مجله پژوهش نفت
پیاپی 97 (بهمن و اسفند 1396)

Selective plugging is one of the most effective mechanisms in microbial and chemical enhanced oil recoveries. In the experimental section, the water solution of purified Acinetobacter sp. and distilled water were injected to an oil saturated heterogeneous micromodel porous media. The main goal of this experiment was to examine the effect of water-bacteria cell solution in the water flooding performance and to compare it with pure water flooding. Pure water injection could expel oil by 41% while the bacterial solution injection was resulted in higher oil recovery, i.e. 7% improvement. In the simulation section, a heterogeneous geometry was used as porous media. To obtain water and oil distribution, Navier-Stokes equations were solved in time-dependent mode. Computational domain was discretised using triangular meshes. Moreover, the mesh independency analysis showed that the results are not dependent to the size of meshes. Seven different models were constructed to evaluate the influences of selective plugging in our porous media’s throats and routes during this process; moreover, the results illustrated that pour size fluid distribution is strongly related to the plugging distribution. After plugging of main diameter, wetting fluid inevitably exits from sidelong routes located in top and bottom of the matrix. It was shown in each model that the oil recovery was increased after throats, and routes were plugged in comparison with no plug model. Models no. 2, 4, and 6 had almost the same recovery while fluid distribution was different. The obtained results showed that Cahn-Hilliard phase field method can accurately predict water-oil displacement on pore scale under the selective plugging mechanism.

One of the most significant problems during oil and gas drilling is shale formation instability when using water-based muds. During underbalanced drilling due to pressure difference induced between drilling fluid and formation, mud filtrate invades to shale. Moreover, because of the large solid particles in drilling mud in comparison with shale pore throats (about 3 to 100 nm), formation of mud cake to prevent the invasion of filtrate to the shale is not possible. Therefore, drilling fluid filtrate continually penetrates to the formation and will cause an increase in pore pressure and instability of shale followed by lost in sidewall. In order to block the shale nanometer pores and to prevent the invasion of filtrate, a synthesis of amorphous silica nanoparticles using a simple and efficient method of waste material from agricultural industry is performed which was called rice husk, and applied in drilling water-based muds at two concentrations of 3 and 5% weight/volume (w/v). By taking rheological properties of base mud and the base mud with nanoparticles and comparing the test results, it was found that nanoparticles used improved the rheological properties of drilling mud such as thermal stability and reducing the amount of filtration. Then, a pore pressure transmission (PPT) device utilized to investigate the effect of the mud containing the nanoparticles to block shale pores and reduce pore pressure. The results showed that using concentrations of %3 and %5 synthesis nanoparticles cause the reduction of the rate of penetration of fluid into the shale at around 5.6% and 43.7% respectively. This phenomenon can be a factor to prevent the mechanical weakening of shale layers and their loss during drilling by water-based muds.

Oil and gas production from reservoirs always causes some problems. Hydraulically, fracturing could somehow mitigate the challenges especially for unconventional gas reservoirs. In order to gain a real knowledge of the reservoir, we should consider the reservoir with its heterogeneity and different layers. In this work, dominant equations of a hydraulically fractured bi-zonal gas reservoir are solved in a dimensionless way; moreover, type curves for well testing of this reservoir are discussed. This reservoir consists of inner and outer zones. The inner zone consists of a vertical hydraulic fracture and a vertical well. As the fracture acts infinitely, whole amount of fluid is produced within the fracture. The outer boundary of the reservoir is closed. Existence of a hydraulic fracture in a bi-zonal tight gas reservoir would cause the dimensionless pseudo-pressure and dimensionless pseudo-pressure derivative to be segmented into five sections. These five sections are caused by hydraulic fracture, radial flow of the inner zone, transient flow between the inner and the outer zones, radial flow of the outer zone, and the boundaries effects respectively.

Due to the influence of many parameters on the drilling fluid, the precise determination of the rheological behavior of the fluid is important. Therefore, the elimination of imprecise experimental methods which have been done based on trial and error, and using logical mathematical intelligence methods such as artificial neural networks instead of previous methods are needed. In the present study, for predicting the rheological properties of drilling mud, including Plastic viscosity, funnel viscosity, and yield point, the data from four wells of the field of X which contains 240 rows of data (4080 data) to test and 23 rows (391 data points) to test the model have been used. This includes 14 types of parameters in a fluid, depth, and temperature formation (a total of 17 parameters). By using artificial neural networks, the structures for predicting the neural network, and the rheological properties of drilling mud were built, and finally, three separate optimization models for the plastic viscosity (PV), funnel viscosity (FV), and the yield point (YP) were designed that in all three models, the network had two layers, 17 inputs and one output in last layer. Moreover, the number of neurons in the hidden layer, 16 neurons for the PV model, 19 neurons for FV model, and 19 neuron for YP model were determined. Finally, the coefficients of determination of these models, which were tested, were R2 PV = 0.99, R2 YP = 0.98, and R2 FV=0.97 indicating a high compliance test results with reality.

