A NOVEL MICROEMULSION SLUG (MES) FOR ENHANCED OIL RECOVERY IN DEPLETED OIL RESERVOIRS

Abstract

ABSTRACT A NOVEL MICROEMULSION SLUG (MES) FOR ENHANCED OIL RECOVERY IN DEPLETED OIL RESERVOIRS The innovative of Microemulsion Slug (MES) systems involves utilizing a blend of anionic and non-ionic surfactants to create a Stable Anionic Nanoemulsion (SAN), which significantly boosts the effectiveness of enhanced oil recovery (EOR) methods. The choice of co-surfactants, such as organic alcohols and alkalis, is determined by their capacity to reduce dynamic interfacial tension (Dy. IFT), thereby enhancing the overall performance of the enhanced oil recovery (EOR) process.

Specification

Description:FIELD OF THE INVENTION
The present invention pertains to a microemulsion composition designed for the enhanced recovery of heavy oil from exhausted reservoirs.

BACKGROUND OF THE INVENTION
Oil reservoirs are vital sources of energy, yet they frequently encounter reduced productivity over time due to depletion and various operational challenges. As the extraction process continues, the pressure within the reservoir diminishes, leading to a decline in oil flow rates. Additionally, the complex interactions between oil, water, and rock formations can hinder the efficient recovery of hydrocarbons. To address these challenges, Enhanced Oil Recovery (EOR) methods have been developed, with surfactant application emerging as a promising solution.

Surfactants, or surface-active agents, play a crucial role in EOR by modifying the interfacial tension between oil and water phases. In traditional oil extraction methods, the high interfacial tension often prevents water from effectively displacing oil within the reservoir. By introducing surfactants, the interfacial tension is reduced, allowing for improved mobilization of oil. This alteration facilitates the movement of oil droplets through the porous rock formations, ultimately enhancing the overall recovery rates. Moreover, surfactants can also alter the wettability of the rock surfaces. In many reservoirs, rocks are naturally water-wet, which means that water preferentially occupies the pore spaces, leaving oil trapped. Surfactants can shift the wettability towards a more water-wet condition, further promoting oil recovery. This dual action of reducing interfacial tension and modifying wettability is essential for maximizing the extraction of remaining oil reserves.

Thus, there is a need of develop a microemulsion with combination of surfactants for Enhanced Oil Recovery by improving the mobilization of oil through the reduction of interfacial tension and the alteration of wettability, surfactants contribute to more efficient extraction processes. As the demand for energy continues to grow, the implementation of such innovative methods will be crucial in sustaining oil production and optimizing resource utilization.

The present invention involves the formulation of the microemulsion slug (MES) through the combination of anionic surfactants, co-surfactant, and alkali with crude oil (CO). The process results in the formulation of Stable Surfactant-Alkali combination termed (SAO), which is prepared by dissolving specific weights of SAO in brine. This solution is then combined with equal volumes of CO to create MES. By utilizing this innovative formulation of MES, the patent aims to optimize the extraction of hydrocarbons from depleted reservoirs, contributing to more efficient and sustainable oil recovery practices in the Upper Assam Basin.


OBJECTS OF THE INVENTION
The objective of the present invention is to introduce an innovative microemulsion for recovery of oil from depleted oil reservoirs.

SUMMARY OF THE INVENTION
The present invention provides to a novel microemulsion composition for enhanced oil recovery, consisting of a carefully formulated blend of surfactants, co-surfactants, and an alkali, denoted as SAO. This composition comprises an oil phase, such as crude oil with fractions of hydrocarbons in the kerosene to diesel boiling point range, and an aqueous phase characterized by brine water with salinities between 2000 ppm and 7000 ppm. The volume percentages of the surfactant combination, oil phase, and aqueous phase are specified to be within 2.25 to 2.5%, 10% to 15%, and 10% to 15%, respectively. Notably, the surfactants include both anionic, specifically Sodium Dodecyl benzenesulfonate, and non-ionic variants such as Tergitiol 15-s-9, with the co-surfactants encompassing organic alcohols and alkali compounds like sodium hydroxide or potassium hydroxide, preferably sodium hydroxide. This innovative approach aims to optimize the efficiency of oil recovery processes by leveraging the synergistic effects of its components.

