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The purpose was to prepare a (3-glycidoxypropyl)-trimethoxysilane (GPTMS)-SiO 2 nanofluid and analyze the effect of nanofluid injection on carbonate reservoirs. GPTMS-modified silica nanoparticles (SNPs) were investigated by Fourier transform infrared spectroscopy (FTIR) and elemental analysis. FTIR spectra of C-H stretching vibrations at 2950 cm−1, indicating silica surface modification with GPTMS, were observed when the GPTMS in the feed was greater than 0.7 mmol/g. Further, a stable nanofluid was obtained when the amount of grafted silane was close to 0.73 mmol/g, the theoretical maximum amount of grafted silanes. To evaluate the performance of surface-modified SNPs for enhanced oil recovery in carbonate reservoirs, wettability alteration tests comprising flotation test and contact angle measurements using powder and plug samples of carbonates, respectively, were performed with different SNP concentrations. Powder samples were successfully changed from oil-wet to water-wet, and the contact angle of the plug sample decreased by up to 62.8% as a result of the reaction of the nanofluid; however, it did not reduce interfacial tension (IFT) as effectively as IFT reducer additives. A coreflooding test was conducted to determine the effective parameters of the enhanced oil recovery with the GPTMS-nanofluid, such as SNP concentration, injection rate, and rock properties. The nanofluid injection increased oil recovery by approximately 20% compared to conventional waterflooding through incremental oil recovery, mainly attributed to wettability alteration. Therefore, we expect the nanofluid to dramatically increase the oil recovery in strongly oil-wet carbonate reservoirs under high-salinity conditions. [Display omitted] [ABSTRACT FROM AUTHOR]

GPTMS ((3-Glycidoxypropyl) trimethoxysilane)-SiO 2 nanofluids have the ability to alter the wettability of a rock surface and high colloidal stability, therefore, they can be used as injection fluids to enhance oil recovery in high-salinity and high-temperature reservoirs. The purpose of this study is to prepare GPTMS-SiO 2 nanofluids that are stable under extreme reservoir conditions and investigate their rheological characteristics. Nanofluids with nanoparticle concentrations of 0.1 to 3 wt% were prepared and dispersed in 10 wt% API (American Petroleum Institute) brine, which served as the base fluid. The apparent viscosity of the base fluid and GPTMS-SiO 2 nanofluids was measured in the shear rate range 3.7 to 93.1 s−1 between the temperatures of 5 and 85 °C. It was observed to be a function of temperature, but remained constant with the increase in shear rate. On the other hand, the nanofluids exhibited pseudoplastic behavior (shear thinning). The apparent viscosity of the nanofluids tended to increase with decreasing temperature and increasing particle concentration. The consistency index and power law index of the power law fluid model are used for the analysis of the flow behavior of the nanofluids. The consistency indices of GPTMS-SiO 2 nanofluids were observed to be well matched with the exponential function, and the power law indices showed high correlations with the specific particle concentration and temperature conditions. The results revealed that the rheological characteristics of GPTMS-SiO 2 nanofluids are functions of particle concentration and temperature at specific conditions. [ABSTRACT FROM AUTHOR]

This study presents nano-smart water synthesized with grafted SiO 2 nanoparticles dispersed potential determining ion (PDI) controlled seawater to enhance oil recovery in carbonate reservoirs with high temperatures and high salinity. Phase behavior observation, dynamic light scattering (DLS), and transmission electron microscopy (TEM) were performed to evaluate the dispersion stability of the synthesized nano-smart water with different particle concentrations at 25 ℃ and 80 ℃. In addition, a fluid miscibility test (FMT) was conducted using seawater with controlled salinity and PDI type and concentration. The results of dispersion stability showed that stable fluids without aggregation and precipitation, with an average particle size of less than 100 nm, could be synthesized at room and high temperature in seawater at the nanoparticle concentration 0.5 wt% or more. The dispersion stability of the synthesized nano-smart water was successfully achieved without aggregation and precipitation, with an average particle size of less than 100 nm, at room and high temperatures when the nanoparticle concentration is higher than 0.5 wt%. After performing the FMT with a high-salinity level of up to 200,000 ppm, and implementing PDI control using K+, Mg2+, Cl-, and SO 4 2-, the nanoparticles in nano-smart water still had an average particle size ranging from 32.2 to 54.1 nm. This indicates that the colloidal dispersion was stable despite the high-salinity levels and PDI control. Therefore, the SW-based nano-smart water is expected to be used as a stable injection fluid in high-temperatures and high-salinity carbonate reservoirs. [Display omitted] [ABSTRACT FROM AUTHOR]

