STUDY ON ENHANCED OIL RECOVERY BY CO2 MICROBUBBLES INJECTION Le Nguyen Hai Nam September 2022 STUDY ON ENHANCED OIL RECOVERY BY CO2 MICROBUBBLES INJECTION A dissertation submitted to the Department of Earth Resources Engineering, Graduate School of Engineering, Kyushu University, Japan in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Earth Resources Engineering by Le Nguyen Hai Nam September 2022 ABSTRACT Injecting carbon dioxide (CO2) to enhance oil recovery (EOR) during the tertiary stage is expected to be a reasonable and sustainable method to dismiss greenhouse gas emissions. However, in many current CO2-EOR projects, their performance is not always achievable due to several drawbacks, such as density effect, gas channeling, and poor sweep efficiency in heterogeneous porous media. All those challenges limit the effectiveness of CO2-EOR and raise the additional cost. Therefore, it is supposed that using CO2 microbubbles would potentially overcome the challenges in the heterogeneous reservoir and promote a practical approach to achieving both oil improvement and CO2 sequestration goals.
Microbubbles – Colloidal Gas Aphrons (CGAs) have been reported as unique bubbles with micro-size (10-100 m) consisting of a multilayer shell of surfactant molecules and a spherical gaseous core. The previous studies reported the significant stability of microbubbles in comparison with conventional foam and their flow restriction ability. However, there have been few sufficient studies on the characteristic of CO2 microbubble and their selective plugging performance to improve oil recovery in the heterogeneous reservoir. In this thesis, CO2 microbubbles injection is proposed and examined with designed laboratory experiments.
Experimental study thoroughly includes CO2 microbubbles system generation, characteristics determination, and flow behavior in porous media from homogeneous sandpack and heterogeneous sandpack models. In addition, various features, consisting of CO2 microbubbles fluid characteristics, formation permeability, and operation conditions, were experimentally evaluated for their influences on flow performance in the simulated reservoir. Based on the findings from flow experiments in porous media, the oil recovery flooding scheme using CO2 microbubbles has been proposed and successfully performed in sandpack models. In conclusion, CO2 microbubbles injection is a promising method to overcome permeability differential issues in heterogeneous reservoirs, thereby enhancing CO2-EOR operation efficiency.
This thesis consists of five chapters. i Chapter 1 reviews the fundamental of the oil recovery process from literature. The overview of CO2-EOR was discussed with the associated challenges. Therein also highlighted the importance of microbubbles used in petroleum engineering.
The research problem statement and objectives were presented in that regard. Chapter 2 introduces the experimental process with an overview of measurement methods and analysis. It evaluated the effects of varying the concentrations of a xanthan gum (XG) polymer, a surfactant (sodium dodecyl sulfate: SDS), and sodium chloride (NaCl) on both the stability and bubble size distribution (BSD) of CO2 microbubbles. CO2 microbubble dispersions were prepared using a high-speed homogenizer in conjunction with the diffusion of gaseous CO2 through aqueous solutions.
The stability of each dispersion was ascertained using a drainage test, while the BSD was determined by optical microscopy and fitted to either normal, log-normal or Weibull functions. The results showed that a Weibull distribution gave the most accurate fit for all experimental data. Increases in either the SDS or XG polymer concentration were found to decrease the microbubble size. However, these same changes increased the microbubble stability as a consequence of structural enhancement.
Stability was also reduced as the NaCl concentration was increased because of the gravitational effect and coalescence. Chapter 3 investigates the plugging performance of CO2 microbubbles in both homogeneous and heterogeneous porous media through a series of sandpack experiments. First of all, CO2 microbubble fluids were generated by stirring CO2 gas diffused into polymer (Xanthan gum (XG)) and surfactant (Sodium dodecyl sulfate (SDS)) solution with different gas: liquid ratios. Then, CO2 microbubbles fluids were injected into single-core and dual- core sandpack systems.
The results show that the rheological behaviors of CO2 microbubble fluids in this study followed the Power-law model at room temperature. The apparent viscosity of CO2 microbubble fluid increased as the gas: liquid ratio increased. CO2 microbubbles could block pore throat due to the “Jamin effect” and increase the resistance in porous media. The blocking ability of CO2 microbubbles reached an optimal value at the gas:liquid ratio of 20 % in the homogeneous porous media.
