Water-rock interaction cannot be ignored for shale reservoirs with high-salinity formation brine and complex rock composition, and stimulated by massive slick-water fracturing treatment. However, there have been few studies on the flowback model fully coupled with different effects of water-rock interaction. This paper presents the development of a coupled hydro-chemical-mechanical model for modeling water-rock interaction in fractured shale during the post-fracturing flowback period. The model considers distinguishing water-rock interaction phenomena, that is, mineral dissolution, clay swelling and chemical osmosis, and accounts for multi-phase flow in a fractured shale reservoir. The coupling and solution method and a numerical simulator were developed. Numerical simulation indicates that the swelling volume of clay minerals occupies the pores and leads to a decline in matrix porosity, while mineral dissolution increases both the matrix porosity and the solute concentration in the aqueous phase in matrix pores. Clay swelling mainly affects the shape of the porosity ratio profiles. The effect of mineral dissolution becomes increasingly stronger as flowback progresses. Mineral dissolution mainly affects the relative positions of the porosity ratio curves with the progress of flowback. The water-rock interaction coupled flowback modeling and the numerical simulation results in this study quantify the effects of chemical osmosis, clay swelling and mineral dissolution. Results from this study provide new insights into the mechanisms of fracturing-fluid flowback and value to flowback transient analysis.

中文翻译：

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压裂流体返排条件下页岩水岩相互作用的数学建模与数值模拟

高盐度地层卤水、岩石成分复杂、大规模滑溜水压裂改造的页岩储层，水-岩相互作用不容忽视。然而，关于完全耦合不同水岩相互作用效应的返排模型的研究很少。本文介绍了用于模拟压裂后返排期间裂隙页岩中水-岩相互作用的水-化学-力学耦合模型的发展。该模型考虑了区分水岩相互作用现象，即矿物溶解、粘土膨胀和化学渗透，并考虑了裂缝性页岩储层中的多相流。开发了耦合求解方法和数值模拟器。数值模拟表明，粘土矿物的膨胀体积占据孔隙，导致基质孔隙度下降，而矿物溶解增加了基质孔隙度和基质孔隙水相中的溶质浓度。粘土膨胀主要影响孔隙率分布的形状。随着回流的进行，矿物溶解的影响变得越来越强。随着返排的进行，矿物溶解主要影响孔隙率曲线的相对位置。本研究中的水-岩相互作用耦合返排模型和数值模拟结果量化了化学渗透、粘土膨胀和矿物溶解的影响。