Iranian Heavy Oil Research Articles

Asphaltene laboratory assessment of a heavy onshore reservoir during pressure, temperature and composition variations to predict asphaltene onset pressure

An Iranian heavy oil reservoir recently encountered challenges in oil production rate, and further investigation has proven that asphaltene precipitation was the root cause of this problem. In addition, CO2 gas injection could be an appropriate remedy to enhance the production of heavy crudes. In this study, high pressure-high temperature asphaltene precipitation experiments were performed at different temperatures and pressures to investigate the asphaltene phase behavior during the natural depletion process and CO2 gas injection. Compositional modeling of experimental data predicted onset points at different temperatures which determine the zone of maximum probability of asphaltene precipitation for the studied heavy oil reservoir. Also, the effect of CO2 gas injection was investigated as a function of CO2 concentration and pressure. It was found that a CO2-oil ratio of 40% is the optimum for limiting precipitation to have the least formation damage and surface instrument contamination.

The Effect of Temperature and Pressure on the Reversibility of Asphaltene Precipitation

A lot of hindrances are seen in petroleum operation, production, and transportation as a results of factors that related to asphaltene precipitation. It has great importance to investigate the reversibility of asphaltene precipitation under changes of effective factors on thermodynamic conditions such as pressure, temperature, and composition. In the present work the reversibility of asphaltene precipitation under changes of pressure and temperature was investigated for two kind of Iranian heavy oil. The stability test shows these samples are located at unstable region in aspect of asphaltene precipitation. The experimental procedure includes two parts, (a) decreasing pressure from initial reservoir pressure to near saturation pressure and surveying asphaltene content hysteresis with redissolution process at reservoir temperature, and (b) investigation of precipitated asphaltene in both precipitation and redissolution processes at different temperature and reservoir pressure. At each step IP143 standard test was used to measure precipitated asphaltene. It was concluded that above bubble point pressure, asphaltene precipitation is nearly reversible with respect to pressure for both samples and it was partially reversible with respect to the temperature for sample A, and accordingly pressurizing is acceptable method for solving the problem in both heavy asphaltenic crude oil samples and increasing temperature is acceptable method for solving asphaltene problem in crude oil sample A. Also density measurement of flashed oil confirmed that there is a little hysteresis in asphaltene content during redissolution and precipitation processes.

Uncertainty assessment and risk analysis of steam flooding by proxy models, a case study

Many uncertainties exist in development of oil fields. Developing proxy models as substitutes for reservoir simulators is a fast method for uncertainty analysis. Artificial neural network (ANN) and polynomial regression models (PR) were used as proxy models in a sector of an Iranian heavy oil reservoir under steam flooding scenario. Screening analysis was used to find influential uncertain parameters. Different experimental designs have been applied to construct proxy models. A combination of Box-Behnken and inscribed central composite designs was most informative design. Comparison between proxy models results and simulator outputs shows that ANN and PR models can accurately predict the simulator outputs. However, the deviation of ANN from actual results is less than quadratic polynomials. The constructed proxy models were used in Monte Carlo simulation to obtain probabilistic production forecasts. The combination of experimental design and proxy models is a fast and accurate tool for risk analysis and prediction.

An Experimental Feasibility Study of In-situ Nano-particles in Enhanced Oil Recovery and Heavy Oil Production

The influence of nanoclays on the asphaltene deposition, the recovery factor, and the solvent consumption of Iranian heavy oil were studied in a vapor extraction process. Experimental setup consisted of two visual sand-packed cells that were packed, one only with glass-beads as oil matrix and the other with glass-beads and modified montmorillonite as nanoclay, while they had similar porosity and permeability. The analysis of variance on simulated, conventional, and nano-assisted vapor extraction processes showed that nanoclays are able to change the matrix heterogeneity. The high content of precipitated asphaltenes in nano-assisted matrix demonstrated that asphaltenes were adsorbed into the nanoclays, dominantly, and distribution of asphaltene showed a reduction in their facial concentration from the injection port to the oil production port in both cells. The results revealed that the nanoclays increase the dissolved efficiency of solvent and the recovery factor by 30(±4)% in all three replicated experiments.

