实验研究碳酸盐岩埋藏溶蚀机制及其有利条件

It is gradually accepted that dissolution porosity is the significant reservoir space type for carbonate rocks. Some authors propose that significant volumes of porosity are created by burial dissolution in carbonate reservoirs. Due to a consistent lack of quantitative treatment, others argue that burial dissolution is unsupported by empirical data and violates important chemical constraints on mass transport. Dissolution simulation experiment is an important method to research carbonate dissolution mechanism and evolution. In this project, we will take Longwangmiao Formation of Lower Cambrian in Sichuan basin as the object of study. To investigate the formation mechanism of solution porosity of carbonate rocks, we used experiment to simulate the process and effort of carbonate burial dissolution. This research plans to choose various types of acid fluids and carbonate rocks as the experiment objects with stimulating experiments of burial dissolution being carried out under buried temperature and pressure. According to some theory as chemical thermodynamics, chemical kinetics, flow dynamics and solute transport, this research tries to find out the relation between carbonate dissolution amount and temperature, fluid properties, and reveal the chemical mechanism of carbonate burial dissolution, dissolved pore evolution and physical properties improvement. The ultimate aim of this study is to provide theory basis for researching the formation and evolution of carbonate large-scale dissolution and effective reservoir.

我国古老海相碳酸盐岩经历了多期次、多种类型的岩溶作用与改造，原生孔隙所剩无几，溶蚀孔（洞）成为重要的储集空间。目前，由于埋藏溶蚀作用机制及其规模发生条件尚不清楚，埋藏溶蚀产生的孔隙缺乏定量数据的支持，所以埋藏溶蚀作用对碳酸盐岩储集层贡献问题存在争议。溶蚀模拟实验是研究碳酸盐岩埋藏溶蚀机制、规模发生条件和储层改善效果评价的重要方法。本项目研究立足于“碳酸盐岩埋藏溶蚀机制及规模溶蚀发生条件”这一科学问题，运用碳酸盐岩溶蚀模拟实验方法，系统开展碳酸盐岩在不同温度和压力条件下与酸性流体的溶蚀实验，建立碳酸盐岩溶蚀量与温度和流体属性的定量关系，定量评价四川盆地下寒武统龙王庙组典型碳酸盐岩的埋藏溶蚀效果。依据化学热力学、化学动力学、水流动力学、溶质传输等理论，揭示埋藏环境下碳酸盐岩溶蚀作用的化学机制和规模溶蚀发生有利条件，最终为碳酸盐岩规模溶蚀和形成高效储层的成因和评价提供理论依据。

针对碳酸盐岩埋藏成岩过程中有机酸溶蚀化学机制、控制因素和埋藏溶孔演化等科学问题，开展了埋藏环境下碳酸盐岩与有机酸反应的模拟实验和理论分析，得到三点认识：①高盐度流体背景模拟实验表明，随着温度增加，碳酸盐岩的溶蚀量具有缓慢下降-缓慢上升-快速下降的特征，由于地层水两种相反离子效应的作用，在80～110℃范围内存在一个有利碳酸盐岩溶蚀的温度窗口；②有机酸溶液中盐离子能提高白云岩的溶蚀量，其中氯化镁体系效果最好，氯化钠体系次之，氯化钙体系提高相对有限。硫酸钠体系本身有利于提高白云岩的溶蚀量，且与氯化镁体系的效果基本一致，但在相对高温环境下白云岩溶蚀生成的Ca2+容易与SO42-结合生成CaSO4沉淀，进而导致白云岩的溶蚀量表现为减少；③通过粒间孔隙型、晶间孔隙型、溶蚀孔洞型、鲕模孔隙型和格架孔隙型五种碳酸盐岩的对比实验，认识到连通孔隙是埋藏溶蚀发生的先决条件和有利区域，碳酸盐岩内部组构差异会进一步加剧储集空间在孔、洞和缝组合上的复杂性。基于埋藏溶蚀孔洞发育主控因素和分布规律认识，通过四川盆地龙王庙组埋藏前孔隙分布图、筇竹寺组烃源岩在70℃-100℃温度窗生烃和生酸强度图、龙王庙组经历70℃-100℃温度窗时古隆起和断裂分布图、龙王庙组经历70℃-100℃温度窗时埋藏时间（Ma）等值线图的编制，预测了龙王庙组埋藏溶蚀孔洞的分布。