Abstract
During enhanced oil recovery (EOR), reservoir heterogeneities and fluids distributions promote preferential flow channels formation. Therefore, different types of gels have been proposed to improve swept efficiency on chemical flooding by plugging high permeability zones. The purpose of this article is to evaluate the effect that nanotechnology has on the inhibition of syneresis and the rheological properties of the Acrylamide Sodium Acrylate Copolymer/Chromium (III) Acetate gel system for conformance applications in mature reservoirs. Thus, a methodology is proposed in four stages: First, (I) nanoparticles synthesis, and characterization, followed by (II) bottle tests to monitor gelation kinetics and syneresis degree at 70 °C, then (III) description of the rheological evaluation on static and dynamic conditions to calculate gelation time and viscoelastic modulus (G’ and G”), and finally (IV) the displacement test with the best gel system in the presence of nanoparticles. Results showed that the best nanoparticle was the chromium oxide (Cr2O3), which represented the lesser syneresis degree and increased gelation time. Syneresis of gel samples in the presence of Cr2O3 at day 30 was under 1% for gels prepared with 4000, 6000, and 8000 mg·L−1 of polymer, and polymer to crosslinker ratio (p/c) of 40:1. Regarding SiO2, MgO, and Al2O3 nanoparticles, results show an improvement of gel strength. However, their thermal stability in terms of syneresis was lower. Displacement test in a triple parallel Slim Tube was able to recover an additional 37% of oil of the total oil present in the sandpacks, confirming the effectivity of the system when 100 mg·L−1 of Cr2O3 nanoparticles are included.
Highlights
High permeability channels generate several problems in waterflooding processes due to the increment in water cut per oil barrel recovered and the incremental costs associated with water treatment [1]
Gelation kinetic and gel strength were monitored by rheological measurements and Sydansk’s Code, while thermal stability was followed by syneresis behavior
Cr2O3 nanoparticles tend to delay gel formation which is favorable for gel location into the target zone
Summary
High permeability channels generate several problems in waterflooding processes due to the increment in water cut per oil barrel recovered and the incremental costs associated with water treatment [1]. The stability of the gels system is subdued to the reservoir conditions such as temperature, water salinity, and pH, carbon dioxide (CO2) or hydrogen sulfide (H2S) presence, and adsorption of the reagents on the rock surface [15] The latter can trigger a process known as syneresis consisting of water expulsion from the 3-dimensional network due to excessive chemical attractive forces within the gel structure or the lack of reagents to crosslink [16]. Gel degradation due to temperature conditions can be monitored through syneresis behavior and the main gel properties, gelation time and gel strength can be studied through rheological tests In this way, several authors have studied the syneresis process in bottle tests and core samples for different systems. Karimi et al [12] studied syneresis behavior in an HPAM/Cr (III) polymer gel system under different parameters and realized syneresis increase with temperature and decrease with higher polymer concentrations
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