【作者】 宋光永；

【导师】 刘树根；

【作者基本信息】 成都理工大学 ， 矿产普查与勘探， 2010， 硕士

【摘要】 本论文以川东南地区上震旦统灯影组白云岩为研究对象,在对区域沉积构造演化、研究区灯影组白云岩岩性特征、沉积特征的解读后,从岩石学特征、地球化学特征角度综合论证了灯影组热液蚀变白云岩的存在。同时,总结了热液白云岩储层岩石学特征及物性特征、地球化学特征,分析了热液白云岩主要成岩作用特征及成岩演化序列,并提出热液白云岩储层形成与演化过程。取得了以下的主要研究成果:川东南地区自晋宁运动基底形成后,其沉积构造演化可以分为五个阶段:①南华大冰期阶段(Nh);②被动陆缘-隆拗演化阶段(Z-S);③峨眉地裂运动阶段(D-P);④前陆隆起演化阶段(T-K1);⑤褶皱隆升阶段(K2-Q)。期间,发生过2期重要的构造-热液事件——“兴凯地裂运动”及“峨眉地裂运动”,为深部流体上涌提供了条件。晚震旦世灯影期,上扬子区为陆表海局限台地沉积,川东南地区沉积了一套潮坪-泻湖相白云岩。灯影组白云岩以原生白云岩为主,同生期-准同生期白云石化为次。川东南地区震旦系灯影组岩石类型主要为微-粗晶晶粒白云岩和藻白云岩。藻白云岩是灯影组特征岩石类型,包括藻粘结白云岩、藻纹层白云岩、藻叠层白云岩、凝块石白云岩等,偶见核形石白云岩。由于成岩改造,发育雪花状白云岩、硅化白云岩及热液白云岩。灯影组白云岩在后期成岩演化过程中,曾遭受热液蚀变,发育热液白云岩储层相。热液白云岩岩石学特征明显:广泛发育具热液指示意义的马鞍状白云石;由马鞍状白云石充填的各种热液特征组构,包括斑马状白云岩、由马鞍状白云石镶边的近水平片状晶洞、由马鞍状白云石胶结的角砾状构造等;临近热液蚀变的灯影组白云岩围岩常出现热褪色现象。由于热液蚀变,热液白云岩常呈斑杂色,遭受风化后显黄褐色;研究区还发育与热液白云岩具有成因联系的MVT型铅锌矿及重晶石-萤石矿等热液矿床。林1井热液白云岩发育段溶蚀孔洞相对发育,具有显著的测井响应。特别是不整合面之下约46m,热液活动强烈,显示出不整合面作为热液优势通道的有利条件。热液蚀变致使灯影组白云岩储集性得到改善。基质白云岩孔隙度、渗透率数据表明热液白云岩段孔渗性优于未受热液影响的层段。而且这些孔隙度、渗透率并未包含溶蚀孔洞及马鞍状白云石晶洞,而后者才是热液白云岩储集空间的主体。热液白云岩中广泛存在的沥青表明热液白云岩曾是油气良好的储集空间。由热液蚀变形成的油气储集空间包括溶蚀孔洞、晶洞、热液重结晶作用形成的晶间孔等。研究区灯影组白云岩中脉体或晶洞充填物与围岩的碳δ13C、氧δ18O、锶87Sr/86Sr同位素值相比,具有碳δ13C值偏小、氧δ18O值偏小、锶87Sr/86Sr值偏大的特征。碳、氧、锶同位素值特征表明灯影组白云岩已遭受成岩蚀变,且这种成岩流体为外源富锶流体。锶87Sr/86Sr比值特征表明这种成岩流体可能是沿断层上涌的热液,来自于下部南华系莲沱组或晋宁运动形成的风化壳(基底)。这种解释得到了包裹体数据和岩石学特征的支持。岩芯、岩石薄片观察和地球化学分析表明,研究区热液白云岩储层的形成主要出现以下成岩作用:白云石化作用、压实压溶作用、硅化作用、胶结作用、溶蚀作用(表生溶蚀及埋藏溶蚀)、重结晶作用、热液蚀变、构造破裂等。对储层孔隙发育产生重要影响的成岩作用是各种溶蚀作用、热液蚀变作用、重结晶作用和破裂作用。而且由于早期形成的溶蚀孔洞缝,在后期成岩阶段几乎被完全充填,最有意义的溶蚀作用应该为热液溶蚀及更晚期的深埋溶蚀作用。热液蚀变的关键时刻可能为早二叠世,是峨眉地裂运动在川东南地区的响应。更多还原

