Impact of Asphaltene Presence in Some Rock Properties

Abstract

Abstract Several studies have shown that asphaltene precipitation at porous medium level leads to changes in some of its properties, such as wettability and hydraulic conductivity. This work shows the results obtained in a study aimed at assessing the effect of asphaltenes and its occasional precipitation on wettability and permeability of rocks found in Venezuelan oil reservoirs. Fluids and cores from five crude reservoirs having different asphaltene contents and Berea cores plugs were used. Wettability measurements were performed by using a variation of Amott method. Similarly, measurements were effected on cores in which precipitation was induced by n-pentane injection. Permeability reduction was evaluated by carrying out displacements tests before and after the precipitation induction. All cases indicated the presence of changes in wettability. Such changes depend on the specific crude asphaltene content and always tend to an intermediate or preferential oil wettability condition, which does not increase during asphaltene precipitation. Mean hydraulic radius reductions in tests where the precipitation was induced were in the range of 93.3 – 47%, which corresponded to asphaltene retention values of 19 and 3.6 %PV, respectively. These reductions depend on the rock nature and the core properties: permeability, porosity and pore size distribution.