Study on the Generation Mechanism of Hydrogen Sulfide by Thermochemical Sulfate Reduction in Heavy Oil Hot Water Flooding at Low Temperature

Hydrogen sulfide (H2S) is a hazardous andcorrosivebyproduct generated during heavy oil recovery, particularly duringhot water flooding. Previous studies on factors influencing H2S generation during hot water flooding have been mainly focusedon high temperatures (>250 & DEG;C), which may not accurately representreservoir conditions. Moreover, the concentration of H2S produced by hot water flooding at low temperatures exceeds thestandard. In this study, experiments were conducted on hot water floodingat low temperatures (110-150 & DEG;C). The mechanism of reactantsand reaction conditions on H2S generation was investigated.The results showed that thermochemical sulfate reduction (TSR) wasthe primary reaction type responsible for H2S generation,while aquathermolysis and pyrite oxidation reactions weakly or didnot occur. The reactivity of TSR was directly proportional to reactiontemperature and time, while inversely proportional to reaction pH.The formation of oxidants ([MgSO4](CIP) and HSO4 (-)) was also found to be crucial for TSRinitiation. Unstable organic sulfur-containing compounds were oxidizedto produce CO2, H2S, SO3, and solidbitumen, which further sustained the autocatalytic reaction. Low temperatureTSR was found to consume the saturated fraction in heavy oil and convertinorganic sulfur to organic sulfide. The increase in pH inhibitedthe conversion of inorganic sulfur to organic sulfur, resulting ina higher percentage of the saturated fraction. This study providesnew insights into the low temperature TSR reaction mechanism and theorigin of H2S, which can aid in better understanding andmitigation of the associated risks during heavy oil recovery.

Automated summary

This study investigated the mechanism of hydrogen sulfide generation during low temperature hot water flooding, and found that thermochemical sulfate reduction (TSR) was the primary reaction type. TSR was directly proportional to reaction temperature and time, while inversely proportional to reaction pH. TSR consumed the saturated fraction in heavy oil and converted inorganic sulfur to organic sulfide. This study provides new insights into the low temperature TSR reaction mechanism and the origin of H2S, which are important for understanding and mitigating risks during heavy oil recovery.