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Estimation of the Front Stable in Heterogeneous Micromodel by Using CCD Technology

Two-phase flow in pore network model have an importance effect in geological engineering processes. The influence of the stability of the interface on the saturation of the CO2/water in the heterogeneous model is of great significance to the CO2 capture and storage. Some of the assumptions or unexplained phenomena on the micro-scale can be explained by the inherent mechanism through the pore scale. In this study, CO2/water drainage and imbibition experiments were conducted in two-dimensional heterogeneous network model at 25 °C and 0.1 MPa. The effect of heterogeneity on the two-phase fluid interface was investigated in two different models. One is composed by cylinder and the other is network with pores and throats. Fluid injections were detected in real time by a CCD camera equipped with a LED light source with high resolution. Two sets of injection methods were chosen as the various velocities. Based on the time lapsed images, a detailed discussion about the instability of CO2/water interface and CO2 saturation variation was conducted. In the beginning, the displacement font is not very smooth but forms capillary fingerings by the influence of heterogeneity, which may decrease the displacement efficiency since it tends to create more water clusters compared to displacement in homogeneous conditions. The heterogeneity of the micromodel increases the instability of the interface. The variation of CO2 saturation is nonlinear and quantitative analysis is carried out. One turn point was found for CO2 saturation related to increasing flow rates. At the beginning, CO2 saturation is mainly dependent on capillary pressure and found that increasing injection rate result in an increase in CO2 saturation. After the turn point viscous force is dominant all injection rates. The effect of heterogeneity embodies in both capillary and viscous domains. The difference between the drainage and imbibition when main control force of the capillary force at low velocity and the viscous force at the high velocity is also described. We found that in imbibition displacement have a great relationship with the local geometry depend on the results about cylinder micromodel and pores and throats network. The viscous domains have the same regular pattern as for drainage. While the capillary domains differed between drainage and imbibition in different velocity and different heterogeneous structure. The saturation variation during the imbibition process showed that in type imbibition is the major displacement mechanism. In this study we use two kinds of injection methods, one is continuous and the other is discontinuous injection, we found that different injection methods can result in different displacement mechanisms and saturations during the experiment. In continuous injection experiment, CO2 saturation increased at the beginning then become decreased in highest speed. For discontinuous injection we will give a detailed discussion