Sharif Digital Repository

Spontaneous imbibition, the capillary-driven process of displacing the nonwetting phase by the wetting phase in porous media, is of great importance in oil/gas recovery from matrix blocks of fractured reservoirs. The question of how properly scaling up the recovery by counter-current spontaneous imbibition has been the subject of extensive research over decades, and numerous scaling equations have been proposed. As a convention, the scaling equations are usually defined analytically by relating the early time squared recovery to squared pore volume. We show this convention does not apply to common scaling practices and, if used, causes nontrivial scatter in the scaling plots. We explain that... 

Spontaneous imbibition, the capillary-driven process of displacing the nonwetting phase by the wetting phase in porous media, is of great importance in oil/gas recovery from matrix blocks of fractured reservoirs. The question of how properly scaling up the recovery by counter-current spontaneous imbibition has been the subject of extensive research over decades, and numerous scaling equations have been proposed. As a convention, the scaling equations are usually defined analytically by relating the early time squared recovery to squared pore volume. We show this convention does not apply to common scaling practices and, if used, causes nontrivial scatter in the scaling plots. We explain that... 

There are several types of drilling methods to increase the productivity of a well, such as horizontal drilling, extended reach horizontal drilling and Multilateral (ML) drilling. It is thought that ML wells could be more economic with higher productivities than horizontal or extended reach horizontal wells. Advances in ML drilling promise reduced costs, greater flexibility and increased profit potential. In the last 20 years, thousands of ML wells have been drilled worldwide, but only a small percentage of the total number of wells is multilateral. The probable reason may be lack of concise information and misconceptions surrounding the costs and perceived risks. However, recent advances in... 

An index for characterizing wettability of reservoir rocks is presented using slope analysis of spontaneous imbibition recovery data. The slope analysis is performed using the known exact analytical solution to infinite acting period of counter-current spontaneous imbibition. The proposed theoretically based wettability index offers some advantages over existing methods: (1) it is a better measure of the spontaneous imbibition potential of rock (because the magnitude is directly proportional to the imbibition rate); (2) there is no need for forced displacement data; (3) there is no need for waiting until the spontaneous imbibition process ceases completely; and (4) the data needed to run the... 

Spontaneous imbibition of water into the matrix blocks because of capillary forces is an important recovery mechanism for oil recovery from naturally fractured reservoirs. In modeling this process, it has been assumed classically that local equilibrium is reached and, therefore, capillary pressure and relative permeability functions are only a function of water saturation, resulting in the appearance of the self-similarity condition. In some works published in the last 2 decades, it has, however, been claimed that local equilibrium is not reached in porous media, and therefore, opposite the classical local-equilibrium/self-similar approach, non-equilibrium effects should be taken into... 

An index for characterizing wettability of reservoir rocks is presented using slope analysis of spontaneous imbibition recovery data. The slope analysis is performed using the known exact analytical solution to infinite acting period of counter-current spontaneous imbibition. The proposed theoretically based wettability index offers some advantages over existing methods: (1) it is a better measure of the spontaneous imbibition potential of rock (because the magnitude is directly proportional to the imbibition rate); (2) there is no need for forced displacement data; (3) there is no need for waiting until the spontaneous imbibition process ceases completely; and (4) the data needed to run the... 

Including gravity and wettability effects, a full analytical solution for the frontal flow period for 1D counter-current spontaneous imbibition of a wetting phase into a porous medium saturated initially with non-wetting phase at initial wetting phase saturation is presented. The analytical solution applicable for liquid-liquid and liquid-gas systems is essentially valid for the cases when the gravity forces are relatively large and before the wetting phase front hits the no-flow boundary in the capillary-dominated regime. The new analytical solution free of any arbitrary parameters can also be utilized for predicting non-wetting phase recovery by spontaneous imbibition. In addition, a new... 

