湖相致密碳酸盐岩微纳米孔隙系统流体运移机理及控制因素-以川中侏罗系大安寨段为例

The lacustrine tight carbonate reservoirs are widely distributed in China, and have vital significance for petroleum industry. The phenomenon of rapid decline and low recovery rate of oil and gas are common for tight reservoirs, and it has been proved that the main controlling factors are fluid migration characteristics in the micro-nano pore system. Current fluid migration studies are mainly based on numerical simulation and theoretical analysis, lacking the support of experimental tests, and most research focus on shale rather than carbonate. The lacustrine tight carbonate reservoirs of the Jurassic Da'anzhai Member in the Central Sichuan Basin develop micro-nano pores, and face serious challenge due to rapid production decrease and low recovery efficiency. Based on a combination of experimental simulation and geological theory, this study develops polar fluids and nanoscale tracers with different molecular sizes and vitality. Additionally, an analytical experiment system for fluid migration in the micro-nano pore system which is suitable for the lacustrine tight carbonate is made. The test system can provide quantification and visualization studies for the microscopic migration of different polar fluids in the micro-nano pore system. Taking rock components as a research link, the control mechanism of rock components-pore structure-wettability on fluid migration are studied. Based on study above, petrological characteristics which are conducive to microscopic migration of tight oil can be obtained, and the phenomenon of rapid decline and low oil recovery efficiency can be explained. The study can provide microscopic migration mechanism references for geological exploration direction and further exploration schemes.

湖相致密碳酸盐岩在我国分布广泛，具有重要的油气意义。致密（页岩）油气初期高产-快速递减与低采收率的现象较为普遍，其主要受控于微纳米孔隙流体运移特征。目前，微观流体运移分析主要以数值模拟和理论分析为主，缺乏微纳米下流体运移规律的实验分析，且研究主要集中在页岩，湖相碳酸盐岩的研究相对缺乏。川中侏罗系大安寨段湖相致密碳酸盐岩微纳米孔隙发育，其快速递减和低采收率的现象较为明显，正面临较大的生产压力。通过研发适用于湖相致密碳酸盐岩的不同极性流体和不同分子大小和活性的纳米示踪剂，以及流体微观运移分析系统的建立和完善，来实现对不同极性流体微观运移规律的定量化和可视化研究；并以岩石组分为研究纽带，探讨孔隙结构、润湿性与岩石组分的耦合关系及其对微观流体运移规律的控制作用，得出利于致密油微观运移的岩石学特征，分析湖相碳酸盐岩致密油低采收率的生产特征，从而为有利地质体和开采方案的确认提供微观运移方面的理论支撑。

湖相致密碳酸盐岩在我国分布广泛，且油气意义已逐渐得到证实，而致密油气初期高产-快速递减与低采收率的现象较为普遍。本项目以川中侏罗系大安寨段湖相致密碳酸盐岩为研究对象，通过流体微观运移分析系统的建立和完善，实现了对微观运移规律的系统研究；以岩石组分为研究纽带，探讨了微观流体运移规律的沉积-成岩控制作用，得出了利于致密油微观运移的岩石学特征；并通过微纳米孔隙系统流体运移规律的分析，解释了湖相碳酸盐岩致密油低采收率的生产特征。大安寨段湖相致密碳酸盐岩具有较为发育的微观储集空间且差异性明显，黏土基质类型可以提供丰富的微纳米储集空间，而碳酸盐质更有利于流体的运移和排出。方解石具有亲水性，但是经过长期地质过程特别是有机酸反应后其润湿性可以逐渐向亲油性转变，由碳酸盐质-硅质-混合质-黏土质基质的碳酸盐岩样品与蒸馏水的接触角逐渐增大，显示其亲油性逐渐增加。基质的不同物质组成导致了微纳米孔隙系统和润湿性的差异，这也决定了流体运移的差异性；非极性流体相对于极性流体来说其微纳米孔隙内运移速率更快。孔-缝双重介质系统是致密碳酸盐岩微纳米孔隙流体有效运移的关键；湖相致密碳酸盐岩微观流体运移需要各级孔缝系统的有效配合。由高能介壳滩，中-低能滩缘，低能滩前湖坡到半深湖相，微纳米储集空间呈现出了逐渐升高的趋势，孔径呈现出了逐渐减小的趋势。致密碳酸盐岩微纳米裂缝发育，可以作为油气运移和渗滤的有效路径，是油气有效补给的关键。纳米级基质孔隙保证了足够的储集空间，逐级有效的裂缝保证了油气能够顺利运移，各级孔缝同时发育对持续稳产具有重要意义。相关研究对于明确湖相致密碳酸盐岩微纳米孔隙特征、流体运移规律及油气生产特征具有重要的理论意义。