Sharif Digital Repository

Carbon dioxide miscible flooding has become a popular method for Enhanced Oil Recovery (EOR) because it not only efficiently enhances oil recovery but also considerably reduces green house gas emissions. However, it can significantly cause asphaltene deposition, which leads to serious production problems such as wettability alteration, plugging of the reservoir formation, blocking the transportation pipelines, etc. It is crucial to investigate the effects of different factors on asphaltene deposition. A novel experimental setup was prepared to employ a high-pressure visual cell for investigation of asphaltene deposition on a model rock under typical reservoir conditions. The evolution of... 

Asphaltene precipitation during natural depletion and miscible gas injection is a common problem in oilfields throughout the world. In this work, static precipitation tests are conducted to investigate effect of pressure, temperature and gas type and concentration on asphaltene instability. Three different oil samples are studied under reservoir conditions with/without nitrogen and methane injection. Besides applying common thermodynamic models, a new scaling equation is presented to predict asphaltene precipitation under HPHT gas injection. Published data from literature are also used in model development. The scaling approach is attractive because it is simple and complex asphaltene... 

The chemical, thermal, and mechanical degradation of polymer chains under high salinity, temperature, and shear rates in oil reservoirs are the current challenges of the polymer flooding process. To answer such a complex requirement, recently, acrylamide (AM)-based thermoassociating graft copolymers (TAP) were synthesized that presented excellent performance as a viscosity enhancer, especially under high temperature and salinity conditions. The purpose of this study was to further investigate the effect of salinity, shear rate, mechanical strength, and adsorption of these TAPs on viscosity-enhancing performance at different temperatures. Finally, the performance of the TAPs was studied in... 

Capillary pressure is one of the most important parameters for reservoir engineering studies. Although different experimental methods are devised to measure capillary pressure, these methods do not represent the physics of fluid flow, which happens at reservoir conditions. Thus, it is attempted to extract the capillary pressure from spontaneous imbibition data, the common mechanism of oil production in water wet porous media. In this work, a new approach is developed to obtain the imbibition capillary pressure curve by using spontaneous water imbibition data in oil-water-rock systems. Comparison of calculated imbibition capillary pressure curves by the new approach with experimental values... 

The efficiency of an acidizing operation is usually assessed through ordinary well testing methods. These methods are performed only after the acidizing operation, and it is difficult to monitor and evaluate real-time efficiency of acidizing operation. Understanding the performance of the acidizing during the service, by analysis of the acidizing data is a viable approach to this costly and challenging process. The estimation of the skin changes needs an appropriate mathematical method that can handle the main aspects of an acidizing operation. It is tedious to model a real acidizing operation due to the heterogeneity of the reservoir, an unknown reaction rate of acid in reservoir condition,... 

This work concerns observing the pressure as well as CO2 mole percentage effects on asphaltene molecular weight distributions at reservoir conditions. A high-pressure, high-temperature asphaltene measurement setup was applied, and the amount of precipitated asphaltene at different pressures as well as CO2 mole percentage in an Iranian heavy crude oil was measured. Moreover, the asphaltene molecular weight distributions during titration of crude oil with different n-alkanes were investigated. The gel permeation chromatography (GPC) apparatus was used for characterization of asphaltene molecular weight under different conditions. It has been observed that some thermodynamic changes such as... 

The performance of CO2 injection into a semi-heavy oil reservoir was investigated at reservoir conditions, using highly permeable sandstone in a complete series of PVT tests and coreflooding experiments. Analysis of involved parameters such as: injection rate, injectant type and reservoir pressure were also considered. Oil viscosity reduction and oil swelling are the most influential mechanisms of enhanced oil recovery in this process. The results demonstrated that CO2 injection would decrease the interfacial tension for the high permeable medium in the absence of capillarity, but this reduction may not improve the recovery drastically. One of the main important aspects of this work is the... 

The performance of CO2 injection into a semi-heavy oil reservoir was investigated at reservoir conditions, using highly permeable sandstone in a complete series of PVT tests and coreflooding experiments. Analysis of involved parameters such as: injection rate, injectant type and reservoir pressure were also considered. Oil viscosity reduction and oil swelling are the most influential mechanisms of enhanced oil recovery in this process. The results demonstrated that CO2 injection would decrease the interfacial tension for the high permeable medium in the absence of capillarity, but this reduction may not improve the recovery drastically. One of the main important aspects of this work is the... 

Through this work, a novel mathematical-based approach was proposed to develop reliable models for calculation of PVT properties of crude oils at various reservoir conditions. For this purpose, a new soft computing approach namely Least Square Support Vector Machine (LSSVM) modeling optimized with Coupled Simulated Annealing (CSA) optimization technique was implemented. The constructed models are evaluated by carrying out extensive experimental data reported in open literature. Results obtained by the proposed models were compared with the corresponding experimental values. Moreover, in-depth comparative studies have been carried out between these models and all other predictive models. The... 

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... 

Microbial enhanced oil recovery (MEOR) is receiving renewed interest worldwide in recent years as a viable method while not damaging the reservoir is proven to be remarkably effective, however to some extent costly. This method is based on microorganisms' activities to reduce residual oil of reservoirs, which is dependent on behavior of inherent microorganisms or injection of bioproduct of external microorganisms. In this work, five bacterial species were taken from MIS crude oil that is one of the aging Persian fractured reservoirs. These microorganisms are substantially strong in increasing oil recovery especially by reducing IFT and other MEOR mechanisms such as change of wettability of... 

