Microscopic Roles of “Viscoelasticity” in HPMA polymer flooding for EOR

Impacts of partially hydrolyzed polyacrylamide (HPAM) on microbial mats from a constructed wetland treating oilfield produced water

Constructed wetlands have been successfully used in the treatment of produced water brought to the surface in large quantities during oil extraction activities. However, with the increasing use of partially hydrolyzed polyacrylamide (HPAM) in enhancing oil recovery, the impacts of HPAM on the biological processes of wetlands is still unknown. Microbial mats in wetlands play a key role in hydrocarbon degradation. Here, we compared the bacterial communities of four wetland microbial mats after flooding with different concentrations of HPAM. Two mats (i.e. the HPAM-free and the 500 ppm HPAM pre-exposed mats) were selected to further investigate the effect of HPAM on respiration and biodegradation activities. The field mats exhibited clear differences in their bacterial community structure, where Cyanobacteria and Alphaproteobacteria became dominant in the presence of HPAM. In the laboratory experiments, the generated CO₂ by the HPAM-free and the 500 ppm HPAM pre-exposed mats did not vary significantly when HPAM was added, although CO₂ values were slightly higher in the presence of oil. Both mats were still able to degrade between 15 ± 14.4 to 50 ± 13.0% of C₁₀ to C₃₀ alkanes in 28 days, and this degradation was not affected by HPAM addition. The HPAM concentration decreased by 22-34% of the initial amount after 28 days of incubation in the HPAM-free mat, versus only 7-18.4% decrease in the 500 ppm HPAM pre-exposed mat. We conclude that the wetland microbial mats seem to have become well adapted to HPAM and could maintain their respiration and hydrocarbon degradation activities.

Study on Permeability Characteristics of Porous Transparent Gels Based on Synthetic Materials

Advanced knowledge of the permeability characteristics of transparent gels play a key role in providing a rational basis for the study of porous polymer permeability and the research on the migration behavior of superpolymer solutions. Thus, a new type of transparent gel was prepared to simulate porous media, with aim to observe and analyze the permeability characteristics of transparent gel under the conditions of our experimental design by combining a transparent soil test and simple particle image velocimetry. The experimental results showed that the permeability of the transparent gel was similar to that through actual soil. The permeability coefficients of the transparent gel under different pressure gradients varied greatly early in the experimental cycle, while changing only slightly afterward, showing an overall trend of decreasing first and then stabilizing. With the increase of the mass ratio, the permeability coefficient of the sample decreased, the distribution of the low-velocity zone of the intercepted section became wider and tended to move upward. Differences in spatial position also caused different patterns of velocity and direction. The findings presented in this paper contribute to providing a new direction for the study of porous polymer permeability and the porous migration of superpolymer solutions.

Polymers for enhanced oil recovery: fundamentals and selection criteria revisited

As the energy demand is escalating tremendously and crude oil being the primary energy source for at least the next two decades, the production of crude oil should be enhanced to meet the global energy needs. This can be achieved by either exploration of new oil fields for crude oil extraction or employing enhanced oil recovery (EOR) technology to recover the residual oil from existing marginal oil fields. The former method requires more capital investment and time; therefore, this review focuses on the latter. In general, the abandoned oil fields still have 50% of crude left which is unrecovered due to lack of technology. Hence, EOR came into existence after the conventional methods of recovery (primary and secondary recovery) were found to be inefficient and less economical. Nineteen percent of the EOR projects are based upon cEOR methods worldwide, of which more than 80% of projects use economically feasible polymer flooding process for oil recovery. Both synthetic and naturally derived polymers have been used widely for this purpose; however, many recent studies have shown the lower stability of synthetic polymers under extreme reservoir conditions of high salinity and temperature. Additionally, naturally derived polymers face microbial degradation as the major limitation. Therefore, a number of novel polymers are currently studied for their suitability as an efficient EOR polymer. Latest findings have also revealed that biopolymers play an important role in wettability alteration, pore evolution by bioplugging, and reducing fingering effect. Injection of biopolymers can also lead to the selective plugging of thief zones which redirects water flood to the inaccessible oil pores. Therefore, the current study focuses on such principle and mechanism of polymer flooding along with the reservoir and field characteristics which affects the polymer flooding. It also discusses the scope of biopolymer along with the screening criteria for use of novel polymers and strategies to overcome the problems during polymer flooding. KEY POINTS: • Discussion of macroscopic and microscopic mechanisms of polymer flooding. • Screening criteria of polymers prior to flooding are essential. • Biopolymers are eco-friendly and are applicable for a wide range of reservoir conditions.

