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ABSTRACT
This study focused on the evaluation of the effect of Nano-silica (SiO2) on hydrate formation conditions in subsea pipelines for a typical gas deepwater field in Nigeria, using a flow assurance simulator ‘PIPESIM’. The subsea flowline simulated was designed to transport recovered hydrocarbons from a deepwater manifold to a topside facility over a 10km distance. At the turndown, normal and maximum conditions, the production rate 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 if flow must be achieved. From available flowline internal diameters of 0.24, 0.29, and 0.34m, a simulation was ran to determine a suitable internal diameter which will not lead to erosion due to the velocity of the flow to achieve flow above 11 bara. In determining the hydrate formation temperature, the wellhead pressure of 25 bara was utilized to run the estimation. Also, in determining the minimum SiO2 volume required to achieve flow above a hydrate appearance temperature of 30 ºC, a simulation was ran at SiO2 volumes of 0, 10, 20 and 30 wt%. From the simulations, it was observed that the minimum SiO2 volume required to keep the fluids above the hydrate formation temperature was 30wt%, while hydrates were estimated to form at a temperature of 11.4 ºC, at a pressure of 25bara. The 30wt% SiO2 volume was able to suppress the hydrate formation temperature by a temperature of 8.9 °C. A slug volume of 8.5 m3 was observed to be adequate to ensure the transport of fluid to the topside. The outcomes and findings of this work also suggests a flowline inner diameter of 0.29m, an overall heat transfer coefficient of 0.81W/m2oC, and an optimum flowrate of 3280 sm3/day that will avoid temperature drop to be optimum for flow assurance.
