Study of Microscopic and Macroscopic Displacement Behaviors of Polymer Solution in Water-Wet and Oil-Wet Media

Evaluating Factors Impacting Polymer Flooding in Hydrocarbon Reservoirs: Laboratory and Field-Scale Applications

Polymer flooding is an enhanced oil recovery (EOR) method used to increase oil recovery from oil reservoirs beyond primary and secondary recovery. Although it is one of the most well-established methods of EOR, there are still continuous new developments and evaluations for this method. This is mainly attributed to the diverse polymers used, expansion of this method in terms of application, and the increase in knowledge pertaining to the topic due to the increase in laboratory testing and field applications. In this research, we perform a review of the factors impacting polymer flooding in both laboratory studies and field-based applications in order to create guidelines with respect to the parameters that should be included when designing a polymer flooding study or application. The main mechanism of polymer flooding is initially discussed, along with the types of polymers that can be used in polymer flooding. We then discuss the most prominent parameters that should be included when designing a polymer flooding project and, based on previous laboratory studies and field projects, discuss how these parameters impact the polymer itself and the flooding process. This research can provide guidelines for researchers and engineers for future polymer flooding research or field applications.

Experimental and numerical investigation of polymer pore-clogging in micromodels

Polymers have been used effectively in the Oil & Gas Industry for a variety of field applications, such as enhanced oil recovery (EOR), well conformance, mobility control, and others. Polymer intermolecular interactions with the porous rock, in particular, formation clogging and the associated alterations to permeability, is a common problem in the industry. In this work, fluorescent polymers and single-molecule imaging are presented for the first time to assess the dynamic interaction and transport behavior of polymer molecules utilizing a microfluidic device. Pore-scale simulations are performed to replicate the experimental observations. The microfluidic chip, also known as a "Reservoir-on-a-Chip" functions as a 2D surrogate to evaluate the flow processes that take place at the pore-scale. The pore-throat sizes of an oil-bearing reservoir rock, which range from 2 to 10 nm, are taken into consideration while designing the microfluidic chip. Using soft lithography, we created the micromodel from polydimethylsiloxane (PDMS). The conventional use of tracers to monitor polymers has a restriction due to the tendency of polymer and tracer molecules to segregate. For the first time, we develop a novel microscopy method to observe the dynamic behavior of polymer pore-clogging and unclogging processes. We provide direct dynamic observations of polymer molecules during their transport within the aqueous phase and their clustering and accumulations. Pore-scale simulations were carried out to simulate the phenomena using a finite-element simulation tool. The simulations revealed a decline in flow conductivity over time within the flow channels that experienced polymer accumulation and retention, which is consistent with the experimental observation of polymer retention. The performed single-phase flow simulations allowed us to assess the flow behavior of the tagged polymer molecules within the aqueous phase. Additionally, both experimental observation and numerical simulations are used to evaluate the retention mechanisms that emerge during flow and how they affect apparent permeability. This work provides new insights to assessing the mechanisms of polymer retention in porous media.

Artificial Neural Network to Forecast Enhanced Oil Recovery Using Hydrolyzed Polyacrylamide in Sandstone and Carbonate Reservoirs

Polymer flooding is an important enhanced oil recovery (EOR) method with high performance which is acceptable and applicable on a field scale but should first be evaluated through lab-scale experiments or simulation tools. Artificial intelligence techniques are strong simulation tools which can be used to evaluate the performance of polymer flooding operation. In this study, the main parameters of polymer flooding were selected as input parameters of models and collected from the literature, including: polymer concentration, salt concentration, rock type, initial oil saturation, porosity, permeability, pore volume flooding, temperature, API gravity, molecular weight of the polymer, and salinity. After that, multilayer perceptron (MLP), radial basis function, and fuzzy neural networks such as the adaptive neuro-fuzzy inference system were adopted to estimate the output EOR performance. The MLP neural network had a very high ability for prediction, with statistical parameters of R² = 0.9990 and RMSE = 0.0002. Therefore, the proposed model can significantly help engineers to select the proper EOR methods and API gravity, salinity, permeability, porosity, and salt concentration have the greatest impact on the polymer flooding performance.

Evaluation of Polymeric Materials for Chemical Enhanced Oil Recovery

Polymer flooding is a promising enhanced oil recovery (EOR) technique; sweeping a reservoir with a dilute polymer solution can significantly improve the overall oil recovery. In this overview, polymeric materials for enhanced oil recovery are described in general terms, with specific emphasis on desirable characteristics for the application. Application-specific properties should be considered when selecting or developing polymers for enhanced oil recovery and should be carefully evaluated. Characterization techniques should be informed by current best practices; several are described herein. Evaluation of fundamental polymer properties (including polymer composition, microstructure, and molecular weight averages); resistance to shear/thermal/chemical degradation; and salinity/hardness compatibility are discussed. Finally, evaluation techniques to establish the polymer flooding performance of candidate EOR materials are described.

