Numerical Study of Microbial Hydrogen Sulphide Generation in Hydrocarbon Reservoirs

The present work aims to represent and predict microbial hydrogen sulphide
generation and to investigate the effects of CO2 components on the souring process
through reactive transport simulation and mathematical modelling. The influence of
key parameters including CO2, salinity, and temperature on the microbial growth of
sulphate reducing bacteria (SRB) is simulated using the kinetic and multispecies
reactive transport simulator PHREEQC coupled with a multiphase Buckley Leverett
model. Simulation results are then validated against some experimental data from the
literature. To assess the role of each of the influential factors, a sensitivity analysis is
performed at varying CO2 concentrations (4.403×10-4 - 52.24×10-4) mol/kgw, salinity
0.5-0.8 meq/ml (40000-27000ppm), and temperature 40-100 F (4.5-37.8°C). The
resulting data are then used to mathematically relate CO2 concentration, salinity, and
temperature to the concentration of hydrogen sulphide and souring onset time by
applying response surface methodology (RSM). The results suggest that the souring
onset time increases as the CO2 concentration increases (CO2 ≥ 52.24×10-4) and also
as injection temperature and salinity increase. Higher temperatures are found to delay
souring onset as the injection water salinity is increased. In Addition, a lower
concentration of CO2 results in an early onset time if the temperature is kept low at
40-60 F (4.5-15.6°C). The findings also indicate that temperature and salinity will
affect the hydrogen sulphide concentration. The highest hydrogen sulphide
concentrations are observed when the temperature is ranged between 40-70 F (4.5-
21.1°C) under a salinity range between 0.5-0.65 meq/ml (40000-33000ppm).
Moreover, CO2 has a significant effect on hydrogen sulphide concentration, where at
temperatures between 40-70 F (4.5-21.1°C), higher hydrogen sulphide concentrations
are obtained.