Asphaltene Precipitation Models: A Review

Abstract

Asphaltenes are the heaviest and the most polar fraction of crude oil and are defined as a solubility class (typically soluble in toluene but insoluble in n-alkanes like n-heptane).Precipitation and deposition of asphaltenes during production, processing and transportation of oil is a major challenge faced by oil industry. Over the last thirty years, a number of different models have been proposed for predicting the onset of asphaltene precipitation and also the amount of precipitated asphaltenes. This article reviews the different models that have been proposed for predicting asphaltene precipitation either at atmospheric pressure or under depressurization. A brief summary of the different modeling approaches is presented followed by description of work done by different research groups. Our focus will be on the description of the basic assumptions underlying different models and also the ability/performance of the model to match the experimental data. Finally, a comparison of models is presented and discussed along with suggestions for improvement. Keywords:Asphaltene precipitation, Thermodynamic models, Solubility models, Equation of state models, Colloidal models INTRODUCTIONAsphaltenes are considered to represent the most polar and the heaviest components in crude oil. 1 They are a solubility class and defined as the fraction that is insoluble in n-alkane (like n-heptane) but soluble in aromatic solvents (like toluene). [2][3] The precipitation and deposition of asphaltenes during production and transport of crude oil is recognized as a serious problem in the oil industry since it can lead to formation damage, plugging of wellbores and production facilities. [4][5] Asphaltene precipitation can be encountered during primary recovery of oil as well as during enhanced oil recovery operations like miscible flooding with CO 2 or natural gas. 6The precipitation of asphaltenes occurs due to a number of reasons. These include changes in pressure, temperature, chemical composition of crude oils, acid stimulation, mixing of oil with diluents, other oil and gas components like CO 2 . 4 Heavy crudes usually have a lower tendency to give asphaltene deposition problems inspite of their higher asphaltene content.This observation is normally attributed to their higher resin content and lower saturate content. 7Asphaltenes are generally assumed to be composed of fused ring aromaticity, small aliphatic side chains and heteroatom functional groups. 8 The molecular weight of asphaltenes has been a source of controversy for a very long time. 9 It is now recognized to be close to 750 g/mol with a factor of 2 in the width of the molecular weight distribution. Solubility ApproachThe solubility models are most commonly used for predicting asphaltene precipitation. These models make use of the concept of solubility parameter and assume that petroleum crude Models based on Solution theory and Flory-Huggins theory assume that asphaltenes have homogenous structure and properties while models based on Scott-Magat theory assum...

Further evaluation of the Re-Os systematics of crude oil: Implications for Re-Os geochronology of petroleum systems

“…The asphaltene molecules tend to aggregate even at low concentrations (50-100 mg/l) in solvents like toluene (Durand et al, 2010;Mullins et al, 2012;Yarranton et al, 2013), forming structures which could occlude and adsorb surrounding molecules. Asphaltene precipitation occurs in response to the changes in physical and chemical conditions within the petroleum system, e.g., pressure decrease and component changes, including gas (CH 4 and CO 2 ) injection and oil mixing (Buenrostro-Gonzalez et al, 2004;Subramanian et al, 2016).…”

Recent Developments on the Elucidation of Colloidal Aspects of Asphaltenes and Their Relevance to Oilfield Problems

“…One can view this process from two approaches: a molecular onebased on specific interactions considering the solubility of the species; and the colloidal one. 22 In the first approach, the assumption is that precipitation results from decreased solubility of dissolved asphaltenes in crude oil. In the second approach, asphaltenes are already present as colloidal particles that can aggregate leading to precipitation.…”

“…In the second approach, asphaltenes are already present as colloidal particles that can aggregate leading to precipitation. 22 The great difference between these two approaches can be considered the structure of interest itself: in the first one, the focus is directly on the molecules; while in the second one the process initiates from molecular aggregates (colloidal particles), with flocculation being the result of the alteration of the composition and/or balance of particle interactions. 22 Solubility models are based on the concept of solubility parameter (e.g., Hildebrand and Hansen), and assume the oil as being composed by asphaltene and maltene (deasphaltened oil).…”

“…Furthermore, changes in the solubility parameter of either phase may disrupt the equilibrium condition and eventually lead to precipitation. 22 Besides, the difference in asphaltenes composition should bring different solubility parameters, because there will be a difference in the balance of intermolecular interactions. 23 The Flory-Huggins theory, originally developed for polymer solutions, is widely used to describe the precipitation of asphaltenes.…”

Enhancing asphaltene precipitation modeling by cubic-PR solid model using thermodynamic correlations and averaging techniques

“…Modeling is coupled with the performed experiments to ensure reliability. Several models have been proposed in the literature to predict the behavior of the asphaltene precipitation process (Subramanian et al 2016). These models could be classified based on how the precipitation process is approached.…”