Synthesis and Solution Properties of a Novel Hyperbranched Polymer Based on Chitosan for Enhanced Oil Recovery

A new type of chitosan-modified hyperbranched polymer (named HPDACS) was synthesized through the free-radical polymerization of surface-modified chitosan with acrylic acid (AA) and acrylamide (AM) to achieve an enhanced oil recovery. The optimal polymerization conditions of HPDACS were explored and its structure was characterized by Fourier-transform infrared spectroscopy, hydrogen nuclear magnetic resonance, and environmental scanning electron microscopy. The solution properties of HPDACS in ultrapure water and simulated brine were deeply studied and then compared with those of partially hydrolyzed polyacrylamide (HPAM) and a dendritic polymer named HPDA. The experimental results showed that HPDACS has a good thickening ability, temperature resistance, and salt resistance. Its viscosity retention rate exceeded 79.49% after 90 days of aging, thus meeting the performance requirements of polymer flooding. After mechanical shearing, the viscosity retention rates of HPDACS in ultrapure water and simulated brine were higher than those of HPAM and HPDA, indicating its excellent shear resistance and good viscoelasticity. Following a 95% water cut after preliminary water flooding, 0.3 pore volume (PV) and 1500 mg/L HPDACS solution flooding and extended water flooding could further increase the oil recovery by 19.20%, which was higher than that by HPAM at 10.65% and HPDA at 13.72%. This finding indicates that HPDACS has great potential for oil displacement.

Modeling and Simulation of Polymer Flooding with Time-Varying Injection Pressure

Polymer flooding is one of the most incipient chemical-based enhanced oil recovery process that utilizes the injection of polymer solutions into oil reservoirs. The presence of a polymer in water increases the viscosity of the injected fluid, which upon injection reduces the water-to-oil mobility ratio and the permeability of the porous media, thereby improving oil recovery. The objective of this work is to investigate strategies that would help increase oil recovery. For that purpose, we have studied the effect of injection pressure and increasing polymer concentration on flooding performance. This work emphasizes on the development of a detailed mathematical model describing fluid saturations, pressure, and polymer concentration during the injection experiments and predicts oil recovery. The mathematical model developed for simulations is a black oil model consisting of a two-phase flow (aqueous and oleic) of polymeric solutions in one-dimensional porous media as a function of time and z-coordinate. The mathematical model consisting of heterogeneous, nonlinear, and simultaneous partial differential equations efficiently describes the physical process and consists of various parameters and variables that are involved in our lab-scale process to quantify and analyze them. A dimensionless numerical solution is achieved using the finite difference method. We implement the second-order high-accuracy central and backward finite-divided-difference formula along the z-direction that results in the discretization of the partial differential equations into ordinary differential equations with time as an independent variable. The input parameters such as porosity, permeability, saturation, and pore volume obtained from experimental data by polymer flooding are used in the simulation of the developed mathematical model. The model-predicted and commercial reservoir (CMG)-simulated oil production is in good agreement with experimental oil recoveries with a root-mean-square error (RMSE) in the range of 1.5-2.5 at a maximum constant pressure of 3.44 MPa as well as with temporal variation of the injection pressure between 2.41 and 3.44 MPa.

Pore-Scale Flow Characterization of Polymer Solutions in Microfluidic Porous Media

Polymer solutions are frequently used in enhanced oil recovery and groundwater remediation to improve the recovery of trapped nonaqueous fluids. However, applications are limited by an incomplete understanding of the flow in porous media. The tortuous pore structure imposes both shear and extension, which elongates polymers; moreover, the flow is often at large Weissenberg numbers, Wi, at which polymer elasticity in turn strongly alters the flow. This dynamic elongation can even produce flow instabilities with strong spatial and temporal fluctuations despite the low Reynolds number, Re. Unfortunately, macroscopic approaches are limited in their ability to characterize the pore-scale flow. Thus, understanding how polymer conformations, flow dynamics, and pore geometry together determine these nontrivial flow patterns and impact macroscopic transport remains an outstanding challenge. This review describes how microfluidic tools can shed light on the physics underlying the flow of polymer solutions in porous media at high Wi and low Re. Specifically, microfluidic studies elucidate how steady and unsteady flow behavior depends on pore geometry and solution properties, and how polymer-induced effects impact nonaqueous fluid recovery. This work thus provides new insights for polymer dynamics, non-Newtonian fluid mechanics, and applications such as enhanced oil recovery and groundwater remediation.

A zwitterionic polymer containing a hydrophobic group: enhanced rheological properties

A zwitterionic polymer containing a hydrophobic long chain, named MANPS, was independently developed by free radical solution polymerization.