BRIEF DESCRIPTION OF THE FIGURES
FIG.1.1 illustrative graph of dynamic interfacial tension (IFT) of combined surfactant and alkali (SAO)
FIG 1.2 (a) illustrates the stability formulation of winsor emulsions on the 1st and the 30th day
Figure 1.2(b) depicts the relative phase volumes of crude oil represented in grey, the middle phase shown in orange, and brine illustrated in blue, along with its salinity.
Figure 1.3 illustrates the SR_(CO & MP) and SR_(B & MP) with varying salinity
FIG 1.4 (a) illustrates the particle size distribution (PSD) of MP at 4000 ppm
FIG 1.4 (b) illustrates the particle size distribution (PSD) of MP at 5000 ppm
FIG 1.4 (c) illustrates the particle size distribution (PSD) of MP at 6000 ppm
FIG 1.4 (d) illustrates the particle size distribution (PSD) of MP at 7000 ppm
FIG 1.5 illustrates the thermal degradation of EOR slugs (MES & SAN) both quantitatively and qualitatively
FIG 1.6 (a) illustrates the microemulsion with different concentration
FIG 1.6(b)illustrates Brine stability of microemulsion after a settling period of 24 hours.

DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to an advanced Enhanced Oil Recovery (EOR) method tailored for depleted reservoirs.
The present invention introduces a unique Microemulsion Slug (MES) for enhancing oil recovery from exhaust. Preparation of innovative Microemulsion Slug (MES) employs a blend of anionic and non-ionic surfactants to create a Stable Anionic Nanoemulsion (SAN), thereby increasing the effectiveness of the enhanced oil recovery (EOR) process. The choice of co-surfactants, such as organic alcohol and alkali, is determined by their capacity to reduce dynamic interfacial tension (Dy. IFT), which further optimizes the EOR method.

The methodology entails the creation of a microemulsion slug (MES) by integrating anionic surfactants, a co-surfactant, and alkali with crude oil (CO). This process yields a Stable Surfactant-Alkali combination (SAO), achieved by dissolving precise amounts of SAO in brine. Subsequently, this solution is mixed with equal volumes of CO to produce the MES. Through this novel MES formulation, the patent seeks to enhance hydrocarbon extraction from depleted reservoirs, thereby promoting more efficient and sustainable oil recovery methods depleted oil reservoirs

This method incorporates a Microemulsion Slug (MES) system that is uniquely formulated using specific surfactants, co-surfactants, alcohols, and alkalis to maximize oil recovery. The method addresses the challenges of diminished reservoir productivity by improving oil mobilization and enhancing the efficiency of surfactant flooding techniques, resulting in significant increases in oil production from aging reservoirs. To formulate the MES, Stable Anionic Nanoemulsion (SAN) serves as the base component. The formulation of SAN is based on the selection of anionic and non-ionic surfactants that exhibit the lowest dynamic interfacial tension (Dy. IFT) values. Among anionic surfactants, Sodium Dodecyl benzenesulfonate (SDBS) is selected due to its exceptional performance, achieving a Dy. IFT of 1.6 mN/m and a Critical Micelle Concentration (CMC) of 0.5 wt%. Non-ionic surfactants, including Tergitiol 15-s-9 (TG9), are also evaluated, with TG9 showing superior performance in reducing interfacial tension and forming a nanoemulsion with SAN. The combination of SDBS, another anionic surfactant, Black Liquor (BL), and TG9 resulted in a stable nanoemulsion.

The next step in the process involves adding an organic alcohol, Propan-2-ol (P2) and Sodium Hydroxide (NaOH) as a co-surfactant and alkali, respectively, to SAN. Propan-2-ol provides stability to the surfactant system, while NaOH reacts with the reservoir's acidic components to create in-situ surfactants. This combination significantly reduces the Dy. IFT to as low as 0.03 mN/m as shown in Figure 1.1, thus creating the final surfactant and alkali combination termed as SAO. Finally, equal volumes of crude oil (CO) are added to the SAO, forming the final MES product that demonstrates enhanced oil recovery efficiency.

Hence, the formula for MES is as follows:
Microemulsion slug (MES) = (SAN + Co−surfactant + alkali) + crude oil = SAO + crude oil ……………(i)

A microemulsion composition designed for enhanced oil recovery consists of a mixture that includes surfactants, co-surfactants, and an alkali (SAO), along with an oil phase and an aqueous phase. The surfactants, co-surfactants, and alkali are present in a volume percentage ranging from 2.25% to 2.5% of the total microemulsion composition, while the oil phase constitutes between 10% and 15%, and the aqueous phase also comprises 10% to 15% of the total volume.

The aqueous phase utilized in this invention comprises brine water with a salinity ranging from 3000 ppm to 8000 ppm. This high salinity level signifies substantial amounts of dissolved salts, influencing numerous chemical and physical characteristics of the solution. Recognizing the effects of this salinity is crucial for applications in environmental science, industrial operations, and the management of water resources.

