Effects of water salinity on the foam dynamics for EOR application

Abstract

Factors limiting foam injection for EOR application are exceptionally low rock permeability and exceedingly high salinity of the formation water. In this regard, foam formation using internal olefin sulfonate is investigated over a wide salinity range (1, 5, 8, 10, and 12% NaCl) through 10 mD limestone. The relationships between pressure drop (dP), apparent viscosity, liquid flow rate, total flow rate, salinity, foam texture, and length of foam drops at the outlet used as an indicator of viscosity are studied. Foaming is observed up to 12% NaCl, compared to a maximum of 8% NaCl in similar core-flooding experiments with 50 mD limestone and 255 mD sandstone. Thus, the salinity limit of foam formation has increased significantly due to the low permeability, which can be explained by the fact that the narrow porous system acts like a membrane with smaller holes. Compared to the increasing dP reported for highly permeable rocks, dP linearly decreases in almost the entire range of gas fraction (fg) at 1–10% NaCl. As fg increases, dP at higher total flow rate is higher at all salinities, but the magnitude of dP controls the dependence of apparent viscosity on total flow rate. Low dP is measured at 1% and 10% NaCl, and high dP is measured at 5, 8, and 12% NaCl. In the case of low dP, the apparent viscosity is higher at higher total flow rate with increasing gas fraction, but similar at two total flow rates with increasing liquid flow rate. In the case of high dP, the apparent viscosity is higher at lower total flow rate, both with an increase in the gas fraction and with an increase in the liquid flow rate. A linear correlation is found between dP or apparent viscosity and liquid flow rate, which defines it as a governing factor of foam flow and can be considered when modeling foam flow.

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“…The flow of foam could mobilize tiny carbonate particles to move through the core. Although such increment in d P was not observed in our previous studies, various substances, such as particles and sediments can significantly decelerate drainage. − For example, the initial drainage was stopped when the particles jammed the confined foam but resumed with the bubble coarsening . This explains the much less dramatic increase in d P at higher f g due to the larger bubble sizes, which more easily pass through the porous medium.…”

“…Since the foam texture passing the core cannot be observed in a closed system, a correlation between the bubble size of the foam at the outlet and the pressure drop was found by Tang and Kovscek . In our previous works, we found an inverse dependence between the length of a foam drop and the apparent viscosity. , Images of foam drops obtained at 0.4 mL/min in test I are compared with the apparent viscosity curve in Figure . The foam texture did not change markedly from minimum to maximum values of dP apparent viscosity in the range of 0.3-0.8 at a fixed gas fraction.…”

“…This implied that the peculiarities of the curve shape can be explained rather by the influence of the porous system than by the type of surfactant. For 10 mD limestone, the d P and apparent viscosity curves decreased linearly at 1% NaCl, while the shoulders were observed at much higher salinities . All d P curves at both total flow rates decreased over the entire f g range, with the exception of f g = 0.1 for 0.4 mL/min II, in which d P was lower than at 0.2 due to the liquid at the end of the foam drop.…”

“…For the 255 mD Berea sandstone with IOS surfactant, the d P curve showed some fluctuation due to fluctuations of the outlet pressure, while the d P curves measured by other transducers along the core were very smooth . The curves of d P and outlet pressure were very smooth using IOS surfactant through 10 mD limestone measured with all four transducers, which could be due to a very narrow porous medium . For a similar 50 mD Indiana limestone using IOS, fluctuations in both inlet and outlet pressures were observed, which caused fluctuations in measured d P along the core at all transducers.…”

“…46 The curves of dP and outlet pressure were very smooth using IOS surfactant through 10 mD limestone measured with all four transducers, which could be due to a very narrow porous medium. 49 For a similar 50 mD Indiana limestone using IOS, fluctuations in both inlet and outlet pressures were observed, which caused fluctuations in measured dP along the core at all transducers. Furthermore, the degree of fluctuation increased with increasing distance from inlet to outlet.…”