Moreover, the selective pugging ability of CO2 microbubbles in dual-core sandpack tests was significant. CO2 microbubbles ii exhibited a good flow control performance in the high permeability region and flexibility to flow over the pore constrictions in the low permeability region, leading to an ultimate fractional flow proportion (50%:50%) in the dual-core sandpack model with a permeability differential of 1. The fractional flow ratio was considerable compared with a polymer injection. At the higher heterogeneity of porous media (0.0 darcy), CO2 microbubble fluid could still establish a good swept performance.
This makes CO2 microbubble fluid injection a promising candidate for heterogeneous reservoirs where conventional CO2 flooding processes have limited ability. Chapter 4 evaluates the performance of CO2 microbubbles on oil recovery from the single sandpack and parallel sandpack flooding tests. All flooding tests were conducted at 45oC. The flooding scheme consisted of the injection of brine water (20000 mg/L NaCl concentration) followed by the CO2 microbubble injection.
In the single sandpack flooding test, about 61.4 % of the original oil in place (OOIP) was recovered after 3 pore volume (PV) of water flooding.5 PV of CO2 microbubble was injected, which caused a blockage in pore spaces. The oil recovery was improved by 23.6% by the chase water flooding at the following stage. In the heterogeneous sandpack model with the low/high permeability ratio of 1:4, the CO2 microbubble could adjust to fractional flows in the heterogeneous reservoir and displace the remaining oil in the low permeability region. As a result, the injection of CO2 microbubbles improved the total oil recovery up to 86.9% compared to the injection of base solution with 75.
When the low/high permeability ratio of the parallel sandpack is reduced to 1:2, injecting CO2 microbubbles enhanced the oil recovery to 93. The displacement efficiency increases with the decrease of sandpack heterogeneity. The results suggest that CO2 microbubble is favorable to enhanced oil recovery in heterogeneous reservoirs. Chapter 5 concludes the present research by highlighting the major findings and further research suggestions.
iii TABLE OF CONTENTS ABSTRACT. I TABLE OF CONTENTS. IV LIST OF FIGURES. VII LIST OF TABLES.
XIII CHAPTER 1 INTRODUCTION .1 Enhanced Oil Recovery Using Carbon Dioxide (CO2-EOR).2 CO2 microbubbles – Colloidal gas aphrons. 10 CHAPTER 2 EXPERIMENTAL DESIGN AND CHARACTERIZATION OF CO2 MICROBUBBLES .1 Preparation of base solutions.2 Preparation of CO2 microbubble fluids .3 CO2 microbubble stability assessments.4 Determination of CO2 microbubble size .4 Results and Discussions .1 Visualization of CO2 microbubbles.3 CO2 microbubble size distribution .4 Factors affecting the BSD of CO2 microbubbles. 39 CHAPTER 3 FLOW PERFORMANCE OF CO2 MICROBUBBLES IN POROUS MEDIA .2 CO2 microbubble fluids preparation .3 Measurement of rheological property .5 Preparation of sandpacks .6 CO2 microbubble fluid flow tests .3 Results and Dicussions .1 Characterization of CO2 microbubbles .2 CO2 Microbubble Fluid Flow in Homogeneous Porous Media .3 CO2 Microbubble Fluid Flow in Heterogeneous Porous Media. 65 CHAPTER 4 EVALUATION OF ENHANCED OIL RECOVERY PERFORMANCE BY CO2 MICROBUBBLES FLOODING.3 Results and Discussion .1 Oil recovery in single sandpack .2 Oil recovery in parallel sandpack.
