In this paper, oil recovery and permeability reduction of a tight sandstone core sample in miscible CO 2 flooding processes due to asphaltene deposition were studied using an Iranian bottom hole live oil sample in order to distinguish between the mechanical plugging and adsorption mechanisms of asphaltene involved in the interfacial interaction of the asphaltene/ mineral rock system. A novel experimental method was designed and proposed to measure the amount of deposited asphaltene due to different mechanisms using the cyclohexane or toluene reverse flooding and spectrophotometer. In this work, the bottom hole live oil sample was injected first to a long core and then CO 2 injection was performed which is close to reservoir conditions, whereas in the majority of previous works, the mixture of recombined oil (mixture dead oil and associated gas) and CO 2 was injected in a short core sample which is far from reservoir conditions. Then, the cyclohexane and toluene reverse flooding was performed, and the amount of deposited asphaltene was measured by spectrophotometer. It was found that by increasing the flow rate of injected CO 2 , pressure drop across the core increased significantly and then decreased. These significant increases in pressure drops indicate more asphaltene deposition and consequently more permeability reduction. Also, it has been found that 20−40% permeability reduction by asphaltene deposition was caused by adsorption mechanism in the CO 2 flooding process during a slow process, whereas 60−80% of formation damage is due to a mechanical plugging mechanism and takes place in a short time. Also, a modified model based on multilayer adsorption theory and four material balance equations (oil, asphaltene, light components, and water phase) was developed to account asphaltene adsorption in core sample during CO 2 flooding and the model was verified using experimental data obtained in this work. The results show that the developed model based on multilayer adsorption theory and four material balance equations is more accurate than those obtained from the monolayer adsorption theory and two material balance equations (the existing models) and is in good agreement with the experimental data reported in this work.

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Appropriate estimation of permeability is considered as one of the significant concerns of petroleum industries. Due to the growing demand for hydrocarbon fossil fuels in numerous industries, Petroleum Engineers always try to provide holistic and sustainable solutions to measure this parameter more accurately and to calculate the proper original oil in place (OOIP) and initial reserve. Hence, this accuracy estimation helps engineers whether the production and exploration operations are profitable or not and it might virtually eliminate the unnecessary expenditures. The term production logging tools (henceforth; PLT) involve a wide variety of measurement tools and many sensors. It, too, carries interpretation tools which evaluate the formation properties, in respect of the way PLTs would analyze the formation fluid movements inside and outside of the wellbore and subsequently estimate the production flow rate for each layer. On the other hand, it gives production and completion engineers the chance to investigate the appropriate efficiency of production and perforation processes to organize the remediation methodologies or preplan proper designing for modifying completion procedures which have based on the production logging tools interpretation. The purpose of this comprehensive research is to compare two different techniques (PLT and core analysis) of permeability measurement in a six-layered fractured reservoir and subsequently normalize each parameter to obtain the proper estimation. As a result, according to the evaluation of each technique, the amount of permeability in the layers 1, 2, 3, and 5 is relatively close to each other. Furthermore, regarding higher expenses of core analysis tests and the reliability of PLTs according to the results of this paper in the four out of six individual layers, Emeraude software by utilizing PLT interpretation could be a substitution and preferable methodology instead of core analysis measurements.

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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 determine the permeability reduction of carbonate, sandstone, and dolomite core samples due to asphaltene deposition using an Iranian bottom hole live oil sample which is close to reservoir conditions in order to study the effect of different parameters on asphaltene deposition mechanisms during dynamic conditions in porous media. The performance of the effective parameters of porous media on asphaltene deposition such as mineral composition and morphology of surface was also studied using X-ray, elemental analysis, and scanning electron micrographs (SEMs). It was found that an increase of the iron content of core sample leads to a less permeability damage and an increase of the calcium content of core sample leads to an increase of the permeability damage during natural depletion due to asphaltene deposition. SEMs of carbonate core sample showed the formation of large clusters of asphaltene with characteristic sizes that greatly exceed the monolayer deposition characteristic size. Also, a novel experimental method was designed and proposed to distinguish between the mechanical plugging and adsorption mechanisms of asphaltene using the cyclohexane or toluene reverse flooding and it has been found that 60−82% permeability reduction by asphaltene deposition was caused by mechanical plugging mechanism during a fast process, whereas 18−40% of formation damage is due to an adsorption mechanism that takes place in a longer time.

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