Assessment of CO₂ Storage Potential in Naturally Fractured Reservoirs With Dual‐Porosity Models

Abstract

Naturally Fractured Reservoirs (NFR's) have received little attention as potential CO2 storage sites. Two main facts deter from storage projects in fractured reservoirs: (1) CO2 tends to be nonwetting in target formations and capillary forces will keep CO2 in the fractures, which typically have low pore volume; and (2) the high conductivity of the fractures may lead to increased spatial spreading of the CO2 plume. Numerical simulations are a powerful tool to understand the physics behind brine‐CO2 flow in NFR's. Dual‐porosity models are typically used to simulate multiphase flow in fractured formations. However, existing dual‐porosity models are based on crude approximations of the matrix‐fracture fluid transfer processes and often fail to capture the dynamics of fluid exchange accurately. Therefore, more accurate transfer functions are needed in order to evaluate the CO2 transfer to the matrix. This work presents an assessment of CO2 storage potential in NFR's using dual‐porosity models. We investigate the impact of a system of fractures on storage in a saline aquifer, by analyzing the time scales of brine drainage by CO2 in the matrix blocks and the maximum CO2 that can be stored in the rock matrix. A new model to estimate drainage time scales is developed and used in a transfer function for dual‐porosity simulations. We then analyze how injection rates should be limited in order to avoid early spill of CO2 (lost control of the plume) on a conceptual anticline model. Numerical simulations on the anticline show that naturally fractured reservoirs may be used to store CO2.

The effect of natural fractures on CO2storage performance and oil recovery from CO2and WAG injection in an Appalachian basin reservoir

“…The dual continuum model is the most common method to evaluate different aspects of fluid transport in fractured reservoirs due to its computational efficiency 11,111–113 . In discrete fracture modeling, fracture networks are presented explicitly as discrete features to represent fractured medium.…”

Transport properties of saline CO2 storage reservoirs with unconnected fractures from brine-CO2 flow-through tests

“…Interconnected fracture networks may act as path-flow in low permeability formations (Nooraiepour et al, 2018). In principle, the high hydraulic conductivity of the fractures would lead to preferential path-flows for CO 2 , diminishing the storage effectivity in the rock matrix and hampering the CO 2 migration control (March et al, 2018). However, when a high density of non-connected fractures exists in the reservoir, their effect on the hydrodynamic behaviour of CO 2 storage systems is unclear, and yet to be investigated.…”

Fluid Flow Characterization Framework for Naturally Fractured Reservoirs Using Small-Scale Fully Explicit Models

“…Naturally fractured reservoirs are often encountered in the exploitation of geothermal energy, hydrocarbon extraction, management of groundwater resources and carbon sequestration (Berkowitz 2002;Bonnet et al 2001;Singhal and Gupta 2010;March et al 2018). In all these applications, the transport of fluids is involved.…”

“…Depending on the purpose of the final upscaled model, various simulation studies can be designed. For example, in carbon sequestration, March et al (2018) highlighted the importance of designing CO 2 injection rates to avoid early spill-a phenomenon where CO 2 flows quickly through the fracture network with minimal displacement of brine in the matrix. Small-scale DFM models can then be used to investigate the sensitivity of CO 2 sequestration to injection rate.…”