81 CHAPTER 5 CONCLUSIONS AND RECOMMENDATION .1 Major findings of the research. 87 vi LIST OF FIGURES Figure 1.1 Long-term world energy consumption with projection to 2050(adapted from U. Energy Information Administration, October 2021) .2 Overview of oil recovery stages .1 Schematic diagram of the preparation of CO2 microbubbles: (1) Homogenizer, (2) Polymer and surfactant solution, (3) Porous stone (gas diffuser), (4) Gas flow meter, (5) Pressure regulator, (6) CO2 gas tank .2 Apparatus of CO2 microbubbles generation .3 Schematic process of drainage test .4 Set up for visualization of CO2 microbubbles: (1) Microscope, (2) charge- coupled device (CCD) camera, (3) computer, and (4) glass-slide.5 Analyzing procedure of a CO2 microbubbles sample. (a) Raw image, (b) 8-bit image enhanced by contrast, (c) Image after thresholding, (d) Bubbles counting and analyzing .6 The difference between CO2 microbubbles and conventional foam, introduced in their structure.7 Experimental photograph of CO2 microbubbles drainage with SDS ( 3g/L) and XG (0 g/L) .8 Effect of SDS concentration on the stability of CO2 microbubbles (with 0 g/L XG) .9 Effect of XG concentration on the stability of CO2 microbubbles (with 3 g/L SDS).10 Effect of NaCl concentration on the stability of CO2 microbubbles (with 3 g/L SDS and 5 g/L XG) .11 Micrographs of CO2 microbubbles: (a) S1 sample, (b) S2 sample, (c) S3 sample, (d) S4 sample, (e) S5 sample, (f) S6 sample, and (g) S7 sample.12 Bubble size distribution (BSD curves predicted by Normal, Log-normal and Weibull model for (a) S1 sample, (b) S2 sample, (c) S3 sample, (d) S4 sample, (e) S5 sample, (f) S6 sample, and (g) S7 sample.13 Q-Q plots for (a) S1 sample, (b) S2 sample, (c) S3 sample, (d) S4 sample, (e) S5 sample, (f) S6 sample, and (g) S7 sample.14 Influence of SDS concentration (1, 2, 3 g/L) upon bubble size.
(b) BSD at three SDS concentrations, experimental and fitted results are represented using icons and solid lines, respectively .15 Influence of XG concentration (1,3,5 g/L) upon bubble size. (b) BSD at three XG concentrations, experimental and fitted results are represented using icons and solid lines, respectively.16 (a) Influence of NaCl concentration (0, 10, 20 g/L) upon bubble size. (b) BSD at three NaCl concentrations, experimental and fitted results are represented using icons and solid lines, respectively .17 Microscopic views of CO2 microbubbles samples, 60 minutes after preparation (a) S1 sample, (b) S2 sample, (c) S3 sample. And (d) Bubble size distribution functions.18 Microscopic views of CO2 microbubbles samples, 60 minutes after preparation (a) S5 sample, (b) S4 sample, (c) S3 sample.
And (d) Bubble size distribution functions.19 Microscopic views of CO2 microbubbles samples, 60 minutes after preparation (a) S3 sample, (b) S6 sample, (c) S7 sample. And (d) Bubble size distribution functions.1 Diagram of the experimental setup for CO2 microbubble fluid flow in sandpacks.2 Flowchart of the experimental procedure.3 Micrographs of CO2 microbubbles with different gas:liquid ratios.4 Bubble size distribution of CO2 microbubbles with different gas: liquid ratios.5 Stability of CO2 microbubble fluids at different gas: liquid ratios.6 Values of (a) R2 and (b) RMSE of fitting models with CO2 microbubble fluids at different gas: liquid ratios.7 Fitting cures of Power-law model for CO2 microbubble fluids at different gas: liquid ratios.8 The plot of viscosity vs. shear rate for CO2 microbubble fluids at different gas: liquid ratios.9 (a) Injection CO2 microbubble fluid; (b) Produced fluid from sandpack; (c) Microscopic image of CO2 microbubbles in porous media.10 Schematic representation of blockage mechanism as CO2 microbubble enters the pore throat.11 Pressure drop changes during CO2 microbubble fluid injecting as a function of gas: liquid ratios. Pressure drop changes during CO2 microbubble fluid injecting into sandpack with different permeabilities.13 Pressure drop changes during CO2 microbubble fluid injecting with different flow rates.14 Fractional flows of (a) CO2 microbubble fluid with = 20% and (b) XG polymer solution (5000 mg/L) in dual-core sandpack (permeability ratio of 1.15 Pressure drops of CO2 microbubble fluid with = 20% and XG polymer solution (5000 mg/L) in dual-core sandpack (permeability ratio of 1.16 Schematic illustration of the flow of CO2 microbubble fluid in heterogeneous porous media.17 Fractional flows of CO2 microbubble fluid with = 20% in dual-core sandpacks with different permeability ratios: (a) 0.18 Pressure drops of CO2 microbubble fluid with = 20% in dual-core sandpacks with different permeability ratios: 0.1 General sketch of problem in this chapter .2 Size distribution of CO2 microbubbles .3 Schematic of sandpack flooding test .4 Oil recovery performance from single sandpack flooding test.5 Oil displacement in micrometers scale and corresponding effluents at the flooding stages ( major flow) .6 Fractional flow in parallel sandpack with base solution injection (Permeability ratio of 1:4) .
