钙质胶结砂岩特征、分布及其对储层的影响

结合野外露头、岩心、薄片观察、元素扫描等资料，探讨了钙质胶结物在鄂尔多斯盆地中西部延长组下组合砂岩中的主要特征、分布规律及其对储层品质的影响。结果显示，下组合广泛发育钙质胶结砂岩，宏观上呈条带状近平行地层产状发育、层内不规则及与裂缝伴生3种发育形式，纵向上可分为薄层砂体全胶结型、厚层砂体顶底胶结型、砂体内分散胶结型及砂层内部韵律式胶结型4种，着重分析了韵律式钙质胶结的成因。钙质胶结物主要为方解石，含量为20%~40%；可分为3期:早期泥微晶状方解石；中期亮晶状嵌晶式方解石胶结、晚期亮晶状方解石充填小孔隙。钙离子来自泥岩或裂缝。钙质胶结物主要形成于成岩早期阶段，降低了储层物性，多形成干层，同时加剧了储层非均质性。

Characteristics and distribution of Calcite-cement sandstone and its effects of reservoir quality

Based on the outcrops，cores，rock flakes，and element scan，the authors discussed the main features and distribution of calcareous cements in sandstones of the lower Yanchang Formation in central and western Ordos Basin.Influences of calcite-cement sandstone on the reservoir quality were discussed simultaneously.Calcite-cement sandstone，which widely developed，striped parallel to the formation of stratigraphic development，irregular layers and crack associated.Three kinds of Calcite-cement sandstone could be subdivided into all cementing type in thin layer of sand，top cementing type in thick sand and sand body and dispersed cementing type.Calcareous cements were mainly calcite，which content was 20% to 40%.Calcite could be divided into three phases:the early mud-like calcite；mid-bright crystalline inlaid calcite cementation，late bright crystalline calcite-filled pores.Calcium ions come from mudstone or cracks.Cements in calcite-cement sandstone was mainly formed in the early stage of diagenesis，which reduced reservoir physical properties and aggravated reservoir heterogeneity.