Pore-scale simulation of water/oil displacement in a water-wet channel

Water/oil flow characteristics in a water-wet capillary were simulated at the pore scale to increase our understanding on immiscible flow and enhanced oil recovery. Volume of fluid method was used to capture the interface between oil and water and a pore-throat connecting structure was established to investigate the effects of viscosity, interfacial tension (IFT) and capillary number (Ca). The results show that during a water displacement process, an initial continuous oil phase can be snapped off in the water-wet pore due to the capillary effect. By altering the viscosity of the displacing fluid and the IFT between the wetting and non-wetting phases, the snapped-off phenomenon can be eliminated or reduced during the displacement. A stable displacement can be obtained under high Ca number conditions. Different displacement effects can be obtained at the same Ca number due to its significant influence on the flow state, i.e., snapped-off flow, transient flow and stable flow, and ultralow IFT alone would not ensure a very high recovery rate due to the fingering flow occurrence. A flow chart relating flow states and the corresponding oil recovery factor is established.

Experimental Study on the Physical Performance and Flow Behavior of Decorated Polyacrylamide for Enhanced Oil Recovery

With the rapid growth of energy consumption, enhanced oil recovery (EOR) methods are continually emerging, the most effective and widely used was polymer flooding. However, the shortcomings were gradually exposed. A novel decorated polyacrylamide might be a better alternative than polymer. In this work, the molecular structure and the properties reflecting the viscosity of decorated polyacrylamide, interfacial tension, and emulsification were examined. In order to better understand the interactions between decorated polyacrylamide and oil as well as the displacement mechanism, the displacement experiment were conducted in the etched-glass microscale model. Moreover, the coreflooding comparison experiments between decorated polyacrylamide and polymer were performed to investigate the displacement effect. The statistical analysis showed that the decorated polyacrylamide has excellent characteristics of salt tolerance, viscosity stability, and viscosification like polymer. Besides, the ability to reduce the interfacial tension in order 10−1 and emulsification, which were more similar to surfactant. Therefore, the decorated polyacrylamide was a multifunctional polymer. The displacement process captured by camera illustrated that the decorated polyacrylamide flooded oil mainly by means of ‘pull and drag’, ‘entrainment’, and ‘bridging’, based on the mechanism of viscosifying, emulsifying, and viscoelasticity. The results of the coreflooding experiment indicated that the recovery of decorated polyacrylamide can be improved by approximately 11–16% after water flooding when the concentration was more than 800 mg/L, which was higher than that of conventional polymer flooding. It should be mentioned that a new injection mode of ‘concentration reduction multi-slug’ was first proposed, and it obtained an exciting result of increasing oil production and decreasing water-cut, the effect of conformance control was more significant.

Improvement of Polymer Flooding Using in-Situ Releasing of Smart Nano-Scale Coated Polymer Particles in Porous Media

The main purpose of this paper is modeling and simulation of in-situ releasing of smart nano-sized core-shell particles at the water-oil interface during polymer flooding. During the polymer flooding process, when these nano-particles reach the water-oil interface, migrate to the oil phase and the hydrophobic layer of them dissolves in this phase. After dissolution of this protective nano-sized layer, the hydrophilic core containing a water-soluble ultra high molecular weight polymer diffuses back into the water phase and with dissolving in this phase, dramatically increases viscosity of flooding water in the neighborhood of the water-oil interface. In this study, two different time-dependent dissolution models are implemented. A swellable-chain disentanglement model with concentration-dependent diffusion coefficient is considered for dissolution of the core polymer into the aqueous phase, whereas, surface chain disentanglement with constant diffusion coefficient is considered for dissolution of the shell polymer in the oil phase. Using finite difference scheme, the governing equations are numerically solved by defining some dimensionless parameters for the main parameters as well as the moving boundaries. In addition, some experimental flooding tests in micromodel were carried out to experimentally investigate the recovery factor of using these particles compared to those of the conventional polymer flooding.

Reservoir-on-a-chip (ROC): a new paradigm in reservoir engineering

In this study, we design a microfluidic chip, which represents the pore structure of a naturally occurring oil-bearing reservoir rock. The pore-network has been etched in a silicon substrate and bonded with a glass covering layer to make a complete microfluidic chip, which is termed as 'Reservoir-on-a-chip' (ROC). Here we report, for the first time, the ability to perform traditional waterflooding experiments in a ROC. Oil is kept as the resident phase in the ROC, and waterflooding is performed to displace the oil phase from the network. The flow visualization provides specific information about the presence of the trapped oil phase and the movement of the oil/water interface/meniscus in the network. The recovery curve is extracted based on the measured volume of oil at the outlet of the ROC. We also provide the first indication that this oil-recovery trend realized at chip-level can be correlated to the flooding experiments related to actual reservoir cores. Hence, we have successfully demonstrated that the conceptualized 'Reservoir-on-a-Chip' has the features of a realistic pore-network and in principle is able to perform the necessary flooding experiments that are routinely done in reservoir engineering.