四川盆地五峰组—龙马溪组页岩储层中碳酸盐矿物特征、形成机制及对储层物性影响

Characteristics,formation mechanism and influence on physical properties of carbonate minerals in shale reservoir of Wufeng-Longmaxi formations,Sichuan Basin

通过携带波谱仪和能谱仪的电子探针显微镜,结合物性、全岩X射线衍射、有机碳等分析测试资料,系统梳理了四川盆地五峰组—龙马溪组页岩储层中碳酸盐矿物特征、形成机制及对物性的影响。结果表明:(1)碳酸盐矿物主要包括方解石、白云石和含铁白云石,方解石以单颗粒形式赋存于矿物颗粒间和充填放射虫硅质壳腔体,含铁白云石总是作为白云石的环边,含铁白云石环白云石结构以单颗粒和集合体形式发育于矿物颗粒间;(2)方解石由海水表层分泌碳酸钙的微生物产生,沉淀在海水中和放射虫硅质骨骼的腔体内,经沉降和部分溶解,沉积至海底并埋藏保存;(3)白云石为水—沉积物界面硫酸菌生理活动的产物,含铁白云石为泥质沉积物埋藏初期甲烷菌新陈代谢的衍生物;(4)有机碳、黄铁矿、石英和黏土矿物含量与物性密切相关,而碳酸盐矿物含量对页岩储层的孔隙度和渗透率总体上没有影响。电子探针显微镜技术的原位探测、元素面扫、尤其是波谱图像为研究页岩储层中碳酸盐矿物特征、形成机制及对物性影响提供了典型岩石学证据,在今后页岩储层成岩作用研究中将会得到更多应用。

By electron probe microscope with spectrometer and energy spectrometer,combined with physical properties and whole rock X-diffraction and organic carbon data,characteristics,formation mechanism and influence on physical properties of carbonate minerals in shale reservoir of Wufeng-Longmaxi formations in Sichuan Basin are systematically studied. And the following research results were obtained. Firstly,carbonate minerals mainly include calcite,dolomite and ferriferous dolomite,and the calcite exists between mineral particles and fills the cavity of radiolarian siliceous shell in the form of the single mineral,and the structure that the ferriferous dolomite always rings the dolomite is among mineral particles in the form of the single mineral and aggregates.Secondly,the calcite is produced by microorganisms secreting calcium carbonate in the surface of seawater and precipitated in both seawater and the cavity of radiolarian siliceous skeleton,and after dissolving partly while settling in seawater the residual calcite deposits on the seabed and is preserved by burial. Thirdly,the dolomite is a diagenetic mineral formed on the water-sediment interface with physiological activities of sulfate bacteria,and the ferriferous dolomite is produced by methanogenic metabolism during the initial burial of muddy sediments.Fourthly,organic carbon,pyrite,quartz and clay minerals are closely related to reservoir physical properties,while carbonate has no effect on porosity and permeability as a whole. The in-situ detection,element area scanning and especially spectrogram from electron probe microscope technology provide typical petrological evidences for the study of characteristics,formation mechanism and influence on physical properties of carbonate minerals in shale reservoirs,which should be popularized in the study of shale reservoir diagenesis in the future.