塔里木盆地志留系沥青砂岩岩石学特征及其意义

为了探讨塔里木盆地志留系沥青砂岩的成因和演化期次 ,利用岩石学、有机岩石学的方法 ,研究了该套沥青砂岩中沥青的表观特征、显微特征、沥青反射率和荧光特征 ,以及砂岩的岩石学特征、成岩作用特征、成岩序列、成岩阶段划分等 ,认为塔里木盆地志留系沥青砂岩中有灰黑色至褐灰色干沥青、软沥青和稠油 .宏观上 ,有均匀分布 (块状 )和非均匀分布 (斑状 ,又分为顺层状、透镜状、裂缝状等 )二种 .微观上可分为充填状和侵染状 .砂岩的成岩序列为 :机械压实 (颗粒塑性变形 )→粘土膜形成及转化→石英自生加大、铝硅酸盐溶解→连晶状方解石沉淀→石英压溶加大→方解石向铁白云石转化→绿泥石沉淀 ,其成岩阶段可划分为 :早成岩 A亚期、早成岩 B亚期、晚成岩 A亚期和晚成岩 B亚期 .沥青反射率 BRo反映了沥青的形成受热作用影响不大 ,BRo大小实际上反映生物降解程度的强弱 ,志留系沥青砂岩主要是由较强烈的生物降解作用而造成的 .志留系沥青砂岩的成岩作用特征等资料证明 ,沥青砂岩的形成是烃类多期次注入的结果 .

Petrological Characteristics of the Silurian Asphaltic Sandstones in Talimu Basin and the Significance of Studying Them

In order to investigate the origin and evolution of the Silurian asphaltic sandstones in Talimu Basin, the authors studied in detail the macrocharacter, microcharacter, reflectance (Ro%) and fluoroscopic character of the asphalts in the sandstones, the characteristics of the sandstones in petrology and diagenesis, diagenetic succession and diagenetic stage division by means of petrology and organic petrology. In the Silurian asphaltic sandstones from Talimu Basin, there are grayish-black—brownish-gray dry asphalts, soft asphalt and viscous crude oil. Macroscopically, there are two types of asphalt distribution, one is uniform distribution (massive), and another is non-uniform distribution (mottled, being further divided into bedding, lenticular and fracturing). Microscopically, they are classified into packing and disseminating distributions. The diagenetic succession of the sandstones is as follows: mechanical compaction (plastic deformation of grains)→ formation and conversion of clay film→ authigenic overgrowth of quartz and dissolution of aluminosilicate→ precipitation of crystal stock calcite→ pressolutional overgrowth of quartz→ conversion form calcite to ankerite→ precipitation of chlorite. The diagenetic stage can be divided into subphase A of eodiagenesis, subphase B of eodiagenesis, subphase A of telodiagenesis and subphase B of telodiagenesis. The asphalt reflectance (BRo) shows that formation of the asphalt was hardly affected by thermal action. Practically, the Silurian asphaltic sandstones were formed mainly by intense bio-degradation and the BRo value reflects the bio-degradation grade of the asphalt. Diagenesis data indicate that the Silurian asphaltic sandstones are the products of multiple fillings of hydrocarbon.