Experimental Investigation of Near-well Fluid Mechanics on the Scaling Mechanism in Narrow Rectangular Slots

Abstract

This experimental study investigates the effect of near-well fluid mechanics on the scaling failure mechanism specific to SAGD production well. The scaling failure mechanism can be triggered by the pressure drop phenomenon and causes the plugging of the slots in the oilfields. The scale formation process has been previously studied to understand the effect of thermodynamic parameters. However, there are very few studies which tried to understand the effect of flow related aspects on the scale formation. Also, an image acquisition system has been rarely used in a dynamic flow and in-situ conditions to monitor the calcium carbonate scale growth, and investigate the pressure loss characteristics. An experimental set-up was developed to simulate the formation and growth of the calcium carbonate as well as to visualize the flow related phenomenon in the narrow rectangular slot. To undertake this, two experimental measurements are needed. Monitoring the growth of the calcium carbonate and measure the subsequent changes in differential pressure during the scaling experiment, and determination of the pressure field from the velocity data using particle shadowgraph velocimetry technique. The experimental set-up mimics the flow through a single rectangular slot of the actual slotted liner design used in SAGD. The scaling performances of industrial slotted liner designs i.e. straight, seamed and keystone were investigated to understand their efficacy in mitigating the scaling issues. The slot width reduces due to calcium carbonate scale formation and subsequent crystal growth. The scale growth is concentrated at the slot entrance where there is a change to a low pressure region. Based on the comparison of the geometries, the keystone design is a superior design to mitigate the scale problems. The study hypothesizes that the cycle of calcium carbonate growth and pressure drop continues until the plugging of the slots. The effect of inlet geometry profile was also assessed on the calcium carbonate scale formation and growth by considering a straight channel with and without a rounded entrance. The flow developed slowly for the rounded slot design indicating a reduction in flow resistance. The pressure loss characteristics for the straight and rounded design were also investigated. The study confirmed that the gradual change at the entrance by rounding the sharp edges reduces the tendency for scaling. Also, an increase in the flow rate in both geometries accelerated the scale formation process. The scale formation and growth mechanism affected the static pressure loss due to a subsequent increase in the kinetic energy and flow convergence.