Abstract
Emulsification has been widely used in the oil industry. The thermal stability of emulsified systems, such as emulsified gels or acids, is critical for the placement success of the emulsified system. Early separation of the system in a tubular well leads to corrosion. In the present study, the stability of emulsified polyacrylamide/polyethylenimine (PAM/PEI) gels is investigated in high-temperature and high-salinity (HTHS) environments. The influences of different parameters such as surfactant concentration, water–oil ratio, salinity, intensity of mixing and temperature on the droplet size and the emulsion thermal stability are studied. The droplet size of the PAM/PEI system, which is emulsified in diesel, decreases, and the separation time increases with increasing mixing speed, surfactant concentration, and salinity. The emulsions with smaller droplets are thermally stable compared with large droplets since the rate of droplet coalescence is low. The effect of emulsion stability on gelation kinetics and gel strength is investigated. The emulsification reduces both the gel strength and the gelation rate. The cross-linking (gelation) rate in the unemulsified PAM/PEI is almost ten times higher than that in the emulsified gels. This gelation process is slow in the case of stable emulsified PAM/PEI solution and is believed to be the result of limited heat and mass transfer. The emulsion stability achieved in this work adds to the current understanding of how to control emulsion stability through different parameters to withstand HTHS environments and how this stability influences the gelation process.
Highlights
Keywords Water in oil emulsion · Thermal stability · Droplet size · Gelation kinetics · Polymeric gel Emulsification techniques have long been used in various fields (Anderson and Daniels 2003; Friberg et al 2004; Dean et al 2009; Kasapis et al 2009; Osemeahon 2011; Rai and Pandey 2013)
The general trend observed was that the stability increased with decreasing droplet size, in agreement with previous reports
This behavior could be due to the low coalescence rate at smaller droplet sizes
Summary
Emulsification techniques have long been used in various fields (Anderson and Daniels 2003; Friberg et al 2004; Dean et al 2009; Kasapis et al 2009; Osemeahon 2011; Rai and Pandey 2013). Emulsification has been broadly applied in different applications in the oil industry (Ebeltoft et al 2001; Sayed et al 2013; Al-Yaari et al 2014). Emulsification techniques were introduced in the oil industry through the use of emulsified acids in 1933. Emulsified acids were invented to address corrosion problems rather than to improve the stimulation job (Al-Mutairi et al 2007). Many researchers have comprehensively studied this technique to better understand the advantages and disadvantages The stability and rheological properties of emulsified acids have been extensively investigated by studying the impact of different parameters such as surfactant concentration, dispersed-phase droplet size and acid volume fraction (see Sayed and NasrEl-Din 2011 and references therein)
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