玛湖凹陷二叠系风城组碱湖云质岩储层成岩作用

通过偏光显微镜和扫描电镜观察，结合能谱、包裹体温度、同位素、X射线衍射及有机地球化学等分析方法，研究了准噶尔盆地玛湖凹陷二叠系风城组碱湖云质岩储层的成岩作用类型和成岩演化序列。研究结果表明：①玛湖凹陷二叠系风城组云质岩储层为典型的碱湖沉积，发育多种云质岩类，以云质凝灰岩和云质沉凝灰岩为主。②云质岩中成岩作用类型较多，其中脱玻化作用较为普遍，析出矿物主要有硅质矿物、钙镁碳酸盐矿物、铝硅酸盐矿物和非钙镁碳酸盐类矿物等；云质岩中的溶蚀作用主要为铝硅酸盐矿物和盐类矿物的溶蚀，发育成岩缝和多期构造缝，具有3期油气充注。③研究区风城组多数云质岩演化已进入中成岩A期，少量进入中成岩B期，脱玻化作用发生在早成岩A期；发育3期白云石，主要发育于早成岩B期；非钙镁碳酸盐矿物主要形成于同生期；存在3期溶蚀作用，以中成岩A期为主；油气最早充注于早成岩B期，以中成岩B期充注时间最长。脱玻化作用、长石和非钙镁碳酸盐矿物溶蚀作用及构造形成的裂缝是玛湖凹陷风城组云质岩成储的关键。④脱玻化作用形成的孔隙为早期油气充注提供了储集空间，碱湖优质烃源岩热演化释放的酸性流体对云质岩中铝硅酸盐矿物和盐类矿物进行溶蚀，有效改善了储层的储集性能。

Diagenesis of alkaline lacustrine dolomitic reservoirs of Permian Fengcheng Formation in Mahu Sag

Based on the data of polarizing microscope identification,scanning electron microscope energy spectrum analysis,inclusion temperature measurement,oxygen isotope analysis,X-ray diffraction and organic geochemical analysis,the diagenesis and diagenetic evolution sequence of alkaline lacustrine dolomitic reservoirs of Permian Fengcheng Formation in Mahu Sag of Junggar Basin were studied. The results show that:(1)The dolomitic reservoirs of Permian Fengcheng Formation in Mahu Sag are typical alkaline lacustrine deposits,and are composed of various dolomitic rocks,which mainly consists of dolomitic tuff and dolomitic sedimentary tuff.(2)Devitrification of dolomitic rocks is common,authigenic minerals mainly consist of siliceous minerals,calcium magnesium carbonate minerals,aluminosilicate minerals and non-calcium magnesium carbonate minerals,dissolution mainly occurs in aluminosilicate minerals and saline minerals,diagenetic fractures and multi-stage structural fractures are generally developed,and hydrocarbon charging exhibits three major stages.(3)Most dolomitic rocks have entered phase A of mesodiagenesis,a few followed by phase B of mesodiagenesis,and devitrification occurred in phase A of eodiagenesis. Authigenic dolomites are formed in three different periods from early to late, and are mostly developed in phase B of eodiagenesis. Non-calcium magnesium carbonate minerals are mainly formed in syndiagenetic stage. Dissolution with three stages is mainly developed in phase A of mesodiagenesis. Hydrocarbon charging began in phase B of eodiagenesis,and kept successive charging for the longest time in phase B of mesodiagenesis. Devitrification,dissolution of feldspar and non-calcium magnesium carbonate minerals,and structural fractures are imperative to the formation of dolomitic reservoirs of Fengcheng Formation in Mahu Sag.(4)The reservoir pores formed by devitrification provide reservoir space for early hydrocarbon charging. The acidic fluid released by thermal evolution of high-quality alkaline lacustrine source rocks dissolved aluminosilicate minerals and saline minerals in dolomitic rocks,which effectively improves reservoir properties.