Blockage detection in pipeline by estimating reflected pressure signal velocity in a dissipative medium*

The removal of a blockage in long oil pipelines requires accurate detection of the blockage location.  The applied pulse propagates with the acoustic speed in a non-dissipative system. However, waxy crude oil at low temperatures shows high viscosity, and hence pressure propagation speed reduces considerably. Thus a dissipative model is required to estimate the true pressure propagation speed. Once the accurate pressure signal speed is known we can find the exact location of the blockage. For estimating accurate speed, the present work utilizes a finite volume method along with volume of fluid method to simulate a multiphase system consisting of a 1 km long oil pipeline with blockage. The blockage mostly consisting of paraffin wax is considered either shear thinning or elasto-viscoplastic with a higher compressibility than free-flowing oil. The transient equations are written in a 2D cylindrical coordinate system for an axisymmetric pipeline, which resolves acoustic time scale. The discretized equations are solved iteratively for both oil and blockage. The time taken by the pulse to reflect and reach the inlet is recorded and is used to calculate the blockage location. The model is able to record accurate blockage location, with errors in calculation ranging from 0.79% to 1.65%.