Chemical flooding is one of the most efficient methods for Enhanced Oil Recovery (EOR). This study demonstrates the efficiency of mixing different concentrations of Ionic Liquid (IL), 1-Ethyl-3-Methyl-Imidazolium Acetate ([EMIM][Ac]), with Weyburn brine to improve a medium oil recovery, Weyburn oil, from an unconsolidated sand pack sample at room conditions. Effects of Slug Size (SS), IL + brine slug initiation time, and combining IL with alkali on the Recovery Factor (RF) were investigated. This study showed that the optimum concentration of ([EMIM][AC]) was 1000 ppm and the most efficient injection time of the chemical slug was at the beginning of the flooding procedure (as secondary flooding mode). In addition, it was proved that the potential of injecting a slug of IL + brine is much better than that of introducing a slug of alkali + brine. Besides, the combination of IL and alkali (AIL) resulted in better RF than injecting either of them alone. Finally, the Surface Tension (SFT), pH, wettability alteration, and viscosity of the displacing phases were measured.
It is crucial to increase oil production from existing reservoirs due to the lack of new oil reservoirs discovered around the world as well as the high cost of exploration and reduction in reservoir drive mechanism [
Today, injecting ionic liquids (IL) has become a pivot application in the oil industry to increase oil recovery. There are many ionic liquid types such as organic salts which have a melting temperature lower than 100˚C [
In this research, experimental measurements were used to study the ability of the IL 1-Ethyl-3-Methyl-Imidazolium Acetate ([EMIM][Ac]) to improve medium oil recovery. Different ([EMIM][Ac]) concentrations mixed with formation brine using different slug size were flooded into an unconsolidated sand pack at room conditions in different scenarios. Moreover, the effect of injecting alkali into sand pack was investigated. Also, the effect of IL on SFT, pH, wettability alteration, and displacing phase viscosity were investigated for the ([EMIM] [Ac]) mixtures and their impact on chemical EOR recovery mechanisms.
In this study, 1-Ethyl-3-Methyl-Imidazolium Acetate ([EMIM][Ac]) with purity of 95 wt% and alkali (Na2CO3) were supplied from Sigma-Aldrich and used without further purification. The chemical structure of the employed IL ([EMIM][Ac]) is shown in
Brine composition (Fraction)
| Cations | Anions | Na | 0.3379 | Cl | 0.571 | K | 0.0084 | Br | Ca | 0.0259 | I | Mg | 0.0058 | HCO3 | 0.0091 | Ba | 0 | SO4 | 0.414 | Sr | 0.0006 | CO3 | 0 | Fe | 0 | OK | 0 | Mn | 0 | H2S | ||||||||||||||||||||||||||||||||||||||||||||
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Cations | Anions | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Na | 0.3379 | Cl | 0.571 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
K | 0.0084 | Br | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Ca | 0.0259 | I | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Mg | 0.0058 | HCO3 | 0.0091 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Ba | 0 | SO4 | 0.414 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Sr | 0.0006 | CO3 | 0 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Fe | 0 | OK | 0 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Mn | 0 | H2S | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Brine µ (cP) Brine ρ (gm/cm3) Oil µ (cP) Oil ρ (gm/cm3) Oil API | 1.017 1.06645 15.355 0.87481 30.25 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Oil SARA fraction (wt%) | Saturates Aromatics Resins Asphaltenes | 60.3 24.1 10.5 3.15 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Displacing fluid (IL + Brine) | C([EMIM][Ac]) 1000 ppm 3000 ppm 5000 ppm | ρ (gm/cm3) 1.075 1.081 1.083 | µ (cP) 1.437 1.597 1.621 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
(Alkali + Brine) | 1.071 | 1.021 |
Cations | Anions | ||
---|---|---|---|
Na | 0.3379 | Cl | 0.571 |
K | 0.0084 | Br | |
Ca | 0.0259 | I | |
Mg | 0.0058 | HCO3 | 0.0091 |
Ba | 0 | SO4 | 0.414 |
Sr | 0.0006 | CO3 | 0 |
Fe | 0 | OK | 0 |
Mn | 0 | H2S |
The selected IL ([EMIM][Ac]) for this study was combined at different concentrations with Weyburn brine. The following steps were taken before the flooding process:
1) Prepare the IL mixtures by adding the following amount of ([EMIM][Ac]), (1000 ppm, 3000 ppm, and 5000 ppm), to the brine, the solution is placed on a stirrer (Cole-Parmer Stable Temp Ceramic Stirring Hot Plate) at 120 rpm for 30 - 45 mints.
