Interactions between Formation Rock and Petroleum Fluids during Microemulsion Flooding and Alteration of Heavy Oil Recovery Performance

Abstract

In situ emulsification/solubilization is an oil recovery technique routinely used to mobilize residual oil after the secondary oil production (waterflooding). The oil is produced after a subsequent reduction of interfacial tension between stranded crude oil and water in the reservoir. Herein, a recovery method is presented for heavy crude oils whose scheme consists of injection of a fully solubilized (or emulsified) oil. Theoretically, the fully solubilized oil, referred hereinafter as microemulsion formulation, reduces the viscous forces that keep residual oil stranded. Different microemulsion formulations were prepared ex situ from two heavy oils (API 11.5 and 16.6), micellar slugs (formulated from cationic Gemini surfactant), and low-saline water (0.1 wt % NaCl). Tertiary heavy oil recovery consisted of displacing residual oil from a waterflooded core by a specific microemulsion formulation followed by low-saline water, which acted as buffer solution. Thirty-one percent of initial oil-in-place (IOIP) was recovered from the waterflooded core by microemulsion followed by an incremental oil recovery of about 20% of IOIP with chase water. The oil recovery efficiency by microemulsion and chase water floodings was lowered to 15 and 28%, respectively, in a strong oil-wet core (i.e., non waterflooded core). Despite the promising results presented herein, the performance of the microemulsion formulations and thus the oil recovery efficiency were found to be strongly dependent on (1) the nature of the core, i.e., its mineralogy, (2) the wetting state of plug, and (3) the chemical composition advancing fluid. The microemulsion formulations prompted a series of chemical reactions which subsequently altered their performance as a displacing agent. Ion tracking analysis of the effluent fractions showed that the pH and concentration in divalent and/or monovalent ions were also altered at each stage of production. When the plug was not waterflooded, the oil was produced along with a deposit of sludge and a high emulsion cut. However, the use of preflush enriched with an alkali (Na2CO3) was found to abate both effects. Furthermore, the spectral analysis of effluent fractions revealed the formation of calcium bridges which are thought to alter the efficiency of microemulsion formulations. Also, a series of chemical schemes are proposed in this investigation to support these results. Lastly, this investigation proposes a simplified electrostatic model that explains further the formation of clusters which were promoted by propagation of displacing fluids.

Enhancing Oil Production Using Silica-Based Nanofluids: Preparation, Stability, and Displacement Mechanisms

“…Likewise, the pressure drop was found to increase with the load in Si-NP. With the knowledge that the pressure drop expresses the mechanistic forces occurring within the oilbearing matrix, 42 it appears at this stage that the Si-NF interacted with the trapped oil, forming an oil bank that pushed out of the pore throats.…”

Effects of Reversibility on Enhanced Oil Recovery Using Sodium Dodecylbenzene Sulfonate (SDBS)

“…However, the surfactant interacts not only with the reservoir fluids, but also with the native formation rocks, and these interactions cause adsorption phenomena which are very important in the economic viability of surfactant flooding 2), 3) . Consequently, oil production by surfactant injection should be regarded as involving physico-chemical reactions between the native minerals of the formation rock and the surfactant solution 4) . Thus, understanding and controlling the adsorption mechanisms could improve the efficiency of CEOR.…”

Effects of Divalent Salts on the Interfacial Activity of the Mixed Surfactants at the Water/Model Oil Interface

“…Due to the amphiphilic structure, the surfactant can effectively reduce the water/oil interfacial tension (IFT) and change the formation wettability, which are the basic mechanisms of surfactant flooding in chemical enhanced oil recovery (EOR) (Zhang et al, ). Focused on the properties of reservoir water (salinity, temperature, viscosity, and so on), many groups modified the surfactant structures to develop their performances in EOR (Ahmadi and Shadizadeh, ; Babu et al, ; Chaturvedi et al, ; Cui et al, ; Hezave et al, ; Jia et al, ; Kamal, ; Kumar and Mandal, , ; Nguele et al, ; Pal et al, ; Pillai et al, , ; Rodríguez‐Escontrela et al, , b; Saxena et al, ; Zendehboudi et al, ; Zheng et al, ; Zhou et al, , ). Cui et al synthesized zwitterionic surfactants with double long alkyl chains to achieve the optimal hydrophile–lipophile balance for the remarkable IFT reduction (Cui et al, ).…”