Effects of ethylene glycol on hydrate formation in subsea pipelines

Abstract

This study evaluated the effect of Mono-Ethylene Glycol (MEG) on hydrate formation conditions in subsea pipelines for a typical gas deepwater field in Nigeria, using a flow assurance simulator 'PIPESIM'. At the turndown, normal and maximum conditions, the production rates were 1640, 2460, and 3280 sm3/day, respectively. The wellhead temperature varies between 50-55oC, and the inlet pressure at the wellhead is 25 bara. The outlet pressure at the topside facility must be 11 bara and above to achieve flow. From available flowline internal diameters of 0.24, 0.29, and 0.34m, a simulation was run to determine a suitable internal diameter which will not lead to erosion due to the velocity. In deciding the hydrate formation temperature, the wellhead pressure of 25 bara was utilized to run the estimation. Also, in determining the minimum MEG volume required to achieve flow above a hydrate appearance temperature of 30 °C, a simulation was run at MEG volumes of 0, 10, 20 and 30 wt%. From the simulations, hydrates were observed to form at a temperature of 11.4 °C, at the minimum MEG volume of 30wt%. The 30wt% MEG suppressed the hydrates to a temperature of 8.9 °C. A slug volume of 8.5m3 was observed to be adequate to ensure fluid transport to the topside. This work's outcomes and findings also suggest a flowline inner diameter of 0.29m, an overall heat transfer coefficient of 0.81W/m2oC, and an optimum flow rate of 3280 sm3/day to avoid temperature drop to be optimum for flow assurance.