Biot Coefficient Research Articles

Multiple failure state triaxial testing of the Montney Formation

Elastic behaviour controls hydraulic fracture propagation and ultimately, the productivity of unconventional reservoirs. Various index tests and single stage triaxial tests are used to characterize elastic moduli but it can be difficult to obtain enough samples and sufficient information. This is partly due to the fissile nature of shales, which results in a paucity of representative core plugs. It is also partially due to the complex and heterogeneous nature of unconventional reservoir's geomechanical behaviour. The failure mechanics of unconventional rocks are poorly understood and seldom incorporated in hydraulic fracturing or geomechanical models. Yet, failure is major influence on fracture complexity and reservoir drainage volumes.The objectives of this study were to evaluate the variability in geomechanical properties and characterize the post-peak behaviour of a stiff siltstone from the Montney Formation in Alberta, Canada. The multiple failure state triaxial test was used to define the pre-peak elastic behaviour, post-peak behaviour, and failure envelope of a single core plug. This is beneficial for practitioners that are faced with a paucity of samples. The multiple failure state triaxial test is difficult to implement for stiff specimens, which fail in a brittle and unstable manner and a methodology to improve the stability near and beyond sample failure was therefore developed.The results from this study, which were also compared to various index tests and publicly available data, show that the samples had low porosity, low clay, and high stiffness. Significant variability in elastic behaviour was observed due to non-linearities in the loading curve – an effect that overshadowed changes due to confining pressure and highlighted that need for careful consideration of elastic parameter variability. Several oriented samples sets were used to characterize elastic and strength anisotropy. The improved test methodology was able to capture stable post-peak behaviour on almost all the tested samples. Brittle stick-slip failure was observed and an exponential model for approximating post-peak behaviour was presented. The combination of triaxial testing and index testing was able to completely characterize the constitutive law and failure envelope of the samples, save the Biot coefficient. These results can be incorporated into both routine and advanced geomechanical models and hydraulic fracturing simulators.

Dynamic stress distribution around the wellbore influenced by surge/swab pressure

The calculation of dynamic stress distribution around the wellbore under surge/swab pressure is an unsolved issue. The conventional method to calculate wellbore stress is only applicable to the steady state without considering the coupled effect of deformation-diffusion. In this paper, an elastodynamics model and a poroelastodynamics model have been established to overcome these deficiencies. The numerical solution is provided by the implicit finite difference method, and it is verified by the analytical solution achieved from Laplace transform and Crump inversion. Through sensitivity analysis, it shows that the period of the sine function (inner boundary condition), Biot coefficient, hydraulic diffusivity, and rock types could influence the stress distribution. Then the dynamic surge/swab pressure predicted based on Lubinski's method is implemented into these two models. Two field cases with different depths have been analyzed, and it demonstrates that the surge/swab pressure is more significant for a shallow formation because the static formation pressure and in-situ stresses are relatively small. If the tripping velocity is high, the stress distribution will be significantly changed. Finally, the stress calculated by these two models is compared with the stress obtained using the conventional solution. The comparison shows that the poroelastodynamics solution is different from the elastodynamics solution because pore pressure is significant in the poroelastodynamics solution. The poroelastodynamics solution is also significantly distinguishable from the conventional solution, which demonstrates the importance of the poroelastodynamics model. Overall, it fills the gap in calculating dynamic wellbore stress under tripping conditions, which can be applied to wellbore stability analysis and contribute to a reduction in both tripping time and drilling costs.

