Workflow Integrating Fracture Permeability Characterization and Multiphase Flow Modeling for CO2 Storage and Risk Assessments in Fractured Reservoirs

Abstract:

Ensuring safe and permanent storage of sequestered CO₂in naturally fractured geological media is vital for the success of geologic storage projects. Critical needs exist to develop advanced techniques to characterize and model fluid transport in naturally fractured reservoirs and seals.

We have developed a scale-independent 3-D stochastic fracture permeability characterization workflow that employs multiple discrete fracture network (DFN) realizations. The workflow deploys a multidirectional flux-based upwind weighting scheme that is capable of modeling multiphase flow in highly heterogeneous fractured media. The techniques employed herein show great promise for increasing the accuracy of capacity determinations and the prediction of pressure footprints associated with injected CO₂ plumes.

The proposed workflow has been conducted in a simulation study of flow transport and risk assessment of CO₂ injection into a deep fractured saline formation using geological parameters from Knox Group carbonate and Red Mountain shale rocks in central Alabama. A 3-D fracture permeability map was generated from multiple realizations of DFN models. A multiphase flow model composed of supercritical CO₂ and saline water was applied to simulate CO₂ plume evolution during and after injection. Injection simulation reveals significant permeability anisotropy that favors development of northeast-elongate CO₂ plumes. The spreading front of the CO₂ plume shows strong viscous fingering effects. Post-injection simulation indicates significant lateral spreading of CO₂ near the top of the fractured formations because of the buoyancy of injectate in rock matrix and strata-bound vertical fractures. Risk assessment shows that although pressure drops faster in the fractured formations than in those lacking fractures, lateral movement of CO₂ along natural fractures necessitates that the injectate be confined by widespread seals with high integrity.