Abstract Using micro-CT imaging and differential pressure measurements, we design a comparative study in which we simultaneously measure relative permeability and capillary pressure on the same reservoir sandstone sample under water-wet and mixed-wet conditions during steady-state waterflooding experiments. This allows us to isolate the impact of wettability on a pore-by-pore basis and its effect on the macroscopic parameters, capillary pressure and relative permeability, while keeping the pore-space geometry unchanged. First, oil and brine were injected through a water-wet reservoir sandstone sample at a fixed total flow rate, but in a sequence of increasing brine fractional flows with micro-CT scans of the fluid phases taken in each step. Then the sample was brought back to initial water saturation and the surface wettability of the sample was altered after prolonged contact with crude oil and the same measurement procedure was repeated on the altered-wettability sample which we call mixed-wet. Geometric contact angles were measured, which discriminated the water-wet and mixed-wet cases with average values of 75° and 89° respectively. Additionally, an energy balance was used to determine the effective contact angles for displacement which indicated that a higher advancing contact angle of 116° was needed to displace oil in the mixed-wet case. For the water-wet experiment the filling sequence was pore-size dependent, with a strong correlation between pore size and oil occupancy. However, in the mixed-wet experiment the principal determinant of the filling sequence was the wettability rather than the pore size, and there was no correlation between pore size and the residual oil occupancy. The oil-water interfacial area had a larger maximum in the mixed-wet case which was supported by the observation of sheet or saddle-like menisci shapes present throughout the sample volume that impede the flow. These shapes were quantified by much larger negative Gaussian curvature which indicated better connectivity of the phases, consistent with the lower residual oil saturation. Mean curvature and associated capillary pressure were positive for the water-wet case but decreased to a negative value for the mixed-wet case pointing to forced displacement from oil-wet pores. This analysis explained why the relative permeabilities for the mixed-wet case were lower than for the water-wet case for the same fractional flow.

中文翻译：

---

在水湿和混湿条件下测量同一储层砂岩样品的相对渗透率和毛细管压力的孔隙尺度成像

摘要 利用显微 CT 成像和压差测量，我们设计了一项对比研究，在稳态注水实验中，我们在水湿和混合湿条件下同时测量同一储层砂岩样品的相对渗透率和毛细管压力。这使我们能够逐个孔地隔离润湿性的影响及其对宏观参数、毛细管压力和相对渗透率的影响，同时保持孔隙空间几何形状不变。首先，将油和盐水以固定的总流速通过水湿储层砂岩样品注入，但按顺序增加盐水分流，并在每个步骤中对流体相进行微 CT 扫描。然后将样品恢复到初始含水饱和度，在与原油长时间接触后，样品的表面润湿性发生变化，对润湿性改变的样品（我们称为混合湿）重复相同的测量程序。测量几何接触角，区分水湿和混合湿情况，平均值分别为 75° 和 89°。此外，使用能量平衡来确定置换的有效接触角，这表明在混合湿情况下需要更高的 116° 前进接触角来置换油。对于水湿实验，填充顺序取决于孔径，孔径与油占有率之间有很强的相关性。然而，在混湿试验中，填充顺序的主要决定因素是润湿性而不是孔径，孔径与剩余油占有率之间没有相关性。油水界面面积在混合湿情况下具有更大的最大值，这得到了整个样品体积中存在的阻碍流动的片状或鞍状弯月面形状的观察支持。这些形状由更大的负高斯曲率量化，这表明相的连接性更好，与较低的残余油饱和度一致。平均曲率和相关毛细管压力在水湿情况下为正值，但在混合湿情况下降至负值，表明油湿孔隙中的强制置换。