The surfactants utilized in this composition include both anionic and non-ionic types. Specifically, the anionic surfactant is Sodium Dodecyl benzenesulfonate (SDBS), which has a dynamic interfacial tension (IFT) of 1.6 mN/m and a critical micelle concentration (CMC) of 0.5 wt%. The non-ionic surfactant identified is Tergitiol 15-s-9 (TG9).

Co-surfactants in this formulation include at least one organic alcohol and an alkali, with the organic alcohol preferably being Propan-2-ol or n-butanol, and the alkali being sodium hydroxide or potassium hydroxide, with a preference for sodium hydroxide. The oil phase is characterized as crude oil, containing hydrocarbons with boiling points similar to those of kerosene and diesel. Additionally, the aqueous phase is defined as brine water with salinities ranging from 2000 ppm to 7000 ppm.

identifying a surfactant formulation effective to form a type-Ill Windsor microemulsion in the mixture of oil and brine upon being mixed with the mixture of oil and brine.

Formation of Winsor Type III (microemulsion)
The present invention also involves the formation of Winsor emulsions, which play a crucial role in the MES system's functionality. Winsor emulsions are classified into three types, with Winsor Type III (microemulsion) being the most desirable for oil recovery, as it signifies a well-balanced system of oil, water, and surfactants. Winsor Type III emulsions form a middle microemulsion phase between the oil and water phases, which is achieved at specific salinity conditions.

The formation of Winsor type I marked as red arrows and Winsor type III marked as blue arrows is shown in Figure 1.2 (a).

The volume of crude oil in grey, middle phase in orange and brine in blue shown in Figure 1.2 (b), is calculated by physical observation from the graduations of the pipettes, Figure 1.2 (a) and graphically represented.

The emulsification index (EI) is used to measure the stability of the MES. This index is determined by the height of the emulsion layer relative to the total height of the mixture. A higher EI indicates a more stable emulsion, which is crucial for ensuring the effectiveness of the MES in oil recovery. EI was tested for MES of Winsor type III formations ranging from 4000 ppm to 7000 ppm, and its stability and effectiveness were confirmed through emulsification index measurements calculated by using eq. (1.2) and tabulated in Table 1.1.
EI= (Height of the undisturbed emulsion layer)/(Total height) X 100………………… (1.2)

Table 1.1: Emulsification index (EI) of the MP
SN Brine Salinity (ppm) Total height of the three phases Height of the MP EI
1. 4000 100 30 30
2. 5000 30 30
3. 6000 28 28
4. 7000 30 30

Optimum salinity:
Optimum salinity is a crucial determinant in assessing the efficacy of microemulsion slugs (MES). The concentration of salt profoundly influences the thermodynamic stability and phase behavior of the microemulsion system, ultimately affecting its performance in enhanced oil recovery and other applications. Deviations from the ideal salinity range can lead to phase separation or reduced mobility, thereby diminishing the overall effectiveness of the MES. Thus, careful calibration of salinity levels is essential to maximize operational outcomes in microemulsion-based processes.

The analysis of solubilization ratios (SR) for crude oil and middle phase (CO & MP), alongside brine and middle phase (B & MP), revealed that the optimum salinity for the MES formulation is 4000 ppm, as illustrated in Figure 1.3. This specific salinity level corresponds to the minimization of interfacial tension between the oil and water phases, thereby significantly optimizing the oil recovery process.


THE INTERFACIAL TENSION (IFT)
The interfacial tension (IFT) of Winsor Type III emulsions has been rigorously analyzed to assess the efficacy of the surfactant system. Utilizing the Chun-Huh equation, IFT values were calculated with a constant of 0.3 mN/m designated for microemulsion surfactants (MES) in enhanced oil recovery (EOR) applications. The resulting IFT values substantiate that the formulated MES significantly reduces interfacial tension, thereby facilitating oil displacement.

