مجله پژوهش نفت
پیاپی 85-2 (بهمن و اسفند 1394)

CO2 injection is one of the most common methods in enhanced oil recovery. Objective of this paper is to simulate continuous CO2 injection in field scale to obtain recovery factor of CO2 flooding and storage capacity of carbon dioxide in an oil field located in South-West of Iran. It has been considered that CO2 is captured from external flue gases in Ramin Power Plant. Using the commercial software and validated compositional reservoir model, the most affecting operational parameters such as injected CO2 volume, injection rate, location and number of injected wells, perforated intervals, GOR constraint of production wells, and CO2 solubility in the aquifer were investigated. Simulation results have shown that increasing the injected volume of CO2 causes increase in storage capacity, but not in the oil recovery factor necessarily. The most effective parameters on oil recovery factor are injection rate and perforated intervals. Injection in lower layers increases the recovery factor and storage capacity, simultaneously. Limiting the production wells with GOR constraint, increases the storage capacity and reduces the oil recovery factor. CO2 solubility in aquifer reduces the recovery factor of the process and increase CO2 storage capacity. Finally, at the best scenario, recovery factor obtained from continuous CO2 injection is around 7.5%, and CO2 storage capacity is 33 BSm3 equal to 60 MM metric Ton.

Control of reactive distillation (RD) column is a challenging task due to its high degree of non-linearity, strong interactions, steady state multiplicity, time delay, process uncertainties, and the large number of possible control configurations. On the other hand, important products such as methyl tertiary butyl ether and ether tertiary butyl are produced via this method. An optimal control of methyl tertiary butyl ether (MTBE) column is studied in this paper utilizing the Multiobjective Genetic Algorithm concept in conjunction of Proportional-Integral-Derivative (PID) controller. The novelty of the work is in the optimal tuning of PID controllers by minimizing of two objective functions (Overshoot and Integral of Absolute Error (IAE)) through Non-Dominated Sorting Genetic Algorithm-II (NSGA-II). Numerical results show that NSGA-II based tuning method has excellent ability in optimal control of MTBE RD column.

Formation fluid migration to the cement column is one of the most common and costly problems occurring in most gas and some oil wells, which could lead to some hazardous consequences. Some major oil companies have designed special additives to mitigate or preferably eliminate the phenomena of gas migration. With respect to most Iranian oil and gas fields, the use of anti gas migration additives is highly required. In one gas filed as a case study, despite the application of anti gas migration additive to the cement recipe, the problem of gas migration through cement is still occurring. In this investigation, the process of quality control of the additive by use of FMA utility has been done and the effects of using this special chemical on all cement properties have been studied. Results showed that adding anti gas migration additives is not the only solution to overcome gas migration problem in cements. The main key in using anti gas migration additives is to optimize additive consumption and design slurry with acceptable properties such as zero free water, total API fluid loss value less than 50 cc, early compressive strength development in less than 5 hours, right angle set pattern in thickening time test (time between 30 and 70 BC must not exceed 25 minutes) and rapid gel strength development between 250 to 500 lb/100 ft2. Fortunately, by use of special anti gas migration additive from domestic source which is called PK-90 all aforementioned criteria had been met.

Shale formation instability is the main source of many problems in drilling operation causing significant costs and wasting time. Prior to drilling, mechanical stresses are less than fracture resistance of rock and chemical conditions are in balance within the formation. Because of that, in this balanced situation, the formation is stable. However, shear, tensile and compressive forces vary around the wellbore after drilling operations. Under these conditions, the rocks around the well become unstable. On the other hand, while the formation contacts with drilling fluid, chemical interactions occur, one of possible reasons for the wellbore instability. Hydraulic pressure transmission and osmotic pressure are the main mechanisms of shale formation instability. Thus it is very vital to delay the pore pressure increase surrounding the well. This can be achieved by adding various salts and applying different types of nano-particles or polymers to block the shale pores to improve the shale membrane properties. In order to prevent consequential problems associated with shale formations, it is necessary to study the formation characteristics and evaluate changes occurred due to rock-fluid interaction. Hence, in this paper, the field equations governing the problem have been derived based on the linear chemo-poroelastic theory. Since Diffusion equations are mainly fully coupled, therefore by using analytical/ numerical methods, these equations have been decoupled and solved finally. The simulation results show that the proposed model can appropriately simulate the pore pressure transmission test (PPTT) and shale formation behavior contact with drilling fluid.

