جستجوی مقالات مرتبط با کلیدواژه « molecular diffusion » در نشریات گروه « مهندسی شیمی، نفت و پلیمر »

DME-enhanced water flooding is considered as a novel enhanced oil recovery method. In this method, DME-rich water is injected into an oil reservoir. In addition, upon the contact of DME-rich water with trapped oil in the reservoir, DME partitions between the oleic and the aqueous phase. Due to the partitioning process DME transfers from the aqueous phase into the oleic phase until reaching a thermodynamic equilibrium. Consequently, two zones are generated in the oleic phase: 1- an interface region, which is DME-rich, and 2- the DME-free zone, which is far from the interface. The variation of DME concentration in the oleic phase causes a DME transfer from the DME-rich zone into the DME-free zone due to the molecular diffusion. The DME dissolution in the oleic phase causes an oil swelling process and thus an increase in the saturation of the oleic phase along with oil viscosity reduction. Moreover, both effects improve the oleic phase mobility leading to a more favorable oil displacement efficiency in porous media. The present work demonstrates the feasibility of application of DME-enhanced water flooding in recovery of heavy oils via a 1D modelling study. Therefore, several pieces of work were performed to achieve proper results. First, mass conservation of components was combined with the Darcy equation while using a constant partition coefficient (linear PVT model) to obtain governing fluid flow equations. Then, the system of equations was completed using auxiliary equations and equations were combined to reduce the number of independent variables. Afterwards, equations were numerically solved using a finite difference scheme to find the independent variables, i.e. pressure and saturation of the aqueous phase, and also concentration of DME in the aqueous phase. Numerical modeling results showed that the use of DME-enhanced water flooding improves oil recovery in heavy oil reservoirs. For instance, the DME-enhanced water flooding led to an additional oil recovery of 17 percent of the OIIP on top of water flooding oil recovery. Moreover, results showed the injection of DME-water into the porous media causes the formation of an oil bank and also a reduction in the water cut. Furthermore, it was shown that a part of DME can be recovered at the injection well, and this can affect the project economy positively. Finally, the results showed the potential application of DME in the recovery of heavy oil.

Molecular diffusion is the controlling mechanism for oil recovery from fractured reservoirs with low permeable and low height matrixes during gas injection process. However, the application of conventional models for simulation of molecular diffusion process faces with some limitations. The main purpose of this study is to investigate the performance of different diffusion molecular models for oil recovery from fractured reservoirs during gas injection process and compare the results with a commercial simulator. Therefore, the models are introduced and implemented as a simulator, then the prepared simulator is validated by experimental data. Lastly, the developed simulator is applied for evaluation of CO2 and methane injection in one matrix block. The difference among the results of different models is based on using irreversible thermodynamic for calculating component concentration in gas-oil interface, using matrix form of molecular diffusion coefficients and using chemical potential gradient as the driving force in generalized Fick and Maxwell-Stefan verse classical Fick. In addition, the results of commercial simulator are near classical Fick model results because of same formulation. Also, mole fraction of methane and CO2 and oil viscosity verse time are compared for gas injection. Finally, the result of this work demonstrates that using classical Fick’s law or the commercial simulator for forecasting oil recovery from fractured reservoirs when the molecular diffusion is the main mechanism is not accurate, so generalized Fick and Maxwell-Stefan are more efficient models.

Electrofusion is among several techniques to join polymer pipes using special fittings. In electrofusion, polymer pipes and fittings are joined together through wires that are installed in their structures. The main difference between the two techniques of common heat fusion and electrofusion is in heat transfer mechanism. In heat fusion, a heating device is used to melt interfaces of the pipes and polymer fitting. In electrofusion, there is internal melting through a conductive substance inside the weld interface or melting by a conductive polymer. The heat is produced through electric current contacting conductive materials installed inside the fittings. In order to have desirable materials and useful products, design and installation is based on proper joints having passed good welding testing conditions. Methods of welding and joining are different and depend on parameters such as the type of polymer pipe, polymer structural changes, requirements imposed on interior or external pressure of the pipe, decreasing leakage, prohibition of strokes and longitudinal impact loads, performance and operational conditions, construction and installation operations and types of products that have to be joined together. In this paper a survey of electrofusion process on dimensional strength, parameters accounted for in joint's integrity and stability, mechanisms related to macromolecular magnitude of joint formation, diffusion of molecules in polymer structures, and formation or rupture of chemical bonds through different experimental and computational methods are reviewed based on researcher's findings.

