Modeling asphaltene precipitation in Algerian oilfields with the CPA EoS

Dounya Behnous,André Palma,Noureddine Zeraibi,João A.P Coutinho

doi:10.1016/j.petrol.2020.107115

Abstract

One of the major flow assurance problems afflicting the oil industry is the asphaltene precipitation during the production, transportation and storage of oil. The precipitation of these heavy compounds is responsible for changes in crude oil properties, increases in oil viscosity, and formation of deposits that reduce oil production and disable equipment leading to significant operational costs. In Algeria, the deposition of asphaltene in reservoirs and pipelines is a severe problem. During production the depressurization of reservoir fluid and the variations of thermodynamic conditions create the need to frequently pig the lines and, in some cases, to inject solvents and dispersants to maintain the production. The understanding of the asphaltene behavior and the prediction of its deposition in flow conditions is crucial to implement appropriate strategies for the prevention or remediation, especially in the wellbore region. In this work we used the CPA EoS to describe the asphaltene phase envelope and predict the PT regions of stability for five Algerian live oils. The model provides a very good description of the experimental behavior of live oils without and with gas injection. The sensitivity to SARA analysis data and its effect on the asphaltene phase boundaries were also analyzed.

Highlights

Asphaltenes are the heaviest constituents of crude oil and are considered a worldwide hazard for the oil industry
According to the modern concept, asphaltenes are fractions defined as a solubility class of petroleum which are insoluble in paraffin with low molecular weight (n-heptane, n-pentane) but soluble in aromatic solvents such as toluene and benzene Herzog et al (1988)
The central part of the asphaltene aggregates consists of a high molecular weight component surrounded and peptized by resins and smaller paraffinic hydrocarbons, which present hydrophilic properties when in presence of aromatics and resins Yen and Chilingarian (1994) According to Leontaritis and Mansoori (1987), asphaltenes are polar molecules bearing electrical charges which are involved in the structure of aggregates

Summary

Introduction

Asphaltenes are the heaviest constituents of crude oil and are considered a worldwide hazard for the oil industry. Equations of state (EoS) like the Cubic-Plus-Association (CPA) and the Perturbed Chain Statistical Associating Fluid Theory (PC-SAFT) have been used by many researchers to model asphaltene precipitation for live oils with or without gas injection, using different approaches. Their applications and limitations to model the phase behavior of asphaltenes have been illustrated in many works (Alhammadi et al, 2015; Gonzalez et al, 2007; Panuganti et al, 2012; Ting et al, 2003 ; Arya et al, 2016) Zhang et al (2012) used both the CPA and PC-SAFT equations of state. To forecast the deposition tendency of precipitated asphaltene particles and to obtain a profile of deposited asphaltenes using deposition simulators, it is essential to perform a characterization of the live oil in order to obtain an adequate thermodynamic model that describes the phase behavior of asphaltenes in the live oil

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Conclusion