Search Results (3)

To address the issues of traditional gels in high-temperature reservoir leakage plugging, such as injection–retention imbalance, poor high-temperature stability, and insufficient thixotropy, this study developed a thixotropic polymer gel system via molecular design and component optimization, aiming to achieve excellent thixotropy, high strength, and wide temperature adaptability (80–140 °C) while clarifying its gelation mechanism. First, the optimal polymer was selected by comparing the high-temperature stability and crosslinking activity of AM/AMPS copolymer (J-2), low-molecular-weight acrylamide polymers (J-3, J-4), and AM/AMPS/NVP terpolymer (J-1). Then, the phenolic crosslinking system was optimized: hexamethylenetetramine (HMTA) was chosen for controlled aldehyde release (avoiding poor stability/dehydration) and catechol for high crosslinking efficiency (enhancing strength via dense crosslinking sites). Urea–formaldehyde resin (UF) was introduced to form a “polymer-resin double network,” improving high-temperature compression resistance and long-term stability. Cyclic shear rheological tests showed the gel system had a larger hysteresis area than the polymer solution, indicating excellent thixotropy before gelation. It gelled completely at 80–140 °C (gelation time shortened with temperature). At 120 °C, its viscosity was 7500 mPa·s, storage modulus (G′) 51 Pa, and loss modulus (G″) 6 Pa, demonstrating good shear thixotropy. The final system (1% J-1, 0.3% catechol, 0.6% HMTA, 15% UF) is suitable for high-temperature reservoir leakage plugging. Full article

To control the filtration loss of drilling fluids in salt–gypsum formations, a novel type of zwitterionic polymer gel (DNDAP) was synthesized by free radical polymerization, which was used as a salt- and calcium-resistant fluid loss reducer for water-based drilling fluids (WBDF). DNDAP was prepared with N, N-dimethylacrylamide (DMAA), N-vinylpyrrolidone (NVP), Diallyl dimethyl ammonium chloride (DMDAAC), 2-acrylamide-2-methylpropaneonic acid (AMPS), and isopentenol polyether (TPEG) as raw materials. Fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance (¹H-NMR) were used to characterize the composition and structure of the DNDAP copolymer. The thermal stability of DNDAP was evaluated by the use of thermogravimetric analysis (TGA). WBDF with DNDAP was analyzed for zeta potential and particle size and the corresponding filter cake underwent energy dispersive spectrum (EDS) analysis and scanning electron microscope (SEM) analysis. The results showed that the thermal decomposition of DNDAP mainly occurred above 303 °C. DNDAP exhibits excellent rheological and filtration properties in water-based drilling fluids, even under high-temperature aging (up to 200 °C) and high salinity (20 wt% NaCl or 5 wt% CaCl₂) environments. The strong adsorption effect of DNDAP makes the particle size of bentonite reasonably distributed to form a dense mud cake that reduces filtration losses. Full article

Relatively smaller volumes of gelling systems had been used to address conformance problems located near the wellbore in oil reservoirs with harsh temperature and salinity conditions. These gelling systems were formulated with high concentrations of low-molecular-weight acrylamide-based polymers crosslinked with polyethylenimine (PEI). However, for in-depth conformance control, in which large gelant volumes and long gelation times were required, lower-base polymer loadings were necessary to ensure the economic feasibility of the treatment. In this study, a gelling system with high-molecular weight 2-acrylamido-2-methylpropane sulfonic acid (AMPS), N-vinyl-2-pyrrolidone (NVP), acrylamide terpolymer, and PEI, with the addition of bentonite as a filler, was formulated. The influence of the gelant formulation and reservoir conditions on the gelation kinetics and final gel strength of the system was investigated through bottle tests and rheological tests. The addition of clay in the formulation increased the gelation time, thermal stability, and syneresis resistance, and slightly improved the final gel strength. Furthermore, samples prepared with polymer and PEI concentrations below 1 wt %, natural bentonite, and PEI with molecular weight of 70,000 kg/kmol and pH of 11: (i) presented good injectivity and propagation parameters (pseudoplastic behavior and viscosity ~25 mPa·s); (ii) showed suitable gelation times for near wellbore (~5 h) or far wellbore (~21 h) treatments; and (iii) formed strong composite hydrogels (equilibrium complex modulus ~10–20 Pa and Sydansk code G to H) with low syneresis and good long-term stability (~3 to 6 months) under harsh conditions. Therefore, the use of high-molecular-weight base polymer and low-cost clay as active filler seems promising to improve the cost-effectiveness of gelling systems for in-depth conformance treatments under harsh conditions of temperature and salinity/hardness. Full article