<p>The J Oilfield in eastern China is rich in oil and gas resources, but hydrogen sulfide (H₂S) contamination has been identified within its production blocks, requiring clarification of its genetic sources. This study combines geological characterization of the target blocks with physicochemical analyses of rock, oil, natural gas, and formation water samples from Block A and Block B, supplemented by sulfur isotope measurements. Results demonstrate that all tested samples contain sulfur. The normal composition of crude oil and the dryness coefficient of natural gas indicate that both blocks produce wet gas. Notably, natural gas from Block B contains elevated carbon dioxide levels (up to 85%), a hallmark of thermochemical sulfate reduction (TSR). Total Dissolved Solids in formation water vary significantly between the blocks: Block A exhibits extreme sulfate ion concentration gradients (13.9 to 4,162.1 mg/L), consistent with bacterial sulfate reduction (BSR), while Block B shows high sulfate ion concentrations (381.2 to 3,459.2 mg/L). Sulfur isotope analysis reveals distinct δ³⁴S signatures: H₂S in Block A ranges from δ³⁴S = -2.5‰ to 3.8‰, H₂S in Block B ranges from δ³⁴S = 14.2‰ to 15.8‰, and the sulfur isotope fractionation values between samples further demonstrate that Block A exhibits BSR-related characteristics, with sulfate ions in formation water inferred as the sulfur source, Block B exhibits TSR-related features linked to Cretaceous evaporite salts as the sulfur source. Laboratory simulations of H₂S genesis were conducted, successfully validating the aforementioned inferences.</p>