长江大学朱光有教授团队以四川盆地震旦系灯影组和寒武系龙王庙组为例，报道了超深白云岩成因及大型储层控制因素。2024年6月19日出版的《中国科学：地球科学》发表了这项成果。

研究结果表明，灯影组和龙王庙组由6种基质白云岩及其胶结物类型组成。灯影组发育于局限台地沉积背景下，发育有特殊的微生物微晶白云岩。白云石晶粒细小(<30μm)，有序度低(最小值=0.55)，晶胞参数大，Na含量极高(最大值=788μm)。白云岩⁸⁷Sr/⁸⁶Sr值与同代海水一致，δ¹³C和δ¹⁸O值低于同代海水。δ²⁶Mg值较小(最小值=-2.31‰)。粉晶白云岩、细晶白云岩和方解石白云岩的δ¹³C值和⁸⁷Sr/⁸⁶Sr值与微生物白云岩和微晶白云岩相似，它们的晶体更粗、更有序。

在灯影组沉积时期，古海相环境有利于微生物的生存。微生物诱导原生白云岩在海水中直接沉淀，在海水成岩期形成微生物白云岩和微晶白云岩。在随后的成岩时期，白云岩经历了溶蚀—重结晶、构造和热液流体的作用。这导致白云石的形成具有较粗的晶体，较高的有序程度和各种类型的胶结物。

龙王庙组发育于以特殊颗粒白云岩为特征的台间滩。颗粒白云石晶粒尺寸大(30μm)，有序度高(最小值=0.7)，晶胞参数小，Na含量高(最大值=432ppm)， Fe和Mn含量低。δ²⁶Mg和δ¹³C值与同代海水一致，δ¹⁸O和⁸⁷Sr/⁸⁶Sr值高于同代海水。多期变化的δ²⁶Mg值与沉积旋回之间存在相互耦合关系。龙王庙组白云岩是石灰岩在海水蒸发作用下交代形成的。龙王庙组白云岩的厚度和规模受海平面周期性变化的控制。震旦系到寒武系的白云岩发育时期，与Rodinia裂解到Gondwana汇聚的过渡时期相吻合。

这些事件导致了震旦纪和寒武纪之间海洋性质、微生物活动和沉积气候背景的巨大差异。这些差异可能是导致两期白云岩成因不同的根本因素。四川盆地震旦系—寒武系沉积相分布及深部构造活动受超大陆的分裂与辐合作用的影响。这一过程对确定超深层白云岩储层的分布、孔隙形成、保存和调节机制起着关键作用。为了有效分析其他区域或层位，特别是特定超大陆裂解和汇聚时期的超深白云岩成因和储层机制，必须综合考虑构造活动驱动下的海水性质、微生物活动、沉积环境和断裂体系等特征。这有助于预测优质、大型超深白云岩储层的分布。

据研究人员介绍，本文以四川盆地震旦系灯影组和寒武系龙王庙组为研究对象，探讨了四川盆地超深层白云岩的成因及大型白云岩储层的影响因素。研究方法包括岩石学、微尺度x射线衍射、微量元素分析、C-O-Sr-Mg同位素实验等。

附：英文原文

Title: Genesis of ultra-deep dolostone and controlling factors of large-scale reservoir: A case study of the Sinian Dengying Formation and the Cambrian Longwangmiao Formation in the Sichuan Basin

Author: Xi LI, Guangyou ZHU, Zhiyao ZHANG

Issue&Volume: 2024/06/19

Abstract: This paper investigates the origin of ultra-deep dolostone and the factors influencing large-scale dolostone reservoirs, focusing on the Sinian Dengying Formation and the Cambrian Longwangmiao Formation in the Sichuan Basin. The study involves petrology, microscale X-ray diffraction, trace element analysis, and C-O-Sr-Mg isotope experiments to provide a detailed analysis. The research findings indicate that the Dengying and Longwangmiao formations comprise six types of matrix dolostone and four types of cement. The Dengying Formation, which developed under a sedimentary background of a restricted platform, contains special microbial and microcrystalline dolostones. The dolomite grains are small (<30μm) and have a low order degree (Min=0.55), with large unit cell parameters and an extremely high Na content (Max=788ppm). The ⁸⁷Sr/⁸⁶Sr value of the dolostone is consistent with contemporaneous seawater, while the δ¹³C and δ¹⁸O values are lower than those of the contemporaneous seawater. The δ²⁶Mg value is small (Min=-2.31‰). Powder crystal, fine-crystalline, and calcite dolostones with coarser and more ordered crystals exhibit similar δ¹³C and ⁸⁷Sr/⁸⁶Sr values to microbial and microcrystalline dolostone. During the sedimentary period of the Dengying Formation, ancient marine conditions were favorable for microbial survival. Microorganisms induced the direct precipitation of primary dolomite in seawater, forming microbial and microcrystalline dolostones during the seawater diagenesis period. During the subsequent diagenesis period, dolostones underwent the effects of dissolution-recrystallization, structures, and hydrothermal fluids. This resulted in the formation of dolostone with coarser crystals, a higher degree of order, and various types of cement. The Longwangmiao Formation was developed in an inter-platform beach characterized by special particle dolostone. The particle dolostone has a large grain size (>30μm), high order degree (Min=0.7), small unit cell parameters, high Na content (Max=432ppm), and low Fe and Mn content. The δ²⁶Mg and δ¹³C values are consistent with the contemporaneous seawater, while the δ¹⁸O and ⁸⁷Sr/⁸⁶Sr values are higher than those of the contemporaneous seawater. There is mutual coupling between multiple-period varying δ²⁶Mg values and sedimentary cycles. The dolostone in the Longwangmiao Formation resulted from the metasomatism of limestone by evaporated seawater. The thickness and scale of the dolostone in the Longwangmiao Formation are controlled by the periodic changes in sea level. The period of dolostone development from the Sinian to the Cambrian coincides with the transition from Rodinia’s breakup to Gondwana’s convergence. These events have resulted in vastly different marine properties, microbial activities, and sedimentary climate backgrounds between the Sinian and the Cambrian. These differences may be the fundamental factors leading to the distinct origins of dolostone formed in the two periods. The distribution of sedimentary facies and deep tectonic activities in the Sichuan Basin from the Sinian to the Cambrian is influenced by the breakup and convergence of the supercontinent. This process plays a key role in determining the distribution, pore formation, preservation, and adjustment mechanisms of ultra-deep dolostone reservoirs. To effectively analyze the genesis and reservoir mechanisms of ultra-deep dolostone in other regions or layers, especially during the specific period of supercontinent breakup and convergence, it is crucial to consider the comprehensive characteristics of seawater properties, microbial activities, sedimentary environment, and fault systems driven by tectonic activities. This can help predict the distribution of high-quality and large-scale ultra-deep dolostone reservoirs.

DOI: 10.1007/s11430-023-1301-x

Source: https://www.sciengine.com/SCES/doi/10.1007/s11430-023-1301-x