Prediction of Acid Gas Generation in the Petroleum Industry

摘要

Although generation of environmentally harmful hydrogen sulfi de is considered to be related to sour gas fi elds, sweet gas reservoirs and waste fl uids, travertine springs and geothermal fi elds may also produce acid gas (H2S and CO2) under certain conditions. The potential parameters infl uencing such a possibility need to be fully investigated to evaluate the extent of the consequences and predict hydrogen sulfi de generation accordingly. Reports on hydrogen sulfi de production at different regions and fi elds were gathered worldwide for the cases when some of them did not have such a problem previously. In order to inspect different aspects of these case studies, some other regions with no hydrogen sulfi de content were selected as control. In all cases water samples were taken carefully for chemical analysis in the laboratory. Besides, mineral compositions were characterised in some cases for better evaluation. In order to give a thorough prospect of hydrogen sulfi de production, a geochemical model was prepared. In situ engineering geological conditions, especially pressure and temperature, were assigned in the model to investigate the possibility of H2S generation using PHREEQC software. The results of modelling revealed that although many similarities existed between mineral compositions of the cases, certain formations were particularly prone to hydrogen sulfi de generation. For better evaluation, important exchangeable cation ratios such as potassium/ sodium, calcium/magnesium and ion proportions like sulfate and chloride were calculated as trends of the formations. As expected, the model could successfully monitor a higher ratio of SO4 2- and Cl- in potential H2S generator formations. Wide variation in percentage of HCO3- was considered as a secondary observatory parameter for better estimation. In addition, it was noticed that higher anion content created an environment ready to absorb any cations and this makes H2S generation easier. Finally, using correlations between predictors and estimators for low depth and deep samples defi ned the degree of effectiveness for every sample.