The semiconducting properties of the heteroleptic and homoleptic bis(phthalocyaninato) holmium complexes bearing electron-withdrawing phenoxy substituents at the phthalocyanine periphery, namely Ho(Pc)[Pc(OPh) 8 ] (1) and Ho[Pc(OPh) 3,9,10,16,17,23,24-octaphenoxyphthalocyaninate] have been investigated comparatively. Using a solution-based Quasi-Langmuir-Sh€ afer (QLS) method, the thin solid films of the two compounds were fabricated. The structure and properties of the thin films were investigated by UV-vis absorption spectra, X-ray diffraction (XRD) and atomic force microscopy (AFM). Experimental results indicated that H-type molecular stacking mode with the common preferential molecular ''edgeon'' orientation relative to the substrate has been formed, and the intermolecular face-to-face p-p interaction and film microstructures are effectively improve by increasing the number of phenoxy substituents of the Pc periphery within the double-decker complexes. The electrical conductivity of Ho(Pc)[Pc(OPh) 8 ] films was measured to be approximately 4 orders of magnitude larger than that of Ho[Pc(OPh) 8 ] 2 films, indicating significant effect of peripheral electron-withdrawing phenoxy groups on conducting behaviour of bis(phthalocyaninato) holmium complexes. In addition, the gas sensing behaviour of the QLS films of 1 and 2 toward electron donating gas, NH 3 , was investigated in the concentration range of 15-800 ppm. Surprisingly, contrary responses towards NH 3 were found for the QLS films of 1 and 2. In the presence of NH 3 , the conductivity of the films of Ho(Pc)[Pc(OPh) 8 ] (1) decreased while the conductivity of the films of Ho[Pc(OPh) 8 ] 2 (2) increased. This observation clearly demonstrated the p-and n-type semiconducting nature for 1 and 2, respectively. Furthermore, compared to the heteroleptic 1 having a hole mobility of 1.7 Â 10 À4 cm 2 V À1 s À1 , homoleptic 2 exhibits an electron mobility as high as 0.54 cm 2 V À1 s À1 . Therefore, the inversion of the semiconducting nature of the double-deckers from p-to n-type can be successfully and easily realized just by increasing the number of peripheral phenoxy groups attached to the conjugated Pc cores.
In situ CO2 enhanced oil recovery (ICE) shows great potential for increasing oil field tertiary recovery. Instead of injecting liquid CO2 directly into the oil reservoir, a solution of a CO2-generating agent is injected to deliver CO2 to the targeted zone. Urea is an attractive gas-generating agent for ICE because it has both low price and exceptional stability in brine with elevated divalent cation concentrations. Besides CO2, urea thermal hydrolysis releases NH3(aq). Both molecules have positive impacts on the tertiary recovery, such as oil swelling, oil viscosity reduction, brine alkalinity increase, and sand surface wettability reversal. Thermal hydrolysis of urea is rapid at 120 °C, but the reaction rate decreases exponentially at lower temperatures. This work compares tertiary recovery from urea hydrolysis at 120 and 80 °C with and without a homogeneous catalyst (NaOH) for the purpose of examining the feasibility of urea-ICE for low-temperature reservoirs. The tertiary recovery was studied and optimized with data from 11 one-dimensional sand pack tests at varying conditions. Since urea hydrolysis produces a reaction intermediate, ammonium carbamate, which is known to precipitate in the presence of divalent cations, brines with elevated calcium concentrations were studied to examine the divalent cation stability of the proposed system. The optimization work included tests with urea concentrations varying from 1 to 35 wt % and different injection strategies and flow rates (0.03–0.3 mL/min). Tertiary oil recovery results of this study show that there are two different optimal concentrations of urea, one that maximizes the volume of tertiary oil produced and another that minimizes the cost per barrel of tertiary oil produced. The urea consumption of the proposed ICE can be as low as 34 kg/barrel with 2.5 wt % chemical slug, and the tertiary recovery can be as high as 48.3% with 10 wt % chemical injection. The optimal injection strategy was strongly dependent on chemical residence time because the tertiary recovery mechanisms vary with the injected concentrations. The aqueous effluent showed increasing solution pH, approaching pH 10. Based on an high-performance liquid chromatography analysis of the aqueous effluent, the mass balance of different tests was calculated. No adverse effect on tertiary recovery was observed in simulated seawater brines, with up to 1 wt % dissolved divalent salts. At higher levels of divalent ions (Ca2+ 7000 ppm) in a so-called API brine, lower tertiary recovery was observed but there was no evidence of formation damage and tubing blockage. In this work, the proposed ICE system showed superior tertiary recovery performance (48.3%) compared to the most recent efforts by our group (29.5%) as well as similar ICE systems (2.4–18.8%) proposed by others. Results illustrate the economic feasibility and the divalent cation tolerance of the urea-ICE process.
