Experimental and theoretical analysis of a pressure-driven logging piston during the liquid displacement process

Liquid displacement by a pressure-driven piston is a common phenomenon encountered in different industries. The main challenge of the displacement process is its inherent fast transient nature. The objective of the current work is to study such a process experimentally and to describe the hydrodynamic behavior of the system. An experimental facility was built to conduct transient measurements of pressure as well as piston and liquid slug velocities. Additionally, the piston itself was equipped with pressure and accelerometer sensors in order to conduct local measurements during its movement. The employed instrumentation was capable of sampling data at a frequency of 1000 Hz. The experiments were conducted for three initial pressure conditions and one liquid slug size. The core finding of the current study was the fact that piston and liquid slug velocities are different, which can be explained by the flow topology forming during the displacement process. It was also determined that the piston drag and friction forces are negligible for the studied conditions. A good agreement (within 10% error range) was observed between experimental velocity data and the solution of momentum and force balances.