In this paper, flux and antifouling performance of PVDF (15wt.%) nanocomposite ultrafiltration mambrane with different functionalized carbon nanotubes (-COOH, -OH, -NH2) are considered. Membranes are prepared with phase inversion method using NMP as solvent. This is the first time that hydrophilicity of different nanocomposite membranes are changing gradually as performance of nanocomposite membrane are considered. Gradually, the change of hydrophilicity explaines the behavior and performance of nanocomposite membrane. Analysing surface pore size by SEM showed no significant diffferent in mean pore size (a few tenths of a micron) of nanocomposite memebranes in comparison with pristine memebrans. The cross section morphology showed that all prepared membranes are asymmetric structure with a compact toplayer and a bottom layer with large pore channels. All modified nanocomposite membranes show better hydrophilicity surface in comparison with pristine PVDF membrane (87°). The results of pure water flux are approved by the results of contact angle and porosity which have been measured. Pure water flux of nanocomposite membranes with optimized carbon nanotube amount is increased more than twofold to pristine membrane (146 L/m2.h). AFM also revealed that nanocomposite membranes have smaller roughness in comparison with pristine membrane (Sa=270 nm). This subject is shown that functional carbon nanotubes have not any detrimental effects on mechanical resistance in modified membranes.

Dolomite successions are the main productive reservoir intervals in the upper Jurassic Arab Formation in many oil fields of the Persian Gulf. In this study, based on the results from core description, petrographic analysis, high mercury injection capillary pressure analysis and cores poroperm data, dolomite facies, and their reservoir characteristics have been investigated in an oil field of the Persian Gulf. On the basis of the dolomite characteristics, four dolomite groups including fabric preserving, fabric destructive, dolomite cements, and partial dolomitization are differentiated. In dolomites of the Arab Formation, intercrystalline and interparticle porosities are the main pore types. Evaporate mineralization is an important digenetic process associated with dolomitization which has had a significant impact on reduction of reservoir properties, i.e. porosity and permeability. Based on the integrated geological and petrophysical study, 12 dolomite facies were identified. The results of this study also demonstrated that in fabric preserving dolomite facies the main factors controlling reservoir quality are the nature of primary texture, and dissolution, and evaporate mineralization as the main diagenetic processes. In this dolomite group, dolomitization has not been significantly altered reservoir properties. In contrast, the dolomitization of dolomite facies related to fabric destructive group, in relation with dolomite crystal size and shape, had a profound destructive or constructive role on type and geometry of pore systems. In dolomite facies, partial dolomitization which have been characterized by the sparse distribution of dolomite crystal within mud dominated facies and pore filling of interparticle porosity have insignificant or negative effects on reservoir quality. Distribution of dolomitic facies in Arab A, B, and C members is mainly fabric preserving dolomite. Moreover, fabric destructive and partial dolomitization are prevailed in D member of Arab formation.

In this research, the application of design of experiment and artificial neural network on conversion of H2 and CO were studied based on the experimental data. The experimental data has been collected from five independent variables based on central composite design such as temperature and pressure of reactor, H2/CO feed ratio, and partial pressure of H2 and CO in reactor. The operating conditions are: T = 320-340°C, P = 2-8 barg, H2/CO = 0.8-2.2, PCO = 0.3-2.7 barg, and PH2 = 0.3-2.5 barg. To generate the conversion models, two methods consist of response surface methodology and artificial neural network were used. The capability and sensitivity of both models were evaluated by some statistical parameters including mean square error and absolute average relative deviation. The result of both models were compared with experimental data and show the best results. To evaluate the maximum conversion of (H2 and CO), a hybrid ANN/GA was performed to solve the nonlinear both models. Finally, all quadratic equations and maximum of both models were performed, and the results were concluded. Also, this method can be used to produce the valuable selective production.

Pore pressure prediction is important in hydrocarbon exploration, production, and drilling activities. The presence of abnormal pressure may cause different problems such as pipe stuck, well blow out, mud loss, and so forth. Using seismic data is the only method for pore pressure prediction before drilling. In the present paper, stacking velocity which has been obtained from 3D seismic data processing was calibrated with acoustic log. The effective pressure was determined using Bower´s equation. Pore pressure would be predicted by overburden pressure and basic Terzaghi´s equation as well as abnormal pressure zones if existed. The results indicated that there have been two abnormal pressure zones existed in the Kupal Oilfield: high pressure zone in Gachsaran Formation (Member 1 or cap rock), in Pabdeh Formation, and two low abnormal pressure zones in the upper part of Asmari Formation. Pore pressure in Lower Asmari section is higher than in the upper part due to higher porosity.

