Abstract
High quality polymer free CO2 foam possesses unique properties that make it an ideal fluid for fracturing unconventional shales. In this paper, the viscosity of polymer free fracturing foam and its empirical correlations at high pressure high temperature (HPHT) as a function of surfactant concentration, salinity, and shear rate are presented. Foams were generated using a widely-used surfactant, i.e., alpha olefin sulfonate (AOS) in the presence of brine and a stabilizer at HPHT. Pressurize foam rheometer was used to find out the viscosity of CO2 foams at different surfactant concentration (0.25–1 wt %) and salinity (0.5–8 wt %) over a wide range of shear rate (10–500 s−1) at 1500 psi and 80 °C. Experimental results concluded that foam apparent viscosity increases noticeably until the surfactant concentration of 0.5 wt %, whereas, the increment in salinity provided a continuous increase in foam apparent viscosity. Nonlinear regression was performed on experimental data and empirical correlations were developed. Power law model for foam viscosity was modified to accommodate for the effect of shear rate, surfactant concentration, and salinity. Power law indices (K and n) were found to be a strong function of surfactant concentration and salinity. The new correlations accurately predict the foam apparent viscosity under various stimulation scenarios and these can be used for fracture simulation modeling.
Highlights
Unconventional reservoirs, such as shales, have garnered much attention due to their significant amount of stored reserves [1,2,3,4]. These huge reserves are unlocked by fracturing shales [5]
C 60 was usedconcentration as foam and stabilizer. It was provided by Evonik Industries
Rheology of polymer free fracturing foam has been presented as a function of surfactant
Summary
Unconventional reservoirs, such as shales, have garnered much attention due to their significant amount of stored reserves [1,2,3,4] These huge reserves are unlocked by fracturing shales [5]. When the shales are fractured using conventional aqueous based polymer solutions, the plugging of nanopores takes place [6,7,8,9,10,11]. These conventional fracturing fluids need high amount of fresh water, increases the formation damage especially in the water sensitive zones and decreases the liquid recovery [9,11]. CO2 gas is more beneficial due to relatively high adsorption ability as compared to CH4 , which is a good aspect for releasing the adsorbed gas and underground carbon sequestration [5,9,12,13,14,15,16,17]
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