Screening Study on Rheological Behavior and Phase Transition Point of Polymer-containing Fluids produced under the Oil Freezing Point Temperature

For an increasing implementation of the low-temperature transportation in oilfield, it is urgent priority initially to study the physical and chemical properties to provide the vital technical support for the low-temperature transport of the polymer flooding. In this paper, the rheological behavior of polymer-containing fluid produced from the Daqing polymer flood were first studied for an adaptation of transportation under the oil’s freezing point temperature. The experiments progressed with different temperature, shear rate, water content and polymer concentration which have great impacts on the viscosity of the fluids produced aiming to find the phase transportation point for the application of the low-temperature transportation. It was displayed that a significant discontinuity in the viscosity occurs at some range of water content. Before the phase transition point, presented in W/O (water-in-oil) emulsion, the viscosity was lifted with the increase of the water content while after the phase transition point, forming the O/W (oil-in-water) type emulsion, the viscosity was dropped with an increase of water content. The phase transition points strongly depend on the polymer concentration in the fluids Produced. It was demonstrated that the phase transition points of polymer-containing fluids were 65%, 70%, 50%, 50% and 50%, corresponding to the polymer concentrations of 315mg/L, 503mg/L, 708mg/L, 920mg/L and 1053mg/L, respectively. The characteristics are attributed to the viscous polymer. The fluidity of the fluid produced was decreased with the increase of polymer concentration.

Numerical Simulation Based Targeting of the Magushan Skarn Cu–Mo Deposit, Middle-Lower Yangtze Metallogenic Belt, China

The Magushan Cu–Mo deposit is a skarn deposit within the Nanling–Xuancheng mining district of the Middle-Lower Yangtze River Metallogenic Belt (MLYRMB), China. This study presents the results of a new numerical simulation that models the ore-forming processes that generated the Magushan deposit and enables the identification of unexplored areas that have significant exploration potential under areas covered by thick sedimentary sequences that cannot be easily explored using traditional methods. This study outlines the practical value of numerical simulation in determining the processes that operate during mineral deposit formation and how this knowledge can be used to enhance exploration targeting in areas of known mineralization. Our simulation also links multiple subdisciplines such as heat transfer, pressure, fluid flow, chemical reactions, and material migration. Our simulation allows the modeling of the formation and distribution of garnet, a gangue mineral commonly found within skarn deposits (including within the Magushan deposit). The modeled distribution of garnet matches the distribution of known mineralization as well as delineating areas that may well contain high garnet abundances within and around a concealed intrusion, indicating this area should be considered a prospective target during future mineral exploration. Overall, our study indicates that this type of numerical simulation-based approach to prospectivity modeling is both effective and economical and should be considered an additional tool for future mineral exploration to reduce exploration risks when targeting mineralization in areas with thick and unprospective sedimentary cover sequences.

Wormlike Micellar Solutions, Beyond the Chemical Enhanced Oil Recovery Restrictions

While traditional oil recovery methods are limited in terms of meeting the overall oil demands, enhanced oil recovery (EOR) techniques are being continually developed to provide a principal portion of our energy demands. Chemical EOR (cEOR) is one of the EOR techniques that shows an efficient oil recovery factor in a number of oilfields with low salinity and temperature ranges. However, the application of cEOR under the harsh conditions of reservoirs where most of today’s crude oils come from remains a challenge. High temperatures, the presence of ions, divalent ions, and heterogeneous rock structures in such reservoirs restrict the application of cEOR. Polymer solutions, surfactants, alkaline-based solutions, and complex multi-components of them are common chemical displacing fluids that failed to show successful recovery results in hostile conditions for various reasons. Wormlike micellar solutions (WMS) are viscoelastic surfactants that possess advantageous characteristics for overcoming current cEOR challenges. In this study, we first review the major approaches and challenges of commonly used chemical agents for cEOR applications. Subsequently, we review special characteristics of WMS that make them promising materials for the future of cEOR.

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.

