四川盆地二叠系热液白云岩储层地质模型研究

As a new type of carbonate reservoir,people gradually realize that hydrothermal dolomite reservoir(HTD) play an important role in exploration. There were multi-period tectonic hydrothermal fluid activities,and they were suit for hydrothermal dolomites development. Predecessors pointed the exist of HTD mainly from the evidence of mineralogy and geochemical.These achievement revealed its significance for reservior,but can not provided a valued serve for exploration.It will take the Permian Sichuan Basin as a case.Based on the dolomite data of core and crop,analysing of mineralogy,isotope,REE,inclusion and buried -thermal-history confirm which is HTD.After this acquaint,analyzing the reservoir performance of HTD,analoging the feature of developed reservoir space well and undeveloped reservoir space well and its seismic profile,establish a geological model for hydrothermal dolomite reservoir from the relationship between HTD and origin rocks facies,fault activity,unconformity and strata structures,and understand the key factors of forming HTD by discussing the origin of rich Mg2+ fluid and priority channel for fluid migration,finally,in order to guide HTD identification and prospecting. The results will not only make a insight into HTD forming condition,but also guide prospecting,and thus be of theoretical and practical significance.

热液白云岩储层是一种新兴的碳酸盐岩储层类型，人们逐渐认识到它在油气勘探中的重要性。四川盆地经历多次构造热液活动，具备热液白云岩发育的背景，前人主要从岩石学及地球化学的角度论证热液白云岩的存在，指出它的储层意义，但这种认识还不能指导油气勘探。研究拟以四川盆地二叠系为对象，以露头和岩心揭示的白云岩为基础，开展岩石学特征、同位素、微量元素、包裹体及埋藏-热史分析，确定哪些为热液白云岩。在此基础上，分析热液白云岩的储集性能，类比储层发育和欠发育井的地质特征及过井地震剖面特征，分析热液白云岩储层与围岩沉积相、断裂活动、不整合面及上下岩性结构的关系，探讨富Mg2+热液流体的来源、热流体优势运移通道，提出热液白云岩储层形成主控因素，建立地质模型，以求能用于指导该类储层的识别和预测。研究结果既能揭示热液白云岩储层的形成条件，又能指导预测，具有理论与实践意义。

热液白云岩储层是一种新兴的碳酸盐岩储层类型，人们逐渐认识到它在油气勘探中的重要性。综合地震资料解释、岩石矿物学观察以及地球化学分析结果，认为四川盆地二叠系发育热液白云岩，并具有以下典型特征：①白云岩单层厚度较大，多呈透镜状产出，横向连续性差，且产出井附近多伴有走滑断裂发育，白云岩层段在对应的地震剖面上见“下凹”反射特征；②基质白云岩多呈中-粗晶，其缝洞中见具有波状消光特征的填隙鞍状白云石，并发育大量的角砾岩，角砾岩间充填白色的白云石，形成斑马构造；③基质白云岩与填隙鞍状白云石的均一温度较白云石化作用时地层的温度要高5℃以上，分别为105.8～159.6℃及113.2～138.6℃；同时二者还具有偏负的氧同位素值特征（-7.64‰～-7.95‰）以及高87Sr/86Sr（0.708369～0.709684）。明确热液白云岩储层形成条件：①高能相带是优质热液白云岩储层形成的物质基础；②峨眉地裂运动是二叠系热液白云岩储层形成的关键；③优质热液白云岩储层与基底断裂伴生。结合热液白云岩储层特征及其形成条件，开展地震资料解释，从区域上及目标评价上提出发育规律及预测要点：①区域上热液白云岩储层主要发育在峨眉玄武岩及基底断裂发育区；②垂向上热液白云岩储层主要发育在三级层序的高位体系域中，单层厚度大且连续性好的高能相带最为有利；③结合断裂解释及蚂蚁体裂缝预测，白云岩储层一般发育在基底断裂带相关的裂缝发育区，且一般具有异常不连续的反射或下凹发射。构造热液白云岩的发育和分布受走滑断裂控制，若与上覆致密灰岩地层有机配置，可以形成良好的岩性油气藏。