Weakly Emulsifying Surfactant Reduces Formation Damage and Enhances Well Productivity in Acid Stimulation
- Liang Xu (Multi-Chem, A Halliburton Service)
- Document ID
- Society of Petroleum Engineers
- SPE Western Regional & AAPG Pacific Section Meeting 2013 Joint Technical Conference, 19-25 April, Monterey, California, USA
- Publication Date
- Document Type
- Conference Paper
- Society of Petroleum Engineers
- 5.1.1 Exploration, Development, Structural Geology, 5.8.6 Naturally Fractured Reservoir, 3.2.4 Acidising, 4.1.5 Processing Equipment, 4.1.2 Separation and Treating, 2.5.2 Fracturing Materials (Fluids, Proppant), 4.3.3 Aspaltenes, 1.8 Formation Damage, 4.3.4 Scale
- acidizing, surfactant, formation damage
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Surfactant is a critical component used during acid stimulation. While many variables, such as interfacial surface tension, wettability, and compatibility with other acid additives, must be considered to tailor a surfactant to specific well conditions, the focus is on the most fundamental property of a surfactant, which is its emulsification tendency. The technical norm for surfactant applications in acidizing, however, is that a non-emulsifying (NE) surfactant should be selected to avoid the formation of tight emulsions. Tight emulsions are thought to block the oil and gas flow by plugging the pore throats in the rocks. While this concept is true to some degree, it neglects the ultimate purpose of surfactant use. In contrast, a weakly emulsifying (WE) surfactant is capable of generating transient oil in water emulsions with lower viscosity; thus, mobilizing the oil more effectively.
In this study, the primary difference between NE and WE surfactant is highlighted in terms of emulsion tendency and using preliminary production data from multiple wells in the Monterey formation.
Surfactant is widely used during acid stimulation. In particular, NE surfactants have been the field standard and are typically added to acid to help prevent acid-oil emulsification (Kalfayan 2008). This conventional approach, however, does not appear to consider the most fundamental property of a surfactant, which is its emulsification efficiency (Xu and Fu 2012). In other words, oil molecules must be dispersed in an acid external emulsion to reach a relatively low interfacial surface tension. By forming oil in acid emulsions, the tendency for oil molecules to migrate from the interior of the reservoir to the wellbore is greatly enhanced, which can be accomplished using a WE surfactant. WE surfactant is fundamentally different from NE surfactant in that it is capable of generating short-lived oil in acid emulsions. Most importantly, the emulsions are thought to break and reform whenever there is any degree of shear flow in the reservoir.
In this study, the primary difference between NE and WE surfactants is highlighted in terms of emulsion tendency and using production comparisons from multiple wells in the Monterey formation.
Oil composition analysis was performed by following standard titration for determining acid and base numbers. Sludge and emulsion tendency tests were conducted by mixing equal volumes of crude oils and 15% HCl acid for at least 30 min at reservoir temperature. A total of 4,000 ppm of either NE or WE surfactant was added to the acid phase before mixing. Spent acid was prepared by adding MgCl2 and CaCl2 to 15% HCl acid, in which the pH was raised to 4.0. Emulsion tendency was monitored by placing samples in an emulsion dispersion analyzer at ambient temperature, and the oil/acid separation rates were tracked by light scattering.
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