不同赋存形态海绿石的成因机制及其与储集空间关系研究

Glauconite, as a kind of sedimentary facies mineral, is always the hot topic of concern because of its wide application in analysis of sedimentation rate and diagenesis environment, K-Ar dating and sequence subdivision. More and more researches show that occurrence form of glauconite is complex and diverse, while the genesis hypotheses proposed by the predecessors cannot interpret the different forms of glauconite. With the continuous improvement of oil and gas exploration and development degree, high-yielding reservoirs were found in the sandstone with glauconite in recent years. While there are few researches on the influence of the diverse glauconite on the reservoir property at present. The project, taking sandstones with abundant glauconite from Neoproterozoic Qingbaikou System in Changping, Beijing and Jixian, Tianjin, and Cretaceous in Oriente Basin, Ecuador，as the research object, will analyze the hosting condition of glauconite and classify their morphology based on field and core investigation, sampling and systematical indoor analysis and laboratory test method such as thin section, X-ray microanalysis, electron microprobe, scanning electron microscope, QUEMScan, pore image analysis and so on. Then the characteristics of the different forms of glauconite including elemental composition, microstructure and maturity will be analyzed based on which the formation condition and genesis mechanism of the different forms of glauconite will be discussed. Finally, the influence of the different forms of glauconite on reservoir property will be determined according to the quantitative relationship of the occurrence form of glauconite and reservoir space & plane porosity. Therefore, the research is significant in theory and practice for enriching the glauconite genesis theory and predicting the favorable reservoir.

海绿石作为沉积相指示矿物，因其在沉积速率和成岩环境分析、K-Ar测年、层序划分等方面的广泛应用一直倍受关注。越来越多的研究发现，海绿石的赋存形态复杂多样，而前人提出的成因假说已无法解释不同形态海绿石的形成。随着油气勘探开发程度的不断提高，近年来在低阻的海绿石砂岩中发现了高产油藏，而不同形态海绿石的存在对储层物性影响研究较少。本项目拟以北京昌平地区和天津蓟县青白口系、Oriente盆地白垩系富含海绿石的砂岩为研究对象，通过野外及岩心观察、取样及薄片鉴定、X-衍射、电子探针、扫描电镜、QUEMScan、孔隙图像等分析化验，对海绿石的赋存形态进行分类，通过分析不同形态海绿石的元素组成、微观结构及成熟度等特征，探讨不同形态海绿石的形成条件和成因机制，并根据海绿石的赋存形态与储集空间和面孔率的定量关系探讨不同形态海绿石对储层物性的影响，对丰富海绿石成因理论和有利储层预测具有重要的理论和和实践意义。

海绿石长期作为特殊的沉积相指示矿物，在地质历史时期有着广泛的分布，在华北地区青白口系、奥连特盆地白垩系发育多套海绿石。本基金项目通过普通和铸体薄片、扫描电镜、电子探针、X衍射、微量元素、QUEMScan分析等多种实验分析，开展海绿石的赋存形态、微观结构、化学组成、成熟度研究，全面分析海绿石的形态分类，探讨海绿石的成因机制及其对于储层物性的影响，对于完善海绿石的成因理论和恢复古地理环境、预测有利储层具有重要的理论和实践意义。研究表明，海绿石发育多种形态，可见颗粒状、碎屑假象状、胶结物状、粪球粒状和晕边状，扫描电镜下主要为片状、裂片状。海绿石的化学组成主要为 K2O、Al2O3、TFeO、SiO2、CaO、Na2O、MgO。依据颜色、形态和化学组成的差异，可将研究区海绿石大体分为绿色颗粒状海绿石，成熟度为成熟-高成熟；黄绿色颗粒状海绿石，成熟度为低成熟-成熟；黄褐色颗粒状海绿石，成熟度较低；黄褐色胶体状海绿石，根据化学成分表明大都不具备海绿石的化学结构；深褐色碎屑状海绿石，其化学成分也表明已经蚀变为铁的氧化物。海绿石的形成受物质来源、氧化还原条件的控制。海绿石形成的基质不同，其形成机制也不同，如以石英、长石为基质形成的海绿石属于假形置换成因，以云母为基质的海绿石可用层型点阵理论解释，以粪球粒为基质的海绿石为生物成因，晕边状海绿石为复合成因。研究区绿色颗粒状海绿石属于假形置换成因，黄绿色颗粒状海绿可用层型点阵理论解释，黄褐色颗粒状海绿石属于假型置换或层型点阵成因叠加后期蚀变复合成因。胶体状海绿石属于早期自生淀胶成因，后期叠加了蚀变成因。异地碎屑颗粒状海绿石属于原地自生淀胶或假型置换形成的海绿石叠加了后期的再搬运和异地再沉积成因，并建立了不同赋存形态海绿石的发育模式。胶结物状的海绿石明显降低储层物性，而颗粒状海绿石对储层物性影响相对较小，海绿石含量越高储层质量越差。海绿石含量越低、颗粒状海绿石磨圆度越好，储层物性越好。海绿石复合成因理论的提出丰富了海绿石成因理论，并为恢复古地理环境和成岩作用条件分析及其有利储层预测提供科学依据。