This paper presents a low-cost, high-temperature-resistant and high-strength polyacrylamide gel system formed by secondary cross-linking. The gel system (named JM186) used phenolic resin and organic zirconium as cross-linking agents, and the performance of the gel system was systematically evaluated under high temperature. The gel properties studied include: gel formation time, gel strength, thermal stability, sand-filled pipe sealing efficiency, and its microstructure. The concentration of polyacrylamide in JM186 gel system was as low as 0.3%, which can control the gelling time in a range of 1–9 h by adjusting the ratio of two cross-linking agents. It can resist temperature up to 120 °C without dehydration, and its highest gel strength can reach H grade. The modulus of elasticity (G’) and viscosity (G”) can reach 32.33 Pa and 3.25 Pa, respectively. DSC (differential scanning calorimetry) test indicated that the temperature of structural failure for this composite gel is 310.5 °C. The average sealing efficiency of the gel is 96.03% in sand-filled pipes. Finally, the gel microstructure was observed by cryo-scanning electron microscopy (Cryo-SEM). It was found that the gel system by secondary cross-linking has a dense and thickened network structure compared with the single cross-linker gel system. The gel is cross-linked by both the coordination bond and covalent bond, and the two cross-linking agents have a synergistic effect. This is the reason why the secondary cross-link gel system is better than the single-cross-linker gel system.
Aiming at the characteristics of low shear resistance and high filtration loss of guar gum-fracturing fluid, a high-efficiency organic zirconium crosslinker was prepared. In addition, the effects of different factors on the filtration coefficient and apparent viscosity of fracturing fluid were studied, and this study explores the micro mechanisms of various factors affecting the filtration coefficient from a molecular dynamics perspective. The results show that the antifiltration ability of guar gum-fracturing fluid is inversely proportional to the fluid viscosity. The increase of crosslinker content and reservoir pressure is beneficial to improve the viscosity and antishear ability of guar gum-fracturing fluid. When the crosslinker content is 0.25% and pressure is 30 MPa, the fracturing fluid parameters are 145 mPa·s and 2.1 × 10 −2 m 3 · min 1/2 , respectively, while the increase of reservoir temperature and the shear rate reduces the rheology and shear resistance of guar gum-fracturing fluid, so that the viscosity and filtration coefficient of fracturing fluid at 180°C and 200 s -1 are 123 mPa·s and 2.3 × 10 -2 m 3 ·min 1/2 , respectively. This work not only paves a new avenue for synthesizing organic zirconium as a crosslinker but also provides an efficient measure to reduce the filtration of guar gum-fracturing fluid on the oil and gas reservoirs.
Konjac glucomannan (KGM) and partially hydrolyzed polyacrylamide (HPAM) have good application prospects in the field of petroleum fracturing field, but few studies on the rheological properties of KGM and HPAM double polymer gel systems have been reported. Optimal conditions for the high temperature and shear resistant organozirconium crosslinked double polymer gel system for petroleum fracturing were explored through optimization experiments. The thickener contained a mass ratio of 2:1 of KGM to HPAM, while the organic zirconium crosslinking agent had controlled molar ratios of 1:4:3:3 of zirconium butoxide to ligand acetylacetone, triethanolamine, and glycerol. This work presents a systematic analysis of the chemical structure, microstructure, delayed crosslinking performance, temperature resistance, and shear resistance of the gel system. The study found that the crosslinking ratio of 100:2 resulted in a controllable delayed crosslinking time of the gel formed by the organic zirconium crosslinking agent and 4.0 g/L KGM/HPAM thickener within 5–25 min at room temperature. The viscosity remained above 81 mPa·s even after shearing for 100 min at 140°C and 170 s −1 . These findings provide a useful reference for the application of organic zirconium crosslinked KGM/HPAM gel system in the petroleum fracturing field.
Guohao Miao,Hai Zhang,Yu Yang,Jin Qu,Xinru Ma,Junping Zheng,Xiaofei Liu
Zirconium is one of the most commonly used crosslinkers for guar gum-based fracturing fluid. Nevertheless, it is difficult for zirconium crosslinkers applied in fracturing to possess both high temperature resistance and adjustable crosslinking time. Meanwhile, few people did systematical research on the crosslinking process of fracturing fluid. In this study, an organic zirconium crosslinker with high temperature resistance and controllable crosslinking time was synthesized. The seawater-based fracturing fluid gel prepared with the crosslinker could perform well under 170°C. Oscillatory shear experiments were conducted to analyze the rheology of the gelation process. Moreover, steady-state shear and micro-rheological tests were conducted to analyze the dynamic and static crosslinking process of the fracturing fluid, respectively. Meanwhile, rheo-kinetic equation was used to fit the data and the effects that various factors had on the gelation process were illustrated thoroughly. This study not only prepared an organic zirconium crosslinker with good performances, but also explored the crosslinking process of fracturing fluid gel, which could improve its further application in oilfields.
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