In this manuscript, we present the results of a systematic approach to investigate the impact of core scale heterogeneity on the efficiency of miscible CO₂ water-alternating-gas (WAG) flooding performance. Both vertical (by layering two axially-cut half plugs with differing permeability) and horizontal (stacking two smaller core samples with differing permeability in series) heterogeneities are explored. In the layered or vertically heterogeneous sample, the permeability ratio (PR) defines the ratio between the permeability values of each half plug. Our special sample construction technique using either a thin impermeable Teflon sheet to prevent flow communication or a thin tissue to promote flow communication has enabled us to investigate the effect of crossflow between half plug on the performance of the WAG flood. For the stacked composite or the horizontally heterogeneous core samples, short cylindrical core segments were used each with a different permeability value. We have also investigated the effect of the EOR injection mode (i.e. secondary vs. tertiary) on our results. For this study, core flooding experiments were performed using n-C₁₀, brine and CO₂ at a temperature of 343 K and a pressure of 12.4 MPa.

The results obtained for homogeneous, layered and composite samples indicate that CO₂ WAG flood performs better in all cases and achieves the highest recovery factor (RF) when conducted under the secondary mode (e.g. homogeneous: 93.4%, layered: 74.0%, and composite: 90.9%) compared with the tertiary mode (e.g. homogeneous: 74.2%, layered: 64.1%, and composite: 71.3%). For the layered samples, it was found that the oil recovery decreases noticeably with an increase in the permeability ratio (PR). For instance, RFs of 93.4%, 90.1%, 78.8%, and 74.0% correspond to PRs of 1, 2.5, 5, and 12.5, respectively. In contrast to our previous findings with continuous CO₂ flooding which showed that crossflow enhances recovery in layered samples, for this study using WAG, crossflow was found to negatively affect the RF. Such an outcome may be attributed to the conformance control achieved by WAG flooding which would be more pronounced in the case of non-communication layers (i.e. no cross flow). In other words, the higher oil recovery of WAG flooding in a non-communicating system may be due to the dominance of viscous forces and, to a lesser extent, the vanishing effect of gravity forces that tend to reduce sweep efficiency. The effect of composite heterogeneity on the RF was also investigated with the results showing that the permeability sequence along the length of a composite sample has a noticeable but more subtle impact on RF.

在这份手稿中，我们介绍了一种系统方法的结果，以研究核心尺度异质性对可混溶CO ₂效率的影响水交替气（WAG）驱油性能。探究了垂直（通过将两个轴向切割的具有不同渗透率的半塞子分层）和水平（堆叠了两个具有不同渗透率的较小岩心样品串联）的非均质性。在分层或垂直非均质样品中，磁导率比（PR）定义了每个半塞子的磁导率值之间的比值。我们的特殊样品构造技术使用了薄的不可渗透的特氟隆薄板来防止流动连通，或者使用薄的组织来促进流动连通，这使我们能够研究半塞之间的错流对WAG驱替性能的影响。对于堆叠的复合材料或水平非均质岩心样品，使用短圆柱状岩心段，每个段具有不同的磁导率值。我们还研究了EOR注入模式（即，二级与三级）对我们结果的影响。在本研究中，岩心驱油实验使用n -C ₁₀，盐水和CO ₂的温度为343 K，压力为12.4 MPa。

均质，分层和复合样品的结果表明，在次级模式下进行时，CO ₂ WAG驱油在所有情况下均表现更好，并且实现了最高的采收率（RF）（例如均质：93.4％，分层：74.0％和复合：90.9％），而三级模式（例如均质：74.2％，分层：64.1％，复合材料：71.3％）。对于层状样品，发现采油率随渗透率（PR）的增加而显着降低。例如，RF的93.4％，90.1％，78.8％和74.0％分别对应于PR分别为1、2.5、5和12.5。与我们先前关于连续CO _2的发现相反洪水表明，错流可以提高分层样品的回收率，对于使用WAG的这项研究，发现错流会对RF产生负面影响。这样的结果可能归因于通过WAG泛洪实现的一致性控制，这在非通信层（即无交叉流）的情况下会更加明显。换句话说，在非通信系统中，WAG驱油的较高采收率可能是由于粘性力的支配，而在较小程度上是重力力的消失，这往往会降低扫掠效率。还研究了复合材料异质性对RF的影响，结果表明，沿着复合材料样品长度的磁导率序列对RF有明显但更微妙的影响。