Spontaneous imbibition of water into the matrix blocks because of capillary forces is an important recovery mechanism for oil recovery from naturally fractured reservoirs. In modeling this process, it has been assumed classically that local equilibrium is reached and, therefore, capillary pressure and relative permeability functions are only a function of water saturation, resulting in the appearance of the self-similarity condition. In some works published in the last 2 decades, it has, however, been claimed that local equilibrium is not reached in porous media, and therefore, opposite the classical local-equilibrium/self-similar approach, non-equilibrium effects should be taken into... 

Wettability is a key parameter affecting petrophysical properties of reservoir rocks. Mirzaei-Paiaman et al. (Energy Fuels 27:7360–7368, 2013) presented an index (referred to as MPMS) for laboratory characterization of wettability of native- or restored-state reservoir rock samples. To use this index two counter-current spontaneous imbibition (COUCSI) experiments are needed, one on the native- or restored-state core sample and another on the strongly water-wet (SWW) reference system. Slope analysis of recovery data in these two systems gives inputs for determination of MPMS index. The two systems must have the same pore structure, initial water saturation, and viscosity ratio. The case of... 

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... 

Aqueous phase trapping in many oil and gas reservoirs is a noteworthy mechanism of formation damage during drilling, completion, work over, and stimulation operation. Aqueous phase trapping can limit the productivity of a well to a high extent, especially in low permeable gas reservoirs. In this article, using aqueous phase trapping laboratory tests on low permeable sandstone cores' effect of key factors on gas reservoir's potential for aqueous phase trapping was investigated. Studied factors were initial water saturation, permeability, water filtrate viscosity, and drawdown pressure. Results showed that severity of formation damage caused by aqueous phase trapping increases as each of the... 

Injection locked frequency dividers (ILFD) are used for frequency division to reduce the overall power consumption. By injecting a high frequency signal to an LC oscillator, injecting signal gets synchronous with oscillator output. All ILFDs analysis reports are based on steady state solution when locking is reached. At the same time, it is important to consider transient analysis too. In this paper a simple model is developed to study phase transient analysis when injecting signal is small in amplitude. This model can be used for large signal injection as a good approximation  

A very low power CMOS, 1.5V, 2.5GHz prescaler was designed. Implemented in 0.25u standard CMOS technology, this prescaler can operate up to 3GHz range. The prescaler consists of three delay flip flops (DFF) that work synchronously with RF sinusoidal clock and divides by 4 or 5 according to control signal  

A 5GHz, 1.5 Volt and low power CMOS frequency synthesizer with LC-tuned VCO (voltage controlled oscillator) is presented. The synthesizer consists of an LC-tuned VCO, an injection-lock frequency divider, a very low power prescaler which brings 2.5GHz range frequency to 11 MHz, a phase-frequency detector and charge-pump with improved architecture. Spiral inductors with Q-factor of 9 are used for the LC-tuned 5 GHz VCO. A fixed 2 frequency divider based on injection-locking phenomenon is used to bring 5 GHz VCO frequency to 2.5GHz. Both VCO and injection-locked divider's oscillators are tuned with NMOS varactors with their bodies are grounded, resulting in about 700 MHz tuning range.... 

We use concepts to make distinctions. Blurring these distinctions results in conflations. So, they are commonly seen as vicious. The claim here is that, by contrast, conflations are virtuous because they can do cognitive work. They enrich our conceptual resources. It is not conflation per se that is destructive but the lack of evaluation. Committing a conflation requires two cognitive acts at once. First, keeping things together and, second, appreciating the gap between them. Conflation thus has a family resemblance with notions like analogy and metaphor. Despite their apparent difference, a shared trait is recognizable in this family: the simultaneous maintenance of similarity and... 

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,... 

This Regular evaluation and analysis of river quality helps accurate management to reach acceptable quality. In this study, water quality indices (WQI) method applied to evaluate quality of Jajrood River which is one of the main sources of Tehran drinking water. It helps to subsidize management actions in Jajrood watershed. Sampling carried out for 9 years during 2001-2010 in 10 stations along the river in wet and dry stations to identify water quality and the main source of pollution. Results show water quality in all stations classifies as medium according to National Sanitation Foundation (NSF) and water quality index in wet season is better than the corresponding value in dry seasons....