Abstract

Simulation of naturally fractured reservoirs is a challenging task. First of all, due to complexity of the geological structure and the structure of the pore space. Anisotropy of fluid flows and difficulty in assessing the recoverable reserves are results of the complex structure.

Naturally fractured reservoirs can be classified into five types according to capacitive and conductive properties of fracture network and porous matrix blocks.

  1. Reservoirs, in which capacitive and conductive properties predominate in the fractured medium.

  2. Reservoirs, in which the capacitive properties predominate in the matrix medium, and the conductive properties predominate in the fractured medium.

  3. Reservoirs, in which the capacitive properties predominate in the matrix medium, and the conductive properties are strong enough in both the fractured and matrix medium.

  4. Reservoirs, in which the capacitive properties predominate in the matrix medium, but at the same time the pore volume of the fractured medium also has a significant influence on the reserves, usually due to the cavernous nature of the fractured medium. The conducting properties in such reservoirs are strong enough in both the fractured and matrix medium.

  5. Reservoirs, in which only the matrix medium has the capacitive and conductive properties, and fractures act as barriers.

The first two types of reservoirs are modeled by dual-porosity model. The third and fourth types are modeled by dual-permeability model. And the fifth type can be represented by the single-porosity model with features, description of which is beyond the scope of this article.

In this paper, on the basis of literature review and personal experience description of dual-porosity/ dual-permeability models are given. The filtration equations of dual-porosity / dual-permeability model and the description of the mechanisms of flow between the pore medium and the fractured medium are presented.

The sensitivity analysis was carried out. It demonstrated that the effective permeability of the fractured medium depends on the absolute permeability of the pore medium in numerical simulation.

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