Polymer Flooding In Oilfields Research Articles

Development of Novel Delayed Swelling Polymer Gel Particles with Salt Resistance for Enhanced In-Depth Permeability Control

Summary Prolonged waterflooding or polymer flooding in oil fields often exacerbates reservoir heterogeneity, leading to premature water breakthrough and high water cut, which significantly hinders efficient oilfield development. To address this issue, polymer gel particles have been prescribed to enhance sweep efficiency and augment waterflooding recovery by plugging preferential pathways within the reservoir. However, inherent weaknesses of polymer gel particles, such as fast water absorption and expansion rates in the initial stage and low post-expansion rates, make it difficult to balance in-depth transportation and plugging performance. Additionally, these gel particles are sensitive to ions in the formation water, resulting in reduced expansion rates under high-salinity conditions. Therefore, there are still challenges in the application of polymer gel particles for in-depth permeability control. In this study, a new type of delayed swelling and salt-resistant polymer gel particle was synthesized through inverse emulsion copolymerization. To achieve delayed swelling, we use a degradable crosslinker and hydrophobic monomer to enhance the crosslinked network density and hydrophobicity of gel particles. Our double crosslinked gel particles keep their original size until Day 2, then gradually swell up to 20 days in NaCl solution with a concentration of 15×104 mg·L−1 at 90°C. In comparison, the traditional single crosslinked gel particles show significant disparities in swelling behaviors and quickly swell when just dispersed in a 15×104 mg·L−1 NaCl solution at 90°C, maintaining roughly the same size over the testing period. Coreflooding experiments demonstrate that the residual resistance before and after aging increases from 2.37 to 6.82. The newly synthesized delayed swelling and salt-resistant polymer gel particles exhibit promising potential for overcoming the challenges associated with reservoir heterogeneity and high salinity.

Exact Solution for Tertiary Polymer Flooding with Polymer Mechanical Entrapment and Adsorption

Two-phase transport with simultaneous component adsorption and mechanical entrapment occurs in numerous suspension and nano-colloidal flows in porous media, including polymer flooding in oilfields. To the contrary of one-dimensional (1D) self-similar solution for polymer flooding that ignores the mechanical entrapment, accounting for this phenomenon breaks self-similarity. However, this non-self-similar problem allows for an exact integration. For the first time, the present work derives an exact solution for polymer injection into a rock saturated by oil and water with simultaneous adsorption and mechanical entrapment. The splitting method that uses Lagrangian coordinate as an independent variable instead of time, splits the 3 × 3 governing system into 2 × 2 auxiliary system that determines suspended and captured polymer concentrations, and the scalar equation for unknown phase saturation. The exact solution reveals two fingerprints of the component entrapment under small entrapped concentrations: stabilisation of the breakthrough concentration at the value below the injected one, and non-stabilised pressure drop growth. Three sets of laboratory polymer core-floodings exhibit a close match by the analytical model.

Study on the Development Effect Standard of Classified Well Groups for Polymer Flooding in Class II Reservoirs

Because of the development characteristics of the second type reservoir, the heterogeneity of the reservoir is obvious, and the development effect of polymer flooding in different well groups is quite different, which is not conducive to the adjustment and evaluation of later development. Therefore, it is necessary to classify the polymer flooding well groups in the second type reservoir according to the dynamic and static physical parameters, and evaluate the development effect of different types of polymer flooding well groups on this basis. By analyzing the dynamic and static data of polymer flooding blocks in type II reservoirs, this paper determines the influencing factors of well group classification evaluation, establishes the method of well group classification combined with grey correlation method and mathematical statistics analysis, uses reservoir numerical simulation technology to predict the development effect of polymer flooding for different types of well groups, gives the development effect standards of polymer flooding for different types of well groups, and plays a certain role in adjusting the development effect of polymer flooding in oilfields.