While injection of CO2 has great potential for increasing oil production, this potential is limited by site conditions and operational constraints such as lack of proper infrastructure, limited cheap CO2 sources, viscous fingering, gravity override at the targeted zones, and so forth. To mitigate some of these common limitations, we explore alternative methodologies which can successfully deliver CO2 through gas generation in situ, with superior IOR performance, while offering reasonable chemical cost. While dissolved easily in reservoir brine, urea is thermally hydrolyzed to CO2 and NH3 after equilibration under reservoir conditions. Therefore, given its exceptional compatibility with reservoir fluids, its CO2 producing capacity and reasonable cost benefit, urea appears to be a promising candidate for delivering CO2 to increase oil recovery. The in-situ gas generation requires single chemical slug, which can minimize the complexity of the injection system. One-dimensional sand pack tests and core flooding experiments were operated at pre-set conditions: different API gravity oils were used, varying from 27 to 57.3. In addition, the reaction rates of the urea hydrolysis and urea solution PVT property were tested separately under reservoir conditions. Most importantly, results of injecting urea solution (as low as 10 % solution) showed superior tertiary recovery performance (as high as 37.97%) are realized as compared to the most recent efforts at our group (29.5%) as well as similar in situ CO2 generation EOR (2.4% to 18.8%) approaches proposed by others. The economic feasibility and operational advantages of this newly developed method were demonstrated in this work. In brief, results of this work served further as a proof of concept for designing in situ CO2 generation formulations for tertiary oil recovery at both onshore and offshore fields under proper conditions.
Polymer solution for oil displacement is mostly used in the middle and late stage of water flooding reservoir development, and reservoir groundwater conditions are often one of the main conditions restricting polymer application. Therefore, it is necessary to develop salt tolerance of polymer solutions with different aggregation behaviors, so as to facilitate the synthesis and optimization of suitable polymer systems. The differences in the micro‐aggregation behavior of three polymers with different molecular structures were explored. On this basis, the effects of divalent metal cations on the properties of the polymer solutions were analyzed by assessing the micro‐aggregation behavior, apparent viscosity, hydrodynamic size, and shear rheological characteristics. The results showed that the linear partially hydrolyzed polyacrylamide (HPAM) was seriously affected by divalent cations, and the viscosity decreased obviously. The aggregation behavior of the polymer changed by hydrophobic association can enhance the salt tolerance of the solution. The hydrophobically modified partially hydrolyzed polyacrylamide (HMPAM) with “chain beam” aggregation behavior has strong intermolecular connection, which enables it to withstand the content of calcium and magnesium ions of 1100 mg l−1. When the content of calcium and magnesium ions exceeds 600 mg l−1, dendritic hydrophobically associating polymer (DHAP) will destroy the interaction between molecular chains, resulting in the decrease of apparent viscosity and hydrodynamic size. For polymer flooding in high‐salinity reservoir, salt tolerant polymer system can be constructed by optimizing molecular weight and hydrophobic group content.
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