致密油储层孔隙尺度注水吞吐油水两相渗流机理研究

Abstract: As the micro-nano pores and throats are widely developed and poorly connected in tight oil reservoirs, it is the foundation for development in tight oil reservoirs by generating factures based on the large-scale volume fracturing technology. The injected water by conventional method would break through the artificial fractures or high permeability zones, resulting in rapid flooding in oil wells and reducing oil recovery. Water-flood huff and puff is an effective way for tight reservoirs development, and the essence is to draw oil from the pore space by dynamic imbibition. Effects of the microstructure, wettability, fluid properties, injection pressure and etc. during water-flood huff and puff process make the percolation of oil and water in the pores and throats is extremely complicate and restrict the effective application of the water-flood huff and puff in development of tight reservoirs. In this project, we mainly focus on cores of tight oil reservoirs, based on the accurate representation of the pore-throat structure, the water-flood huff and puff experiments combining the NMR and the dynamic network simulation are introduced to represent the water-flood huff and puff process. Effect of varies influencing factors is clarified and the mechanism of the dynamic imbibition in micro-nano pores and throats is also revealed, which laid the foundation for the parameters optimization during water-flood huff and puff in tight oil reservoirs.

摘要（不超400字）：致密油储层基质主要发育微-纳米孔喉、连通性差，大规模体积压裂促生的缝网是致密油藏开发的基础。常规注入水极易沿裂缝等优势通道突进而极难注入基质孔隙空间，导致油井快速水淹，油藏采收率低。注水吞吐作为致密油藏开发方式之一，其实质为通过动态渗吸将基质孔隙空间油相采出。致密油藏注水吞吐过程储层微观结构、润湿性、流体性质、注水压力等均会对油水两相渗流产生影响，导致微纳米孔喉动态渗吸两相渗流规律复杂，制约了注水吞吐在致密油藏开发中的高效应用。课题基于致密油储层岩心开展相关研究，在表征储层微观孔喉结构的基础上，结合核磁共振注水吞吐实验和动态网络模拟表征孔隙尺度动态渗吸油水渗流过程，弄清不同因素影响下动态渗吸油水两相渗流规律，揭示基质微-纳米孔隙动态渗吸两相渗流机理，为致密油藏注水吞吐开发工艺参数优选奠定基础。

随着全球油气资源需求量持续增长和常规油气资源日益枯竭，以致密油为代表的非常规油气藏逐渐成为石油勘探开发的热点之一。致密油藏储层基质以微纳米级孔喉组合为主，储层物性极差，原始地层条件下孔喉内流体无法自然流动，单井几乎无自然产能，因此合理的开发方式和技术手段成为提升致密油藏采收率的关键基础。注水吞吐作为对常规直接注水工艺的改进，其实质为注入水通过动态渗吸作用进入储集空间实现驱油，达到提升油藏采收率目的。项目以新疆准噶尔盆地芦草沟组组和鄂尔多斯盆地长七致密油储层岩心为研究对象，通过开展铸体薄片、扫描电镜和高压压汞、恒速压汞、核磁共振等实验测试实验，分析提取储层微观结构特征参数，建立了表征致密油储层微观孔隙结构表征方法，获取了致密油储层基质完整孔喉分布，明确了了致密油储层二维孔隙结构参数与三维参数间的相关关系；结合致密油储层孔喉分布，建立了基于随机函数的致密油储层基质等效立方孔隙网络，构建了考虑微纳米孔喉空间油水两相微尺度效应、毛管力、粘滞力和重力耦合作用的动态模型，并引入逐次超松驰迭代法实现两相渗流模拟过程循环迭代的稳定收敛，在模型准确性验证的基础上，开展了不同注水压力、孔喉分布、润湿性、驱替时间和油水性质等条件下油水两相渗流过程模拟，表征了不同条件下致密油储层基质孔隙空间油水两相渗流特征，明确了不同因素对油水两相渗流及空间分布的影响，揭示了致密油储层水驱油及剩余油空间残余机制；同时，结合低场核磁共振技术，开展了致密油储层岩心水驱油核磁共振实验，结合T2谱和核磁共振成像揭示了孔喉空间分体分布变化规律。项目研究初步弄清基质微-纳米孔隙不同因素影响下动态渗吸油水两相渗流规律及两相渗流机理，为致密油藏注水吞吐开发工艺参数优选提供理论支撑。