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The performance of polymer gel to plug a hydraulic fracture is greatly affected by its distribution patterns and gelling effect. In this study, the migration of a gel plugging agent in a fracture and its plugging after gelling were investigated by physical simulation experiments. In addition, the distribution patterns of the gel plugging agent and...
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... In the second approach, phenolic crosslinkers are formed by the polycondensation of Agrade phenolic resins in the system. Phenol undergoes condensation with formaldehyde to produce hydroxymethylphenol or phenolic resin, and then HPAM reacts with hydroxymethylphenol/phenolic resin to produce polymer gels ( Figure 4) [34]. Chen et al. [35] synthesized a heat-resistant and salt-resistant polymer gel using phenol, HMTA and resorcinol crosslinkers, as well as acrylamide/AMPS copolymers, and it maintained a gelation strength of 90% after 100 days of aging at a high temperature of 130 °C in a high-salinity environment of 223,000 mg/L, demonstrating excellent stability. ...
... Crosslinking mechanism of phenolic resin. (Reprinted/adapted with permission from Ref.[34], 2020, Zhang et al.) ...
Polymer gels are widely used in oil–gas drilling and production engineering for the purposes of conformance control, water shutoff, fracturing, lost circulation control, etc. Here, the progress in research on three kinds of polymer gels, including the in situ crosslinked polymer gel, the pre-crosslinked polymer gel and the physically crosslinked polymer gel, are systematically reviewed in terms of the gel compositions, crosslinking principles and properties. Moreover, the advantages and disadvantages of the three kinds of polymer gels are also comparatively discussed. The types, characteristics and action mechanisms of the polymer gels used in oil-gas drilling and production engineering are systematically analyzed. Depending on the crosslinking mechanism, in situ crosslinked polymer gels can be divided into free-radical-based monomer crosslinked gels, ionic-bond-based metal cross-linked gels and covalent-bond-based organic crosslinked gels. Surface crosslinked polymer gels are divided into two types based on their size and gel particle preparation method, including pre-crosslinked gel particles and polymer gel microspheres. Physically crosslinked polymer gels are mainly divided into hydrogen-bonded gels, hydrophobic association gels and electrostatic interaction gels depending on the application conditions of the oil–gas drilling and production engineering processes. In the field of oil–gas drilling engineering, the polymer gels are mainly used as drilling fluids, plugging agents and lost circulation materials, and polymer gels are an important material that are utilized for profile control, water shutoff, chemical flooding and fracturing. Finally, the research potential of polymer gels in oil–gas drilling and production engineering is proposed. The temperature resistance, salinity resistance, gelation strength and environmental friendliness of polymer gels should be further improved in order to meet the future technical requirements of oil–gas drilling and production.
The most popular oil displacement technique in oilfield development is water flooding, yet sustained water flooding makes it simple to create water channeling in the formation, lowering development efficiency. A high strength agar was synthesized by using raw agar and 3-chloro-2-hydroxy-propyl trimethyl ammonium chloride, and it was then combined with PAM to prepare a plugging system to address the issue of water channeling in old oilfields. The successful synthesis of a modified agar was demonstrated by FITR, EM, TG/DSC, and its temperature resistance and agar strength were improved. Gelation and flow experiments were used to test the gelation and plugging characteristics of the plugging system. The results show that the plugging system is a pseudoplastic fluid, the temperature resistance less than 120 °C, the salinity resistance less than 1 × 10⁵ mg/L, the gelation time of is 1 ∼ 3d, the gelation strength reaches grade I, the resistance coefficient less than 10, the breakthrough pressure gradient greater than 20 MPa·m⁻¹, the plugging ratio greater than 90%, and the oil recovery ratio increases 22.8%. This work’s study has a significant impact on enhancing oil recovery.
In this study, novel pre-crosslinked gel particles were synthesized to form a new heterogeneous composite system with a weak alkaline-surfactant-polymer (ASP) system. The microscopic visualization model is used for oil flooding and macroscopic core flooding experiments and advanced testing methods to describe the microscopic morphology of the pre-cross-linked gel particles and their retention state in the porous medium, revealing the microscopic plugging mechanism of the novel heterogeneous composite system in the porous medium. Scanning electron microscope images showed a uniform force on the pre-crosslinked gel particle network structure during the stressing process, with no mechanical weak points and improved tensile properties. The maximum pressure induced by the pre-cross-linked gel particles passing through the 0.5 mm diameter pore plate was 4.8 times higher than that of the conventional bulk particles. The elasticity factor of the pre-cross-linked gel particles was eight times higher than that of the conventional body expansion particles. Adding pre-cross-linked gel particles to the composite system improves the interfacial tension stability and effectively reduces the amount of chemicals under the same interfacial tension level. In a three-tube parallel core flooding experiment, the final heterogeneous composite flooding recovery after polymer flooding was 7.3% higher than that of ASP. The heterogeneous composite flooding system improves the recovery of crude oil after polymer flooding by blocking pore flow steering, wetting reversal, co-emulsification, and poly merging oil zone mechanisms. Thus, the implementation of heterogeneous composite flooding after polymer flooding can achieve the synergistic effect of blocking the dominant seepage channel and improving the oil washing efficiency, which can significantly improve the degree of remaining oil utilization. To clarify the microscopic blocking mechanism of the heterogeneous composite system, it is important to guide the development of post-polymer flooding composite flooding technology and research its microscopic flooding mechanism.