2) The viscosity of Weyburn oil (15.355 cP), Weyburn brine (1.07 cP), and displacing solutions was measured by using an A Brookfield DV-II viscometer.
3) An Anton Paar DSA 5000 M instrument was used to measure the densities of the aqueous solutions.
4) KRUSS K100 device was used to measure the surface tension of the displacing mixtures using Wilhelmy plate method. Clean the sample vessel and the plate by acetone first and then by clean water before every measurement. Also, the lower edge of the plate is placed straight and parallel to surface of the liquids.
5) The pH of the displacing phases was measured by a Navi pH Meter. An average value was calculated after every third measurement.
A sand pack column with a bulk volume of 235.7 cm3 was packed with dry Ottawa sand to prepare an unconsolidated sand pack. The average size of the sand, 40 - 80 mesh, was measured using sieving analysis. The PV, porosity, absolute permeability, and fluid saturations were measured and listed in
A vertically oriented core holder, with a length of 18.75 cm and an inside diameter of 4 cm, was packed with dry unconsolidated sand. After packing the sand and fixing the caps, the sand pack sample was 100 % vacuumed using a pump until no air bubble came out and then saturated by Weyburn brine to obtain the porosity from the difference between the dry and saturated weight divided by brine density and bulk volume. The column was injected by brine at different injection rates to determine the absolute permeability using Darcy’s Law. After taking the petrophysical properties, the core holder was connected to the core flooding system, a conventional core flooding system, vertically and then the sand pack samples was flooded by the medium oil at a rate of 1 cc/min until no water drop came out from core holder outlet. Total displaced brine represents the original oil in place while the remaining represents the irreducible water saturation. In the next stage, the injection rate was held at a constant rate of 2 cc/min, and the core was placed horizontally and flooded by brine and IL mixtures at different scenarios to obtain the optimum concentration, slug size as well as initiation time. Eventually, all the above procedures were repeated in each experiment with fresh sand to maintain the same properties.
Surface tension (SFT) was considered to determine the Critical Micelle Concentration (CMC) of the displacing solutions at room conditions. The CMC is the concentration at which surfactant solutions surface tension could not be reduced further, as the concentration increased [
The pH values of ([EMIM][Ac]) and Weyburn brine mixtures were measured at 21.5˚C. It was found, in another study, that the pH values of the solutions increased with increasing ([EMIM][Ac]) concentration in the mixtures while the effect of temperature was marginal [
Electrical conductivity of displacing phases was measured which increased
PV (cm3) | Ø (%) | K (md) | Swi (%) | Soi (%) |
---|---|---|---|---|
98.5 (±2) | 41 (±2) | 5.2 (±0.5) | 17 (±1) | 83 (±1) |
with increasing ([EMIM][Ac]) concentration. Similar to the CMC values that obtained from conductivity as function of tributylmethyl phosphonium dodecylsulfate concentration which was in good agreement with the CMC that attained from surface tension measurements [
After preparing the sand pack sample in each experiment, the rock properties were measured, as presented in
was almost identical and the RF values are close to (63% ± 1%) at the end of the first stage. The increase in IL concentration from 1000 ppm to 5000 ppm increased the RF from 77% to 80.64% of original oil in place (OOIP) at end of flooding. Compared to using only water flooding which recovered about 71.17% of the oil in the sand pack sample, the addition of (1000 ppm, 3000 ppm, and 5000 ppm) ([EMIM] [AC]) with the displacing fluid lead to an increase in the oil recovery by 6.57% OOIP, 7.37% OOIP, and 8.77% OOIP, respectively. Finally, as we can see in
