TSR对深部碳酸盐岩储层的溶蚀改造——四川盆地深部碳酸盐岩优质储层形成的重要方式

Dissolution and alteration of the deep carbonate reservoirs by TSR:an important type of deep-buried high-quality carbonate reservoirs in Sichuan basin.

四川盆地海相层系发现的大气藏部含或高舍硫化氢,都发育一定厚度的优质储层,而且优质储层与硫化氢分布具有密切的关系,即气藏硫化氢含量越高,储层性质越好,气藏产能也越大。研究发现,在 TSR(硫酸盐热化学还原反应)过程中,随着膏质岩类的溶解(为 TSR 反应提供 SO_4^(2-)),使储集孔隙初步得到改善;而 TSR 产生的硫化氢溶于水形成的氢硫酸,具有强烈腐蚀性,加速了储层中白云岩的溶蚀,形成孔隙极其发育的海绵状孔洞体系,并呈层状分布。电镜下可以清晰看到白云石晶面的溶蚀坑及溶孔中 TSR 产生的硫磺晶体。溶孔中自生碳酸盐的碳同位素在-10.3‰～18.2‰,而地层碳酸盐的碳同位素在+3.7‰～+0.9‰,证实了 TSR 过程中有机-无机的相互作用,即有机成因烃类中的碳转移到次生碳酸盐岩中。包裹体分析表明,次生方解石中的包体富含硫化氢,且均一温度多数在160℃以上,具备 TSR 发生的温度条件;硫化氢和硫磺的硫同位素比地层硫酸盐的硫同位素偏轻8‰左右,是 TSR 作用的证据。因此高含硫化氢气藏的优质储层是在早期埋藏溶蚀作用的基础上,后期发生 TSR 及其形成的酸性流体对深埋碳酸盐岩储层再次进行深刻改造和强烈溶蚀作用的结果;同时可以运用硫化氢来预测碳酸盐岩优质储层的分布。

By probing into the high H：S-bearing gas reservoir in Sichuan basin,this text found the close relationship between highquality reservoir and H2S： the higher H2S content the strata bear, the better the reservoirs become and the high gas yield the strata produce. The entire big gas reservoir has some or high contents of H2 S in the marine strata of Sichuan basin, which developed some high-quality reservoirs, so therer is certain connection between H2S and reservoirs. TSR （thermochemical sulfate reduction ） is the chemical process between hydrocarbon and sulfate in thermodynamic drive, which is the process that sulphate minerals deoxidized to generate H2S and CO2 by hydrocarbon in the high temperature. So,TSR is the main process of H2S generation. The research found that the reservoirs pore have preliminary improvement due to dissolution of gypsiferous rock （SO4^2-）. While H：S from the TSR dissolved in the water, the hydrosulphuric acid was generated largely, the strong resolving ability of hydrosulphuric acid accelerate the burial dissolution of dolostone in the carbonate reservoirs and form the bedded characteristical, and mossystructure pore and vug system with extremely good porous and permeability. The disolution pores and inter sulphur grains were seen distinctly in the thin section. The carbon isotopes of authigenic carbonate are between - 10.3‰ and - 18.2‰ in the corroded pore,and those of the strata carbonate are from ＋ 3.7‰ to 0.9‰. It proved the organic and inorganic interaction, the organic hydrocarbon carbon transferred to secondary carbonate. The analysis show the calcite inclusion contain high-grade H2 S, and the homogenization temperature is usually above 160℃ which satisfy the TSR reaction temperature. The sulfur isotopes of H2S and sulphur are depleted about 8‰ that compare to that of strata carbonate,which is a proof of TSR. Based on the early burial dissolution, the high-quality reservoirs with high H2S-bearing gas pool were generated as the late TSR and its producing acidic liquid corrode the deep burial carbonate reservoirs again. Based on this conclution, we can predict the perspective area of the high-quality carbonate reservoirs by the H2S content in strata.