Numerical modeling of the fluid flow impact of thin baffle laminae in cross bedding (original) (raw)

Fault zone architecture and fluid flow: Insights from field data and numerical modeling

GEOPHYSICAL MONOGRAPH-AMERICAN …, 1999

Fault zones in the upper crust are typically composed of complex fracture networks and discrete zones of comminuted and geochemically altered fault rocks. Determining the patterns and rates of fluid flow in these distinct structural discontinuities is a three-dimensional problem. A series of numerical simulations of fluid flow in a set of three-dimensional discrete fracture network models aids in identifying the primary controlling parameters of fault-related fluid flow, and their interactions, throughout episodic deformation.

Permeability of Fractured Rock: Effect of Fracture Size and Data Uncertainties

Water Resources Research, 1982

Equations are derived for equivalent Darcy permeability of a fracture system that consists of nonextensive fractures having arbitrary orientations with respect to the rock block considered. It is shown that in the case of nonextensive fractures, one cannot proceed to the limiting process where the volume of the bounding rock block can be reduced to an arbitrarily small value. Therefore, the dimensions of the block along with the dimensions of the fractures appear in the equations for the nine components of permeability. This leads to a situation where the equivalent permeability matrix is not only nonsymmetric, but also it does not follow the tensorial rules of axis rotation. This leads to the conclusion that, in the case of nonextensive fractures, the equivalent permeability cannot be defined as a characteristic intrinsic property of the medium as is possible in the case of porous medium or in a fractured medium that has extensive fractures. To analyze the effect of uncertainties in the field data on the estimation of equivalent permeability, a 'second-order' statistical analysis is proposed. The method is quite general and can be used to analyze the propagation of parameter uncertainties in models. A numerical example using preliminary fracture data from the Columbia River basalt in Washington State is presented. The mean and standard deviation of the equivalent permeability of a 5 x 5 m block is estimated. Assuming that each component of the equivalent permeability has log normal distribution, the probability of their assuming values different from the mean is found to be significant. This points out the uncertainty that would be inherent in the flow simulation, if the mean value of permeability is used. INTRODUCTION A geologic medium, for the purpose of describing flow through it, is classified as fractured rock f the major part of the flow occurs through discrete interconnected channels. These channels exist because of the geologic features such as faults, joints, and fractures in the rock. This is in contrast to the porous medium, in which it is not practical to distiniguish between individual pores, and flow can be assumed to occur in a continuum.

Finite element analysis of laminar/turbulent flow in porous and fractured media

1985

LIST OF FIGURES 2.1 The geometry of a single fissure (after Louis, 1969) 2~2 Hydraulic flow regions 2.3 Variation in dimensionless conductivity with hydraulic gradient 3.1 Flow domain for a plane fracture 4.1 Validation of numerical solution against analytical results for laminar and turbulent flow 4.2 Variation of discharge as a function of driving head for a well intersecting a single horizontal fissure 4.3 Head loss along a tapered fissure 4.4 Head versus radial distance from well for unconfined flow in rockfill (iii) 4 20 ' .

Fault zone architecture and permeability structure

Geology, 1996

Fault zone architecture and related permeability structures form primary controls on fluid flow in upper-crustal, brittle fault zones. We develop qualitative and quantitative schemes for evaluating fault-related permeability structures by using results of field investigations, laboratory permeability measurements, and numerical models of flow within and near fault zones. The qualitative scheme compares the percentage of the total fault zone width composed of fault core materials (e.g., anastomosing slip surfaces, clay-rich gouge, cataclasite, and fault breccias) to the percentage of subsidiary damage zone structures (e.g., kinematically related fracture sets, small faults, and veins). A more quantitative scheme is developed to define a set of indices that characterize fault zone architecture and spatial variability. The fault core and damage zone are distinct structural and hydrogeologic units that reflect the material properties and deformation conditions within a fault zone. Whether a fault zone will act as a conduit, barrier, or combined conduit-barrier system is controlled by the relative percentage of fault core and damage zone structures and the inherent variability in grain scale and fracture permeability. This paper outlines a framework for understanding, comparing, and correlating the fluid flow properties of fault zones in various geologic settings.

The impact of fault envelope structure on fluid flow: A screening study using fault facies

AAPG Bulletin, 2011

Structural elements of deformation-band fault zones are implemented as volumetrically expressed building blocks, that is, fault facies, in a series of synthetic reservoir geomodels and simulation models. The models are designed and built to reproduce a predefined range of fault system configuration, sedimentary facies configuration, and fault zone architecture. Using petrophysical properties derived from published field studies, the geomodel realizations are run in a reservoir simulator to monitor reservoir responses to variations in modeling factors. The modeled fault zones act as dual barrier-conduit systems, resulting in simulation models that can capture contrasting waterfront velocities, changes in waterfront geometries, and flow channelizing and bifurcation in the fault envelopes. The simulation models also show the development and sweep efficiency of bypassed oil and poorly swept regions because of the presence of the fault zones. Statistical analysis reveals that the fault facies modeling factors can be ranked according to impact on reservoir responses in the following descending order: fault core thickness, the type of displacement function, sedimentary facies configuration, the fraction of total fault throw accommodated by fault core and damage zones, fault system configuration, and maximum damage zone width. Fault core thickness is the most important factor because it governs the space available for fluid flow in the fault-dip direction. Other modeling factors affect the reservoir responses by controlling

Numerical modelling of the effects of fault slip on fluid flow around extensional faults: Reply

J Struct Geol, 1997

in regions of fractured rock around extensional faults have been modelled using distinct element methods (UDEC code). The basic methodology is described in terms of a simple model of a planar normal fault zone, at the Earth's surface. The model is then modified to simulate deformation at greater depths and to investigate irregularities in fault shape (including dilational and anti-dilational fault jogs). The results obtained show that the deformation of a faulted region resulted in significant variation in fracture dilation (porosity), stress distribution, fluid pressure and fluid flow. The geometry of models and the applied boundary conditions had important effects on deformation and fluid flow. At shallow depth, dilation and fluid flow occurred both in the fault zone and the hangingwall, with little change in the footwall. At greater depth, the higher compressive stresses tended to close all fractures, except within the fault zone where the shear displacements caused local dilation. The presence of anti-dilational bends reduced the dilation and fluid flow in the fault zone, but promoted greater deformation in parts of the hangingwall.

Computational modeling of fluid flow through a fracture in permeable rock

Laminar, single-phase, finite-volume solutions to the Navier-Stokes equations of fluid flow through a fracture within permeable media have been obtained. The fracture geometry was acquired from computed tomography scans of a fracture in Berea sandstone, capturing the small-scale roughness of these natural fluid conduits. First, the roughness of the two-dimensional fracture profiles was analyzed and shown to be similar to Brownian fractal structures. The permeability and tortuosity of each fracture profile was determined from simulations of fluid flow through these geometries with impermeable fracture walls. A surrounding permeable medium, assumed to obey Darcy's Law with permeabilities from 0.2 to 2,000 millidarcies, was then included in the analysis. A series of simulations for flows in fractured permeable rocks was performed, and the results were used to develop a relationship between the flow rate and pressure loss for fractures in porous rocks. The resulting frictionfactor, which accounts for the fracture geometric properties, is similar to the cubic law; it has the potential to be of use in discrete fracture reservoir-scale simulations of fluid flow through highly fractured geologic formations with appreciable matrix permeability. The observed fluid flow from the surrounding permeable medium to the fracture was significant when the resistance within the fracture and the medium were of the same order. An increase in the volumetric flow rate within the fracture profile increased by more than 5% was observed for flows within high permeability-fractured porous media.