A modeling approach for analysis of coupled multiphase fluid flow, heat transfer, and deformation in fractured porous rock

This paper provides a review of hydromechanical (HM) couplings in fractured rock, with special emphasis on HM interactions as a result of, or directly connected with human activities. In the early 1960s, the coupling between hydraulic and mechanical processes in fractured rock started to receive wide attention. A series of events including dam failures, landslides, and injection-induced earthquakes were believed to result from HM interaction. Moreover, the advent of the computer technology in the 1970s made possible the integration of nonlinear processes such as stress–permeability coupling and rock mass failure into coupled HM analysis. Coupled HM analysis is currently being applied to many geological engineering practices. One key parameter in such analyses is a good estimate of the relationship between stress and permeability. Based on available laboratory and field data, it was found that the permeability of fractured rock masses tends to be most sensitive to stress changes at shallow depth (low stress) and in areas of low in-situ permeability. In highly permeable, fractured rock sections, fluid flow may take place in clusters of connected fractures which are locked open as a result of previous shear dislocation or partial cementation of hard mineral filling. Such locked-open fractures tend to be relatively insensitive to stress and may therefore be conductive at great depths. Because of the great variability of HM properties in fractured rock, and the difficulties in using laboratory data for deriving in-situ material properties, the HM properties of fractured rock masses are best characterized in situ.

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The role of hydromechanical coupling in fractured rock engineering

Modelling permeability for coal reservoirs: A review of analytical models and testing data

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Development of an Efficient Embedded Discrete Fracture Model for 3D Compositional Reservoir Simulation in Fractured Reservoirs

Interactions of multiple processes during CBM extraction: A critical review

The purpose of this study is to examine Biot`s two-phase (fluid and rock), isothermal, linear poroelastic theory from the conventional porous fluid-flow modeling point of view Not`s theory and the published applications are oriented more toward rock mechanics than fluid flow Our goal is to preserve the commonly used systematic porous fluid-flow modeling and include geomechanics as an additional module By developing such an approach, complex reservoir situations involving geomechanical issues (eg, naturally fractured reservoirs, stress-sensitive reservoirs) can be pursued more systematically and easily We show how the conventional fluid-flow formulations is extended to a coupled fluid-flow-geomechanics model Consistent interpretation of various rock compressibilities and the effective stress law are shown to be critical in achieving the coupling The {open_quotes}total (or system) compressibility{close_quotes} commonly used in reservoir engineering is shown to be a function of boundary conditions Under the simplest case (isotropic homogeneous material properties), the fluid pressure satisfies a fourth-order equation instead of the conventional second-order diffusion equation Limiting cases include nondeformable, incompressible fluid and solid, and constant mean normal stress are analyzed

Coupled fluid flow and geomechanics in reservoir study. I. Theory and governing equations

The purpose of this study is to formulate a coupled fluid-flow/geomechanics model of a naturally fractured reservoir. Fluid flow is modeled within the context of dual-porosity (more generally, overlapping-continuum) concept while geomechanics is modeled following Biot's isothermal, linear poroelastic theory. The development follows along the line of the conventional and existing porous fluid-flow modeling. The commonly used systematic fluid-flow modeling is therefore preserved. We show how the conventional fluid-flow dual-porosity formulations are extended to a coupled fluid-flow/geomechanics model. Interpretation of the pore volumetric changes of the dual continua, fractures and matrix-blocks, and the associated effective stress laws are the most difficult and critical coupling considerations. New relations describing the dual rock volumetric changes are presented. These relations allow a smooth and consistent transition between single-porosity and dual-porosity concepts and are in terms of measurable quantities. Reduction to the single-porosity is presented to demonstrate the conceptual consistency of the proposed model.

Coupling Fluid-Flow and Geomechanics in Dual-Porosity Modeling of Naturally Fractured Reservoirs

The influence of production-induced changes in reservoir stress state on compressibility and permeability of weakly cemented sandstones has been analyzed. Laboratory experiments simulating reservoir depletion have been conducted for the full range of stress paths that a reservoir may follow. Samples were loaded by reducing the pore pressure and controlling the confining pressure according to the desired stress path from initial reservoir conditions. The results show that compressibility of weakly cemented sandstones are stress path dependent. Compressibilities measured under uniaxial strain conditions, or a stress path with a K value lower than the one associated with uniaxial strain, are more than twice the corresponding value found under hydrostatic loading conditions. In contrast, matrix permeability measured in the maximum stress direction show no significant stress path dependence. Independently of stress path, the observed permeability reductions fall within the general trend expected for a sedimentary rock of relatively high initial permeability. A significant permeability decrease was only observed as the shear stress exceeded the yield limit of the rock, probably due to both mobilization of fine arains and an increase in tortuosity due to collapse of pore space. Results of this study suggest that stress path dependent properties of weakly cemented sandstonesmore » is a consequence of the heterogeneous nature of the sedimentary rock. Material properties are affected by grain-scale inelastic deformation processes and the pattern of these deformation processes is primarily controlled by reservoir stress path.« less

Lawrence W. Teufel

Papers

Coupled fluid flow and geomechanics in reservoir study. I. Theory and governing equations

Coupling Fluid-Flow and Geomechanics in Dual-Porosity Modeling of Naturally Fractured Reservoirs

Influence of Reservoir Stress Path on Deformation and Permeability of Weakly Cemented Sandstone Reservoirs

Numerical Simulation of the Impact of Flow-Induced Geomechanical Response on the Productivity of Stress-Sensitive Reservoirs

The Effect of Geological and Geomechanical Parameters on Reservoir Stress Path and Its Importance in Studying Permeability Anisotropy