Experimental study on the wax removal physics of foam pig in crude oil pipeline pigging

Mechanical pigging is the most conventional method to mitigate the wax deposition in the field pipeline. However, wax removal physics of foam pig is still poorly understood. In this work, wax removal physics of foam pig is experimentally investigated in the pigging facility. Furthermore, wax removal physics of foam pig is proposed and further evaluated. Due to the energy absorption of foam pig during its elastic buckling, the wax resistive force of foam pig presents five phases including the build-up phase, pre-plug phase, damping phase, plug phase, and production phase. In the five-phase pigging process, the initial wax breaking force has a high risk of the pig stuck in the field compared to the steady wax breaking force. It is also noted that the wax removal physics changes when the wax yield stress and the wax layer thickness are increased. The effects of foam pig density, wax yield stress, and wax layer thickness on the wax breaking force and the wax removal efficiency are discussed. Furthermore, force analysis physical models and the energy absorption of foam pig are proposed to illustrate the experimental results. The effect of foam pig density on the wax breaking force is different for the wax layers with different strength. The wax removal efficiency of the low-density foam pig is significantly reduced for high strength wax layer.