泡沫对基质—裂缝双重介质系统渗透性的影响

泡沫作为一种两相分散软物质体系，在非均质油藏调剖、裂缝性油藏防窜及非常规油藏压裂酸化中得到日趋广泛的应用。但泡沫体系在基质-裂缝系统运移过程中，会导致局部捕集、滞留、堆积等现象，影响系统尤其是基质的渗透能力。研究以表面活性剂泡沫和纤维素纳米纤丝（NCF）强化泡沫为对象，建立了评价泡沫体系对基质裂缝双重介质系统渗透性影响的评价方法，并阐明了两类泡沫的运移和分布规律。实验采用4个级别渗透率（0.13~239.60 mD）的岩芯，建立了压差、基质侵入深度、残余阻力因子与渗透率的关系。研究发现，泡沫体系可以顺利通过23.00 mD的岩芯，不会影响基质渗透能力；当泡沫侵入低渗透和致密基质（低于3.13 mD）后，由于物理吸附、机械滞留等作用，基质渗透率显著下降，NCF泡沫和表面活性剂泡沫对基质渗透性的影响程度接近。另外，NCF起泡液主要滞留在裂缝壁面，尤其是在渗透率不高于8.5 mD的基质-裂缝系统中，起泡液整体滤失量少，去除表面堆积后，基质渗透率可以快速恢复。研究结果可为泡沫在基质-裂缝系统尤其是低渗/致密基质中运移和分布规律提供参考，为评价泡沫对系统渗透能力的影响提供方法。

Impact of Foam on the Permeability of Matrix-fracture Dual Systems and Evaluation Method

As a favorable two-phase dispersive soft mater, foam is being extensively used for conformance control in heterogeneous reservoirs, gas channeling prevention in fractured reservoirs, and fracturing acidification in unconventional reservoirs. However, during transporting in matrix-fracture systems, foam usually leads to local capture, retention and accumulation, which might affect the permeability of the whole system especially matrix. In this study, we propose a method that assess the impact of foam on the permeability of matrix-fracture dual systems by using a surfactant foam and a cellulose nanofibrils (NCF) strengthened foam. The flow behaviors and distribution of foam systems in matrix-fracture systems are revealed. In total of four permeability-grade cores were used (0.13~239.60 mD), and the correlations between differential drop, invading depth, residual resistance factor and permeability are established. The results show that the foam could successfully flow through the cores with the permeability larger than 23.00 mD. The invasion of foam into low permeability(less than 3.13 mD) and tight-matrix leads to the reduction of permeability because of adsorption and/or mechanical retention. The influence degree of NCF foam is found to be analogous to that of surfactant foam. In addition, the foaming agent in the presence of NCF mainly retains on the fracture surface with few mass loss especially for the matrix with permeability lower than 8.50 mD. The permeability of the matrix is rapidly retrieved once the deposition is rinsed off the surface. The results of this study guide the investigation of foam transport and distribution in matrix-fracture systems especially for low permeability and tight matrix, and also provide method to assess the impact of foam on the permeability of matrix-fracture systems.