Impact of Organic Acids/Chelating Agents on Rheological Properties of Amidoamine Oxide Surfactant
- Lingling Li (Texas A&M University) | Hisham A. Nasr-El-Din (Texas A&M U.) | James B. Crews (Baker Oil Tools) | Kay E. Cawiezel (BJ Services Company)
- Document ID
- Society of Petroleum Engineers
- SPE International Symposium and Exhibiton on Formation Damage Control, 10-12 February, Lafayette, Louisiana, USA
- Publication Date
- Document Type
- Conference Paper
- 2010. Society of Petroleum Engineers
- 4.2.3 Materials and Corrosion, 5.2.1 Phase Behavior and PVT Measurements, 4.1.2 Separation and Treating, 3.2.4 Acidising, 4.1.5 Processing Equipment, 5.4.10 Microbial Methods, 1.8 Formation Damage, 2.5.2 Fracturing Materials (Fluids, Proppant), 1.10 Drilling Equipment, 5.8.7 Carbonate Reservoir
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Surfactant-based acids have been used for acid diversion because they are less damaging to the formation. Amphoteric viscoelastic surfactant is the main type of surfactants being used today. Low viscosity is observed in the live acid systems, whereas significantly increased viscosity is found when HCl reacts with carbonate and generates divalent salts. The surfactant-acid system can be broken after acid treatments by mixing with reservoir hydrocarbons, or by using an external or internal breaker.
Amidoamine oxide, an amphoteric surfactant, was examined in this work. The prepared surfactant-based live acid system contained 20 wt% HCl, 4 wt% surfactant and 1 wt% corrosion inhibitor. Different organic acids/chelating agents were added to live and spent acids. Calcium carbonate particles were used to neutralize live acids. The objective was to examine how these organic acids/chelating agents affected the rheological properties of spent acid systems. Measurements were made at temperatures from 75 to 200 oF, at a shear rate of 10 s-1 at 300 psi. Several simple organic acids (formic acid, acetic acid, propionic acid, and butyric acid), chelating agents (glycolic acid, lactic acid, gluconic acid, citric acid, tetrasodium EDTA, tetrasodium GLDA and disodium HEIDA) that are used in the field were examined.
Experimental results indicated that the addition of organic acid/chelating agents significantly reduced the viscosity of spent acids. This reduction in viscosity increased with the number of carbon atoms in the acid. The addition of organic acids reduced the temperature range where the surfactant can be used. Chelating agents (a-hydroxyl carboxylic acids and amino acids) also tended to break the surfactant gel if enough acid was used. Based on the results obtained, organic acids can be used to break surfactant gel. TEM tests were first conducted to examine how organic acids/chelating agents interfered with the formation of rod-like micelles in the surfactant-based acid. The results showed that the addition of organic acids to the spent acid generated less elongated micelle structures and resulted in less apparent viscosity. In addition, if chelating agents or simple organic acids are used, then the concentration of the surfactant should be increased to compensate for the loss of viscosity induced by the addition of the organic acids.
Surfactant-based acids were introduced over the last few years to overcome the potential disadvantages of polymer-based acids (Chang et al. 2001, 2002; Qu et al. 2002; Nasr-El-Din et al. 2003c; Fu and Chang 2005). Unlike conventional crosslinked acids, surfactant-based acid fluids do not require any metallic crosslinker and they can reduce friction pressure significantly through coiled tubing. These systems were successfully used in both matrix stimulation (Al-Mutawa et al. 2005; Nasr-El-Din et al 2006b; Lungwitz et al. 2007), and acid fracturing (Al-Muhareb et al. 2003; Nasr-El-Din, 2003b).
After the acid reacts with the carbonate rock, pH increases and concentrations of divalent cations (Ca (II) and Mg (II)) increase in the spent acid. The presence of salts and increased pH cause the surfactant molecules to form long rod-like micelles, which significantly increase the apparent viscosity of the solution. Converting rod-like micelles to spherical micelles is necessary to break the gelled spent acid. This can be achieved in water injectors by reducing the concentration of salts and/or surfactant. Hydrocarbon phase, oil or condensate, can be used to break the surfactant gel in oil and gas wells. External (mutual solvent) and internal breakers have also been used to break the rod-like micelle successfully (Nelson et al. 2005; Crews 2005; Crews and Huang 2007).
Field application using surfactant-based acids was very positive (Samuel et al. 2003; Nasr-El-Din and Samuel 2007). However, Al-Nakhli et al. (2008) noted that amphoteric and cationic surfactants contained functional groups that can interact in concentrated HCl acid solutions with Fe (III). Viscoelastic surfactants can form a complex with iron (III) which precipitates at high iron (III) concentrations.
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