The objective of this study was to experimentally investigate the performance of water-alternating gas (WAG) injection in one of Iran's oil reservoirs that encountered a severe pressure drop in recent years. Because one of the most appropriate studies to evaluate the reservoir occurs generally on rock cores taken from the reservoir, core samples drilled out of the reservoir's rock matrix were used for alternating injection of water and gas. In the experiments, the fluid system consisted of reservoir dead oil, live oil, Co 2, and synthetic brine; the porous media were a number of carbonate cores chosen from the oilfield from which the oil samples had been taken. All coreflood experiments were... 

Asphaltene precipitation during natural depletion and miscible gas injection is a common problem in oilfields throughout the world. In this work, static precipitation tests are conducted to investigate the effects of pressure, temperature and gas type and concentration on asphaltene instability. Three different oil samples have been studied under reservoir conditions with/without nitrogen and methane injection. Besides applying common thermodynamic models, a new scaling equation is presented to predict asphaltene precipitation under HPHT gas injection. Extensive published data from the literature are also used in model development. The scaling approach is attractive because it is simple and... 

Despite the numerous experimental studies concerning asphaltene, the extent of reversibility of asphaltene aggregation at reservoir conditions remains still an elusive and controversial issue in the available literature. In this work, a series of depressurization and repressurization experiments were performed on three different live oils for qualitative and quantitative evaluation of the reversibility of asphaltene aggregation under typical pressure and temperature conditions of oil fields. The obtained results reveal that the kinetics and the extent of reversibility of asphaltene aggregation at elevated pressure and temperature are majorly controlled by the characteristics of the reservoir... 

Interfacial tension (IFT) is known as the critical parameter affecting the efficiency of CO2 flooding during the enhanced oil recovery (EOR) process. Besides, the asphaltene precipitation phenomenon is reported as the most significant problem during CO2 injection into asphaltenic oil reservoirs. Accordingly, it is important to examine the effect of asphaltene precipitation on the IFT behavior of the oil-CO2 system at reservoir conditions. The main objective of this research work is to study of the effect of asphaltene and its type on the IFT behavior of the oil-CO2 system. The IFT between pure CO2 and a model oil both with and without asphaltene was measured using an axisymmetric drop shape... 

Interfacial tension (IFT) is known as the critical parameter affecting the efficiency of CO2 flooding during the enhanced oil recovery (EOR) process. Besides, the asphaltene precipitation phenomenon is reported as the most significant problem during CO2 injection into asphaltenic oil reservoirs. Accordingly, it is important to examine the effect of asphaltene precipitation on the IFT behavior of the oil-CO2 system at reservoir conditions. The main objective of this research work is to study of the effect of asphaltene and its type on the IFT behavior of the oil-CO2 system. The IFT between pure CO2 and a model oil both with and without asphaltene was measured using an axisymmetric drop shape... 

Carbonated brine (CB) injection, known as one of the effective enhanced oil recovery processes, is highly dependent on the reservoir conditions (i.e. temperature and pressure) as well as the type of dissolved salt in aqueous solution. This study is aimed to investigate the influential parameters on the swelling of crude oil as the most important mechanism during CB injection. The swelling of crude oil in the presence of different CB solutions consisted of different salts such as KCl, NaCl, CaCl2 and MgCl2 with constant concentration of 15,000 ppm is studied using a high-pressure, high-temperature visual cell which measures the volume of drop using image processing software based on... 

The influx of solid or liquid particles of drilling mud into the pores of rock or mud loss phenomenon and clay swelling can sometimes lead to severe productive formation damage and cause to wettability alterations of reservoir rock from hydrophilic to oleophilic. Therefore, designing an appropriate fluid that is compatible with formation fluids and could reduce reservoir damage and increase the productivity of wells is very important. The two main mechanisms of surfactants are reduction of the surface tension and wettability alteration of rock reservoir that are effective in taking the oil. Regarding the importance of the wettability in reservoir productivity, this article is aimed to study... 

The influx of solid or liquid particles of drilling mud into the pores of rock or mud loss phenomenon and clay swelling can sometimes lead to severe productive formation damage and cause to wettability alterations of reservoir rock from hydrophilic to oleophilic. Therefore, designing an appropriate fluid that is compatible with formation fluids and could reduce reservoir damage and increase the productivity of wells is very important. The two main mechanisms of surfactants are reduction of the surface tension and wettability alteration of rock reservoir that are effective in taking the oil. Regarding the importance of the wettability in reservoir productivity, this article is aimed to study... 

In this work, a new model based on the multilayer adsorption kinetic mechanism and four material balance equations for oil, asphaltene, gas, and water phase has been developed to account for asphaltene deposition in porous media under dynamic conditions and the model was verified using experimental data obtained in this work and also with those reported in the literature. The results showed that the developed model based on multilayer adsorption kinetic mechanism can correlate more accurately the oil flooding experimental data in comparison to the previous models based on the mechanical plugging mechanism, in particular in carbonate core samples. Also, a series of experiments was carried to...