The asphaltene formation in the reservoir Essay

The asphaltene formation in the reservoir is introduce additional issues by injection of CO2 and light hydrocarbon gas. in fact , the destabilization of asphatene can be improve by the presence of light components in the crude oil. some searches have been done to discover the parameters influencing asphaltene precipitation and desposition in the production system . the main factor for the precipitation and desposition of asphaltene in the reservoir and wellbore is existence heavy component content in the crude oil. however ,there are some additional terms which influence asphaltene precipitation such as saturate components fraction( Carbognani, et al. 1999) and resin concentration in the crude oil (Hammami, et al. 1998). the variable such as pressure and temperature also affect the amount of asphaltene precipitation ,decreasing the fluid pressure until bubble point pressure increases asphaltene precipitation . although ,the asphaltene precipitation is decreased by decreasing the pressure to below the bubble point pressure .in fact, pressure reduction causes more expansion in the relative volume fraction of the light components with respect to heavy components. adding light hydrocarbon fraction in the fluid which destabilizes asphaltene showes similar behavior. in the other hand , the stability of asphaltene in the fluid is increase below bubble point pressure . light components are evaporated and the remaining fluid becomes more asphaltene soluble if the pressure decreases to below bubble point . but about the temperature, the affect of this feature on asphaltene is not well understood so far.
there are two classes of models which describe the asphaltene precipitation i) models involve the use of asphaltene properties, ii) the models based on the scaling approach .
those models which are based on asphaltene properties can be classified as the first class. the molecular weight, density and solubility parameters of asphaltenes are the terms which these models need. some good examples of these models could be Polymer Solution Modeling by Hirschberg et al. (1984), EOS Based Model by Gupta (1986), or solid model by Nghiem et al. (1993), Statistical Associating Fluid Theory by Chapman et al.(1989) , colloidal model by Victorov and Firoozabadi (1996) and etc.
measuring or estimating the solubility parameter and density of asphaltene is not too difficult although, finding the exact molecular weight cannot be reached easily . the reason of this fact is that asphaltenes are poly-disperse in both molecular size and polarity , and chemical associations are involved. if all models of this type assume that the asphaltene components can be lumped into a single pseudo-component, it would not be so hard to overcome this difficulity. In this way, the serious deviation in the calculated results can be cuased by this oversimplified assumption as indicated by the vapor-liquid equilibrium calculations of reservoir fluid mixture. the prevalent thermodynamic models are incapable of predicting asphaltene precipitation with out extensive data fitting based on many recent investigations there are two main reason for that i) lack of knowledge of the properties of asphaltene , and ii)some of assumptions involved which are not justified.