| dc.description.abstract | The initial wetting of carbonate reservoirs is of great importance to the overall oil recovery and smart water processes. Crude oil is a complex mixture of organic components, and the polar components present in it can have a large impact on wettability. This study aims to improve the understanding of the initial wetting in chalk, caused by adsorption of polar organic oil components. The main objective is to obtain a better understanding of the adsorption of basic crude oil components onto carbonate chalk surfaces.
In this study two chalk cores were cleaned and flooded at 50 °C with a synthetic crude oil, containing a higher amount of bases compared to acids. The acid number (AN) and base number (BN) of the injected oil was known (AN=0.07 and BN=0.32), and effluent samples were collected and analyzed. Furthermore, the wettability of the cores after oil flooding was assessed. In order to see how the adsorption affected the initial wettability of the chalk cores, spontaneous and forced imbibition experiments were performed with formation water. This was followed by chromatographic wettability tests in order to confirm the wetting state. A 100% water-wet reference core was prepared for comparison purposes, and spontaneous imbibition by formation water and chromatographic wettability test was performed on the reference core.
The results showed that initially there was instantaneous adsorption of bases. The BN values reached equilibrium quite rapidly, before 2 PVs injected. The AN values obtained are within the area of uncertainty, possibly due to their relatively low concentration. Most likely the basic material is being complexated to the acidic components. Comparing the results to those of an oil with the same BN, but a higher AN, showed a large difference in adsorption. The adsorption of basic components, BNads, was quantified to 0.26 and 0.36, which are low values compared to those of ANads presented in previous studies. This strengthens the belief that the bases follow the acids. Spontaneous imbibition and chromatographic wettability tests compared to a 100% water-wet reference core, showed that the wettability was altered from very water-wet to quite water-wet. | nb_NO |