【Abstract】 This paper focuses on hydrothermal dolomite of Upper Sinian Dengying Formation in southeast Sichuan basin. After a detailed observation of regional tectonic evolution, lithology and sedimentary features of Dengying dolomite in study area, His conclusion from petrological and geochemical aspects are that some hydrothermal alteration occurred in Dengying dolomite. At the same time, this paper sums up reservoir petrography and geochemical charecteristics of hydrothermal dolomite, and points out main diagenetic features in reservoir formation. Finally, reservoir formation and evolution of hydrothermal dolomite is presented. Through these processes, the paper finally gets some significant results below:After formation of the basement due to Jingning Movement, the sedimentary and tectonic evolution of study area can be divided into five stages:①Nanhua glacial period(Nh);②passive continental margin and uplift/depression formation stage(Z-S);③Emei Taphrogeny period(D-P);④foreland evolution stage(T-K1);⑤folding and uplifting stage(K2-Q). During this evolution history, two important structurally controlled hydrothermal events took place—Xingkai Taphrogeny and Emei Taphtogeny, which formed upward conduits for deep hydrothermal fluids.The Upper Yangtze region was a restricted platform during Late Sinian. The study area is comprised dolomite deposited in tidal flat and lagoon environment. This dolomite is interpreted to be mostly primary in origin, little of it could be produced by dolomitization. Crystalline dolomite from fine to coarse crystalline and algal dolomite are the main types of the rocks. Algal dolomite is critical for Dengying Formation. It’s including algal bindstone, algal stratifera, algal stromatolite, algal thrombolite and seldom algal oncolite. In addition, snowflake dolomite, silicified dolomite and hydrothermal dolomite formed during diagenesis are also important.Hydrothermal dolomite reservoir was generated when Dengying dolomite was subjected to hydrothermal alteration during late diagenesis. Hydrothermal alteration may produce a range of dissolution and precipitation features, and may have variable impact on Dengying reservoir characteristics. For instance, it is common to see saddle dolomite, a critical indicator of hydrothermal setting, and many distinct rock fabrics including zebra textured dolomite, subhorizontal sheet vugs lined or infilled by saddle dolomite dilational, floating clast dolomite breccia cemented by massive saddle dolomite; Thermal discoloration occours on wall rock of hydrothermal dolomite. Because of hydrothermal alteration, Dengying dolomite appears to be mottled; There are also MVT deposits and barite-fluorite ores, which are suggested to have genetic link to hydrothermal dolomite.Hydrothermal dolomite in Lin One well has abundant solution pores, giving good log response. Especially, within 46m from the disconformity between Cambrian and Sinian, where hydrothermal fluid were particularly active. This may indicate that the unconformity was a advantage fluid passage. The fact that hydrothermal alteration enhances porosity of Dengying dolomite is demonstrated by porosity and permeability experimental data of Lin One well. These data show matrix porosity, don’t include vug porosity which is the main contributor to reservoir. Abundant bitumen is found in pores of hydrothermal dolomite implicating that hydrothermal dolomite once was good hydrocarbon reservoir. Hydrothermal dolomite porosity includes solution pores, vugs and intercrystalline pores.In comparison to wall rock(original Dengying dolomite), dolomites in veins or/and vugs show lowerδ13C andδ18O values, higher 87Sr/86Sr values.δ13C,δ18O and 87Sr/86Sr values imply that Dengying dolomite was subjected to diagenetic alteration, and that the diagenetic fluid was from outside source. 87Sr/86Sr values indicate this diagenetic fluid may be hydrothermal fluid flowing up via active fault, from Liantuo Formation of Nanhua System below or basement. This conclusion is supported by homogenization fluid-inclusion temperature data and petrographical characteristics.By core and thin section examination and geochemical analysis, it’s concluded that the following main diagenetic events in hydrothermal dolomite reservoir of study area are: dolomitization, compaction and pressure solution, silicification, cementation, dissolution, recrystallization, hydrothermal alteration, tectonic fracturing and so on. Among them, dissolution, hydrothermal alteration, recrystallization and tectonic fracturing have important control on reservoir porosity. Because early formed porosity is infilled during late diagenesis, the most significant dissolution is supposed to be the hydrothermal dissolution and deep-burial dissolution. Hydrothermal alteration ocourred during the Early Permian, and could be reflection of Emei Taphrogeny in southeast Sichuan basin.更多还原