Biological Responses in Rats Exposed to the Hebei Spirit Oil Spill Constituents

Background : The Hebei Spirit Oil Spill, the largest oil spill in Korea, occurred in December 2007,. Many crude-oil components are well-known potential carcinogens and developmental toxicants. Aims : To evaluate the acute to chronic effects of crude oil exposure on hematological and blood biochemical toxicities. Methods : Sprague-Dawley rats were given oral doses of 0, 50 or 100 mg/kg BW/day of Iranian heavy crude oils for four weeks. Results : In the acute phase of exposure (one day after four weeks of oil treatment), decrease in the weight of thymus, serum level of interferon gamma (IFN-?), superoxide dismutase (SOD) and catalase activities in liver or kidney was found, and increase in the weight of adrenal gland occurred after the oral administration of crude oil. In body weight, histopathological examination, hematological, and blood biochemical analyses in the acute phase of exposure, there were no significant differences among the experimental groups. In the subchronic and chronic phase of exposure (two months and six months after four weeks of oil treatment), the changes of biomarkers were normalized except for the indicators of oxidative stress. Conclusions : Our findings show that the bioassay on the indicators of oxidative stress is a sensitive method for determining exposure to crude oil in rats.

Evaluation of biological responses in rats experimentally exposed to crude oil

To evaluate the acute to chronic effects of crude oil exposure on hematological and blood biochemical toxicities, Sprague-Dawley rats were given by oral doses of 0, 50 or 100 mg/kg BW/day of Iranian heavy crude oils for four weeks. In the acute phase of exposure (1 day after 4 weeks oil treatment), decreases in weight of thymus, serum level of interferon gamma (IFN-γ), superoxide dismutase (SOD) and catalase activities in liver or kidney, and increase in weight of adrenal gland occurred after oral administration of crude oil. In body weight, histopathological examination, hematological and blood biochemical analyses in the acute phase of exposure, there were no significant differences among the experimental groups. In the subchronic and chronic phase of exposure (2 months and 6 months after 4 weeks oil treatment), the changes of biomarkers were normalized except the indicators of oxidative stress. Our findings show that the bioassay on the indicators of oxidative stress is a sensitive method for determining exposure to crude oil in rat.

The Determination of Effective Diffusivity Coefficients in a Solvent Gas Heavy Oil System for Methane

In this investigation, an accurate high pressure and temperature diffusion setup was applied to measure the diffusion coefficients of methane in Iranian heavy oils in presence and absence of porous media by using the pressure-decay method. The solvent diffusivity in heavy oil was determined by both graphical and numerical methods. In addition, the effects of the porous medium and the temperature on the molecular diffusion coefficient of the solvent gas in the liquid phase were discussed and finally, using experimental data, a functionality dependence of molecular diffusivity on temperature and porous medium characteristics was proposed.

An Experimental Investigation of Viscosity Reduction for Pipeline Transportation of Heavy and Extra-Heavy Crude Oils

Due to the increase in the world energy demand, the use of all hydrocarbon resources, especially heavy and extra heavy crude oils, is required. But transportation of these oils is very difficult due to their high viscosity and low mobility. There are many different methods to reduce heavy crude oils viscosity, such as heating, blending, water in oil emulsion formation, upgrading, and core annular flow. The authors aimed to investigate experimentally some of these methods for reduction of viscosity of two Iranian heavy crude oils. Naphtha, light crude, and kerosene were blended with the oils. Results show that heating decreases the viscosity very rapidly and naphtha is the best blend type that can decrease the viscosity of Soroosh and Nowrooz crude oils to 200 cp, which is the appropriate viscosity for pipeline transportation, by using 15 and 5 vol% of naphtha, respectively. Alternatively, emulsion formation was carried out using Triton X-100 as the emulsifying agent, and it was established that a practical level of reduction is achievable at 75–85 vol% oil content.

Improvement of Heavy Oil Recovery in the VAPEX Process using Montmorillonite Nanoclays

In this paper, the nanoclay particles were introduced as mobile adsorbents in oil reservoirs to adsorb the asphaltenes, reduce the viscosity and enhance the dispersion. The objective of this paper is experimental investigation of enhanced heavy oil recovery using in situ nanoparticles for the first time. Moreover, two thermal analysis methods (thermogravimetry and differential thermal analysis) were used to analyze the asphaltene content of residue hydrocarbons in the swept chambers in nano-assisted and conventional VAPEX processes. Experiments were carried out using Iranian heavy oil and propane: the setup consisted of two sand-packed cells; one packed only with glass beads as the oil matrix and the other with glass beads and modified montmorillonite as the nanoclay, while they had similar porosity and permeability. The content of deposited asphaltene in swept matrixes, the propagation pattern of vapor chambers in heavy oil matrixes, and the rates of solvent consumption and oil production were determined. The results elucidated that montmorillonite changed the matrix heterogeneity and led to forming enhanced breakthroughs, to increasing the interfacial surface of vapor/bitumen and to accelerating the oil production. It was found that not only was the rate of vapor injection diminished, but the heavy oil recovery was also markedly enhanced by 30(±4)%.

