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通过大量的岩石薄片显微观察,结合其他成岩阶段划分的标志,认为研究区花港组成岩阶段主要处在晚成岩阶段B期;采用光学显微镜、扫描电镜等观察分析东海陆架盆地西湖凹陷花港组储层砂岩自生矿物种类、组合及岩石结构、孔隙类型和结构特征,识别出酸性成岩环境和碱性成岩环境2种类型。酸性成岩环境以长石溶蚀+次生溶孔+自生高岭石+石英次生加大为特征;碱性成岩环境则以石英溶蚀+晚期亚铁碳酸盐充填、交代为特征。酸性和碱性成岩环境演化机理主要受控于烃源岩中干酪根核外围含氧羧基和酚基通过热裂解产生一元和二元水溶性羧酸以及酚类。在中成岩阶段A期,当RO值在0.5%～1.3%之间变化时,有机质通过脱羧基作用生成一元、二元有机酸,并释放出CO2,导致孔隙流体性质为酸性;当烃源岩中有机质演化程度升高,有机酸遭到破坏,脱羧基作用减弱,CO2来源减少,孔隙流体性质逐渐由酸性向碱性演变。
Through the observation of a large number of thin sections of rocks and the identification of other diagenetic stages, it is considered that the Huagang’s diagenetic stage is mainly in late-diagenetic stage B. The optical microscope and scanning electron microscope are used to observe and analyze the Huai-Hang of the West Lake Sag in the East China Sea shelf basin. The types, assemblages and rock structures, pore types and structural characteristics of the self-generating minerals of the reservoir sandstones are identified, and two types of acidic diagenetic and alkaline diagenetic environments are identified. The acidic diagenetic environment is characterized by feldspar dissolution + secondary dissolution pores + metakaolin + quartz secondary growth; alkaline diagenetic environments are characterized by quartz dissolution + late ferric carbonate filling. The evolutionary mechanism of acidic and alkaline diagenetic environments is mainly controlled by the oxygen-containing carboxyl groups and phenolic groups at the periphery of the kerogen nuclei in the source rocks that generate monohydric and binary water-soluble carboxylic acids and phenols by thermal cracking. During the middle diagenetic stage A, when the RO value varies from 0.5% to 1.3%, the organic matter generates monohydric and dibasic organic acids through decarboxylation and releases CO2, resulting in the acidic nature of the pore fluid. When the source rock In the evolution of organic matter increased, the organic acid was destroyed, the role of decarboxylation weakened, CO2 source decreases, pore fluid properties gradually evolved from acid to alkaline.