The fluid flow dynamics of the matrix and fractures are significantly different from each other. Fractures are high-permeability flow channels that serve as the main flow units. On the other hand, the Matrix takes up the majority of the reservoir volume and is generally regarded as the main storage unit. The primary goal of this research is to investigate numerically the effects of fractures and polymer gel treatment on oil recovery during waterflooding of artificially fractured core plugs. In this study, the MATLAB Reservoir Simulation Toolbox (MRST) was used for the numerical solution. Different numerical models were developed using MRST to describe three main cases: non-fractured core plug, fractured core plug, and polymer gel treated core plug. Following the creation of the physical models, 2 PV water was introduced into all core plugs. Oil recovery and water saturation profiles vs. time plots were obtained. The standard Buckley-Leveret solution is utilized to evaluate the numerical model, and the fractures are modeled using the Embedded Discrete Fracture Model (EDFM). The results of the simulations were compared with the results of the experiments. In the experiments, results were recorded after 2 PV water injections. For the polymer gel treated core plugs, 2 PV more water was injected after the polymer gel operation. same injection volumes as used in the MRST model. For an artificially fractured core sample, initial oil recovery was measured as 28.57% experimentally and 28.87% with MRST. Then polymer gel was applied to the core plug, increasing the oil recovery to 42.85% experimentally and to 40.83% with MRST. Similarly, before and after polymer gel operation, mean water saturation was measured as 58.34% and 66.5%, respectively. MRST results showed mean water saturation of 58.38% and 65.45%. It is clear from both numerical and experimental models that the existence of fractures decreases the overall hydrocarbon recovery. Polymer gel treatment decreases fracture permeability, resulting in a more uniform sweep and increased overall recovery. Additional oil recovery was observed after polymer gel treatment. Besides, polymer gel treatment of the matrix is also efficient for increasing the recovery and leads to the same results. Moreover, the effects of the fracture aperture and fracture permeability on the recovery were also investigated. Fracture aperture directly impacts the recovery of the low aperture values when the permeability is constant. Similarly, permeability directly affects recovery for high values when the aperture is constant. Finally, the results showed that experimental and numerical findings are significantly close to each other for all non-fractured, fractured, and polymer gel-treated cases.
A cross-linked polymer gel system used for lost-circulation control during drilling with a high-temperature resistance of 160 °C was prepared from a formulation containing 1% of polymer ZB-1/ZB-2 (1:1 ratio), 0.2% of catechol, 0.4% of hexamethylenetetramine, and 0.3% of thiourea. The effects of time, temperature, and salinity on the gelation performance of polymer gel were analyzed. The results indicate that the gelation time of the polymer gel lost-circulation system at high temperature (160 ℃) is 6-20 h, with the maintenance of the storage modulus after gelation at greater than 60 Pa with the loss modulus retained at above 20 Pa. The polymer gel displayed excellent gel strength and viscoelasticity. The salinity has little influence on the viscoelasticity of the gel system, indicating that the gel system has excellent salt-resistance and is suitable for lost circulation control in the drilling process of high-temperature and high-salinity formations. The plugging performance of the polymer gel lost circulation material system on fractures with different widths and roughness was studied. The results show that the bearing resistance capacity of the gel gradually decreases as the fracture width increases, and the lost circulation control performance of the gel is significantly better on rough walls than on smooth walls. In addition, as the fracture width increases, the gel strength contributes to the bearing resistance capacity. This study indicates the excellent lost-circulation-control performance gained using the polymer gel LCM for fractures. To improve lost-circulation-control performance, the gel strength and the cementing force between the gel and the fractured wall must be improved.
Polymer gels are widely used as drilling plugging materials. In this paper, titanium bis(triethanolamine)diisopropoxide (TE) and polyvinyl alcohol (PVA) solution were chemically cross‐linked to obtain a gel material. It shows that the OH on the PVA molecular chain are chemically cross‐linked with the Ti ion in TE crosslinking agent through complexation reaction, and the cross‐linked segment can inhibit the chain motion, resulting in a stable “crab structure” gel configuration. The gel materials synthesized under this configuration were characterized and analyzed by SEM, TG‐DSC, GPC, and contact angle measurement. It was demonstrated that the gel performance is optimal when the concentration of TE crosslinking agent is 2.2 wt%, considering the gel strength and gelation time. In addition, the simulated plugging experiment of the gel showed that the service life of the gel was about 72 days, and the sealing performance and tensile recovery performance were significantly improved compared with the previous ones, which would provide a new perspective for the novel plugging materials.
