Surfactant-alternating-gas (SAG) is a favored method of foam injection, in part because of excellent gas injectivity. However, liquid injectivity is usually very poor in SAG. We report a core-flood study of liquid injectivity under conditions like those near an injection well in SAG application in the field, i.e., after a prolonged period of gas injection following foam. We inject foam [gas (nitrogen) and surfactant solution] into a 17-cm-long Berea core at temperature of 90 °C with 40 bar back pressure. Pressure differences are measured and supplemented with CT scans to relate water saturation to mobilities. Liquid injectivity directly following foam is very poor. During prolonged gas injection following foam, a collapsed-foam region forms near the inlet and slowly propagates downstream, in which water saturation is reduced. This decline in liquid saturation reflects in part liquid evaporation, also pressure-driven flow and capillary effects on the core scale. In the collapsed-foam region, liquid mobility during subsequent liquid injection is much greater than downstream, and liquid sweeps the entire core cross section rather than a single finger. Mobility in the region of liquid fingering is insensitive to the quality of foam injected before gas and the duration of the period of gas injection. This implies that at the start of liquid injection in a SAG process in the field, there is a small region very near the well, crucial to injectivity, substantially different from that further out, and not described by current foam models. The results can guide the development of a model for liquid injectivity based on radial propagation of the various banks seen in the experiments.

中文翻译：

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表面活性剂交替气体泡沫提高采收率液体注入的实验室研究

表面活性剂交替气体 (SAG) 是一种受欢迎的泡沫注入方法，部分原因在于出色的气体注入能力。然而，SAG 中的液体注入能力通常很差。我们报告了在现场 SAG 应用中，例如在注入井附近的条件下，即在泡沫产生后的长时间注气后，液体注入的岩心驱替研究。我们在 90 °C 的温度和 40 bar 的背压下将泡沫 [气体（氮气）和表面活性剂溶液] 注入 17 厘米长的 Berea 岩心。测量压力差并辅以 CT 扫描，以将水饱和度与流动性联系起来。紧接泡沫后的液体注入性非常差。在泡沫之后的长时间注气过程中，在入口附近形成一个塌陷的泡沫区域并缓慢向下游传播，其中水饱和度降低。液体饱和度的下降部分反映了液体蒸发，也反映了岩心尺度上的压力驱动流动和毛细管效应。在塌陷泡沫区域，后续液体注入过程中的液体流动性比下游大得多，并且液体扫过整个岩心横截面而不是单个手指。液体指法区域的流动性对气体注入之前注入的泡沫质量和气体注入时间的持续时间不敏感。这意味着在现场的 SAG 过程中液体注入开始时，有一个非常靠近井的小区域，对注入能力至关重要，与更远的区域大不相同，并且当前的泡沫模型没有描述。