Prediction of Asphaltene Precipitation During Solvent/CO2 Injection Conditions: A Comparative Study on Thermodynamic Micellization Model With a Different Characterization Approach and Solid Model

Summary There are different thermodynamic models that have been applied for modelling of asphaltene precipitation caused by various reasons, such as solvent/CO2 injection and pressure depletion. In this work, two computer codes based on two different asphaltene precipitation thermodynamic models--the first being the thermodynamic micellization model with a different characterization approach and the second being the solid model--have been developed and used for predicting asphaltene precipitation data reported in the literature as well as in the obtained data for Sarvak reservoir crude, which is one of the most potentially problematic Iranian heavy oil reserves under gas injection conditions. For the thermodynamic micellization model, a new approach was obtained by applying the characterization method taken from the thermodynamic solid model for oil component characterization. This new approach introduced a new matching parameter to the model, representing the interaction coefficients between asphaltene components and light hydrocarbon components, which resulted in a significant improvement in the thermodynamic micellization model predictions of asphaltene precipitation data under gas injection conditions. The model parameters obtained from a sensitivity analysis were applied in both thermodynamic models, and the experimental data of asphaltene precipitation were predicted. The asphaltene precipitation predictions from the solid model showed good agreement with the data taken under gas/solvent injection conditions. Especially for the trend of the titration curve after the peak point, reasonable agreements were observed which could rarely be found in the available literature. It has been observed that although the thermodynamic micellization model with a different characterization approach is more complex than the solid model, it is able to predict the trends of asphaltene precipitation curves for gas titration conditions reasonably well. Also, its predictions matched well with more experimental data points in comparison to the solid model predictions.

The Semi-Analytical Modeling and Simulation of the VAPEX Process of “Kuh-e-Mond” Heavy Oil Reservoir

The vapor extraction process (or VAPEX) uses vaporized solvents injected into a horizontal well to form a vapor chamber within the reservoir. Vapor dissolves in the oil and enhances the oil production by decreasing the oil viscosity in heavy oil reservoirs. To evaluate the process we conduct a simulation study on an Iranian heavy oil reservoir called Kuh-e-Mond. In addition, a semi-analytical investigation of the VAPEX process has been performed. The idea is to perform VAPEX simulation for a laboratory model and find a methodology to compare the results of the simulator with the semi-analytical Butler's model. In particular, a semi-analytical dimensionless correlation for production rate that incorporates all involved physical parameters in the VAPEX process is developed. Also, we performed a sensitivity analysis on the proposed correlation to obtain its adjustable parameters and optimize using available experimental data.

An oil spill accident and its impact on ozone levels in the surrounding coastal regions

Abstract An oil spill on the west coast of the Republic of Korea was investigated with regard to its impact on ozone (O 3 ) concentration levels in the surrounding regions. The accident occurred on December 7, 2007 with the total estimate of 12,500 tons of Iranian Heavy plus Kuwait Export crude oils. The evaporation rates of the volatile hydrocarbon fractions in these crude oils were estimated based on the molar fractions of crude oils and their mass transfer coefficients. Their emission rates parameterized with several key environmental parameters (e.g., wind speed, seawater temperature, and salinity) along with oil type information were then applied in the 3-D chemical transport model. Photochemical production of O 3 in winter just after the accident was relatively insignificant due to very low photochemical activity. For the case/sensitivity study, the photochemical production of O 3 simulated under the hot summer weather conditions was predicted to be significant at the same magnitude of the oil spill. This study confirms that an oil spill, if occurring around coastal regions, can alter O 3 levels to a large extent depending on the meteorological conditions.

Prediction of Asphaltene Precipitation during Pressure Depletion and CO2 Injection for Heavy Crude

In this work, a thermodynamic approach is used for modeling the phase behavior of asphaltene precipitation. The precipitated asphaltene phase is represented by an improved solid model, and the oil and gas phases are modeled with an equation of state. The Peng-Robinson equation of state (PR-EOS) was used to perform flash calculations. Then, the onset point and the amount of precipitated asphaltene were predicted. A computer code based on the solid model was developed and used for predicting asphaltene precipitation data reported in the literature as well as the experimental data obtained from high-pressure, high-temperature asphaltene precipitation experiments performed on Sarvak reservoir crude, one of Iranian heavy oil reserves, under pressure depletion and CO2 injection conditions. The model parameters, obtained from sensitivity analysis, were applied in the thermodynamic model. It has been found that the solid model results describe the experimental data reasonably well under pressure depletion conditions. Also, a significant improvement has been observed in predicting the asphaltene precipitation data under gas injection conditions. In particular, for the maximum value of asphaltene precipitation and for the trend of the curve after the peak point, good agreement was observed, which could not be found in the available literature.

