The answers to these questions are often surprising, even counterintuitive. In this paper, the general equations for the balance of fluid momentum are combined with the equilibrium equation for the pipe. The effective force then emerges as a natural combination of pipe-force and fluid-force terms. Pipe displacement is usually formulated in terms of the actual axial force, but the necessary modifications to this formulation are presented for the effective force.