Aperture modelling for the flow-based determination of fracture-matrix ensemble saturation functions for naturally fractured reservoirs

DFN (fracture-only) and DFM (fracture and rock matrix) modelling is a rapidly growing field. While more and more geometrically realistic models get published, fracture aperture is often treated as single-valued or as set-by-set constant parameter. However, this is incompatible with field observations indicating variable apertures, lognormal or multimodal aperture distributions, and-or partial sealed fractures in naturally fractured hydrocarbon reservoirs. This presentation explores how realistic aperture variations across multiple sets of intersecting fractures can be modelled taking into account geometry (orientation, length versus frequency distributions, abutting relationships), mechanical rock properties, in situ stress, and pore pressure. New algorithms are used to account for fracture dilatation, asperity gliding, asperity crushing, and dissolution-precipitation. They are used in concert to produce physically realistic aperture models. These techniques are already part of a fracture modeling and upscaling workflow that has been applied in the field, and flow simulation highlights the first-order control that the ensuing variable apertures exert on permeability, anisotropy and flow localisation. The key remaining challenge, however, is the modeling of mechanical interactions between fractures and rock fragments. As an important aspect of this, here we address whether far-field-stress-based fracture aperture computations are applicable to rock fragmented by multiple fracture sets

Role of geomechanically grown fractures on dispersive transport in heterogeneous geological formations

A second order in space accurate implicit scheme for time-dependent advection-dispersion equations and a discrete fracture propagation model are employed to model solute transport in porous media.We study the impact of the fractures on mass transport and dispersion. To model flowand transport, pressure and transport equations are integrated using a finite-element, node-centered finite-volume approach. Fracture geometries are incrementally developed from a random distributions of material flaws using an adoptive geomechanical finite-element model that also produces fracture aperture distributions. This quasistatic propagation assumes a linear elastic rock matrix, and crack propagation is governed by a subcritical crack growth failure criterion. Fracture propagation, intersection, and closure are handled geometrically. The flow and transport simulations are separately conducted for a range of fracture densities that are generated by the geomechanical finite-element model. These computations show that the most influential parameters for solute transport in fractured porous media are as follows: fracture density and fracture-matrix flux ratio that is influenced by matrix permeability. Using an equivalent fracture aperture size, computed on the basis of equivalent permeability of the system, we also obtain an acceptable prediction of the macrodispersion of poorly interconnected fracture networks. The results hold for fractures at relatively low density

Effect of supercritical-CO2 interaction time on the alterations in coal pore structure

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