STUDIES OF IRANIAN HEAVY OILS PERTINENT TO RESERVOIR CONDITIONS FOR THEIR AUTO-IGNITION TO INITIATE FIRE FLOODING

In this work, the potential for the auto-ignition of Iranian heavy oil during in situ combustion (ISC) process conditions was studied. Kinetic studies were carried out using thermal analysis techniques. Effects of oxygen partial pressure, reservoir pressure, and clay on the auto-ignition condition were investigated. Based on the experimental results obtained, a kinetic equation was derived for each of the different oil samples in the presence of different sands. The effect of partial pressure of oxygen in the injected air showed that at atmospheric pressure, low temperature combustion (LTC) was initiated at 275°C. Also, enriching the injected air by oxygen lowers the initial LTC temperature by up to 50°C. ARC experiments were undertaken to extend the studies to reservoir pressure conditions (1300 psi). It was found that activation energy in the LTC region was lowered as a consequence. As a result, initiation of LTC commenced at 115°C when air was injected. The effect of clay as a catalyst was also studied, and it was found that the activation energy decreases considerably when clay is present in the system. Experiments in a high-pressure combustion tube showed that LTC was initiated in the temperature range 120°–150°C, which is in line with the results obtained in the ARC. Fire flooding was sustained during the combustion tube test.

Effect of Fracture Spacing on VAPEX Performance in Heavy Oil Fracture Systems

The vapor extraction (VAPEX) process, a solvent-based enhanced oil recovery process has been found promising for some heavy oil reservoirs. In this work, the VAPEX process is studied using a compositional simulator on a number of single-block and multiple block fractured systems. PVT data of one of an Iranian heavy oil reservoir are used to tune the equation of state. Effects of fracture spacing on the performance of process were studied. It was found that the fracture network enhances the VAPEX process in low-permeabil ity systems by increasing the contact area between solvent and oil contained in the matrix blocks. Also, the fracture network reduced the instabilities in the system pressure and damped pressure surges in the system during the VAPEX process. In addition, results showed that solvent traverse between fracture network delayed the onset of solvent breakthrough and provided more residence time for the solvent to be in contact with heavy oil. In other part, effect of well location on the performance of process was studied. It was found that the oil production decreased as the well spacing increased. When the injection and production wells were far from each other, the oil production was governed by displacement for quite a long time rather than the gravity drainage enhanced by the VAPEX process. Also, improper location of the injection and production wells may results in the shortcut between injector and producer, which would lead to early solvent breakthrough and increased gas production through the system. The well location is a critical issue when applying the VAPEX process in fractured systems.

Dynamic Dilational Properties of Oil–Water Interfacial Films Containing Surface Active Fractions from Crude Oil

The dilational viscoelasticity behaviors of oil–water interfaces formed by surface active fractions of different average molecular weights and H/C atom ratios, which were distilled by supercritical fluid extraction and fractionation (SFEF) methods from Iranian heavy oil, and influences of pre‐equilibrium time on them were investigated. The interfacial relaxation processes were investigated by interfacial tension relaxation methods. The dilational moduli, elasticities and viscosities all increased and phase angles also regularly changed along with increasing number average molecular weights and decreasing H/C atom ratios. Along with increasing pre‐equilibrium time, the dilational moduli of samples increased and the phase angles decreased to the equilibrium values, as a result of the enrichment of surface active fractions into the interface. It took longer to reach the equilibrium for relatively high molecular weight samples than for low molecular weights samples. Along with increasing average molecular weights and decreasing H/C atom ratios of the samples, slow relaxation processes gradually appeared and their contribution increased. The characteristic relaxation times of similar processes of different samples also increased. The results of interfacial tension relaxation experiments and dilational viscoelasticity parameters determined by sinusoidal oscillation of interfacial area perfectly coincided with each other. The results for interfacial dilational viscoelasticity measurements, number average molecular weight and H/C atom ratios, and interfacial tension relaxation experiments illustrated that the fractions containing large condensed ring aromatic compounds that have large conjugated structures played a more important role in film‐forming and film rigidity than fractions of smaller molecules.

Study of carbonaceous mesophase through the e.s.r. spectra of vanadyl chelates

The behaviour of vanadyl chelate complexes in Iranian heavy oil and ethylene tar pitch during the carbonization process has been investigated by the e.s.r. technique to obtain information on the mesophase transformation. Activation energies for rotation of chelates incorporated with aromatic lamellae, and ordering parameters, are estimated from correlation times and intensities of e.s.r. spectra. The molecular plane of the chelates incorporated into the mesophase was found to be oriented parallel to the applied field. The value of activation energy is higher for a mesophase of small size than for a larger one.