The main challenge of nanotechnologies for enhanced oil recovery (EOR) in carbonate reservoirs is to maintain the colloidal stability of nanoparticle dispersion (nanofluid) under the reservoir conditions with high salinity and high temperature. This study presents a nanofluid as an injection fluid for EOR under the extreme condition. The nanofluid was composed of surface-modified silica nanoparticles by a silane coupling agent (GPTMS, (3-Glycidoxypropyl)trimethoxysilane). The particle size distribution and particle aggregation were measured and observed to evaluate colloidal stability of the nanofluid by the light scattering and electron microscopy methods. As a result, the colloidal stability of the nanofluid was achieved at the salinity up to 20 wt% of base fluid at 90 °C, when the amount of GPTMS was 1 mmol/g. The wettability alteration test of carbonate rocks was carried out to validate the applicability of the nanofluid in the reservoir conditions. The results showed that the rock wettability of dolomite and limestone was effectively altered to neutral-wet and water-wet from strongly oil-wet, respectively, by the nanofluid with a small portion of particle concentration. Therefore, it is believed that the nanofluid can be an effective EOR agent in carbonate reservoirs. [ABSTRACT FROM AUTHOR]

This study presents the application of artificial neural network (ANN) to predict storage efficiency of CO 2 sequestration in deep saline aquifers. To a create training database used as input and output neurons in ANN, sensitivity analysis of parameters considering the aquifer characteristics was performed by numerical simulation. Based on the analysis, the factors and their ranges influencing CO 2 sequestration in deep saline aquifers were determined and 150 representative realizations used as a training database were generated with trapping indices of the residual CO 2 and solubility trapping mechanisms. The ANN model was designed with optimum architecture minimizing the mean squared error (MSE) for testing data set and it was tested with validation samples. The results showed that the proposed ANN model had a high prediction performance with a high coefficient of determination (R 2 ) of over 0.99 on comparing with the target values, a low MAPE (mean absolute percentage error) of 1.26%, and RMSE (root mean square error) of 0.41 for TEI (total trapping efficiency index). As a field application, the model has also been evaluated with the field scale data on the Gorae V structure in Block VI-1, Korea. The results of prediction were well matched with the targeted values and accuracy between the ANN predictions and field scale data was achieved with a high coefficient of determination (R 2 ) of more than 0.96, a low MAPE of 4.40%, and RMSE of 3.58 for TEI. From these results, it is believed that the newly developed ANN model can predict storage efficiency with high accuracy and it can also be considered as a useful and robust tool to evaluate the feasibility of CO 2 sequestration in deep saline aquifers. [ABSTRACT FROM AUTHOR]

This study presents a diagnostic plot model to evaluate the injection performance of polymer flooding in a heterogeneous reservoir. To develop the model, comprehensive equation using an analytical method was proposed considering fully-developed cross-flow and saturation distribution due to polymer effects. The developed model was compared with the results from reservoir simulation to verify its accuracy. The comparison indicated that the model yields more accurate results than the other previous methods. Additionally, case studies have been performed to check whether any unexpected geological problem in the reservoir could be detected. From the results, the model can indicate the variation of the injectivity through geological problems such as semi-sealing and permeability improvement. Therefore, the model can provide specific information to improve injectivity and enhance the operational efficiency of polymer flooding. [ABSTRACT FROM AUTHOR]

This study presents an experimental apparatus to investigate the adsorption characteristics in shale samples of two major US basins. The adsorption measurement is based on volumetric method, and the results are analyzed by Langmuir isotherm at various pressures. To analyze the impact of temperature on the adsorption characteristics, the experiments were conducted on the samples. The experimental results revealed that the change of adsorption capacity became constant with the increase of pressure and the decrease of adsorption capacity was dependent on the increase of temperature. This study allows us to evaluate shale gas in place and production forecast through adsorption characteristics. [ABSTRACT FROM AUTHOR]

