4.1 Article

Geomechanical Response of Fractured Reservoirs

Journal

FLUIDS
Volume 3, Issue 4, Pages -

Publisher

MDPI
DOI: 10.3390/fluids3040070

Keywords

fractured reservoirs; thermal-hydro-mechanical (THM) coupled analysis; caprock integrity; fluid injection; cooling

Funding

  1. Iran's Ministry of Science, Research and Technology
  2. ZoDrEx project
  3. ERANET Cofund GEOTHERMICA from the European Commission [731117]
  4. Spanish Ministry of Economy, Industry and Competitiveness (MINECO)
  5. H2020 Societal Challenges Programme [731117] Funding Source: H2020 Societal Challenges Programme

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Geologic carbon storage will most likely be feasible only if carbon dioxide (CO2) is utilized for improved oil recovery (IOR). The majority of carbonate reservoirs that bear hydrocarbons are fractured. Thus, the geomechanical response of the reservoir and caprock to IOR operations is controlled by pre-existing fractures. However, given the complexity of including fractures in numerical models, they are usually neglected and incorporated into an equivalent porous media. In this paper, we perform fully coupled thermo-hydro-mechanical numerical simulations of fluid injection and production into a naturally fractured carbonate reservoir. Simulation results show that fluid pressure propagates through the fractures much faster than the reservoir matrix as a result of their permeability contrast. Nevertheless, pressure diffusion propagates through the matrix blocks within days, reaching equilibrium with the fluid pressure in the fractures. In contrast, the cooling front remains within the fractures because it advances much faster by advection through the fractures than by conduction towards the matrix blocks. Moreover, the total stresses change proportionally to pressure changes and inversely proportional to temperature changes, with the maximum change occurring in the longitudinal direction of the fracture and the minimum in the direction normal to it. We find that shear failure is more likely to occur in the fractures and reservoir matrix that undergo cooling than in the region that is only affected by pressure changes. We also find that stability changes in the caprock are small and its integrity is maintained. We conclude that explicitly including fractures into numerical models permits identifying fracture instability that may be otherwise neglected.

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