Abstract

Asphaltene deposition is one aspect of the serious causes decreasing the production capacity, and a common phenomenon during CO2 flooding in ultra-low permeability reservoirs. Prior to asphaltene deposition, the asphaltene first precipitates from the crude oil. It is urgent to find out the asphaltene precipitation and deposition mechanisms, influencing factors and distribution characteristics.

Laboratory experiments and numerical simulations were conducted to study the asphaltene precipitation and deposition influencing factors and adverse effects. Visible microscope detection experiment and static PVT cell experiment were employed to qualitatively and quantitatively investigate the asphaltene precipitation under the influence of pressure, temperature and asphaltene content respectively. Core flooding experiments were designed to study the adverse effects of asphaltene deposition on porous medium porosity and permeability under different pressure, temperature and asphaltene content. Models describing asphaltene precipitation and deposition were built up and validated by experimental data. The asphaltene deposition characteristic was studied using a permeability heterogeneity conception model with five-point injection pattern under different pressure.

The results obtained by experimental studies indicate that the amount of asphaltene precipitation increases as the pressure rises to minimum miscibility pressure (MMP) and then decreases slowly. The increased temperature and asphaltene content result in the increased asphaltene precipitation. The adverse effects caused by asphaltene deposition on porosity and permeability have the same change trend as asphaltene precipitation under the influence of pressure, temperature and asphaltene content. The simulation results show that asphaltene deposition characteristics are mainly influenced by pressure, oil composition change and permeability heterogeneity.

The asphaltene precipitation mechanisms and asphaltene deposition adverse effects and distribution characteristics investigated in this research are encouraging. They can propose efficient and referable solutions about reducing formation damage and maintaining well productivity during CO2 flooding.

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