مجله پژوهش نفت
پیاپی 121 (بهمن و اسفند 1400)

During the Acidizing process in oil and gas reservoirs, the injected acid reacts with the rock grains, changes the rock pore structure and affects the flow conditions. Due to the presence of a concentration gradient at the vicinity of the rock grains and the continuous changes in rock-fluid interfaces, the continuum assumption of the effective local mass transport coefficient and porosity-permeability relation in the continuum scale modeling of this process has been remained debatable. Therefore, the need for pore scale modelling is evident. The novelty of this study relies in adapting the grid refinement method on reactive flow modeling that implements the Lattice Boltzmann method to compute the effective local mass transport coefficient on the pore scale and in changing porous media. Quadtree grid refinement method is a multiscale mesh refiner that adjusts the grid resolution based on recursive subdivisions, and it is able to reduce the computational load while keeping the desired precision. The simulation results with one- and two-level refinements show that quadtree is two to three times faster relative to uniform fine grid model. Meanwhile, this study uses the constructed model to regenerate the experimental results of wormhole dissolution pattern and discusses the variation in the porosity-permeability relation and the mass transport coefficient due to rock dissolution at different flow conditions that are characterized using the dimensionless numbers of Damkohler, Peclet and Sherwood. The simulation results demonstrate the relation between the dissolution and the Sherwood number and indicate that accurate investigation of the variation in porosity-permeability relation can be performed through analyzing the Kozeny-Carman relation in different flow conditions. Therefore, grid refinement method provides a Pore-Darcy scale bridging tool by achieving larger simulation domains on the pore scale.

Low salinity water (LSW) injection and alkaline flooding are two common enhanced oil recovery (EOR) methods. Although these methods have a lot of advantages, they could cause some formation damages. One of the main problems during LSW injection and alkaline flooding is fine migration. Fine migration might reduce reservoir permeability or produce and damage well facilities. Ionic strength and pH are two main factors that could control fine migration in these EOR methods. In this paper, the effect of four salts NaCl, KCl, CaCl2, and MgCl2 was studied as an ion strength parameter on fine migration. To investigate the effect of pH, four pH of 6.5, 8, 10, and 12s was considered. The results showed that the presence of salts decreases the amount of fine migration compared to distilled water injection, and divalent salts have a better performance than monovalent salts. The results also showed that the simultaneous presence of divalent ions in the injection fluid increases the intensity of fine migration. Furthermore, studies on pH’s effect indicate that increasing the injection fluid’s pH causes the more fine migration. Zeta potential measurements prove that the potential of fine particles surfaces increases by raising fluid pH. As a result, the repulsive forces between fine particles are greater at the higher pH which causes to increase fine migration.

By using petroleum products in the petrochemical industry and performing series of chemical processes, various and value-added products can be obtained. Propylene is one of these very important and basic products that can be used to produce various materials. Therefore, in the present study, a two-dimensional steady state model of the process of oxidative dehydrogenation of propane to propylene in a micro-channel reactor was performed in the COMSOL simulator. Then, a multi-objective optimization with the purpose of increasing propylene (increasing production) and decreasing CO (preventing coke formation) was performed, for the first time. Comparison of the simulation results with laboratory data shows an error of about 7%, which is acceptable based on the model assumptions. In order to analyze the process, effect of temperature, feed flow rate, feed composition and heat transfer coefficient on the amount of propylene and CO production was investigated. To optimize the performance of the reactor and due to computational cost of the COMSOL model and optimization process, an alternative model for the micro-channel reactor was presented based on the design of experimental (DOE) method. Finally, the multi-objective optimization of the process was performed based on the prepared model by the response surface method (D-optimal), and the optimal pareto front was obtained. According to optimization results increasing propylene leads to an increase in CO production, which it shows a trade-off between objectives. After optimization, the results of one of the optimal points of the Pareto front were presented. The optimum temperature and velocity at this point is 513°C and 0.103 m/s, and in these conditions, the maximum concentration of propylene and the minimum amount of CO are set equal to 0.195 and 0.088 mol/m3, respectively.

