Sharif Digital Repository

Spontaneous imbibition, defined as the displacement of nonwetting phase by wetting phase in porous media by action of capillary forces, is important in many applications within earth sciences and in particular in naturally fractured oil and gas reservoirs. Hence, it is critical to investigate the various aspects of this process to correctly model the fractured reservoir behavior. In this study, twenty four experiments were conducted to study the effect of rock properties, lithology of porous medium, brine viscosity and boundary conditions on displacement rate and final recovery by cocurrent spontaneous imbibition (COCSI) in brine-oil systems. The results can be extended to brine-gas systems,... 

The formation of liquid bridge is pertinent to many fields including seepage into underground fractured rocks as an environmental issue and capillary continuity between matrix blocks which controls oil recovery in fractured reservoirs. Evaporation from the surface of liquid bridge into the surrounding gas could affect the stability of liquid bridge and fracture capillary pressure, which is not well discussed in the available literatures. In this research, by the aid of analogy between the diffusive flux and electrostatic potential, a new model for predicting evaporation rate from a liquid bridge inside a horizontal fracture is presented. The proposed model is then coupled with Young-Laplace... 

Capillary continuity between adjacent matrix blocks through formation of liquid bridge controls the recovery factor of gravity drainage process in fractured reservoirs. However, stability of liquid bridges as well as related capillary pressure in horizontal rough fractures is not well discussed in the available literature. In this work, new models of rough-walled fracture are developed and the role of roughness size and frequency on formation of liquid bridge and fracture capillary pressure are investigated. The Young-Laplace equation is numerically solved to characterize the liquid bridge formed in the proposed models of rough fractures. Critical fracture aperture for a range of liquid... 

The formation of liquid bridges can maintain capillary continuity between matrix blocks during gas/oil gravity drainage in fractured reservoirs. A travelling oil drop draining into a fracture either forms a liquid bridge or breaks into detached drops. However, the different characteristics of a travelling drop during its elongation and required conditions for transformation into a liquid bridge are not well described in the published literature. In this work, a one-dimensional model based on slender-drop theory is employed that holds gravity, viscosity, and surface tension forces but ignores inertia. This model, together with Young-Laplace equation, gives the fracture capillary pressure.... 

Gas-oil gravity drainage that takes place in the gas-invaded zone of fractured reservoirs is the main production mechanism of gas-cap drive fractured reservoirs as well as fractured reservoirs subjected to gas injection. Interaction of neighboring matrix blocks through reinfiltration and capillary continuity effects controls the efficiency of gravity drainage. Existence of capillary continuity between adjacent matrix block is likely to increase the ultimate recovery significantly. Liquid bridge formed in fractures has a significant role in maintaining the capillary continuity between two neighboring matrix blocks. The degree of capillary continuity is proportional to capillary pressure in... 

Capillary imbibition is an important recovery mechanism in naturally fractured reservoirs when water-filled fractures surround water-wet matrix blocks. A large amount of studies of imbibition process is simply total or partial immersion of nonwetting phase saturated rock in aqueous wetting phase. However, water advance in fractures during water flooding or water encroachment from an active aquifer introduces time dependent boundary conditions where invariant exposure of rock surface to water is not representative. In this work, a laboratory simulated matrix-fracture system was used to investigate different aspects of imbibition in the presence of fracture fluid flow (namely dynamic... 

γ-Alumina is used to catalyze the Cannizzaro reaction in the absence of any base under microwave irradiation in high yields. In the case of terephthalaldehyde the reaction is carried out with high selectivity  

Enolizable ketones have been reacted in a one-pot method with aromatic aldehydes, acetyl chloride and acetonitrile at room temperature in the presence of SnCl4/SiO2 to furnish the corresponding β-acetamidoketones in improved yields. Acetylation of an aromatic hydroxyl group was observed while using 4-hydroxybenzaldehyde or vanillin and the corresponding β-acetamidoketones were isolated in an excellent yield  

The boundary layer integral method is used to investigate the development of the turbulent swirling flow at the entrance region of a conical nozzle. The governing equations in the spherical coordinate system are simplified with the boundary layer assumptions and integrated through the boundary layer. The resulting sets of differential equations are then solved by the fourth-order Adams predictor-corrector method. The free vortex and uniform velocity profiles are applied for the tangential and axial velocities at the inlet region, respectively. Due to the lack of experimental data for swirling flows in converging nozzles, the developed model is validated against the numerical simulations. The... 

