The Research On Diagenesis And Aqueous Medium In Upper Paleozoic Of Zizhou-Qingjian

By visual observation,identification and statistics of many casting thin sections and by means of scanning electron microscope and X-Ray diffraction, the major types,the distribution of the authigenic minerals and diagenesis of the Upper Paleozoic sandstone reservoirs in Zizhou-Qingjian gas area are studied as well as characters of aqueous medium influencing the authigenic minerals about the sandstone reservoirs in the Upper Paleozoic. The aqueous medium of the Zizhou-Qingjian gas area shows that into two stages.It had been a long acid stages first.The acid medium resulted form the carboxylic acid generated during the maturation of kerogen and the percolation of the fresh water having carbon dioxide second. It's concluded that the history of the pore can be classified into two stages in this area: the secondary porosity formed and it reduced.This area have experienced diagenesis of mechanical compaction, cementation, metasomasis and dissolution. Based on synthesis analyses of autogenous minerals associations and clay minerals transform and pore types as well as evolution of organic matter etc, The Upper Paleozoic sandstone have already entered into the late diagenesis A subage and most have reached the late diagenesis B subage even C subage.The formation of secondary pore contributes to feldspthic and carbonate corrosion as well as dehydration reaction of clay mineral.Resulting of CO₂ and organic acid, providing by inorganic diagenesis and organic thermal mature evolution, corroding soluble components.According to the characters of the porosity and diagenesis of the sandstone, we discussed the diagenesis' effects or controlling factors on the porosity. It suggest that the cements occupied the most porosity and dissolution provides more secondry porosity, it is positive to the reservoir.Base on all the study, we conclude out that the diagenesis controls the reservoir quality besides sedimental facies. Because of less compacting, more chlorite coating, less cementation and dissolution the dissolution of early cements together with the chlorite coating generated abundant secondary porosity in the sandstone of the Upper Paleozoic section.