The performance of two-phase (gas-liquid) separator was investigated in this paper. Two-phase (gas-liquid) separator was designed and manufactured using empirical correlations. The simplifying assumptions were used in these empirical equations, which their results of are less valuable. The effect of inlet diverter was neglected in designing, and the diameter of the liquid droplets assumed constant and predetermined. In these designing approaches, it was assumed that the liquid droplets were falling from the top of the two-phase (gas-liquid) separator, but in practice, the inlet diverter leads to separate the majority of liquid droplets because of momentum changing. The fundamentals of the turbulent multi-phase flow were not considered in these designing methods. The two-phase (air-water) flow loop was designed and manufactured. Air and water flows were mixed together at mixing section that is a 45° Tee and two-phase flow was formed. The two-phase (gas-liquid) flow had been considered as developed two-phase flow after passing 160 times greater than pipe diameter along pipe. Water and air flow rates were in ranges 0-2.5m3/h and 0-100m3/h, respectively. The maximum of operational pressure was 202650 Pascal at the ambient temperature. The liquid droplets trapper with 20 micron filter was mounted at gas outlet section of the two-phase separator to measure the volume fraction of the liquid phase in outlet gas flow and photography of liquid droplets in order to determine the diameter of the liquid droplets in outlet gas flow. Finally, the dimensionless groups were developed in order to model and investigate the two-phase (gas-liquid) separator performance. One of the most important achievements of this paper was providing the suitable platform to design well head (gas-liquid) two-phase separators based on the production conditions.

A large part of reservoir rocks is composed of carbonate rocks, which are more complicate. The most important challenge in oil production form the carbonate reservoirs, which decreased the ultimate oil recovery is that a great volume of oil remains in the rock. Enhanced oil recovery (EOR) techniques play an important role in improving oil production. Injecting smart water into the oil reservoir is one of the new methods of increasing oil extraction, which is designed by adjusting and optimizing the composition of ions in the injected water. Smart water injection into oil reservoirs is widely used in the oil industry due to its low cost compared to other methods of EOR. Generally, the objective of this study is better utilization of water flooding methods to increase the oil recovery efficiency from the carbonate reservoirs. Therefore, in this research, the effect of magnesium, sulfate and calcium ion concentrations in the process of enhanced oil recovery by smart water injection method on oil recovery coefficient from carbonate rock is investigated. By comparing the recovery factors for the double-distilled water and water types containing divalent ions, it was found out that the presence of divalent ions has a positive effect on the ultimate recovery from the carbonate reservoirs. In addition, changing the divalent ion concentrations in the designed smart water proved that an increase in the concentration of magnesium, sulfate, and calcium promotes the oil recovery factor. By comparing the final oil recovery coefficient of smart waters 4, 5 and 6 compared to smart water 3, it was found that by increasing of ions concentration of  Mg+2, SO4-2 and Ca+2 increase of the final oil recovery coefficient from 55%, 57.7%, 56% and 59% are in carbonate rocks, respectively. In other words, increasing the concentration of calcium ions had the greatest effect on oil recovery factor and increasing the concentration of sulfate ions had the least effect on the oil recovery factor.

Positive displacement compressors are one of the most important and expensive components of the vapor compression refrigeration cycle, it is very important to protect this equipment during operation and against destructive phenomena. The compressive mechanism of this type of compressors is based on the compressibility of gases and the pressure increases by reducing the volume and compressing the refrigerant gas. One of the destructive phenomena that causes main failure and mechanical damage to this type of compressors is the liquid flood back that occurs when liquid refrigerant returns to the compressors suction line. This research focuses on design, fabricate and test a protecting system to protect the compressor against liquid flood back. This protecting system is based on electronic processing of effective parameters including operating pressure, operating temperature, superheat temperature, superheat degree and type of refrigerant. The protection system processes based on the relevant thermodynamic formulas and issues the appropriate command based on the processing result. Validated researches prove electronic processing method is better than mechanical processing. The protection system installed successfully on a 30 ton Positive displacement compressor with R-22 refrigerant.

Accurate estimation of in-situ hydrocarbon is one of the most important objectives for oil/gas reservoir description. Fluid saturation is an essential parameter for this purpose. In this context, it is assumed that fluid content in a reservoir can cause seismic wave attenuation and dispersion. This assumption, however, has been confirmed using rock physics and numerical modeling and other research approaches. In this research, based on a White’s rock physics model, three types of sandstone reservoirs of different depth and degree of compaction were synthesized. A MATLAB code was developed to investigate the impact of saturation and porosity variations on velocity, attenuation, vertical reflection coefficient and phase angle, and the results were implemented on the data from an oil field in the Persian Gulf. These investigations revealed that among different attributes, frequency related velocity and frequency related reflection angle at different saturation status show similar trends. In this research, approximate reflection angle was carefully obtained for estimation of dispersion. Analysis of reflection coefficient and velocity reveals that gas saturation and porosity affect dispersion. Finally, reflection coefficient and dispersion cross plots were successfully used to estimate gas saturation.