This study proposes a new apparatus which can simultaneously measure the physical properties such as low-permeability and porosity in a tight gas reservoir. The apparatus can also measure bi-directional permeability efficiently. The measurement of bi-directional permeability is designed in consideration of flow direction which can cause different results by heterogeneity. Using the apparatus, the experiments have been carried out to measure the low-permeability and porosity of three tight sand core samples which are from Gyeongsang sedimentary basin in Korea. As the results, the porosity ranges from 5.63% to 11% and the permeability measured in forward and reverse direction is 0.0004 md and 0.0005 md for TS-1, 0.0007 md and 0.0011 md for TS-2, and 0.0062 md and 0.007 md for TS-3, respectively. To investigate the effect of geological characteristics inside core sample on rock properties, X-ray scan of the core samples was taken by Microfocus X-ray CT. Obviously, the value of permeability and porosity are subject to geological features such as micro-crack. This means that the micro-crack plays an important factor in terms of permeability variation by its direction and length in a tight gas reservoir. For verification of measurement accuracy, regression analysis was carried out using the dimensionless pseudo-pressure between the measured data and analytical model. As the results, it is shown that both are approximately equal in terms of permeability and porosity. [ABSTRACT FROM AUTHOR]

The aim of this study is to investigate the diffusion characteristics of nanoscale gas flow in a shale gas reservoir. An experimental apparatus was designed and set up to measure porosity and permeability at the nanopore scale. The measured properties have been used to determine a diffusion coefficient by classification standard of gas flow regime. To investigate the impact of pressure and pore size, the analysis of diffusion flow was conducted using Knudsen and Fick diffusion coefficients. From the results, it was revealed that Knudsen diffusion coefficient gradually increased with the growth of pressure and pore radius and Fick diffusion coefficient was dependent on the gas molecular diameter and temperature. It was also found that Knudsen diffusion coefficient was equal to Fick diffusion coefficient if pore radius is too small. The study implied that the characteristics of gas diffusion should be implemented by using the diffusion coefficient theory based on gas flow regime in shale gas reservoirs. [ABSTRACT FROM AUTHOR]

In synchronous systems, clock tree causes high peak current at clock edges, increasing power/ground noise significantly, if the clock tree is not carefully designed. This paper addresses the problem of minimizing power/ground noise in the clock tree synthesis. Contrary to the previous approaches which only make use of assigning polarities to clock buffers to reduce power/ground noise, our approach solves a new problem of simultaneous consideration of assigning polarities to clock buffers and determining buffer sizes to fully exploit the effects of buffer sizing together with polarity assignment on the minimization of power/ground noise while satisfying the clock skew constraint. Specifically, the contributions of this paper are: 1) precisely estimating peak currents by clock buffers and reflecting them on the power/ground noise minimization; 2) proposing a pseudo-polynomial time optimal algorithm based on dynamic programming for solving the integrated problem, together with the proof of intractability of the problem; 3) devising a systematic design flow framework for reducing the power/ground noise over the entire chip; and 4) considering the effect of thermal variation on the clock skew bound and the noise minimization. [ABSTRACT FROM AUTHOR]

This study aims to investigate the propagation characteristics of an optimum wormhole to make an efficient acid treatment in carbonate matrix acidizing based on wormhole visualization using micro X-ray computerized tomography (CT) with high resolution. Five cases comprising 25 core-flood experiments under different experimental conditions using Indiana limestone cores were carried out at various injection rates to obtain the optimum injection rates. From the results, the optimum injection rates tended to increase with permeability but was not related to acid concentrations. The pore volume to breakthrough (PVBT), the amount of acid consumption required to breakthrough, was lower at higher permeability and acid concentration. This means that less amount of acid is consumed to generate the wormholes. Wormhole visualization with X-ray CT imaging showed that the wormhole diameters were gradually reduced along with the wormhole propagation axis in all cases. In addition, the mean of wormhole diameter tended to increase according to the higher permeability and acid concentration. The tortuosity, which is the ratio of actual wormhole length to core length, was exceeded at least 1.35 in each case. This implies that the actual flow length of the optimum wormhole is much longer than the core length. However, previous studies of wormhole propagation regarding the configuration of optimum wormhole are sparse, more intensive research would be required. Therefore, these propagation characteristics of optimum wormholes should be considered to improve the wormhole prediction model, and the wormhole prediction results would be more accurate and realistic than those of the existing models. Further study is needed to develop a new wormhole prediction model considering the propagation characteristics, such as diameter reduction and actual flow length. • Core-flood experiments were performed under various permeabilities and acid concentrations. • Wormhole visualization was conducted by micro X-ray CT to analyze propagation characteristics. • Wormhole diameter can be reduced along with the wormhole propagation axis. • The actual wormhole lengths are at least 1.35 times longer than the core length. [ABSTRACT FROM AUTHOR]