The correlation between low tectonic stress and the Appalachian Basin Quiet Zone

In order to assess the nature of the Appalachian Basin Quiet Zone (ABQZ), a region of low seismic activity, a minimum horizontal stress profile from sonic logs was calibrated using hydraulic fracture stress measurements in a well from McKean County, PA. The calibrated minimum horizontal stress profile that best fits with the hydraulic fracture stress data was established using an extended Eaton's model that treats rock as a transverse isotropic material with a vertical symmetry axis (TIV). To achieve a best fit, several assumptions are introduced: (1) a constant tectonically-induced elastic strain of εHmax = 3.3 × 10−4, (2) an anisotropic velocity model ANNIE approximation for shales, and (3) a bimodal pore pressure distribution with abnormally high pore pressure in the Marcellus gas shale. Other calibration methods assume an isotropic medium, a constant tectonic strain gradient corresponding to zero stress at ground surface, or constraints from sidewall core data to estimate stiffness constants. By testing four calibration methods, we find that stress profiles are affected by multiple factors, including the ratio of maximum tectonically-induced elastic strain over minimum tectonic strain, pore pressure in the Marcellus, Biot's coefficients, and elastic properties. Sensitivity analysis was conducted to analyze the influence of these parameters. Our stress profile is most influenced by pore pressure and tectonically-induced elastic strain while other factors had much smaller effects. Tectonically-included strain in the ABQZ is insufficient to achieve the critical stress necessary to induce frictional slip on favorably oriented faults in the sedimentary cover which presumably speaks to the lack of earthquakes in the basement of the ABQZ. However, induced earthquakes from deep disposal wells suggest that basement at the edge of the ABQZ may be decoupled from the sedimentary cover, in which case the cover has relaxed through a time-dependent deformation mechanism such as pressure solution creep.

Effective stresses and estimations of the apparent Biot coefficient in stacked clay layers

In materials with nanometric pores, such as clays, confinement effects alter the way the pressure of fluids is transferred to the solid. Even for liquid-saturated porous materials with poorly compressible solid skeleton, this can translate into apparent Biot coefficients (defined as the partial derivative of the stress orthogonal to the clay layer with respect to the bulk pressure of water at fixed volume) of adsorbing materials being higher than 10 or even negative. In this paper, molecular simulations of saturated clay layers are presented. From these simulations, the apparent Biot coefficient is derived as a function of the basal spacing. It is observed that the strains of an infinite stack of clay layers are generically not governed by the Terzaghi effective stress; but apparent Biot coefficients remain in the range 0–1 for stable basal spacings larger than 1·5 nm. For the sake of comparison, results of molecular simulations of a confined Lennard–Jones fluid are also provided. In this case, Biot coefficients vary from a negative value up to more than 15 according to the pore size.

The Biot coefficient for a low permeability heterogeneous limestone

This paper presents the experimental and theoretical developments used to estimate the Biot coefficient for the heterogeneous Cobourg Limestone, which is characterized by its very low permeability. The coefficient forms an important component of the Biot poroelastic model that is used to examine coupled hydro-mechanical and thermo-hydro-mechanical processes in the fluid-saturated Cobourg Limestone. The constraints imposed by both the heterogeneous fabric and its extremely low intact permeability [ $$K \in (10^{-23},10^{-20})~\hbox {m}^{2}$$ ] require the development of alternative approaches to estimate the Biot coefficient. Large specimen bench-scale triaxial tests (150 mm diameter and 300 mm long) that account for the scale of the heterogeneous fabric are complemented by results for the volume fraction-based mineralogical composition derived from XRD measurements. The compressibility of the solid phase is based on theoretical developments proposed in the mechanics of multi-phasic elastic materials. An appeal to the theory of multi-phasic elastic solids is the only feasible approach for examining the compressibility of the solid phase. The presence of a number of mineral species necessitates the use of the theories of Voigt, Reuss and Hill along with the theories proposed by Hashin and Shtrikman for developing bounds for the compressibility of the multi-phasic geologic material composing the skeletal fabric. The analytical estimates for the Biot coefficient for the Cobourg Limestone are compared with results for similar low permeability rocks reported in the literature.