The governing equations of two-dimensional steady density currents are solved numerically using a finite volume method. The v2̄-f turbulence model, based on standard k - s model, is used for the turbulence closure. In this method, all Reynolds stress equations are replaced with both a transport equation for v2̄ and an elliptic relaxation equation for f, a parameter closely related to the pressure strain redistribution term. The Simple-C procedure is used for pressure-velocity coupling. In addition, Boussinesq's approximation is used to obtain the momentum equation. The computed height of the progressive density current is compared to the measured data in the literature, resulting in good... 

The deposition behavior of fine sediment is an important phenomenon, and yet unclear to engineers concerned about reservoir sedimentation. An elliptic relaxation turbulence model (v2̄ - f model) has been used to simulate the motion of turbid density currents laden whit fine solid particles. During the last few years, the v2̄ - f turbulence model has become increasingly popular due to its ability to account for near-wall damping without use of damping functions. In addition, it has been proved that the v2̄ - f model to be superior to other RANS methods in many fluid flows where complex flow features are present. Due to low Reynolds number turbulence of turbidity current,(its critical Reynolds... 

In this paper, an analytical solution for steady creeping motion of viscoelastic drop falling through a viscous Newtonian fluid is presented. The Oldroyd-B model is used as the constitutive equation. The analytical solutions for both interior and exterior flows are obtained using the perturbation method. Deborah number and capillary numbers are considered as the perturbation parameters. The effect of viscoelastic properties on drop shape and motion are studied in detail. The previous empirical studies indicated that unlike the Newtonian creeping drop in which the drop shape is exactly spherical, a dimpled shape appears in viscoelastic drops. It is shown that the results of the present... 

In this paper, creeping motion of a viscoelastic drop falling through a Newtonian fluid is investigated experimentally and analytically. A polymeric solution of 0.08 % xanthan gum in 80:20 glycerol/water and silicon oil is implemented as the viscoelastic drop and the bulk viscous fluids, respectively. The shape and motion of falling drops are visualized using a high speed camera. The perturbation technique is employed for both interior and exterior flows, and Deborah and capillary numbers are considered as perturbation parameters up to second order. The product of Deborah and capillary numbers is also used as a perturbation parameter to apply the boundary condition on the deformation on the... 

In this paper, we consider the problem of minimizing the uplink delays of users in a 5G cellular network. Such cellular network is based on a Cloud Radio Access Network (CRAN) architecture with limited fronthaul capacity, where our goal is to minimize delays of all users through an optimal resource allocation. Earlier works minimize average delay of each user assuming same transmit power for all users. Combining Pareto optimization and Markov Decision Process (MDP), we show that every desired balance in the trade-off among infinite-horizon average-reward delays, is achievable by minimizing a properly weighted sum delays. In addition, we solve the problem in two realistic scenarios;... 

Microwave induced Cannizzaro reaction, which was performed in presence of neutral γ-alumina as a polymeric catalyst, was discussed. Cannizzaro reaction was carried out on alumina surface and other unknown products were also obtained. Solvent extraction method was utilized to isolate mild and selective benzyl alcohol and carboxylic acids  

A well known method to reduce the intrinsic complexity of Multiple Input Multiple Output (MIMO) systems is to choose a subset of available antennas which have stronger links than the others, in order to perform the specified MIMO algorithm. The data resulted from the antenna selection process (at the receiver side) is sent back to the transmitter side via a feedback channel. There seems to be a need to reduce the number of feedack bits, specially when the number of antennas is not small. In this paper, we investigate the problem of reducing the number of feedback bits in antenna selection techniques. We've proposed two methods using vector quantization techniques to perform feedback bit... 

Nowadays, deployment of peer-to-peer video streaming systems over wireless mesh networks has attained raising popularity among large number of users around the world. In this paper, we present an efficient peer-to-peer live video streaming architecture over multi-hop wireless mesh networks. In our proposed architecture, we take the physical topology of network into account and based on a distributed distributed locality-aware neighbor selection algorithm in the overlay construction phase, we generate an efficient mesh-based overlay on top of wireless mesh networks. In locality-aware neighbor selection algorithm, instead of choosing randomly, peers find their best neighbors based on their...