Due to the growing consumption of natural gas in the world, underground natural gas storage (UGS), as a way to cope with the imbalance of gas supply and demand especially during cold seasons, seems to be really indispensable. The largest part of investment in a UGS plan development is allocated to providing cushion gas; this gas is required to maintain reservoir pressure during withdrawal cycles and insure adequate deliverability rate. Since economic evaluation of gas storage projects is of great significance, recently implementing UGS in low quality gas reservoirs such as nitrogen reservoirs has become highlighted. In such a case, reservoir low quality gas will be used as cushion and not only it leads to a higher production rate but also it considerably reduces the cost of preparing and injecting cushion gas into the reservoir. However, there may be a problem related to mixing between reservoir low quality gas and natural injecting gas; this phenomenon shall be effectively controlled by choosing the suitable production strategy. This study investigates underground natural gas storage in an abandoned gas reservoir which mainly consists of nitrogen (%85 Nitrogen). The effect of initial injection period and therefore total injection volume around the well, as well as the factors affecting the extent of mixing between reservoir’s low quality gas and injected natural gas in molecular scale such as diffusion and dispersion will be investigated.

One of the common methods of enhanced oil recovery in naturally fractured reservoirs is gas injection. The majority of Iranian hydrocarbon reservoirs are fractured reservoirs. Producing mechanisms is different in fractured reservoirs in comparison with conventional reservoirs. Molecular diffusion is one of the mechanisms that along with gravity drainage can increase oil recovery in fractured reservoirs during gas injection. In this work, the effect of molecular diffusion in CO2 and hydrocarbon gas injection as an EOR (enhanced oil recovery) process is investigated using compositional simulation in a single matrix block and a sector model of an Iranian natural fractured reservoir. The effect of the matrix permeability, matrix and fracture permeability difference, matrix porosity, matrix gas-oil capillary pressure and injection gas composition are checked in single matrix blocks, and then the influence of diffusion is investigated on the recovery of the sector model during the CO2 and hydrocarbon gas injection. The results show that molecular diffusion raises oil recovery by increasing the mass transfer rate between the matrix and fracture during miscible gas injection (CO2 and hydrocarbon gas). The low matrix permeability and high gas-oil capillary pressure within the matrix oil make smaller displacement efficiency during gravity drainage. In the sector model, the molecular diffusion increases the ultimate oil recovery by about %2 and %5 in CO2 and hydrocarbon gas injection, respectively by delaying gas breakthrough in an production well and maintaining reservoir pressure.

Iranian oil reservoirs are mainly fractured. Performance of such reservoirs could be significantly different form the conventional reservoirs. That is mainly due to some additional flow displacement mechanisms, which take place in fractured reservoir. One of these mechanisms is molecular diffusion, which could play a key role on oil production. The impact of molecular diffusion on flow displacement during gas injection for either displacement or storage purposes would be more pronounced in a fractured reservoir compared to that in a conventional reservoir. It is mainly because of different oil trapping types and huge difference between contact area of the in situ oil and the injected gas phase in these two kinds of reservoir. In this study, the process of natural gas storage in an Iranian heavy oil fractured reservoir isinvestigated. In this paper, specifically the impact of molecular diffusion on the primary oilproduction and different stages of gas storage process are studied using a commercial simulator. The results of this study show that molecular diffusion could play an important role on injection/ production rates as well as the average reservoir pressure during injection process. This impact would be more pronounced when a gas with different composition compared to that in the reservoir is used for storage purposes.

Diffusion and dispersion are considered as the two fundamental mechanisms for the miscible gas injection process in the oil reservoirs, which unfortunately are mostly disregarded in the reservoir simulators. In fact, these two phenomena tend to control the miscibility of the injected fluid with oil in the porous media. Neglecting theses (existing) phenomena in reservoir simulators may bring about erroneous results, which may subsequently role an unreliable basis to be applied into the gas injection projects. The aim of this work is to exhibit the error that should be emerged in case of neglecting these phenomena, in a quantitative manner. Initially, the effects of diffusion and dispersion are shown during a miscible gas-injection process using a one-dimensional model under different scenarios. Such scenarios include both considering and neglecting the diffusion and dispersion terms. A comparison between the results from each scenario should demonstrate if a considerable error should arise in the simulation results by neglecting these effects. It would also show if such neglecting will result in inaccurate estimation of gas composition change, oil recovery factor, and the gas breakthrough time. Based on the expected results, an appropriate dispersion coefficient for accurate design of miscible gas injection processes will be estimated and introduced.