Morphology of polyacrylamide in solution: effect of water quality on viscosity

When used in polymer flooding for enhanced oil recovery, polyacrylamide (PAM) is an effective viscosifying agent and has been widely used for polymer flooding in oilfields in China for many years. Practical experience has shown that the use of oilfield treated produced water instead of fresh water, driven by economic and environmental considerations, leads to reduced viscosity of PAM solutions and hence poorer performance. To better understand the causes of viscosity degradation and to be able to control it, the morphology of polymer in different water quality conditions was investigated to reveal the relationship between the morphology and viscosity of PAM solutions. The effect of water quality on viscosity of PAM solution was also analyzed. The results show that the morphology of PAM solution prepared with deionized water exhibited a uniform three‐dimensional network structure. Both divalent metal ions and suspended substances have significant effects on PAM morphology and viscosity, but the effect of suspended substances is larger than that of divalent metal ions. Copyright © 2015 John Wiley & Sons, Ltd.

Study on emulsification stability of wastewater produced by polymer flooding

Abstract In order to improve the oil–water separation of wastewater produced in polymer flooding of oil field, the emulsification stability of wastewater was investigated by using laser particle-size distribution analyzer, potential measurement and flocculation test. The influences of polymer, water treatment agent, solution viscosity and temperature on emulsification stability were analyzed. The experimental results show that the emulsification stability is mainly determined by the size distribution of oil droplets in wastewater. The addition of polymer will enhance steric hindrance among oil droplets and decrease the efficiency of collision of oil droplets, which results in lower size of oil droplet and slower floating speed. The higher the polymer concentration, the more stable the emulsion. Therefore, the key for improving the efficiency of oil–water separation is to decrease the activation energy barrier for oil droplets coalescence, which can promote the coalesce of tiny oil droplets to from large ones.

Contribution of Main Pollutants in Oilfield Polymer-Flooding Wastewater to the Total Membrane Fouling Resistance

Polymer flooding technology has been used in the oilfield, but huge amounts of polymer-flooding wastewater are produced with oil extraction. Therefore, the treatment and recycle of this wastewater become very significant. In this study, the membrane technology was used to treat synthetic oilfield polymer-flooding wastewater in laboratory-scale dead-end/cross-flow test unit with flat polyvinylidene fluoride (PVDF) membrane (MW 100 kDa). We systematically inspected the membrane fouling mechanism, the variety of total fouling resistance, the dominant resistance, and the filtration proceeds in the filtration process. The orthogonal method and multivariate linear regression method were applied to analyze the influencing degree of main pollutants concentration which contains partially hydrolyzed polyacrylamide (HPAM), oil and suspended solid on the total membrane fouling resistance. According to a comparison of the average rates of change of total membrane fouling resistance for the HPAM concentration, oil concentration, and suspended solid (SS) concentration in single solute solution, double solute solution, synthetic oilfield polymer-flooding wastewater, and the value of pH, HPAM can decrease the average rate of change of total membrane fouling resistance for other two solutes and has the crucial effect on the total membrane fouling resistance. The sequence of influence degree on the total membrane fouling resistance is the HPAM concentration > oil concentration > suspended solid concentration. Moreover, the membrane cleaning effect was studied by using SEM images and the pure water flux.

Photocatalytical visbreaking of wastewater produced from polymer flooding in oilfields

Wastewater produced from polymer flooding in oilfields features a high viscosity and oily content because of a residue of high concentration of polyacrylamide (PAM). It is more difficulty efficiently to treat than that from water flooding by a conventional treatment system including gravitational settling and filtration. In this paper, initially by analyzing emulsification action and role of PAM in the wastewater, a process of photocatalytical visbreaking was proposed and investigated by taking aim at viscosity breaking and degradation of PAM in favor of further treatments. The experimental results show that viscosity of wastewater produced from polymer flooding is greatly decreased to the same level as that of distilled water under illumination of 5–10 min using photocatalytic degradation over TiO 2 powders. The rate of PAM photogradation is above 90% within illumination of 90 min. The efficient breaking of viscosity favors treatments to feed the conventional system used in the water flooding with low viscosity of wastewater.