Gas Diffusivity in Reservoir-Fluid Systems

Dear Colleagues,

Diffusion is a core transport process that plays a very important role in various disciplines of science and engineering such as chemical engineering, petroleum engineering, biology, ocean engineering, and civil engineering. In particular to petroleum engineering, especially in the oil recovery processes, it may be the dominant process where convective forces are weak or absent (e.g., far in the reservoir, or ahead of the moving fronts) or when direct frontal contact and mixing is not possible. Examples include gas injection in unconventional reservoirs, heavy oil and bitumen recovery, compositional grading, and characterization of materials for various applications. Diffusive mixing may be a relatively slow process as compared to convective mixing and might be ignored for certain cases; however, it might be important in geological timescales. Therefore, the applications of diffusion and the outcome, especially in multiphase and multicomponent systems, become important for a wide spectrum of problems, from large-scale subsurface applications to the design of porous materials for various purposes. For example, in the application of gas injection in unconventional reservoirs for recovery enhancements, it is crucial to understand the mass transfer between gas and the oil in a composite acting as a porous medium to design and evaluate the performance of the recovery processes. Similarly, in heavy oil and bitumen recovery, injected light hydrocarbons can diffuse into the oil beyond the potential fronts and/or convective zones and promote the effectiveness of the displacement process, therefore reducing in situ viscosities, which in turn enhances the oil recovery. In addition, in other processes such as CO₂ sequestration, it is important to know the timescale of CO₂ being trapped in the geological structures, which is governed mainly by the diffusivity of CO₂ in the formation. Further, in gas re-dissolution processes, such as in lighter hydrocarbon systems, aqueous systems, or depleted reservoirs, the diffusivity and solubility control how much gas will be dissolved in oil and/or water and how long it will take to dissolve in the absence of mechanical/convective mixing, as well as the pressure history during the process. Thus, accurate determination of these parameters is essential for understanding and designing these processes.

Generally, diffusion in multiphase, multicomponent, or composite systems is not well understood, especially in terms of real industrial applications. From that point of view, this Special Issue will focus on multicomponent systems and consider the multiscale, multiphysics aspects of the problems. Thus, the topics of interest include but are not limited to the following:

• Application of diffusivity for subsurface processes and implications:
  1. Recovery processes;
  2. Pressure history;
  3. CO₂ sequestration;
  4. Gas storage.
• Experimental processes:
  1. Parameter estimation;
  2. Experimental data and methodologies;
  3. CO₂ and reactive transport.
• Porous material design:
  1. Gas or liquid permeation or penetration in porous materials;
  2. Treatment of porous materials (increasing/decreasing the permeation);
  3. Adsorption, phase behavior, and diffusive transport in unconventional reservoirs.
• Mathematics of diffusion subsurface engineering applications:
  1. Natural gases and oils;
  2. CO₂ dissolution and propagation.

Dr. Birol Dindoruk
Dr. Ram Ratnakar
Guest Editors

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