普光气田长兴组白云岩地球化学特征及其成因意义

普光气田区长兴组白云岩的矿物组成与地球化学特征研究表明，自东南向西北方向，由普光8井至普光5井至普光6井，长兴组白云岩白云石颗粒的结晶程度和有序度总体上逐渐变高，其Fe、Mn、AI、K、Na、Sr含量及Mg^2＋／Ca^2＋比值总体呈降低的趋势；而氧同位素值逐渐降低，碳同位素值略增高，两者具负相关关系，这反映出白云石化作用与混合水无关；普光6井结晶白云岩87Sr／86Sr比值高于晚二叠世末古海水，说明白云石化流体并非长兴期古海水。研究认为长兴组泥-微晶白云岩由长兴期蒸发浓缩形成的高镁卤水交代灰泥丘而形成，属准同生白云石化作用成因，为非-差储层；结晶白云岩及碎裂化白云岩的白云石化流体应来自二叠纪高盐度海源地层水。属埋藏成因，可为优质储层。

Geochemical characteristics and formation of dolostones from the Changxing Formation at Puguang gas field in Sichuan Basin

The study on mineral and geochemical characteristics of dolostones from Changxing Formation at Puguang gas field in Sichuan Basin shows that the degrees of crystallization and order are generally increased from southeast to northwest. For dolostone samples from well Puguang 8 to Puguang 5 and Puguang 6, Fe, Mn, Al, K, Na and Sr concentrations and Mg2＋/Ca2＋ decrease gradually, δ18OPDB, also decreases, whereas δ18OPDB increases slightly,showing a negative relationship, which suggest that the dolomitization was not related to mixed water. Meanwhile, 87Sr/86Sr Of crystalline dolostones of well Puguang 6 are systematically higher than that of paleo-seawater of the Late Permian, suggesting the dolomitization fluid was not derived from Changxing stage paleo-seawater. It is concluded that the micritic dolostones and dolomicrites of Changxing Formation are mainly penecontemporaneous dolostones formed from rapid metasomatic diagenesis by hypersaline water, which replaced limestone. These rocks are not gas reservoir or are bad gas reservoir. The crystallized dolostones and cataclastic dolostones formed through buried diagenesis and the dolomitization fluid were hypersaline formation water derived from Permian seawater, and thus can be excellent gas reservoirs.