热液活动对四川盆地中西部地区二叠系茅口组白云岩的影响  

Influence of hydrothermal activity on the Maokou Formation dolostone in the central and western Sichuan Basin

作　　者：黎霆 诸丹诚 杨明磊 李平平[1,2] 邹华耀[1,2] Li Ting;Zhu Dancheng;Yang Minglei;Li Pingping;Zou Huayao(College of Geosciences,China University of Petroleum(Beijing),Beijing 102249,China;State Key Laboratory of Petroleum Resource and Prospecting,Beijing 102249,China)

机构地区：[1]中国石油大学(北京)地球科学学院,北京102249 [2]油气资源与探测国家重点实验室,北京102249

出　　处：《石油与天然气地质》2021年第3期639-651,共13页Oil & Gas Geology

基　　金：中国科学院战略性先导科技专项(A类)(XDA14010306);国家科技重大专项(2017ZX05005-003-003)。

摘　　要：二叠系茅口组热液白云岩储层是近几年四川盆地勘探的热点领域,受到峨眉山玄武岩喷发的影响,热液活动在茅口组白云岩中十分普遍,但对于热液如何影响白云岩储层还缺乏系统的认识。基于野外观测、岩心和岩石薄片观察、阴极发光、包裹体均一温度和地球化学分析,取得了以下几点认识。①根据宏观产状,茅口组白云岩可分为层状白云岩和斑块状白云岩,层状白云岩是主要的类型。根据微观结构,层状白云岩可进一步分为粉-细晶白云岩和细-中晶白云岩,斑块状白云岩则由中-粗晶白云石组成。②细-中晶白云岩多呈斑块状分布在粉-细晶白云岩中,具明显的不等晶结构,且发育与热液相关的构造和矿物,与粉-细晶白云岩相比,细-中晶白云岩具有较高Fe和Mn含量、较强的阴极发光、较高的包裹体均一温度、偏负的δ18 O(PDB)值及较高的87 Sr/86 Sr值,表明细-中晶白云岩是粉-细晶白云岩在热液作用下重结晶形成。③热液对茅口组白云岩储层的建设性作用表现在热液活动形成裂缝系统和角砾,热液溶蚀形成溶蚀孔洞,热液交代原始灰岩形成白云岩;破坏性作用表现在热液矿物沉淀充填先前孔、缝、洞和热液重结晶,重结晶过程有新的Mg 2+和CO 32-加入,导致重结晶后白云岩物性变差。④茅口组储层储集空间形成的主要驱动力是早期大气淡水溶蚀,热液可以作为储层发育的一个潜在信号,因此针对茅口组储层,应以滩控早期岩溶为核心思路进行勘探。The hydrothermal dolostone in the Permain Maokou Formation of Sichuan Basin has been targeted frequently for natural gas during the past few years.Though quite common in the formation as a result of the Emeishan flood basalt eruption, hydrothermal activities and their effect on dolostone reservoirs are not sufficiently understood.Based on observation of outcrops, cores, and thin sections along with analysis of cathodoluminescence, homogenization temperature of fluid inclusions and geochemistry, we reached the following conclusions.Firstly, dolostone in the Maokou Formation can be divided into laminar dolostone and patchy dolostone.The former, the dominant type, can be further subdivided into very fine to fine-crystallized dolostone(D1) and fine to medium-crystallized dolostone(D2).The latter is composed of medium to coarse-crystallized dolomite(D3).Secondly, D2,mainly developed in D1 as patches, shows inequigranular texture and develops hydrothermal-related structures and minerals.Compared with D1,D2 has higher Fe and Mn content, stronger cathodoluminescence, higher homogenization temperature of fluid inclusions, higher 87Sr/86Sr, and more negative δ18 OPDB value, indicating that D2 is generated by recrystallization of D1 under the influence of hydrothermal fluids.Thirdly, hydrothermal process can be both constructive and destructive to the development of Maokou Formation dolostone reservoirs.It is constructive in that hydrothermal activities led to the formation of rupture system and breccia, hydrothermal dissolution to dissolved pores and cavities, and hydrothermal metasomasis to dolomitization of limestone.It is destructive in that the physical properties of dolostone were affected by mineral sedimentation that plugged previously formed pores, ruptures, and cavities and by recrystallization that added more Mg2+ and CO_(3)^(2-) to the system.Lastly, the main driving force for the formation of reservoir space in the Maokou Formation is an early-stage meteoric freshwater dissolution, and the footprint of hydroth

关 键 词：热液 层状白云岩 斑状白云岩 重结晶 茅口组 四川盆地 

分 类 号：TE122.2[石油与天然气工程—油气勘探]