مجله پژوهش نفت
پیاپی 95 (آذر و دی 1396)

Cavitation technique can be used to increase the efficiency of the refining process of the heavy atmospheric and vaccum residuals and to upgrade the heavy stocks. The adiabatic collapse of the bubbles generated as a consequence of pressure reduction can produce conditions of very high localized temperature and pressure whilst the global conditions remain with no sensible change. In such a case, the bonds between atoms of molecules trapped in the bubble would be broken, some active radicals may be generated, chemical reactions may occur, and some catalyst particles may be activated. This paper investigated upgrading an Iranian refinery heavy fuel oil in a hydrodynamic cavitation setup. The system contains a feed tank, an internal 2 kW heating element, an additive container, a rotary pump (model DRP 16 lpm) with a 2.2 kW electric motor, a cavitation chamber, recycle pipe and a light products container. The stainless steel cavitation chamber consists of two narrow grooves at the top, a cone shape body and a collector at the bottom. Gasoline as a hydrogen donor and iron nanoparticles as catalyst were added to the cavitational heavy oil upgrading process. The results indicated that the cavitational processing in the presence of gasoline can reduce the viscosity and the total sulfur content of the heavy oil sample. Adding 1 vol% gasoline to a 10-minutes cavitational cracking process at 80 °C and atmospheric pressure can reduce the viscosity of heavy oil by 19%. In addition, iron nanoparticles increase the rate of hydrogen uptake and therefore the rate of viscosity reduction of heavy oil, in the presence of proper hydrogen donor.

The Sarvak Formation with the late Albian-early Turonian age is the most prolific hydrocarbon reservoir of the Abadan Plain region. Permeability estimation in heterogeneous carbonate reservoirs; such as, the Sarvak Formation, due to the complexity of pore characteristics is challenging, and porosity-permeability relationship in these reservoirs is dependent on pore type, size and connectivity of pore systems. In this study, permeability estimation has been accomplished using the pore facies concept and empirical formula. Based on the core description, thin sections’ studies and SEM images, pore types were identified and described. Afterwards, with respect to the petrophysical nature of pore systems and their porosity-permeability relationships, four pore facies microporosity (PF-1), microporosity-vuggy (PF-2), vuggy (PF-3) and vuggy-interparticle (PF-4) were introduced. In each pore facies, an empirical formula for the permeability estimation based on porosity-permeability relationship were determined. Comparison the results with the permeability values estimated in previous studies demonstrates that the estimation of permeability on the basis of pore facies concept has higher concordant with depositional and diagenetic characteristics. Generally, the intervals with microporosity and separate vugs, due to the weak pore system connectivity, a lower value of permeability will be estimated. In contrast, the intervals with interconnected pore systems such as touching vugs and interparticle pore spaces show higher permeability in comparing with the other pore types with the same values of porosity. Regarding the importance of pore type and geometry on permeability distribution within the reservoir, permeability estimation in term of pore facies can be useful in investigating the reservoir properties of heterogeneous carbonate reservoirs.

In order to accurately predict the performance of a gas condensate well, a numerical simulation with local grid refinement is inevitable, otherwise the effects of condensate blockage and high velocity of gas could not be properly captured. But, the complexities of such calculations make the numerical simulation time-consuming. On the other hand, to conduct an uncertainty analysis on the reservoir and well parameters, this calculation package must be repeated thousands of times. Therefore a faster method for calculation of gas condensate well flow rate is valuable. In this paper a fast semi-analytical method is introduced for calculation of flow rate in gas condensate wells and then based on Monte-Carlo procedure, an uncertainty analysis study is conducted for different well geometry. An uncertainty analysis is absolutely necessary at the beginning of a reservoir´s life, and it can help the reservoir managers to make the most possible realistic decision for development plan, infrastructure, and the sale contracts for produced gas and condensate. The results of the study show that investment on accurately determination of porosity is a wise decision for the specific studied reservoir. However this property can be different for another reservoir, depending on the reservoir and well properties.

We consider the problem of designing a new natural gas transmission network and expanding an existing network while minimizing the total investment and operating costs. We develop a mixed-integer nonlinear optimization model to determine pipelines in the network, compressor stations with their capacity as a variable, and their instalation schedule in a multi-period planning horizon. The model further decides on the amount of the produced natural gas in the steady-state flow for each period in the network. The model is solvable using Baron solver in Gams. We conduct computational studies on various cases generated using realistic network structure and data based on the natural gas network in Iran. Our analysis provides insights into sensitivity of network configuration and operations within different periods in the planning horizon and cost parameters of natural gas networks. Result proved 30 percentage decrease in cost of gas network transmission.

Gas reservoir sandstones of the Whicher Range field in the Perth Basin, as a part of unconventional reservoirs, consist of sandstone, siltstone, shale and thin coal interlayers which have been developed in a meandering river system. Thin inerlayers of coal intercalated with fine grained silt and shale sediments are considered as the gas sources within the sandstones. In this study, in order to recognize these coals interlayers based on their well log characteristics, gamma ray, density and sonic logs in one well of the studied field in concordance with core properties were investigated. The results show that these units generally are characterized with low density log, high sonic and medium gamma ray values in comparison with the other reservoir units (i.e., clean sands, shaly sands, shales). Regarding the thin layering attitude and also the association and intercalation of the coal units with fine grained shaly and silty sediments, their gamma and sonic values have been to some extent affected, and have overlapping with the other reservoir rock units. Therefore, density log provides more reliable responses for their study. Also, in reservoir studies of the field for their differentiation, it is better to consider these units as thin coal bearing intervals. The results of this study can be used in the more exact evaluation of petrophysical properties, and sequence stratigraphy studies of the reservoir sandstones in the field.