Three experiments were performed to select the optimum slug size (SS). In those experiments, the sand pack samples were initially flooded with 1.25 PV of formation brine, followed by different SS (0.5, 1 and 2 PV) of 1000 ppm ([EMIM] [Ac]), and then the samples were flushed with formation brine. As shown in
In order to obtain the appropriate initiation time of the chemical slug, the optimum concentration and slug size of ([EMIM][Ac]) were investigated at three different injection times, as shown in
flooded with 1 PV of 1000 ppm ([EMIM][Ac]), and then it was flushed with 2 PVs of formation brine. The results showed that the RF increased from 71.17% OOIP of only brine flooding to 81.31% OOIP. Second, the injection time investigation occurred when the sand pack was flooded with 0.5 PV formation brine; followed by 1 PV of 1000 ppm ([EMIM][Ac]), then finally, the sample was flushed with 1.5 PV of formation brine, as shown in
In this section, the efficiency of injection 3 PV of 1000 ppm on the RF was studied. As can be depicted from
One of the upsides of injecting alkali is its ability to react with oil component in order to generate surfactants [
To investigate the effect of ILs on wettability alteration, relative permeability (kro & krw) curves have been calculated and plotted for two flooding experiments (IL + Weyburn brine flooding and Weyburn brine flooding only) under the same conditions. So, kro and krw of 1000 ppm ([EMIM][Ac]) + Weyburn brine and just Weyburn brine were calculated using step by step graphical technique that was explained by Jones and Roszelle (1978) [
This paper studied the application of ([EMIM][Ac]) as an alternative surfactant to increase the medium Weyburn recovery factor from unconsolidated Ottawa sand pack at room conditions. The work began by measuring the surface tension of the ([EMIM][Ac]) IL mixed with brine at different concentrations. The ([EMIM][Ac]) was able to reduce the SFT of the displacing fluid from 65.4 mN/m to 57.2 mN/m and the CMC point was investigated when the ([EMIM] [Ac]) concentration was 1000 ppm in the displacing fluid, which was the minimum reduction on SFT and in a good agreement with conductivities values versus ([EMIM][Ac]) concentrations. A series of flooding experiments on Ottawa sand pack samples were done to demonstrate the effect of ([EMIM][Ac]) ionic liquid at different conditions, (concentration, slug size, and initiation time), on oil recovery. From the flooding results, all showed an increase of the recovery factor. Recovery factor was possible to reach up to 84% of OOIP when 1000 ppm ([EMIM][Ac]) + brine mixture injected into sand pack sample as secondary recovery mode either as a one pore volume the flushed by brine or a continuous ionic solution flooding. Moreover, the recovery factor was higher when IL combined with alkali (AIL) flooded at the same condition and selected mode, secondary mode flushed by brine. The relative permeability curves of continuous brine flooding and 1000 ppm ([EMIM][Ac]) + brine flooding indicated wettability alteration toward a slight increase in rock water wet characteristics. The ([EMIM][Ac]) ionic liquid increases the viscosity of the ([EMIM][Ac]) + brine mixtures, which is one of the mechanisms increasing the recovery factor.
Alarbah, A., Shirif, M. and Shirif, E. (2017) Efficiency of Ionic Liquid 1-Ethyl-3-Methyl-Imidazolium Ace- tate ([EMIM][Ac]) in Enhanced Medium Oil Recovery. Advances in Chemical Engineer- ing and Science, 7, 291-303. https://doi.org/10.4236/aces.2017.73022
C([EMIM][Ac]) ([EMIM][Ac]) concentration
C(Na2CO3) (Na2Co3) concentration
ppm parts per million
PV pore volume
K absolute permeability
kro oil relative permeability
krw water relative permeability
Swi initial water saturation
Soi initial oil saturation
Greek Letters
Ø Porosity
ρ Density
µ Viscosity