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

By probing into the high H_2 S-bearing gas reservoir in Siehuan basin,this text found the close relationship between high- quality reservoir and H_2S:the higher H_2 S 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 H_2S in the marine strata of Sichuan basin,which developed some high-quality reservoirs,so therer is certain connection between H_2 S 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 H_2S and CO_2 by hydrocarbon in the high temperature.So,TSR is the main process of H_2S generation.The research found that the reservoirs pore have preliminary improvement due to dissolution of gypsiferous rock(SO_4~(2-)).While H_2 S from the TSR dissolved in the water,the hydrosulphuric acid was generated largely,the strong resoMng ability of hydrosulphuric acid accelerate the burial dissolution of dolostone in the carbonate reservoirs and form the bedded characteristical,and mossystructure pore and rug 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 authigenie 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 H_2 S,and the homogenization temperature is usually above 160℃ which satisfy the TSR reaction temperature.The sulfur isotopes of H_2 S 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 H_2 S-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 H_2S content in strata.