Experimental study of wax deposition in pipeline – effect of inhibitor and spiral flow

Abstract

Wax deposition is one of the main flow assurance problems in the oil industry. It can result in the restriction of crude oil flow in the pipeline, creating pressure abnormalities and causing an artificial blockage leading to a reduction or interruption in the production. Wax can precipitate as a solid phase on the pipe wall when its temperature (inlet coolant temperature) drops below the Wax Appearance Temperature (WAT). An experimental flow loop system was built in the lab to study the variation of wax deposition thickness under the single phase transport. A series of experiments were carried out at different flow rates (2.7 and 4.8 L/min) to study wax deposition and measure the wax thickness using four different techniques including direct technique pigging, pressure drop, heat transfer and Liquid Displacement-Level Detection (LD-LD). The effect of factors on wax formation such as inlet coolant temperature, inhibitor and spiral flow has been examined. The results show the wax inhibition percentage (WI)% was 40% and 45% at flow rate 2.7 and 4.8 L/min respectively of the inhibitor W802 (polyacrylate polymer (C16-C22)) at inlet % was 65% and 73% at flow rate 2.7 and 4.8 L/min respectively of the spiral flow at inlet coolant temperature 14 º C. This percentage of inhibition will increased rapidly by increasing the inlet coolant temperature.

Wax deposition process: mechanisms, affecting factors and mitigation methods

“…The mechanism of shear dispersion was studied by; 43 they found that the wax deposition rate did not increase with the increasing shear rate of the fluid, casting the first doubt on this mechanism for wax deposition. [44][45][46][47]…”

Experimental Methodology Followed to Evaluate Wax Deposition Process

“…The pigging technique is a procedure followed to measure wax deposit thickness inside the test section. The concept of this technique is pass a sphere through the pipe and measuring the wax volume removed [1,2,6]. A plastic conical was used during this study instead of the sphere to pig the deposit wax.…”

“…This technique is considered an online technique due to it does not require depressurisation and restart to obtain wax thickness measurement [6]. This procedure was used in this study to estimate wax thickness inside the test section depending on the concept of increasing the pressure drop along the test section due to reducing the hydraulic diameter because of wax deposition [1,2,6,7]. The wax thickness can be calculated accurately from wax equation 3 (3)…”

“…A thermal resistance term due to heat conduction through the wax layer is added to the total resistance to heat transfer from the flowing fluid to the environment. The following heat transfer equation can be used to estimate wax deposit thickness [1,2,6]. the film heat transfer coefficient from the flowing fluid to the wax layer, k p and k w are the thermal conductivities of the pipe wall and deposited wax respectively, and δ w is the thickness of the wax layer.…”

“…Several methods have been used to reduce or prevent wax deposition by using one or combination of chemical, mechanical, and thermal remediation methods. Though, with the deep production, offshore drilling and ocean floor completions, the use of thermal and mechanical inhibition methods becomes high-priced economically; therefore, the chemical additives become more prevalent [1]. Selected chemical inhibitor was tested in the current work to study its effect on wax deposition.…”