In this study, a series of laboratory tests were conducted using a hydraulic fracturing system on the cement block specimens to investigate the hydraulic fracturing propagation and interaction with pre-existing fracture under true tri-axial stresses regime. The pre-existing fracture was prepared with different dip and strike angles in the test blocks. The Experimental results demonstrated two basic types of hydraulic fracture propagation in interaction point with pre-existing fracture; crossing and no crossing modes. They can be clearly identified from the relationships among strike angle, dip angle and in situ stresses. Two empirical relationships were proposed to describe the interactions between the pre-existing and hydraulic fractures. These relationships can be useful to predict the hydraulic fracture propagation behavior in naturally fractured reservoirs, although its accurate determination requires the more experimental and theoretical studies.

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.

Loss of drilling fluid in the reservoir formations in oil fields can cause loss of investments and serious damages to the hydrocarbon producible formations. Due to presence of severe losses in some reservoir formations, proposing preventing solutions for this undesirable phenomenon has significant importance. On the basis of mentioned matter, this research is focused on the study and prediction of fluid loss in Asmari formation and modeling critical loss zones using geostatistical method of indicator kriging in one of the southwestern oil fields. For this purpose, at the first step, the distribution of fluid loss was determined throughout the reservoir using data of 363 oil wells. Then using indicator kriging algorithm with supposing a critical limit for fluid loss, the data was transformed to binary and using variography, the variability and anisotropy of data were analyzed. At the final step, by building a block model, the probability of presence of critical losses was estimated throughout the reservoir using indicator kriging. The estimated results show that the fluid loss has high variability in Asmari formation and critical loss points (higher than 100 Bbl/h) are located in northwest parts in sector 2 and in southeast parts in sector 9, especially dispersed in deeper zones.

A series of visible light sensitive photocatalysts of Fe2O3/ZnO composites with different Fe2O3 contents (25, 50, and 75wt%) were successfully prepared by a solution combustion method. The material structure and morphology of photocatalysts and their optical properties have been examined using X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), energy dispersive X-ray analysis (EDX), photoluminescence (PL) spectra, and diffuse reflectance UV–visible spectroscopy. The characterization results showed that the morphology, crystallite size, and optical properties of Fe2O3/ZnO composites varied significantly with the Fe2O3 contents. The as-synthesized photocatalysts were used for direct photocatalytic conversion of greenhouse gases (CO2 and CH4) in a batch photoreactor, under visible light irradiation. The highest rates of photocatalytic conversion of CO2 and CH4 by Fe2O3/ZnO nanocomposite were 16% and 21% respectively.

The aim of this paper is the numerical analysis of the effects of cold plasma obtained from applying electric field on the parameters of combustion and its pollutants and comparing the results with experimental works. The main method for doing this study is the use of influencing parameters and variables such as temperature, voltage, and the variables dependent on the fuel. The results obtained from simulations and tests indicate that the positivity of the central electrode potential leads to increase the flame temperature in the combustion chamber and wall proximity, which means the flame is getting closer to the wall. For this reason, heat transfer to the chamber wall increases in this state. The electric field causes creating a negative acceleration in the chamber center. By increasing the power of positive electric field, the flame temperature in the chamber center decreases and causes the flame length to be shortened. By applying the field, it was specified that the percentage change of index pollutants (i.e. carbon dioxide and nitrogen oxides such as nitrogen monoxide) are decreased %6 and 8 %, respectively. In the negative polarity and the chamber exhaust, because of the swirl effect the axial velocity is partly reduced. In an electric field of 3 kV and positive polarity, heat transfer to the walls is about 52 % greater than the condition without electric field.

Wellbore instability is one of the main or principal problems during drilling. Instability’s issues may cost lots of money and time for companies. Therefore, immense efforts have been devoted to solve it. In this article, using a Mechanical Earth Model and various failure criteria, this problem has been analyzed, and the best stable trajectory has been determined in order to avoid drilling induced wellbore failures. On this purpose, first, the mechanical properties of rock have been specified through log and core data altogether. By the help of (1) density log, (2) Stress Polygon, (3) drilling reports and (4) wall failure data, the magnitude and azimuth of stresses in the region have been calculated. Then to find the stable well path and examine the effect of choosing failure criteria on this procedure, three failure criteria applied to determine safe mud window for all of the possible trajectories. Mohr – Coulomb, as the prevalent criteria, and Mogi - Coulomb and Modified Lade, as criteria that include effect of intermediate stress, are utilized. The results show that, a trajectory characterized by 60 degree inclination from a vertical well and 70-80 degree Azimuth is optimum orientation. Also it is founded out that various failure criteria give same results.

Fingering phenomena in porous media has a lot of applications and various models in industries and natural issues. Recently several studies have been done on the stability of fluid in porous media. In this paper, the nonlinear instability of viscous fingering in a homogenous porous media is studied. Using a Fourier spectral method as the basic scheme for numerical simulation, equations transferred to Fourier space. The effect of mobility ratio on mixing length, sweep efficiently and transversely average concentration is examined and results indicate that in a high mobility ratio, sweep efficiently decrease and mixing length increase. Also estimation on beginning of viscous fingering instability has been done by analyzing of mixing length›s graph. In this paper, a new finger interaction mechanism is reported for the first time and named trifurcated tip, other mechanisms reported by previous researcher in the case of high mobility ratio, all are observed in this paper. Also the development of the new finger structures is explained by examining the velocity field which is superposed on the concentration contour.