Z-pred
Some of the key factors which impact where the H₂S and sulfide species exist in a sour system are pressure, temperature, fluid volumes, aqueous phase pH and partitioning coefficients.
The Rawwater Z-pred sulfide-partitioning calculator computes equilibrium sulfide concentrations in aqueous, oil and gas phases for any temperature, pressure and water chemistry. Essential for understanding the severity of oilfield reservoir souring, the software also forms part of the modules used in DynamicTVS©. Z-pred provides calculation of the partitioning of hydrogen sulfide in all wellstream fluid phases for both two-phase and three-phase systems under defined downhole and topside conditions.
In the simple examples below, we show how changes in temperature, pressure and pH each result in an increase in the gas phase H₂S concentration as result of the redistribution of the same total mass of sulfide species in the closed system.
The actual Z-pred calculator, which resides in our Client Area, allows for multiple changes to pressure, temperature, water phase pH, fluid volumes and oil density – as well as different starting point H₂S or sulfide measurements – to be inputted, for total phase results to be displayed.
Example 1 – shows the starting conditions, before any changes are made
Example 2 – temperature increase from 50°C to 80°C
Note that the increase in system temperature from 50°C to 80°C results in an increase in the gas phase H₂S concentration from 911.7ppmv to 1,076.4ppmv, as result of the redistribution of the same total mass of sulfide species in the closed system.
Example 3 – pressure decrease from 25atma to 5atma
Note that the decrease in system pressure from 25atma to 5atma results in an increase in the gas phase H₂S concentration from 911.7ppmv to 1,584.0ppmv, as result of the redistribution of the same total mass of sulfide species in the closed system.
Example 4 – pH decrease from 6.5 to 4.5
Note that the decrease in the aqueous phase pH from 6.5 to 4.5 results in an increase in the gas phase H₂S concentration from 911.7ppmv to 976.9ppmv, as result of the redistribution of the same total mass of sulfide species in the closed system.
All changes, at a glance
