فهرست مطالب negahdar hosseinpour

Asphaltene deposition in porous media during miscible injection, as an enhanced oil recovery method, results in permeability impairment and thus formation damage. The degree of the permeability reduction due to asphaltene deposition is a function of the asphaltene deposition pattern. In this study, the effects of viscous and gravitational forces on the deposition pattern of asphaltene during miscible displacement of oil in a glass micromodel were studied. Dead oil was dissolved in a toluene/gasoil mixture to prepare model oil. A homogeneous micromodel with the pore and throat sizes of 160 and 80 μm, respectively, was prepared and employed for the miscible displacement of the model oil by normal hexane at the injection flow rate of 0.04 mL/h. The flow rate leads to a very low Reynolds number which is a characteristic of laminar flow in the porous media. To shed light on the contribution of the gravitational force to the deposit amount and deposition pattern, the displacement tests were conducted at the dip angles of 0, 10, and 20 degree in the injection direction. It is found that the deposition mechanism of asphaltene is divided into three main categories of deposition on surface, pore throat blocking, and internal filter formation. The deposition mechanism and thus deposition pattern of asphaltene depend on whether the viscous or diffusion/dispersion force is the dominant force in the porous media. The breakthrough time and thus the oil recovery factor is improved in the tilted displacements. In addition, in comparison to horizontal flow, the deposit amount of the asphaltene is decreased by 70.5 and 82.3% at the dip angles of 10 and 20 degree, respectively. Diffusion/dispersion increases the deposit amount of asphaltene, leading to a harsh damage. However, the viscous force may either strengthen or weaken the asphaltene deposition.

Asphaltene precipitation/deposition in reservoir formation has detrimental influences on the oil production. The stability of w/o emulsions, the high viscosity of oil, and unfavorably changing the reservoir rock properties are induced in part by the asphaltene instability. Nanoparticles exhibit acceptable capacities for the adsorption and control of the precipitation of asphaltene. In this study, in-situ synthesis of iron oxide nanoparticles in reservoir oils has been followed to evaluate the effects of the thus-prepared nanoparticles on the control of asphaltene damage in tight carbonate core plugs. Model oil has been prepared by dissolving dead oil in a toluene/gasoil mixture. Following the preparation of stable emulsions of precursor iron salt aqueous solution in the model oil, Fe2O3 nanoparticles have been synthesized at a typical reservoir temperature and high-enough pressure in an autoclave. Two series of core-flooding experiments have been performed by the injection of n-C6 and monitoring the hydrocarbon effective permeability before and after the damage. Two core plugs with the same flow zone index have been selected, one of which has been saturated with the model oil and the other with the emulsion, and the asphaltene damage has been induced by the core flooding test. The results of XRD and FESEM have indicated the crystalline structure and the mean particle size of 65 nm for the in-situ prepared nanoparticles, much smaller than the pore/throat sizes of the plugs. It is found out that the nanoparticles are effective in the control of the asphaltene damage at high injection/production flowrates. However, at low drawdown or injection/production flowrates, the in-situ synthesis procedure leads to a higher drop in the hydrocarbon effective permeability when compared to that observed during the displacement of the virgin model oil. Finally, this may be ascribed to the trapping of aqueous droplets in pore-throats, resulting in a significant reduction in the hydrocarbon permeability by the phase trapping.

In this study, a new approach based on the molecular structure of asphaltene is developed to model asphaltene precipitation by the cubic plus association equation of state (CPA EoS). The accuracy of the proposed approach has been proved by reproducing the experimental data of asphaltene precipitation in two different live oil samples. In this approach, five similar association sites were assigned to the asphaltene molecules. Self-association between the asphaltene molecules and cross-association between the asphaltene and heavy hydrocarbon component were considered. The critical pressure of the heavy component was tuned using a single experimental bubble point pressure of the oils. Results revealed that the approach is able to predict the bubble point curve of the oil samples with the average absolute relative error (AARE) of lower than 1.54%. To model the asphaltene onset point, the cross-association energy between the asphaltene and the heavy component () was considered as the only tuning parameter of the model. It was assumed that the  was temperature-dependent and three different dependency were considered. The results showed that the cross-association energy is inversely proportional to absolute temperature. The CPA EoS reproduces the asphaltene onset point of the oil samples with the AARE of lower than 5.50%. At reservoir temperature, the asphaltene onset pressure for the two reservoir oil samples is 527 and 262 bar which is predicted by the CPA EoS as 502.5 and 250.4 bar respectively. As a conclusion, the proposed approach can not only predict the bubble point pressure but also accurately predict the general trend of asphaltene onset pressure with temperature.