Study on the origin of primary sulfur in natural gas of Daniudi gas reservoir

H₂S has always been found in the long-term production process in multi-gas wells of Daniudi lower Paleozoic gas reservoir, but the cause of sulfur formation has been unclear. In this paper, the whole causes of sulfur in gas reservoir were comprehensively analyzed and investigated one by one. On the basis of confirming the origin of thermochemistry, δ³⁴S isotope analysis was used to determine the H₂S of Daniudi gas reservoir as the thermochemical reduction TSR of sulfate. Then through the reduction reaction simulation test, full-rock XRD scanning, residual organic matter detection, etc., the formation mechanism, reaction conditions and control factors of H₂S in lower Paleo gas reservoir were ensured. It is revealed that the necessary conditions for the formation of TSR reaction of sulfate thermochemical reduction are rich gypsum, enough hydrocarbon gas, closed reduction environment, over 200 ℃ and the participation of formation water.