During the development of the Fuyu oil reservoir in the Longxi block of Daqing,hydrogen sulfide (H2S) was discovered and exceeded the threshold value (15.0 mg/m3), but its generation mechanism is still unclear. To investigate this, the mechanism of H?S generation in the Longxi block formation was investigated through laboratory experiments on H?S generation,combined with numerical simulations using PHREEQC and CMG software.The results show that the mechanism of H2S generation in high?temperature reservoirs (100~125 ℃) is sulfate thermochemical reduction reaction, with viscosity of H2S generated ranges from 3.20 mg/m3 to 6.10 mg/m3.In low?temperature reservoirs (≤60 ℃),the mechanism of H2S generation is sulfate?reducing bacteria reduction reaction,with a maximum H2S viscosity of up to 29.70 mg/m3.Fracturing fluid reduces the temperature in the near?wellbore zone, promoting SRB proliferation, and the viscosity of H2S generated in a short time increases by 7.5 times compared to the sulfate?reducing bacteria reduction reaction in produced water. The mass concentrations of H2S generated by the reaction of 1 m3 acid with the core and plug containing 0.80 mol FeS are 3 330.69 mg/m3 and 11 466.75 mg/m3,respectively. Therefore, fracturing and acidification are the main mechanisms for the generation of H2S during the development of the Fuyu oil reservoir in the Longxi block.