Validation OF performance and stability of the MES:
To assess the performance and stability of the microemulsion system (MES), comprehensive particle size distribution (PSD) analysis and thermal gravimetric analysis (TGA) are performed.
1.Particle Size Distribution (PSD)
The analysis of Particle Size Distribution (PSD), depicted in Figures 1.4 (a) to 1.4 (d), indicates that the microemulsions exhibit particle sizes ranging from 5 to 50 nm. This size range supports the stability of microemulsions and highlights their efficacy in improving oil recovery methods. Detailed particle size information is provided in Table 1.2.
Table 1.2: Interpretation of Figure 1.4 (a) to Figure 1.4 (d)

SN Sample

Diameter (nm)
% Present Z-Average diameter (nm)
Dispersed phase, MP
Continuous phase, Brine (ppm)
1.
MES 4000 5.652 32 40.22
2. 5000 7.474 26 46.62
3. 6000 7.611 33 70.08
4. 7000 8.293 28 99.63

Thermogravimetric analysis (TGA):
Referring to Figure 1.5, The TGA results indicate that the microemulsion exhibits thermal stability at reservoir temperatures, with only negligible weight loss noted during the heating process. Notably, the MES displayed reduced thermal degradation in comparison to SAN, This evidence suggests that MES can maintain its stability even at the highest oil reservoir temperatures and is capable of enduring the thermal conditions present in depleted Upper Assam Basin reservoirs without considerable degradation.

Brine stability tests:
Brine stability tests are essential evaluations to ensure their optimal performance in applications such as oil and gas extraction, de-icing, and food preservation. Ultimately, these assessments are critical for enhancing the reliability and safety of processes that utilize brine.
Brine stability tests further confirm that the MES system remains stable across a wide range of salinities (2000 ppm to 5000 ppm), without any precipitation or phase separation as shown in Figure 1.6. This stability ensures that the MES can be effectively utilized in different reservoir brine conditions, thereby increasing its applicability for oil recovery in various settings.

Hence, from the formation of seven different types of Winsor emulsions, three of them were observed to be Winsor I and the remaining four were Winsor III having middle phase with salinity of 4000, 5000, 6000 and 7000 ppm. These four Winsor III emulsions are target for the next set of studies. emulsification index (EI) is found best for Winsor III in 40000 ppm salinity, the better the emulsification index (EI) better will be the recovery of crude oil.

The optimum salinity is obtained at 4000 ppm salinity. At optimum salinity SRCO & MP = SRB & MP suggesting lowest IFT in the middle phase. Further at optimum salinity an ultra-low IFT of 0.0008 mN/m was observed from Chun Huh equation of relation between the SRCO&MP and IFT. Winsor III emulsions are further subjected to particle size analysis and are found that the particle diameter of the dispersed phase of the middle phase are dominant in nm. The least particle size is observed for MP of 4000 ppm brine. Therefore, MP formed at 4000 ppm was the formulated MES.

Overall, the invention presents an innovative method for enhancing oil recovery in depleted reservoirs by employing a novel MES system. This method effectively combines anionic and non-ionic surfactants, co-surfactants and alkali at an optimum salinity to create a stable microemulsion capable of reducing interfacial tension, improving oil mobilization, and increasing oil production. The extensive testing conducted on the MES system, including emulsification indices, salinity optimization, particle size distribution, thermal stability, and brine stability, all demonstrate its potential for successful application in the Upper Assam Basin and other similar reservoirs.
 
, Claims:We claim,

1. A composition of microemulsion for enhanced oil recovery, comprises a mixture of:
a combination of surfactants, co-surfactants and an alkali (SAO);
an oil phase, and
aqueous phase,
characterized in that, the combination of surfactants, co-surfactants, and alkali (SAO) has a percentage by volume between 2.25 to 2.5% of the volume of the composition of microemulsion,

the oil phase has a percentage by volume between 10% and 15% of the volume of the composition of microemulsion; and
the aqueous phase having 10% and 15% of by volume of the composition of microemulsion.

2. The composition as claimed in claim 1, wherein the surfactants comprise of an-ionic and non-ionic surfactants.

3. The composition as claimed in claim 1, or 2, wherein the ionic surfactants are Sodium Dodecyl benzenesulfonate (SDBS) and Black Liquor (BL).

4. The composition as claimed in claim 1 or 2, wherein the non-anionic surfactant is Tergitiol 15-s-9 (TG9.)

5. The composition as claimed in claim 1, wherein the SAO exhibits dynamic interfacial tension (Dy. IFT) is as low as 0.03 mN/m.

6. The composition as claimed in claim 1, the co-surfactants comprise of at least one organic alcohol and alkali.

7. The composition as claimed in claim 6, wherein the organic alcohol is selected from propan-2-ol or n-butanol, preferably Propan-2-ol.

8. The composition as claimed in claim 6, wherein alkali is selected from sodium hydroxide or potassium hydroxide, preferably sodium hydroxide.

9. The composition as claimed in claim 1, wherein the oil phase is crude oil comprises a fraction of hydrocarbons with boiling point in the range of kerosene and diesel.

10. The composition as claimed in Claim 1, wherein the aqueous phase consists of brine water with salinities ranging from 2000 ppm to 7000 ppm.

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