Browsing by Author "Zhou, Yi"

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    Evaluation of Alpha-Phased Zirconium Phosphate Nanoparticles as a Clay Stabilizer and an EOR Agent
    (2014-12-15) Zhou, Yi; Nasr-El-Din, Hisham A; El-Halwagi, Mahmoud; Schechter, David
    Fines migration, which is the detachment and movement of fines from sand surfaces, leads to the plugging of throats in porous media and becomes an important reason for formation damage. Enhanced Oil Recovery (EOR) is the technique to extract more oil after secondary recovery. Nanoparticles are used as clay stabilizers and EOR agent because of their very small size, large surface area, and surface electrical charge. In this paper, an α-ZrP nanoparticle-based treatment is developed to prevent fines migration in sandstone formations and recovery more oil in carbonate. To test the ability of α-ZrP nanofluids as a clay stabilizer, coreflood tests were conducted using alpha phased zirconium phosphate based nanofluids as a clay stabilizer with Berea sandstone cores (6 in. in length, 1.5 in. in diameter) under a pressure of 1000 psi and temperature of 300°F. In these experiments, α-ZrP nanofluids were injected at concentrations of 0.1, 0.5, and 1.0 wt% at a flow rate of 2 cm^3/min. Both DI water and brine were used as diluting agents. After each treatment, a post-flush of fresh water was applied. The pressure drop across the core was measured, the core effluent samples were collected, and the permeability changes were calculated. Also, the surface tensions and viscosities of the treatment fluids were measured. Lab results indicated that α-ZrP nanofluid mitigated fines migration in Berea sandstone up to 300°F. Because fresh water tends to cause formation damages, nanoparticles diluted with brine showed less permeability change than those diluted with DI water. The best treatment we had was the α-ZrP nanofluid diluted with brine (5 wt% KCl) at a concentration of 0.5 wt%. To use α-ZrP nanofluids as an EOR agent, Indiana limestone core was pre-flushed with brine, and then saturated with oil (dodecane). In addition, brine was injected again with different flow rates of 0.5, 1.0 and 2.0 cm^3/min for about 5 PV each. After that, 1 PV of EOR agent was injected at 0.5 cm3/min from bottom to top. A post-flush of brine was applied and the effluents were collected to find out the total oil recovered. The test result gave a 13.68% oil recovery in the EOR stage. The alpha-phased zirconium phosphate nanofluids had never been applied before for subsurface use. It was discussed as an clay stabilizer and EOR agent in this study. This work provides new insights into the application of nanoparticles in the oil and gas industry.
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    Sensitivity of OFDM Systems to Synchronization Errors and Spatial Diversity
    (2012-02-14) Zhou, Yi; Serpedin, Erchin; Qaraqe, Khalid; Georghiades, Costas N.; Karsilayan, Aydin; Amato, Nancy M.
    In this dissertation, the problem of synchronization for OFDM-based wireless communication systems is studied. In the first part of this dissertation, the sensitivity of both single input single output (SISO) OFDM and multiple input multiple output (MIMO) OFDM receivers to carrier and timing synchronization errors are analyzed. Analytical expressions and numerical results for the power of inter-carrier interference (ICI) are presented. It is shown that the OFDM-based receivers are quite sensitive to residual synchronization errors. In wide-sense stationary uncorrelated scattering (WSSUS) frequency-selective fading channels, the sampling clock timing offset results in rotation of the subcarrier constellation, while carrier frequency offsets and phase jitter cause inter-carrier interference. The overall system performance in terms of symbol error rate is limited by the inter-carrier interference. For a reliable information reception, compensatory measures must be taken. The second part of this dissertation deals with the impact of spatial diversity (usage of multiple transmit/receive antennas) on synchronization. It is found that with multiple transmit and receive antennas, MIMO-OFDM systems can take advantage of the spatial diversity to combat carrier and timing synchronization imperfections. Diversity can favorably improve the synchronization performance. Data-aided and non-data-aided maximum likelihood symbol timing estimators for MIMO-OFDM systems are introduced. Computer simulations show that, by exploiting the spatial diversity, synchronization performance of MIMO-OFDM systems in terms of mean squared error (MSE) of residual timing offset becomes significantly more reliable when compared to conventional SISO OFDM systems. Therefore, spatial diversity is a useful technique to be exploited in the deployment of MIMO-OFDM communication systems. In MIMO systems with synchronization sequences, timing synchronization is treated as a multiple hypotheses testing problem. Generalized likelihood ratio test (GLRT) statistics are developed for MIMO systems in frequency flat channels and MIMO-OFDM systems in frequency selective fading environments. The asymptotic performance of the GLRT without nuisance parameters is carried out. It is shown that the asymptotic performance of the GLRT can serve as an upper bound for the detection probability in the presence of a limited number of observations as well as a benchmark for comparing the performances of different timing synchronizers.