石油伴生H2S的成因分析——以鄂尔多斯盆地彭阳油田为例

彭阳油田是鄂尔多斯盆地新探明的低H₂S含量的油田，其主力产层为侏罗系延安组，原油伴生H₂S含量最高为0.115%，明确H₂S成因机制对于油田合理开发及安全生产具有重要意义。基于储层硫化物及油田水硫同位素的系统分析，预测了侏罗系延安组原油伴生H₂S的成因。延安组主要发育集块状、斑点状、斑块状、星点状等黄铁矿类型，其δ³⁴S值为-1.9 ‰~10.1 ‰，其中，斑块状、集块状黄铁矿为沉积早期快速结晶成因，斑点状、星点状黄铁矿为硫酸盐还原菌还原作用成因。石膏的δ³⁴S值在16.8 ‰~17.7 ‰，为后期成岩阶段的产物，其并非H₂S的硫元素来源。油田水的δ³⁴S值较高，平均为37.9 ‰，这主要是由于硫酸盐还原菌还原作用消耗地层水中的³²S，使水体相对富集³⁴S。黄铁矿后期溶解和硫酸盐还原菌还原有机硫化物均可释放SO₄^2-，使侏罗系油田水具有较高的SO₄^2-浓度，为H₂S的生成提供了充足的物质基础。侏罗系地层水的矿化度、pH值及地层温度等物理化学条件均利于硫酸盐还原菌的生存，为硫酸盐还原菌还原作用提供了适宜的反应场所。综合分析认为，彭阳油田侏罗系原油伴生H₂S为硫酸盐还原菌还原成因。

Genesis analysis of the petroleum associated H2S: a case study of Pengyang oilfield in Ordos Basin

Pengyang oilfield is a newly explored oilfield with low H₂S content in Ordos Basin. Its main oil-producing layer is Jurassic Yan'an Formation, and the content of the petroleum associated H₂S is up to 0.115%. To clarify the H₂S generation mechanism is of great significance for rational development and safe production of the oilfield. Based on the systematic analysis of sulfides in reservoir and sulfur isotopes in oilfield water, the paper predicts the origin of petroleum associated H₂S in the Jurassic Yan'an Formation. Yan'an Formation is dominated by lumpy, spotted, patched and star-pointed pyrites, of which δ³⁴S value ranges from -1.9 ‰ to 10.1 ‰. Among them, patched and lumpy pyrites are rapidly crystallized in the early sedimentation period, while spotted and star-pointed pyrites are deposited due to the reduction by sulfate reducing bacteria. The δ³⁴S value of gypsum ranges from 16.8 ‰ to 17.7 ‰, indicating that it is the product in the later diagenetic stage and is not the source of sulfur element of H₂S. The δ³⁴S value of oilfield water is relatively high, with an average of 37.9 ‰. The reason for this is that ³²S in the formation water is consumed by the reduction of sulfate reducing bacteria, and thus ³⁴S is relatively rich in the water body. The late dissolution of pyrite and the reduction of organic sulfide by sulfate reducing bacteria can generate SO₄^2-, by which the oil reservoir water of the Jurassic system possessed a high concentration of SO₄^2- and provided a sufficient material basis for H₂S generation. Physical and chemical conditions of the Jurassic formation water such as salinity, pH value and formation temperature were conducive to the survival of sulfate reducing bacteria and offered a suitable reaction zone for the reduction of sulfate reducing bacteria. The comprehensive analysis indicates that the petroleum associated H₂S of the Jurassic system in Pengyang oilfield is the product of the reduction of sulfate reducing bacteria.