One of the major problems in drilling process of zone 4 of the member 7 of Gachsaran Formation in Marun oilfield is casing collapsing. This problem is investigated in this paper in view of geological prospect. To study the petrography it is used 500 thin sections and different well logs such as gamma ray, sonic, graphic well logs are applied to plot stratigraphic columns and wells correlation and also provide isochors and isobar maps. The petrographic study indicated that the main lithology of zone 4 is marl with a minor association of limestone and anhydrite. The collapse problem in marly intervals is more common while drilling program. According to isochor maps provided for zone 4 there is max thickness in the axial part, southern flank of the north eastern part and east end of the field. According to the isobar maps, high pressure points of Zone 4 are in the axial part and western end of the field and low pressure locations are in the curvature part of the anticline and northern part of the field. By comparing the stratigraphic column, the isobar and isochor maps it can be concluded that the formation pressure changes in zone 4 is affected by variation in thickness, lithology, structural shape and tensions trends exerted on Marun anticline structure.

The drilling fluids play a significant role in the drilling of oil and gas wells. Bentonite is one of the consumable components of the drilling fluid which is used to reduce the fluid loss. The production of high quality bentonite resources which are suitable for drilling is declining in our country, Hence it is necessary to improv the quality of available bentonites. Using polymer additives is a conventional method for improving the quality of bentonites which has attracted the attention of researchers. However, some disadvantages of these compounds such as expensive production procedures and formation damages motivate researchers for developing some new improving methods to reach the high quality drilling fluids. The main aim of this research is to improve the quality of poor bentonites through amencling water absorption capability and increasing the rheological properties. The Properties of 12 types of bentonite were investigated and two compounds B9 with the lowest quality and B6 with the highest quality were selected for further investigations. Carbon ate and magnesium base chemical substances were then added to such compounds and their properties were investigated, too the results showed that adding Carbonate and magnesium compounds could result in a quality improvment of bentonites which satisfied the API RP 13-A standard requirements. The modified bentonite showed about 6.5 times better rheological properties and 2-5 folds lower fluid loss as compared to the untreated sample. The results also showed that the modified bentonite could be a good choice for replacement of the conventional carboxymethyl cellulose and starch in the polymeric drilling fluids, based on their 2.5 to 4 times better rheological properties.

Through this research, the ability of orange Azo β-NapHtol’s decolorization by Halomonaz Strain Gb bacteria and the efect of conectration, PH adn temoeratureon decolorization studied. The optimal conditions for decolorization were obtained via changing the level of different factors while keeping one factor in each test constant, is assayed. The final result shows the maximum percentage of decolorization (88%) by 40 ppm concentration, 38˚C and pH = 9 after 6 days of process. As a result of testing in a wide range of concentration (15-125 ppm), decolorization ability of the bacteria divided in two parts: examinations with concentration of less than 40 ppm and more than 40 ppm. The most effective factor was pH and increasing pH in a range of 6-10 caused a remarkable increase in decolorization. Temperature of 35-40˚C did not too have much effect on the decolorization. Comparison of arising spectrums from HPLC and UV-Vis before and after decolorization and observing the totomery ph enomenon in arising spectrums from IR confirmsthe considerable decolorization. Because of halopHilic and halotolerant bacteria, the amount of %5 (W/V) Sodium Chloride was added during all the tests.

One of the major problems in Enhanced Oil Recovery (EOR) processes is the precipitation and deposition of asphaltene. This may lead to formation damage or partial and utter obstruction of flow passages around the well, deposition of asphaltene on the surface of reservoir rock as well as wettability alteration from water- to oil-wetted, and deposition in processing units. The present study investigates the miscibility of synthetic oils with or without asphaltene and compares it with that of crude oil from one of the Iranian oil fields in the presence of CO2 gas using vanishing interfacial tension (VIT) technique. The experiments were conducted at a given temperature but for different pressures. The experimental results showed that normal paraffin, in the oil phase, served as instability agent for the precipitation of asphaltene. The higher content of n-paraffin resulted in more and faster precipitation of asphaltene at the gas/oil interface. Once this occurred then the slope of IFT curve between gas and oil increased resulting in decreased CO2 solubility. Furthermore, based on IFT measurements, the speed of approaching to miscibility is reduced in vicinity of the onset of asphaltene precipitation. Thus, asphaltene aggregation in the gas/oil interface is accompanied by reduced slop of VIT curve which made the miscibility condition harder to reach.

