Effect of Particle Size and Viscosity on Erosion in Annular and Slug Flow

Abstract

Solid particle erosion is a mechanical process in which material is removed from a surface due to impacts of solid particles transported within a fluid. It is a common problem faced by the petroleum industry, as solid particles are also produced along with oil and gas. The erosion not only causes losses resulting from repairs and decreased production but also causes safety and environmental concerns. Therefore, the metal losses occurring in different multiphase flow patterns need to be studied and understood in order to develop protective guidelines for oil and gas production equipment. A large scale boom loop, which is capable of generating a wide variety of multiphase flow regimes was used for conducting experiments. Specifically, this work examines erosion measurements in multiphase slug and annular flow regimes. These flow regimes are selected since they produce higher metal losses than other flow regimes, and they also occur for a wide variety of operating conditions. Experiments are performed on a horizontal 0.0762 m (3-inch) diameter pipe, with superficial gas velocities ranging from 15.2 m/s (50 ft/s) to 45.7 m/s (150 ft/s) and superficial liquid velocities ranging from 0.46 m/s (1.5 ft/s) to 0.76 m/s (2.5 ft/s), for liquid viscosities of 1 cP and 10 cP. Carboxymethyl Cellulose (CMC) was used to increase the viscosity of the liquid without significantly altering the density of the liquid. Three different sand sizes (20, 150 and 300 micron sand) were used for performing tests. The shapes of the sand are also different with the 20 and 300 micron sand being sharper than the 150 micron sand. Erosion measurements are taken using Electrical Resistance (ER) probes which relate the change in electrical resistance to the change in the thickness of an exposed element resulting from erosion. Two probes are placed in a bend and another probe is placed in a straight section of pipe. The probes in the bend are flat-head probes, and they are placed flush with the outer wall in the 45 and 90 degree positions. The probe in the straight pipe is an angle-head probe which protrudes into the flow with the face placed in the center of the pipe. Under the flow conditions investigated, the angle-head probe measures the maximum erosion due to its placement. Results demonstrate a significant increase in the metal loss occurs when increasing the superficial gas velocity and decreasing the superficial liquid velocity. The effect of changing the viscosity of the liquid is not as clear. Results suggest a slight increase in metal loss by increasing the viscosity from 1cP to 10 cP in slug flow. However, for annular flow, higher erosion occurs for the lower liquid viscosity considered.