Wettability Alteration at Elevated Temperatures: The Consequenses of Asphaltene Precipitation

Abstract

Abstract Asphaltenes are undoubtedly one of the important difficulties in the oil industry; its precipitation can impose specific affects on the productivity of the producing zone, as well as in the surface facilities and transportation lines. The main in situ consequences are their effect on the permeability by pore blockade, and on the wettability alteration by surface precipitation. In this paper, thermally induced wettability alteration is studied experimentally. The changes in the rock mineral content after imposing heat as the effect of thermal oil recovery are also studied using XRD. The results verify that asphaltene precipitation could be considered as the main platform for wettability reversal and the permeability reduction in the treated zone. The results also clarify the contradictory doubts around wettability alteration during thermal treatment in the literature. The experimental data shows that the media is gradually altered to strongly oil-wet in the temperature range of 150 – 400°C and subsequently changed to water-wet as the temperature increased. Furthermore, the effects of temperature on asphaltene destabilization and precipitation is studied and the required thermodynamic criterion for asphaltene precipitation is found. The asphaltene precipitation in the formation by the thermal oil recovery techniques is thermodynamically modeled using regular solution theory. The simulated date obtained using the model verifies by the experimental results. The model shows that as formation temperature increases toward crude oil's bubble point, its molar volume increases and solubility of the asphaltene decrease. This leads to asphaltene precipitation, and alteration of wettability toward strongly oil-wet condition. At temperatures higher than the crude oil bubble point, precipitated asphaltene start to dissolve, mainly due to evaporation of crude oil saturates. This stimulates a wettability shift toward more water-wet condition.