摘要
深层-超深层碳酸盐岩是目前油气勘探聚焦的重点领域，其储层的形成和保持机制是制约深层储层预测的关键科学问题。为了明确埋藏溶蚀作用下酸性流体对碳酸盐岩储层物性的影响，有必要开展烃源岩地层孔隙生烃模拟和溶蚀模拟实验（简称生烃及溶蚀模拟实验），定性定量厘清中、深层埋藏环境下烃源岩与碳酸盐岩储层演化过程。采用自主研发设计的生烃模拟实验装置和溶蚀模拟实验装置，以塔里木盆地奥陶系鹰山组灰岩和云南禄劝低成熟烃源岩为实验对象，利用岩相学和地球化学相结合的分析手段，查明中、深埋藏环境下生烃热演化过程中伴生的复杂酸性流体改造碳酸盐岩储层的过程及其控制因素，探索烃源岩生烃过程对碳酸盐岩围岩的改造规律。实验表明：中、深层埋藏环境下烃源岩热演化过程中伴生的有机酸和CO等酸性流体对碳酸盐岩储层产生明显溶蚀作用，扩大原有储集空间并提高孔隙度，并且随着埋藏深度增加，溶蚀作用明显减弱；流体在运移过程中是否能够改善储层物性，由流体中的碳酸钙饱和度、流体流速、水岩比以及原始孔隙结构等因素共同决定。此研究能够为深层-超深层碳酸盐岩优质储层的预测提供一定的理论基础。
Abstract
The deep and ultra-deep carbonate reservoirs are the major targets of exploration, but their prediction is quite complicated due to the poor understanding of their formation and maintenance mechanism. It is essential to perform hydrocarbon generation and dissolution simulation experiments to quantitatively and qualitatively clarify the evolution process of source rocks and carbonate reservoirs in deep layers. In this study, a series of experiments were conducted with the limestone samples from the Ordovician Yingshan Formation in the Tarim Basin, and the low maturity source rock samples from Luquan County, Yunnan Province, via self-designed hydrocarbon generation and dissolution simulation equipments. The controlling factors accounting for the alteration of carbonate reservoirs and dissolution modification process by the complex acidic fluids associated with hydrocarbon generation in medium-to-deep burial environments were investigated using petrographic and geochemical methods. In the meantime, the transformation mechanism of surrounding carbonate reservoirs during hydrocarbon generation process of source rocks was explored. The results show that: during the medium-deep burial stage, acidic fluids including organic acid and CO associated with thermal evolution of source rocks could dissolve carbonate reservoirs, expanding their reservoir space, and thus improving porosity. Dissolution would decrease with the increasing burial depth. Whether the migrating fluids could improve the physical properties of reservoir largely depends on such factors as calcium carbonate saturation, fluid velocity, water/rock ratio, and original pore structure. The study can provide a theoretical basis for prediction of high-quality carbonate reservoirs in deep and ultra-deep formations.
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