湖相富火山组分的混积岩致密油储层的成岩、成储机理研究

Mixed siliciclastic-volcaniclastic-carbonate (MSVC) rocks have been widely recognized in Santanghu, Junggar, and Erlian basins. MSVC sediments usually form tight reservoir, in which tight oil has been discovered. However, only a few of research has been conducted to investigate the reservoir pore structure, diagenesis, and formation mechanism of MSVC rocks. This study will take MSVC rocks of Lucaogou Formation in Santanghu and the one of the Lower Cretaceous in Erlian basins as examples, four main aspects will be studied in this project. Firstly, the mico-nano pore system heterogeneity will be studied by means of the slice observation, scanning electron microscope, nano CT and mercury injection to establish the relationship between pore throat distribution. Secondly, the diagenetic minerals and its evolution will be analyzed by petrological methods such as the slice observation and XRD. In addition, based on laser microscope sampling, electronic probe and MC-ICP-MS, the origin of diagenetic minerals and the relationship between it and volcanic material will be studied. Lastly, the relation modes between the geological parameters including pore throat distribution and composition, diagenetic strength, reservoir qualities will be established. The results of the study are expected to clarify the reservoir properties, processes of formation and diagenesis of MSVC rocks, which will lay a solid foundation for the exploration and development of tight oil resources in MSVC rocks.

在三塘湖、准噶尔和二连等盆地广泛发育由火山碎屑、碳酸盐和碎屑颗粒混杂沉积形成的“富火山碎屑的混积岩”，在其中已发现致密油，是一种新型的致密油储层。但有关储层孔喉结构、成岩和成储机理的研究甚少。本项目试图以三塘湖盆地和二连盆地为例，利用铸体薄片、扫描电镜、纳米CT、恒速压汞等方法研究致密油储层微米-纳米孔喉系统的非均质性；综合运用岩石薄片、阴极发光、场发射扫描电镜、全岩分析等岩石学分析手段，区分和鉴定各种成岩矿物的类型、赋存方式及含量，判断成岩矿物的形成期次，建立成岩演化模式；应用激光显微取样、电子探针、多接受激光等离子质谱测试等先进手段，分析成岩矿物来源，探讨火山组分对其形成的制约和促进作用；建立致密储层孔喉分布与成分、成岩程度、物性及其它地质因素的关系模型或图版。以期对混积岩储层孔隙结构、成岩和成储机理研究取得新进展，为混积岩致密油气的勘探开发奠定理论基础。

随着勘探的深入，在国内多个盆地发育一套粒度偏细、岩性复杂的致密油储层，由陆源碎屑岩、碳酸盐岩和火山碎屑岩混积而成。这套混积岩储层在多个探区见油气显示，但仍未获得较大油气突破，主要由于混积岩储层的成因和致密化过程不清导致。本论文选取三塘湖盆地和二连盆地为研究对象，通过综合运用岩石薄片、阴极发光、场发射扫描电镜、全岩分析等岩石学分析手段和流体包裹体、碳氧同位素等地化手段，对这套混积岩储层岩石学、孔喉结构、成岩作用、成因机理及成储差异展开研究。结果表明，混积岩储层具有岩性类型多、岩性变化快、矿物产状各异等特点。基于陆源碎屑岩的岩性划分方案，混积岩划分为3大类，16小类。其中，凝灰岩主要分布在深湖－半深湖亚相，夹于厚层泥岩中；沉凝灰岩和复杂岩性泥岩主要发育在滨浅湖亚相，与厚层泥岩及粉砂岩相邻；复杂岩性砂岩主要发育在三角洲和重力流成因的扇体前端，常与粉砂岩、砂岩互层。此外，混积岩储层主要发育晶间孔、粒间孔、粒内孔及微裂缝，具有微、纳米孔隙结构，属于低－超低孔、渗储层。在白云石的宏观产状和矿物学特征基础上，结合微量元素和碳氧同位素特征，建立了3种白云石化成因模式：准同生成因白云石，主要存在白云岩中，具有它形泥粉晶，形成于沉积期的咸化湖盆中。甲烷生成作用成因的白云石，主要存在纹层状和星点状云质泥岩或云质沉凝灰岩，具有它形－半自形微粉晶结构，形成于成岩早期，Mg2+离子主要来源于富火山灰的凝灰物质大量水解蚀变。埋藏成因白云石，分布在块状云质沉凝灰岩或云质砂岩，具有自形粉细晶结构，晶体结构较好，Mg2+离子主要来源于长石等颗粒溶解及深层黏土矿物转化。