The amount of total organic carbon (TOC) is one of the major geochemical parameters, which is used to evaluate hydrocarbon generation potential of source rocks. Measurement of such an important parameter requires performing tests on small-scale drill cuttings which is too expensive and time-consuming. Meanwhile, it is measured using a limited number of samples. However, petrophysical data are accessible for all drilled wells in a hydrocarbon field. In this paper, artificial neural network technology was used to estimate TOC from petrophysical logs. The correlation coefficient between the estimated and measured TOC data from Rock Eval pyrolysis is 71% ,which is an acceptable value. The results of this study show that artificial intelligence is successful in estimating TOC data. Formation source rocks of the studied oilfield are Kazhdumi and Gadvan which constitute the main source rocks of Iran. The presented methodology is illustrated by using a case study from one well of Azadegan oil field in Abadan plain

Recent developments in the environmental regulations of benzene emission indicate the growing awareness about the adverse effects of this compound. The BTEX (i.e. benzene, toluene, ethyl benzene and xylen isomers) which are absorbed by the glycol solvent during dehydration of natural gas, will be emitted to the atmosphere upon thermal regeneration of the solvent. In the present work, quantitative and qualitative analysis of the BTEX emissions from a glycol dehydration unit in southern Iran were performed and an appropriate mitigation method for these emissions was proposed. In order to investigate the effect of operational parameters and the mitigation methods on the BTEX emissions, the glycol dehydration unit was simulated in Aspen HYSYS. The results showed that the emission of benzene, toluene, ethyl benzene and xylen isomers to the atmosphere were about 3770, 1007, 15 and 20 kilogram per year, respectively. Furthermore, the simulation results revealed that the BTEX emissions could be reduced by using an air cooler condenser after glycol regeneration tower while the benzene emission meets the Canada standard level at 1997.

Physical and chemical methods are among the most common methods used for removing oil pollutions. But these methods are very difficult, dangerous and costly.
Under certain circumstances, biotechnology could offer more effective approaches for decontaminating polluted sites. To that effect, the objective of this research is to assess the efficacy of bioaugmentation technique in the elimination of oil pollutions.In this research, Diesel fuel contaminated soil was held for 100 days in cubic columns measuring one cubic meter in the ambiance temperature with relative humidity at 50%. This soil was compared with diesel-contaminated soil before undergoing microbial inoculation. Bioaumengtation was done with microbes achieved from screening and parameters, pH and gas chromatography analysis. The results obtained from the total count of microorganisms and gas chromatography analysis indicate that during 100 days period following microbial inoculation, the soil columns have seen an increase in microbial population from 2×106 to 2.6×1010. Biochemical and molecular tests showed that gram negative bacilli (pseudomonas) were the most dominant microorganism and the qualitative and quantitative analysis with gas chromatography device shows that some components in the treated samples have disappeared or declined by bioaugmentation. Studies conducted on Diesel fuel soaked samples by gas chromatography device showed bioremediation of Diesel fuel contamination by microbes obtained from the screening stage.

In order to evaluate the hydrocarbon potentiality of Mobarak Formation in Mighan Section (situated in North-East Shahrood City), of East Alborz, 19 surface rock samples were collected for Rock-Eval-2 pyrolysis. The obtained Results indicated that the Mobarak Formation in Mighan section region has relatively high TOC, adequate Tmax values and with moderate hydrocarbon potentiality, have passed diagenesis stage. Plotting of Tmax values verses Hydrogen index (VanKrevelen diagram) for the given samples revealed that The Mobarak Formation in Mighan section has kerogen of type III with little amount of mixed type II/III kerogen. The organic matter of Mobarak Formation in the Mighan section with Tmax between 455-498°C has already crossed the oil window and has reached the wet gas generating stage. Based on OI and HI indices and distribution of samples on organic facies diagram, the majority of samples are belonging to CD and D groups region, indicating slightly an oxidized environment for Mobarak Formation. With respect to S2/S3 ratios, the upper horizons of Mobarak Formation contain has higher quality of organic matter in comparison to lower sediment layers. With increase of TOC contents, apparently input of organic matter with terrestrial origin with sedimentation fixed rate, has been prevailed in sedimentary basin.