The stuck pipe is one of the most important problems that it is costly and time consuming in drilling. Studies show that the parameters such as torque and the structure of the ground during drill operation are effective in the stuck pipe. Experience has shown that the torque suddenly rises in the moment of stuck, and drill bit rotates (rotation per minute RPM) get more slowly. Because this approach has many weaknesses with regard to the possibility to human mistakes and lack sufficient precision, thus, by detecting torque and rotation per minute spikes, the stuck moment can be detected. Various methods have been introduced to spike detection in the proposed method. In addition, smooth nonlinear energy operator is used. In this method, signal is detected positive and negative changes. In this study, a method for the detection of positive spike for torque and negative spike for RPM has been introduced. Moreover, it has been shown that the suggested method needs less time for analyzing a signal; therefore, it can be used in the immediately systems.

Photocatalytic process is one of the modern treatment methods which can be efficiently used for the treatment of wastewaters containing pollutants with priority such as hexavalent chromium. So in this study, the effects of various operating parameters and optimum conditions for the reduction of Cr (VI) in the presence of ZnO/HZSM-5 nanocomposite were investigated using a full factorial design method. In this study, ZnO/HZSM-5 nanocomposite was sanitized by Hydrothermal/impregnation method. The structure and morphology of Nanocomposite were studied by XRD, UV/vis, and FESEM techniques. In order to evaluate the photocatalytic reduction of hexavalent chromium using ZnO/HZSM-5 nanocomposite, full factorial technique was used. The effects of reaction time, pH, UV intensity, and initial chromium concentration were studied. The results of XRD showed that the nanocomposite was properly formed and had a crystalline phase. FESEM images showed that active phase (ZnO) was uniformly spread on the surface in nanometric size. The results of Fisher test (F-Value) indicated that the initial concentration of hexavalent chromium plays the most important role in the process. Under optimal conditions (initial concentration of chromium = 10 mg/L, UV light intensity = 125 W, pH = 5, and reaction time = 60 minutes), the removal efficiency was 98.72% with a desirability of 0.985 for hexavalent chromium. Finally, the normal probability analysis indicated that the data had a normal distribution. According to the result, it was indicated that the initial concentration of chromium was the most effective parameter in the process. Hence, the full factorial method can be used as an effective method for optimizing the conditions of the photocatalytic process in removing hexavalent chromium.

During recent years, various types of gels are used to control excess water in oil wells. The exploiting of preformed particle gels (PPG) can be considered as a good candidate to shutoff water channels without blocking of oil bearing zones. In this research, the preformed particle gel has been synthesized from Sulfonated polyacrylamide copolymer and chromium acetate (III) as crosslinker. The analysis of low amplitude oscillatory shear method was used to study on gel strength, complex viscosity, ultimate storage, and viscous modulus. The complex viscosity and ultimate storage modulus of gel were determined about 5919 Pa.s and 35.4 kPa respectively. The core flooding test was used to study of PPG performance in porous media. Further, two different size particle gels (63-106 and 106-188 micron) were applied to investigate the particle size effect on injection pressure and residual resistance factor of water and oil. The disproportionate permeability reduction index of 3.196 and 4.038, and water residual resistance factor of 41.42 and 53.22 were determined for small and large particle gels respectively. The results showed that the gel particle size on the residual resistance factor of water was more effective than the oil residual resistance factor.

The simultaneous utilization of Disulfide Oil (DSO) and Condensate is known as a novel mixture that has drawn researchers’ attention. The usage of such products is applicable when only precise experimental physico-chemical data are available. The DSO is produced as a waste and byproduct of gas sweetening process, which contains several disulfide components. Moreover, condensate is known as a valuable industrial product that is liquid at atmospheric temperature and pressure. Adding condensate to DSO makes it more economically feasible for export and may upgrade thermo-physical properties of DSO.Moreover, adding condensate to DSO promotes its potential applications. In this research work, different volume fractions of these two products from zero (0%) to 100% of DSO were tested by Refractometer, Tensiometer, Rheometer, Salinometer, and Calorimeter. It was found that the obtained refractive indexes linearly decreased from 1.5215 to 1.4277 by increasing the volume fraction of condensate at ambient temperature and pressure.Subsequently, the surface tension values decreased from 30.6 to 19.9 mN/m via quadratic function. The Rheometer results showed that various mixtures of these two products depicted a Newtonian fluid behavior in which their viscosity increased from 0.54 to 0.69 mPa.s by adding DSO at a standard temperature of 15.5˚C. The salt concentrations in condensate and DSO were achieved 26.096 and 30.265 g/m3 respectively. The calorific value of DSO was almost half of that of condensate value. It was observed that the condensate heat of combustion reduced by adding DSO.