中国三叠系陆相砂岩中自生绿泥石的形成机制及其与储层孔隙保存的关系

研究了中国三叠系陆相砂岩中自生绿泥石的产状、成因及其与储层发育的关系,证明了以孔隙环边衬里方式产出的绿泥石是深埋地层中孔隙保存的重要机制,环边绿泥石的沉淀及其在成岩过程中的再生长不仅提高了岩石的机械强度和抗压实能力,还降低了自生石英在碎屑颗粒上的成核数量并抑制石英的次生加大,从而使砂岩中的原生和次生孔隙得以保存.砂岩中自生绿泥石的成因还表明这种产状的绿泥石是三角洲前缘推进的良好标志,同时也说明中国中新生代的湖泊可能并不是真正的淡水湖泊,它们或多或少具有一定的盐度,其对海源流体具有继承性.

Formation mechanism of authigenic chlorite and relation to preservation of porosity in nonmarine Triassic reservoir sandstones, Ordos Basin and Sichuan Basin, China

The occurrence and formation mechanism of authigenic chlorite are studied in this paper. The cases are from Upper Triassic nonmarine reservoir sandstones of Ordos Basin and Sichuan Basin, China. Pore lining and grain coating are the most important occurrences of chlorite, which are similar to the (marine) sandstones reported by published literature. Chlorite precipitation occurred at the early stage of (diagenesis), but continued chlorite growth would have been localized on existing chlorite surfaces. This (occurrence) of chlorite plays an important role in protection of porosity in deeply buried reservoir sandstones by the following mechanism: (1) the pore lining and grain-coating chlorite and its overgrowth during buried diagenesis have enhanced the mechanical strength of rocks and ability of resistant to compaction; (2) the chlorite isolates detrital quartz surfaces from contact with pore water, thus preventing nucleation of authigenie quartz and consequently preserving pores in sandstone. It has been found that more authigenic chlorites are distributed in the propulsive delta environment, especially the delta front in the setting of lakes. This shows that Mesozoic-Cenozoic lakes in China are not really freshwater lakes. They have more or less salinity and some successive character for ocean-origin fluid.