An Investigation of the Effect of Aromatic, Anionic and Nonionic Inhibitors on the Onset of Asphaltene Precipitation

Document Type : Research Paper

Authors

1 Tarbiat modares University

2 Semnan University

3 Tarbiat Modares University

4 Islamic Azad University, Shahreza Branch

Abstract

The organic deposition particularly asphaltenes has many detrimental effects on the oil industries, such as plugging in pipelines, wellbore and facilities and subsequently, considerable reduction in well productivity.Asphaltenes are the most polar fractions, which they have been dispersed as colloidal clusters in crude oil. The accumulation of these clusters lead to the flocculation of colloids, and accordingly, formation of precipitation. Adding inhibitor is one of the ways to prevent clustering of asphaltene precipitation in crude oil. In this study, the effect of inhibitors to prevent asphaltene precipitation was investigated by viscometric method. At first, the different concentrations (1000 ppm, 2000 ppm, 10000 ppm and 20000 ppm) of some aromatic, anionic and nonionic inhibitors were prepared in a dead crude oil sample, and then the inhibition strength of samples was measured. The results showed that inhibition strength of inhibitors in low to moderate (1000 ppm – 10000 ppm) concentrations has a regular pattern, and it is associated with functional groups in chemical structure of inhibitors.
 
 

Keywords


 

 

1. Introduction

Asphaltenes are the most polar fractions which are dispersed as colloidal clusters in crude oil.  The accumulation of these clusters lead to the flocculation of colloids, and accordingly, formation of precipitation. The amphiphile molecules, often used as dispersants and preventive agents, cause the aggregation of asphaltene clusters. Actually, natural resins play the role of inhibitor in crude oil, and their functional groups act as a bridge between polar (asphaltenes) and nonpolar medium (bulk of oil) [1]. Whenever normal alkanes are added to a sample, the balance between micelles and bulk of oil is impaired; consequently, the concentration of monomeric asphaltenes increases in the bulk phase. As soon as the concentration of monomers reaches to the concentration of onset point, the process of deposition starts. The compounds with a nature similar to resins or those with acidic polar head groups that can be attached to micelles, can contribute to stabilization of the micelles. These chemical compounds can include natural resins which are derived from crude oil, or amphiphiles dissolved in oil (surfactants). The amphiphile molecules basically, at least consist of a polar head group and a long hydrocarbonic tail. The amphiphiles dissolved in oil (surfactants), is more effective than aromatics in prevention of asphaltene precipitation [2]. Middea (1991), investigated the amphiphiles dissolved in oil, and found that the head group polarity has a key role in stabilization of asphaltenes. Chang and Fogler (1994) showed that there are two important factors in stabilization of asphaltene: 1) the adsorption of amphiphile on asphaltene surface, 2) the establishment of a stable layer around asphaltene molecules. The researchers also found that an amphiphile should be an acid or similar to acid, because proton of H+ has an interaction with asphaltenes.  If H+ replaces another group, amphiphile loses its activity. Alsahaf et al. (2002) studied the inhibition effects of resins, toluene, deasphalted Oil (DO) and some of the surfactants [3,4].

Rocha Junior et al. (2006) investigated the inhibition capacity of some new chemical additives on three samples of Brazilian crude oil. The Ethoxylated Nonylphenol (low molecular mass), vegetable oils (Coconut Essential Oil, Sweet Almond, Andiroba and Sandalwood Oil) and organic acids (Linoleic، Caprylic and Palmytic) showed a strong effect in the prevention of asphaltene precipitation [5]. Ghloum et al. (2010), compared inhibition effect of three commercial and three non-commercial inhibitors (light cycle oil (LCO), heavy cycle oil (HCO) and diesel) for Marrat Kuwaiti Reservoirs crude oil. They concluded that commercial basic inhibitors in crude oil contain low saturation and high resins, and acidic inhibitor in crude oil containing high polarity are very effective in prevention of asphaltene precipitation [6]. The capacity of nanoparticles (TiO2, ZrO2 and SiO2) in organic-based nanofuilds for stabilizing asphaltene particles in oil was investigated by Mohammadi et al. (2011). They measured the hydrogen bonds between asphaltene and nano-particles by using Dynamic Light Scattering (DLS) method. The results showed that TiO2 nanoparticles in the acidic environment can greatly increase the stability of the asphaltenes. On the other, hand ZrO2 and SiO2 nanoparticles have less effect on the stability [7].

 

 

2. Research Method

 

 

The crude oil used in this study included a dead oil sample obtained from Iranian petroleum fields. The resins, saturates and aromatics and asphaltenes of oil sample was specified by SARA test method (Table 1).

 

 

Table 1. Characteristics of the used crude oil

Saturation

Aromatic

Resin

Asphaltene

Density (°API)

30.79

42.10

13.36

13.75

17.96

 

 

 

 

The inhibitors used included aromatic (Toluene), anionic (Linear DBSA, Branched DBSA, Triethanolamine Lauryl Ether Sulfate and Sodium Lauryl Ether Sulfate), nonionic (Coconut Diethanolamide and Ethoxylated Fatty Alcohol 9 Mole). The characteristics of the inhibitors are listed in Table 2 and their chemical structures are shown in Table 3.

 

Table 2. Characteristics of the used inhibitors

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---

---

Density at 20 0C(gr/cm3)

Molecular weight(gr/grmol)

Aromatic Inhibitors

---

---

---

0.8667

92.14

Toluene

% Anionic Active

Acidity

(mgr KOH/gr)

% Free Oil

%  Free Sulfuric Acid

Molecular weight(gr/grmol)

Anionic Inhibitors

96.4

183.9

1.89

1.35

322

Linear DBSA

96

180

2.2

1.8

321

Branched DBSA

 

70.17

---

1.94

---

387

Sodium Laurylether Sulfate

39.92

---

---

---

511

Triethanolamine Lauryl Ether Sulfate

ISO2271

ISIRI3178/23

ISRI3513

-

-

Test Method

Density at 20 0C(gr/cm3)

% Free fatty acid

%Free amine

% Free fatty matter

% Amid content

 

Non-Ionic Inhibitors

0.9971

0.21

3.24

4.3

82.68

Coconut Diethanol Amide

 

---

ISIRI2053

ISIRI2053

ISIRI2053

ISIRI2053

Test Method

---

---

Molecular weight(gr/grmol

Density at 60 0C(gr/cm3)

Acidity

(mgr KOH/gr)

---

---

---

662.96

0.9998

0.08

Ethoxylated Fatty Alcohol 9 Mole

---

---

ISIRI4722

---

AOCS Te 1a-64

Test Method

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table3. Chemical structure of the used inhibitors

inhibitor

Chemical structure

Toluene

 

Linear DBSA