Compatibility and Phase Behavior Studies Between Corrosion Inhibitor and Surfactants-Based Acids
- Lingling Li (Akzo Nobel Surface Chemistry LLC) | Hisham A. Nasr-El-Din (Texas A&M University) | Jian Zhou (Akzo Nobel Surface Chemistry LLC) | Stuart Peter Holt (Akzo Nobel Surface Chemistry LLC)
- Document ID
- Society of Petroleum Engineers
- SPE International Symposium and Exhibition on Formation Damage Control, 15-17 February, Lafayette, Louisiana, USA
- Publication Date
- Document Type
- Conference Paper
- 2012. Society of Petroleum Engineers
- 1.8 Formation Damage, 4.1.5 Processing Equipment, 5.4.10 Microbial Methods, 4.2.3 Materials and Corrosion, 5.8.7 Carbonate Reservoir, 5.2.1 Phase Behavior and PVT Measurements, 3.2.4 Acidising, 4.1.2 Separation and Treating, 2.5.2 Fracturing Materials (Fluids, Proppant)
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A good surfactant-based acid should have the following properties: thermal stability, compatibility with cations, low viscosity in live acids but high viscosity in spent acids, ease to be removed by internal or external breakers, and no harm to the environment. Corrosion inhibitors must be added to the acid system to protect well tubulars and minimize the Fe contamination. The components of corrosion inhibitor usually contain short-chain alcohols (e.g. isopropyl alcohol) that can significantly affect the properties of surfactant-based acids. Therefore, corrosion inhibitor plays an important role in evaluating acid systems.
Two amine oxide surfactants (S and SW) were examined in this work. The composition of the surfactants was similar, but there was more 1,2 propanediol in surfactant SW. Three corrosion inhibitors (A, B, and C) were tested and all of them contained a certain amount of propargyl alcohol. However, there was a larger amount of isopropanol in corrosion inhibitor A, and more butanol in corrosion inhibitor B. A HPHT rheometer was used to measure the rheological properties (viscosity, G' and G'') of surfactant-based water system, live and spent acids from 75 to 300oF at 300 psi.
The results show that the addition of corrosion inhibitor to spent acid significantly reduced its elastic (G') and viscous modulus (G''). The maximum temperature that these two surfactants can be used was 220oF. Compared to surfactant-based acids made with corrosion inhibitor B or C, the acids with corrosion inhibitor A showed a much higher viscosity, but phase separation was observed after heating to 300oF. Although corrosion inhibitor B was compatible with surfactants, it adversely influenced the rheological properties of acids. If corrosion inhibitor C was used, the system with surfactant SW can be effectively used at temperatures above 150oF; whereas acids prepared with S1 can be efficiently applied at lower temperatures (<150oF). Cryo-TEM studies showed that corrosion inhibitors affected the rod-like micelle network, which caused the reduced apparent viscosity. Results of this work can be used to better select acid additives to maximize the performance of amine oxide-based acids.
Surfactant-based acids were introduced over the last few years to overcome the potential disadvantages of polymers (Chang et al. 2001; 2002; Qu et al. 2002; Nasr-El-Din et al. 2003b; Fu and Chang 2005). These systems were used successfully in both matrix stimulation (Taylor et al 2003; Al-Mutawa et al. 2005; Nasr-El-Din et al. 2006; Lungwitz et al. 2007) and acid fracturing (Al-Muhareb et al. 2003; Nasr-El-Din et al. 2003a). Field application using surfactant-based acids was very positive (Samuel et al. 2003; Nasr-El-Din and Samuel 2007).
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. Both factors cause the surfactant molecules to form long rod-like micelles that will increase the apparent viscosity of the solution significantly. 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 by the injection water. Hydrocarbon phase 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).
Corrosion inhibitors must be used in the surfactant-based acids to protect tubings and avoid Fe contamination. Nasr-El-Din et al. (2008) and Li et al. (2010) reported that the addition of corrosion inhibitor to surfactant-based acid reduced its apparent viscosity. Besides, it also affected the compatibility between the surfactants and acid additives.
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