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分析白云岩及储层形成过程的流体特征,对探讨白云岩形成机理和储层特征具有重要意义。以靖边气田马五段白云岩作为研究对象,分析其稀土元素特征,并探讨了其中蕴含的成岩流体信息。研究结果表明,海水标准化后所有样品的稀土元素配分特征相近,均表现为正Ce异常(δCe=12.2~14.7),LREE稍富集,HREE配分曲线平坦,显示海水来源的特征。泥晶灰岩标准化后均表现为正Eu异常、LREE富集的特征,说明在白云岩化过程中,HREE减少最多,Eu减少最少,推测与热液流体的水—岩作用有关。与未溶蚀的白云岩相比,溶蚀白云岩的∑REE值减少30%,REE配分模式基本不变,且越接近古地表∑REE值和δCe值越大,符合成岩—成烃流体水—岩反应时REE的变化特征,而与大气水的淋滤效应明显不同。现今白云岩中的溶蚀孔可能主要与白云岩再次埋藏时的成岩—成烃流体有关。
Analyzing the fluid characteristics of dolomite and reservoir formation process is of great significance to the exploration of dolomite formation mechanism and reservoir characteristics. Taking the Ma5 Member dolomite in Jingbian gas field as a research object, the characteristics of rare earth elements were analyzed and the diagenetic fluid information contained therein was discussed. The results show that the rare earth elemental compositional characteristics of all the samples after seawater normalization show similar positive Ce anomaly (δCe = 12.2 ~ 14.7), LREE is slightly enriched, HREE distribution curve is flat, showing the source of seawater. After normalization of the dolomitic limestone, both positive Eu anomalies and LREE enrichment characteristics show that during the dolomitization, the HREE decreases most and the Eu decreases least, which is presumed to be related to the water-rock interaction of hydrothermal fluids. Compared with the undissolved dolomite, the ΣREE value of dissolved dolomite is reduced by 30%, and the REE partitioning pattern is basically unchanged. The closer the ΣREE value and δCe value are, the more coincident with the diagenesis-hydrocarbon generation fluid water-rock REE characteristics of the reaction characteristics, while the leaching effect with atmospheric water significantly different. The dissolution pores in today’s dolomites may be mainly related to the diagenesis-hydrocarbon generation fluids when the dolomites are buried again.