塔中地区志留系沥青砂岩成岩作用及其对储层性质的影响

运用沉积学原理对塔中地区志留系经历复杂成岩演化的沥青砂岩进行研究分析,了解到该岩石主要经过压实作用、胶结作用和溶蚀作用等成岩作用。其胶结物的主要类型有绿泥石、伊利石、高岭石、伊-蒙混层等粘土矿物以及碳酸盐矿物、石英、长石、黄铁矿等。孔隙类型以粒间孔隙、粒内孔、铸模孔、特大孔、裂缝孔隙等为主,其中以粒间孔隙最为发育,低地温梯度有利于在深层形成次生孔隙。志留系沥青砂岩储层物性受沉积和成岩双重因素的影响,成岩演化阶段处于晚成岩A期。根据影响储层物性的储层成岩作用,可将成岩相类型划分为不稳定碎屑溶蚀成岩相、压实-弱溶蚀成岩相、压实充填成岩相、压实压溶成岩相、碳酸盐胶结成岩相等几种主要类型,成岩相类型决定了储层性质,不稳定碎屑溶蚀成岩相和压实-弱溶蚀成岩相是本区较好的油气储层。

DIAGENESIS OF SILURIAN ASPHALT SANDSTONES IN TAZHONG AREA AND ITS IMPACT ON RESERVOIR QUALITY

Silurian asphalt sandstones in Tazhong Area have undergone a complex diagenetic evolution.According to the detailed examination of petrography,SEM,Xray diffraction,electron microprobe and cathodoluminesecence,diagenetic events in the sandstone principally is involved in compaction,cementation and dissolution.The main diagenetic minerals of the sandstones include:authigenetic albite minerals,illite,kaolinite,calcite cement,quartz,feldspar overgrowth and pyrite et al.The pores in studied region include:intergranular pores,intragranular pores,mold pores,oversized pores,micropores and fissures.Intergranular pores were the main type of pores in studied region.Based on diagenetic events related to temperature,reservoir diagenetic stages can be dividable into A substage of later diagenesis.Reservoir quality of Silurian asphalt sandstones is controlled mostly by sedimentary microfacies and diagenesis.According to diagenesis,the reservoirs can be divided into five types:(1) unstable clastic dissolution,(2)compaction and dissolution,(3) compaction and cementation,(4) compaction and silica cementation,(5)carbonate cementation.Diagenetic facies influence the reservoir quality,and the rocks with unstable clastic dissolution and compaction and dissolution diagenetic facies are better than others.