热化学硫酸盐还原作用对碳酸盐岩气藏的化学改造——以川东北地区长兴组-飞仙关组气藏为例

目前在川东北地区长兴组—飞仙关组已发现普光、渡口河、铁山坡、罗家寨等多个高含H2S的大、中型气田。通过天然气地球化学特征、流体包裹体盐度和岩心及薄片的镜下详细观察后认为,川东北地区长兴组—飞仙关组的大多数气藏遭受了热化学硫酸盐还原作用(TSR)的化学改造,TSR的改造主要表现在3个方面:1使C2 重烃相对于CH4、12C相对于13C优先被消耗,造成天然气干燥系数变大和碳同位素变重;2由于TSR产生的大量淡水的加入,使气藏的原生地层水被稀释,造成地层水盐度降低;3TSR相关流体(烃类和H2S等)与储层岩石之间的相互作用使储层被溶蚀和硬石膏发生蚀变,造成储层孔隙度增大,从而对改善其物性具有重要意义。

Effect of Thermochemical Sulfate Reduction upon Carbonate Gas Reservoir: An Example from the Northeast Sichuan Basin

Gas geochemistry, fluid inclusion salinity, core observation and thin section analysis indicate that the Permian-Triassic Changxing-Feixianguan gas reservoir experienced chemical alteration of thermochemical sulfate reduction (TSR) since the middle Yanshanian period. The TSR alteration is mainly shown in three aspects: (1) The C_ 2 and 12C relationships to CH_4 and 13C are preferentially consumed, resulting in the gas dryness coefficient to be larger and carbon isotope heavier; (2) A great deal of water produced by TSR makes the original formation water in the gas reservoir diluted, so that the salinity of formation water is reduced correspondingly; (3) TSR and its products, CO_2 and H_2S, make the dolomite and anhydrite dissolved, which increases the porosity and then improve the physical property of reservoir.