Impact of Spacer and Hydrophobic Tail on Interfacial and Rheological Properties of Cationic Amido-Amine Gemini Surfactants for EOR Application

The impact of spacer length, spacer rigidity, trans and cis conformation of spacer double bond, and hydrophobic tail length of amido-amine cationic gemini surfactants was investigated by means of interfacial and rheological properties. For the study, six cationic amido-amine gemini surfactants were synthesized and used a cationic polyacrylamide. The interfacial tension (IFT) of the surfactants between crude oil and water was measured as a function of the surfactant concentration. It has been observed that the nature of the spacer and hydrophobic moiety have a significant effect on the oil/water interfacial tension. Rheological measurements of the surfactant-polymer hybrid system were performed at various surfactant concentrations, shear rates and temperatures. All synthesized cationic gemini surfactants were compatible with the cationic polyacrylamide since no precipitates were observed. By increasing the surfactant concentration, the storage modulus, as well as viscous properties of the cationic polyacrylamide, decreased at all temperatures because of the effect of charge shielding. On the other hand, the effect of concentration of surfactant was only significant at low shear rates. The storage modulus and viscous properties of the cationic polyacrylamide were also decreased significantly upon increasing surfactant tail length (C12 to C18). However, spacer rigidity, length, and conformation of spacer double bond caused a slight decrease in the storage modulus and viscous properties of cationic polyacrylamide. IFT, rheological properties, and compatibility tests showed huge potential of investigated surfactant-polymer system for enhanced oil production.

Investigation of Injection Strategy of Branched-Preformed Particle Gel/Polymer/Surfactant for Enhanced Oil Recovery after Polymer Flooding in Heterogeneous Reservoirs

The heterogeneous phase combination flooding (HPCF) system which is composed of a branched-preformed particle gel (B-PPG), polymer, and surfactant has been proposed to enhance oil recovery after polymer flooding in heterogeneous reservoirs by mobility control and reducing oil–water interfacial tension. However, the high cost of chemicals can make this process economically challenging in an era of low oil prices. Thus, in an era of low oil prices, it is becoming even more essential to optimize the heterogeneous phase combination flooding design. In order to optimize the HPCF process, the injection strategy has been designed such that the incremental oil recovery can be maximized using the corresponding combination of the B-PPG, polymer, and surfactant, thereby ensuring a more economically-viable recovery process. Different HPCF injection strategies including simultaneous injection and alternation injection were investigated by conducting parallel sand pack flooding experiments and large-scale plate sand pack flooding experiments. Results show that based on the flow rate ratio, the pressure rising area and the incremental oil recovery, no matter whether the injection strategy is simultaneous injection or alternation injection of HPCF, the HPCF can significantly block high permeability zone, increase the sweep efficiency and oil displacement efficiency, and effectively improve oil recovery. Compared with the simultaneous injection mode, the alternation injection of HPCF can show better sweep efficiency and oil displacement efficiency. Moreover, when the slug of HPCF and polymer/surfactant with the equivalent economical cost is injected by alternation injection mode, as the alternating cycle increases, the incremental oil recovery increases. The remaining oil distribution at different flooding stages investigated by conducting large-scale plate sand pack flooding experiments shows that alternation injection of HPCF can recover more remaining oil in the low permeability zone than simultaneous injection. Hence, these findings could provide the guidance for developing the injection strategy of HPCF to further enhance oil recovery after polymer flooding in heterogeneous reservoirs in the era of low oil prices.

Associating Polymer Networks Based on Cyclodextrin Inclusion Compounds for Heavy Oil Recovery

This work evaluates an approach to improve the enhanced heavy oil recovery performance of hydrophobic associating polymer. A polymeric system based on water-soluble hydrophobic associating polymer (WSHAP) and cyclodextrin (CD) polymer was proposed in this work. Addition of CD polymer to WSHAP forms interpolymer bridges by inclusion of CD groups with hydrophobic tails, and thereby the network structure is strengthened. The proposed system offers good viscoelasticity, pronounced shear thinning, and interesting viscosity-temperature relations. Sand pack tests indicated that the proposed system can build high resistance factor during the propagation in porous media, and its moderate adsorption phenomenon was represented by the thickness of the adsorbed layer. The relationship between effective viscosity and oil recovery increment indicated that the proposed system can significantly reduce the residual oil saturation due to the “piston-like” propagation. The overall oil recovery was raised by 5.7 and 24.5% of the original oil in place compared with WSHAP and partially hydrolyzed polyacrylamide (HPAM), respectively.

Further enhanced oil recovery by branched-preformed particle gel/HPAM/surfactant mixed solutions after polymer flooding in parallel-sandpack models

How to further sweep residual oil from unswept areas is crucial to enhance oil recovery after polymer flooding, which is widely used.

Mechanism of anomalously increased oil displacement with aqueous viscoelastic polymer solutions

Single-phase flows of viscoelastic polymer solutions in both microfluidic devices and rock cores exhibit apparent flow thickening. We demonstrate that this thickening occurs above a critical Deborah number corresponding to the onset of spatio-temporal fluctuations. These fluctuations are observed to occur over a broad range of spatial and temporal scales consistent with elastic turbulence. The fluctuations provide a previously unreported mechanism for enhancing the displacement of a second, capillary trapped, immiscible phase.