Over the past decade, catalytic methanol-to-olefin conversion has been among the most highly developed processes for light olefin production. In this study, computational fluid dynamics (CFD) and COMSOL software were used to investigate the process of methanol conversion to light olefins. The Eulerian-Eulerian model was used to solve continuous and scattered phase flows. A simplified kinetic model was used for methanol conversion to olefin, including a catalyst effect, coke deposition, and the finite element method used to solve the equations. MATLAB software was used to obtain the kinetic parameters of the methanol to olefin process using a kinetic model and a genetic algorithm. A comparison was made between the experimental results and the proposed model for the main products, which showed a good agreement. For ethylene, propylene, and butene, the mean relative error was 2.40%, 1.35%, and 3.11%, respectively. Following the model validation, various parameters such as solid-phase distribution in the bed, velocity vectors, particle size, bed pressure drop, and average mass fraction of the components are investigated on reactor performance. Examining the solid phase distribution in the bed at various input velocities and times revealed that the solid concentration in the whole bed is almost dilute in the Ergun drag model. The flow structure appears generally homogeneous. By studying the particle size effect on velocity vectors, it is found out that as particle diameter increased, the turbulence of flow vectors increased and the number of vortices forming in the bed increased. Furthermore, the average mass fraction of hydrocarbons achieved during reactor output increased. Moreover, the methanol conversion reached more than 90%.

Sustainable production from hydrocarbon resources is very important in economic stability, maintaining production capacity, and fulfilling the export commitments of governments in providing energy sources from hydrocarbon fuels. Drilling and completing oil and gas wells in the safest and most efficient manner is possible in order to meet sustainable production objectives from oil and gas reserves. One of the threats to sustainable production from oil and gas reservoirs is the wellbore integrity failure and missing isolation for various underground layers from the inner space of the well. Alternatively, the leakage of gas and saltwater from the liner lap or casing shoe due to the micro-annulus phenomenon at the margin of the cement bond is another threat to oil and gas wells. To fulfill the aims of separating subsurface layers and directing the appropriate flow of hydrocarbon fluid to the production duct, the cement sheath acts as a sealing barrier against formation layers with varying fluid content and pore pressure. Cement slurry is pumped to the annular space after driving the steel casing. Improving the properties of cement structures is a continuous technical-engineering effort to increase the durability of structures and prevent the destruction or occurrence of problems related to weakness in these structures. Cement design requirements for oil and gas wells are accompanied by perfect sealing of the well. This research seeks to provide an efficient solution to cover the gas and fluid migration issues due to cement sealing inefficiency. Combining the superior rheological properties of latexes in cement with the strength properties of silica nanoparticles is an idea that has been developed in this research. In experiments, the effect of silica nanoparticles on improving the compressive strength of cement, reducing porosity, and effective permeability in gas migration has been well established. Polymer latex also helps cement slurry by developing thixotropic properties in the slurry and reducing the transient time window to minimize the gas migration possibility in critical times when the cement column is not able to effectively resist the formation fluids and restrict the opportunity for formation fluid invasion.

Interfacial tension (IFT) is one of the most important parameters that directly affects the capillary forces, which affects oil recovery. This research investigates the effects of asphaltene concentration and water-soluble divalent ions on IFT. A mixture of toluene and n-heptane, which is called heptol, is used as the model oil, and then asphaltene was added into Heptol to study its effect on the surface-active properties of the model oil. Brine in a salinity of sea water (SW) with a concentration of 40,000 ppm was considered as the base aqueous phase. A diluted brine with a concentration of 4000 ppm was prepared as a low salinity water (LSW), and a concentrated 80,000 ppm aqueous solution is considered high salinity water (HSW). Afterwards, the dynamic IFT of the oil phase/aqueous phase interface was measured using the pendant drop method. Results show that with the increase in the asphaltene concentration, IFT of heptol/brine system was decreased. The lowest value of IFT was observed in the salinity of 40,000 ppm. This may show an optimum salinity range to facilitate migration of asphaltene molecules into brine/heptol interface, which led to an IFT reduction from 23 to 16 mN/m. Results indicated that an asphaltene concentration of 0.5% can be was considered as the critical micelle concentration. At the end, the effect of divalent ions, i.e. calcium, magnesium and sulfate ions in the aqueous phase was investigated, and it is shown that the calcium ion has a larger effect on IT reduction compared to the magnesium and sulfate ions.