四川盆地栖霞组非均质砂糖状白云岩交织共生与储层形成机理

Sucrosic dolomite have long been a heated topic in the fields of carbonate sedimentology and reservoir geology for their high porosity and permeability. This study aims to investigate a special, heterogeneous sucrosic dolomite in Middle Permian Qixia Formation, northwestern Sichuan Basin, which are interlaced paragenesis of medium-coarse crystal sucrosic dolomite with different structures and physical properties. Based on comprehensive analyses including thin section observation, SEM analysis, NMR measurement, and CT scanning, this study will finely scribe the petrological characteristics of such dolomite. Subsequently, bulk-rock and in-situ geochemical analysis will be combined to clarify the sources and properties of the fluids in the dolomite-forming process as well as the mechanism of their interaction with rocks. Finally, based on the results of petrological and geochemical analysis, efforts will be made to reconstruct the formation and evolution of dolomite and its reservoir in the geological framework, and attempts will be made to establish the universal mode for the formation of heterogeneous sucrosic dolomite. Results of this study are expected to enrich the basic theory and research significance of the sucrosic dolomite in the oil and gas geology field, and they can also provide scientific basis for regional oil and gas exploration. Therefore, this study is of important basic scientific meaning and great practical application significance.

砂糖状白云岩通常以高孔高渗为特征，因而长期以来是碳酸盐沉积学家和储层地质学家关注的热点。本项申请，拟针对四川盆地西北部中二叠统栖霞组发育的一类较特殊的非均质砂糖状白云岩，其以不同结构-孔渗中-粗晶砂糖状白云岩交织共生为特征，展示出非均质性，通过较系统的岩心薄片、扫描电镜、核磁共振、CT扫描研究，精细刻划白云岩岩石学特征。在此基础上，结合全岩以及原位微区地球化学分析，查明白云岩及其储层形成过程中的流体来源、性质及其与岩石相互作用机理。基于岩石学和地球化学分析结果，在地质格架中重构白云岩及其储层形成演化过程，建立具有普适性的非均质砂糖状白云岩及其储层形成模式。研究结果可望丰富发展砂糖状白云岩这一领域研究热点的基础理论与油气地质意义研究，另一方面也可为区域油气勘探提供科学依据，故而可望具有重要的基础科学与实践应用研究意义。

砂糖状白云岩是全球范围内海相油气勘探的重要对象，但非均质的砂糖状白云岩及其储层因沉积背景复杂，且经历过多期成岩流体改造，使得成因研究极其困难，是当前碳酸盐岩沉积学与储层地质学领域的研究难点。本文以最近勘探取得重大突破的四川盆地西北部超深层中二叠统栖霞组为例，通过宏微观岩石学和微观地球化学证据，厘定了白云岩化时间、重构了白云岩化流体和作用过程，剖析了准同生暴露岩溶及与白云岩化和储层发育的关系，明确了储层发育的主控因素，建立了储层成因演化模式，为勘探方向遴选提供理论依据。.结果表明研究区栖霞组发育不同结构-孔渗性的中-粗晶砂糖状白云岩，它们交织共生、纵向层位不稳定、横向变化快，储层质量变化大。栖霞组沉积型台缘有利相带为叠置迁移型台缘丘滩复合体，颗粒滩粒间孔是孔洞和针孔型白云岩储层形成的物质基础，储层质量后者优于前者。.栖霞组白云岩化早于准同生期岩溶，但受到准同生期深部海水循环热液的叠合改造，从而形成特殊的准同生期具雾心亮边砂糖状白云岩，且过度的热液叠加充填了早期孔洞。多级海平面升降变化控制的准同生期暴露叠合改造储层，不同岩溶强度叠加形成了斑块状白云岩、针孔状、孔洞型白云岩以及角砾白云岩等产状类型，岩溶强度可使储层质量出现改善和反转双重效应。.建立了基于丘滩迁移而受限的准同生期蒸发浓缩-回流渗透与海水循环热液复合的“二元”白云岩化模式，岩溶强度控制的优化-反转的储层改造模式，复合形成了台缘丘滩、准同生期“二元”白云岩化、岩溶强度等“三元”控储的白云岩成因演化模式，为上扬子北缘带状白云岩发育分布模型提供了理论支撑，提出了区内向北西方向的龙门山前带的断下盘仍存在规模性的白云岩储层，为下步勘探指明了方向。如何准确预测非均质储层展布是制约规模性、效益性勘探和开发的重大生产问题。