Deposition of organic rich black shales and argillaceous limestones in the Berriasian-Turonian interval have been documented from different parts of the world. The Early Cretaceous Garau Formation, based on geological and geochemical reports is well exposed in northwest of Zagros, Iran (Lurestan Zone) as a hydrocarbon source rock. However, these reports lack comprehensive results of experimental analysis and studies. In this study, samples from Garau Formation obtained from Anjir anticline (n=12 cuttings from well ANR-1) and Kabir Kuh anticline (n=5 cuttings from well KAK-1 and 11 outcrop samples from Tange Garau) from Lurestan Zone were subjected to Rock–Eval pyrolysis, Gas Chromatography(GC), Gas Chromatography-Mass-Spectrometry (GC-MS) and vitrinite reflectance measurement (Ro%) techniques. Analytical results show that average values for TOC (1.75 and 2.55%), Tmax (445 and 475оC) and Ro (0.895 and 0.974%) in these two anticlines respectively, suggesting good to very good hydrocarbon source rock with late oil window and early gas generation maturity. Most samples have a mixture of kerogen types II/III and type III. Biomarker characteristics including normal alkanes, distribution of the hopanes and steranes indicated the presence of dominant marine organic matter with a minor terrestrial organic input that were deposited in a marine environment under reducing conditions. The results obtained from characteristic biomarkers also suggest that the Garau Formation is thermally mature in the above mentioned two anticlines which are in agreement with the results of Rock-Eval pyrolysis and vitrinite reflectance measurements.

Usually, multiphase flow often occurs in producing wells of gas condensate reservoirs. Different correlations were proposed for predicting pressure drop in such reservoirs. However, no correlation or model is found to predict pressure drop in a wide range of operating conditions. In this paper, pseudo spontaneous potential logging (PSP) data measured at field conditions are used to compare the performance of different correlations in predicting pressure drop and liquid holdup in four gas condensate producing wells. Measured field data from four layer wells were used to tune the vertical lift performance (VLP) correlations and best correlations were recommended from matching between measured data and tuned correlations. Finally, measured wellhead pressure and gas flow rate were used to calculate and compare bottom-hole pressure from correlations of pipesim and after-before tuned correlations of prosper with minimum error. By comparing simulation results, Gray, from pipesim software and hagedorn & brown and petroleum expert2 correlations were found most accurate correlations for gas condensate wells from prosper sftware. Results of this study open a new screening criteria for selecting the best correlations to be applied in lean gas condensate wells.

In this study, polyvinyl chloride based heterogeneous cation exchange membranes were prepared by solution casting techniques using tetrahydrofuran as solvent and cation exchange resin powder as functional groups agent. The effect of functionalized multi walled carbon nano tubes and also Cu nanolayer coated MWCNTs composite nanoparticles on physico/chemical properties of membranes was studied. The Cu nanolayer coated MWCNTs composite nanoparticles were prepared by magnetron sputtering method. Scanning electron microscopy and scanning optical microscopy were utilized to investigation of membranes’ structural properties. The images showed uniform particles distribution for the membranes. Also the electrochemical characteristics of membrane were studied. The results revealed that membrane transport number, selectivity and flux were improved by using both nanoparticles in membrane matrix. Also the modified membrane containing Cu nanolayer coated Multi Walled Carbon Nano Tubes showed higher selectivity and ionic flux compared to membrane containing MWCNTs and un-modified membrane.

In this study, a series of laboratory tests using a real Tri-axial Hydraulic Fracture System were performed to investigate the mechanism of fracture initiation and propagation on thecement blocks in different reservoirs in normal and tectonic stress regimes. The influences of crustal stress field, confining pressure, and natural fractures on the fracture initiation and propagation were discussed. Experimental results demonstrate that stress concentration around the hole would significantly increase the fracture pressure of the rock. At the same time, natural fractures in the borehole wall would eliminate the stress concentration, which leads to a decrease about two thirds in the fracture initiation pressure. Two interaction types between induced fractures with pre-fracture were observed including crossing and opening the pre-existing fracture. In a normal stress regime, hydraulic fracture crossed the pre-fracture. But in tectonically stressed or shallow reservoirs, due to high interaction between hydraulic and natural fractures, hydraulic fracture was arrested by opening of the pre-fracture.