| As two important parameters involved in the process of oil displacement, wettability and interfacial tension play a key role on the distribution and flow of crude oil and have an important influence on oil exploitation. Therefore, it is of great significance to change wettability of rock and select a system which has a suitable interfacial tension so that a higher oil recovery can be got after ASP flooding.In this paper, the pore structure of natural cores, artificial cores and Berea cores were studied. Three kinds of cores with two different permeabilities(about 300×10-3μm2 and 800×10-3μm2) were selected for mercury penetration experiment and capillary force graph is plotted. The pore and throat’s characteristics of different cores were analyzed. The results show that compared with artificial cores,Berea cores is greatly similar to natural cores no matter in pore structure or displacement rules. But problems exist that experimental results are in poor repeatability and parallel comparison test can not be conducted easily when natural cores used to do experiments because of the different clay content of natural cores in the same region. Therefore,the experiments results which carried out by Berea core are repeatable and can reflect the displacement characteristic of different ASP systems.ASP systems of three different interfacial tension levels, that is 10-1mN/m,10-2 mN/m,10-3 mN/m, were selected by TeaXs-500 Spinning Drop Interface tensiometer. In order to analysis how interfacial tension impact on recovery, displacement experiments were carried out in Berea cores with ASP systems of different interfacial tension levels. The experiment results express that chemical flooding recovery greatly improved with decreasing interfacial tension. The highest recovery will be achieved when interfacial tension reduces to 10-3mN/m.Berea cores in the permeability of 300×10-3μm2 were selected and placed in oleic acid solution with different concentration. Amott method was used to measure the wettability of cores. The results indicate that the average wettability index of original core is 0.79, performing strongly hydrophilic. The average wettability index of core which has been aged by 0.5% oleic acid is 0.28, performing slightly hydrophilic. Middle wet was expressed when Berea core was aged by 1.0%, with average wettability index is-0.07. The average wettability indexs of cores which have been aged by oleic acid in concentration of 1.5%、2.0%、3.0% and 5.0% are-0.28,-0.44,-0.45 and-0.43, performing slightly oil-wet or oleophylic. All results illustrate that oleic acid can change the wettability of rock. The degree of wetting reversal expands with increasing concentration of oleic acid. However, wettability of cores can not be changed more when the concentration of oleic acid rise to 2.0%, which means oleic acid can only change the wettability to slightly oleophylic or oleophylic.Oil displacement experiments with Berea cores were carried out under the condition of 10-3mN/m interfacial tension. The result shows that the recovery efficiency of water wet core is higher than that of oil wet core. In addition, there is not a big difference in the recovery between weak water wet core and intermediate wet, and both of them are higher than strongly wet core. |
PDF Full Text Request