基于模拟实验探讨断裂-流体-岩石体系中的矿物溶解-沉淀过程

Exploring the mineral dissolution-precipitation processes in fracture-fluid-rock systems based on simulation experiments

丁茜 王静彬 杨磊磊 朱东亚 江文滨 何治亮

Qian DING Jingbin WANG Leilei YANG Dongya ZHU Wenbin JIANG Zhiliang HE

断裂体系中的流体-岩石相互作用及其成储意义一直都是业界关注的热点问题。流体沿断裂流动运移，溶解围岩矿物，沉淀新矿物，改变储集空间的形态，对碳酸盐岩储层形成与分布、油气运移及分布起十分重要的控制作用。查明深层-超深层含断裂碳酸盐岩储层的成因机理，具有重要的理论和实际意义。为此设计了基于塔里木盆地顺北地区奥陶系一间房组的高温高压溶蚀-沉淀模拟实验，并结合TOUGHREACT等数值模拟软件，以查明沿断裂流动的含CO盐水和碳酸盐岩相互作用的过程，考察温度、压力、流体性质、物理非均质性等因素的影响程度，计算裂缝内的钙离子扩散特征以及矿物溶解-沉淀的趋势。实验和计算结果显示：实验时间内整体反应以碳酸钙溶解为主，反应后样品储集性能得到改善，样品内裂缝宽度、数量和体积增加，样品渗透率和孔隙度增加。研究明确了样品物理非均质性和流体水力性质促进主裂缝成为主要流动通道。主裂缝内流动过程和反应过程相互促进，并且共同决定了主裂缝不仅是流体流动的优势通道和水-岩反应发生的主要场所，也会是具有潜力的优势储集空间。

Water-rock interactions in fracture systems and their significance to reservoir formation have always been a hot topic of interest for scholars around the world. Fluid may flow and transport along the fractures， dissolve surrounding rocks， precipitate new minerals， and change the morphology of storage space， all playing critical roles in the formation and distribution of carbonate reservoirs as well as hydrocarbon migration and accumulation. It is therefore of great theoretical and practical significance to identify the genetic mechanism of deep and ultra-deep fractured carbonate reservoirs. In this study， we carried out high-temperature and high-pressure dissolution simulation experiments on samples from the Ordovician Yijianfang Formation in the Shunbei area of Tarim Basin and performed numerical simulation with tools such as TOUGHREACT to identify the interaction mechanism between brine with dissolved CO and carbonate rocks， to investigate the influence of temperature， pressure， fluid property and physical heterogeneity， and to calculate the Ca diffusion properties and mineral dissolution/precipitation trends. The results show that the overall reaction is dominated by calcite dissolution with an increase in fracture width， number and volume， as well as sample permeability and porosity， indicating improvement of reservoir quality. This study clarifies that the physical heterogeneity and fluid hydraulic properties promote the main fractures as the main flow channels. The flow and reaction processes promote each other and together determine that the main fractures will not only be the dominant channels for fluid flow and the main place where water-rock reactions occur， but will also be the dominant reservoir space for oil and gas.

10.11743/ogg20230113