四川盆地须家河组砂岩储层中自生绿泥石的来源与成岩演化

由于在成岩过程中能有效抵抗上覆岩层的机械压实作用，抑制石英在颗粒表面成核的数量，自生绿泥石包膜对四川盆地须家河组砂岩储层的原生粒间孔的保存起到了重要的作用。须家河组早期自生绿泥石物质来源主要有同沉积的富铁沉积物的溶解、河流溶解铁的絮凝沉淀以及相邻泥岩压释水的贯入，主要以新生沉淀形式集中形成于同生期至早成岩早期。成岩中后期，由于下伏富Mg流体沿裂缝系统的持续进入，须2段的自生绿泥石的继续生长得到了充足的物质来源，其MgO的含量随地层深度明显增加，而须4段后期再生长现象不明显。该区自生绿泥石包膜对储层物性的影响通过绿泥石含量与参与孔隙度的关系以及孔隙度分布频率图可以得到较好的评估。从对储层的影响来说，自生绿泥石包膜存在一个最合适的厚度值，超过或低于这个值就会对储层造成负面影响而无法保护储层，该区此最适合的厚度值为5～10 μm。

Origin and Diagenesis of Authigenic Chlorite within the Sandstone Reservoirs of Xujiahe Formation, Sichuan Basin, China

The authigenic chlorite grain coatings or pore linings play an important role in preserving primary porosities effectively by resisting the compaction of the overlying rock and decreasing the number of nucleation of authigenic quartz on the surfaces of grains in reservoir sandstones of Xujiahe Formation, Sichuan basin, China. The early materials forming the grain coatings of chlorite are involving the solution of the syn depositional Fe rich sediments, flocculation of the soluble fluvial Fe and the intrusion of the compacting fluids in the adjacent shale bed. And moreover, the grain coatings mainly formed as news neomorphic precipitations between syngenesis and early eodiagenesis. Due to the Continuous intrusion of the Mg rich fluids through the fracture system ,the authigenic chlorites in Xujiahe Formation II are in possession of the enough materials to re grow in mesodiagenesis, furthermore, the contents of MgO are increasing with the increasing depths distinctly. However, in Xujiahe Formation IV sandstones, the re growth of chlorite is not obvious. The impact of the chlorite grain coatings to the reservoir properties are well evaluated by the relation of the chlorite contents versus the porosity values and the porosity distribution figure in study area. As for the influence to reservoir quality, there is an "optimum thickness" for chlorite grain coatings to effectively preserve the porosities, but without radically decreasing permeability and increasing the microporosity in reservoirs. Within Xujiahe Formation sandstones, the optimum thickness of chlorite grims seems to between 5 μm and 10 μm.