Improving the Thermodynamic Properties of Export Gas Through Condensate Spiking

Abstract

Disposal of condensate produced from stranded gas field have been a major concern to producing companies due to unavailability of nearby oil flow stations to receive the condensate, which have resulted to abandonment of such fields. This work seek to improve the thermodynamic properties (Heat Capacity, Heating Value, Specific Heat capacity, Heat of Vaporization and Enthalpy) of the export gas through condensate spiking. This was carried out by simulating a natural gas plant, consisting of condensate line and spiking mixer. The simulation was done using Aspen HYSYS, to include the point at which the condensate stream was spiked into the high-pressure dry natural gas stream. Phase envelope and hydrate formation curve for the streams (dry natural gas and the mixture after spiking) were obtained. Case study in HYSYS was used to carry out Sensitivity analysis, to determine the effect of temperature, pressure and flow rate of the condensate on the mixture (export gas). Economic analysis of the project was carried out. Results obtained from the thermodynamic analysis shows that the thermodynamic properties of the export gas after spiking improves, such that the heating value and enthalpy of the export gas increases. The phase envelops shows that hydrate will not form in the export gas streams. Through the sensitivity analyses, the effect of variation in the parameters of the condensate shows that the vapour fraction of the export gas increases as the temperature increase and decrease as the pressure increases. The maximum condensate flow rate was obtained to be 12,500 bbl/day, at a dry gas flow rate of 382.2 MMScfd, for a maximum vapour fraction of 0.953, with this operating parameters, flow assurance problem of hydrate formation, liquid holdup and high pressure drops along the pipeline with be eliminated. Hydrocarbon dew point of −13.41°C was obtained showing that liquid hydrocarbon will not condense out of the gas during transportation. Economic analysis shows that the NPV and IRR are $432.778 million and 33%, indicating that the project is viable for investment. Therefore, it is possible to spike condensate into treated export gas without causing flow assurance problems, and helps mitigate against risk associated with environmental pollution.