Hydro-mechanical modeling of hydraulic fracture propagation based on embedded discrete fracture model and extended finite element method

In this study, an efficient hydro-mechanical model of hydraulic fracture propagation is proposed using the embedded discrete fracture model in conjunction with the extended finite element method. Fracture is embedded into a common computational grid for both stress and pressure fields. A hybrid scheme of fixed stress split and Picard iterative method is presented to deal with the hydro-mechanical coupling and fracture propagation. The model is verified against other numerical solution of hydro-mechanical coupling problem and analytical solution of fracture propagation available from literature. Numerical results show that as matrix permeability increases, more fracturing fluid is required to get a desired length of fracture. The effect of Biot's coefficient is similar to that of matrix permeability. Finally, the model is extended to simulate simultaneous propagation of multiple hydraulic fractures. It's interesting to find that the effect of stress shadowing could be weakened by the poroelastic stress when accounting for hydro-mechanical coupling. The study indicates that the hydro-mechanical coupling could have significant influence on hydraulic fracturing, especially for multi-cluster fracturing of horizontal wells.

Numerical prediction of in situ horizontal stress evolution in coalbed methane reservoirs by considering both poroelastic and sorption induced strain effects

As an organic-rich dual-porosity medium, coal distinctively manifests unique deformation and permeability evolution behaviors due to the adsorption/desorption induced matrix swelling and/or shrinkage. Being different from the elastic strain, the sorption induced strain shows a non-linear behavior with continuous sorbing gas injections, and these two types of strains are competing process of the volumetric change for coal. With primary gas depletion, the horizontal stress decreases within coalbed methane (CBM) reservoirs due to the in situ boundary confinement, namely, uniaxial strain boundary condition. However, the coal solid skeleton deformative behavior with primary depletion is not specifically clear due to the difficulty both in field and lab measurement of horizontal stress. This paper, based on a gas-solid coupling model incorporated with swelling effect, focuses on the horizontal stress variation with respect to the primary depletion under uniaxial strain condition. It was found the simulated results of volumetric change under the hydrostatic condition well agree with experimental data. The increase of horizontal stress for methane is four times as for helium, with injected pore pressure at 7.6 MPa. Also, the conceptual dual-material model is proposed to demonstrate the competing process of compression and swelling, which leads to the bulk modulus change of coal. It was found the Biot's coefficient can be larger than unity and be a variable during the primary depletion due to the swelling induced equilibrium negative bulk modulus.

Experimental study and micromechanical interpretation of the poroelastic behaviour and permeability of a tight sandstone

This study focuses on the poroelastic behaviour and permeability of tight sandstones, which are characterized by a low porosity, a low gas permeability and a strong sensitivity to in-situ stress. Experimentally the Biot coefficient takes a value close to 1 at low confinement and decreases with increasing confining pressure; the permeability shows an important reduction with increasing confining pressure. This behaviour can be attributed to pore entrapment and to the closure of cracks and joints. Micromechanical models, considering low permeable sandstones as made up of an assemblage of grains with interfaces and pores, reproduce well the observed trends of Biot coefficient and permeability.

Coupled Thermo-Poro-Elastic modeling of near wellbore zone with stress dependent porous material properties

In this study, the Thermo-Poro-Elastic approach was applied to investigate the dynamic shear and tensile failure condition in the near wellbore zone. The necessary data to perform the analysis were collected from literature. To increase the simulation accuracy, the stress dependency of the material properties such as porosity, permeability, bulk density, bulk compressibility, bulk heat capacity, bulk thermal expansivity, bulk thermal conductivity, and Biot's poroelastic coefficient was also considered. The coupled study was conducted with cool, isothermal, and hot wellbore fluid to investigate the temperature influence. The obtained results were compared with the results of the uncoupled static approach. The computations take into account the changes in material properties due to the stress alteration in near wellbore zone. Results revealed that the pore pressure in the near wellbore zone was very sensitive to the wellbore fluid temperature which consequently influences the dynamics stress distribution in the studied near wellbore zone and its stability state. For the first case, when wellbore fluid temperature was lower than the formation temperature, shear strength decreased abruptly at the early time steps and then increased to a steady value, which is equal to the shear failure stress estimated by the uncoupled approach. The estimated tensile strength was high originally and descended to the value estimated by the uncoupled approach at infinity. In the isothermal and hot wellbore fluid cases, an abrupt change occurred in the shear strength; however, for hot wellbore fluid, the shear strength then decreased permanently with a slope depending on the wellbore fluid temperature. At the first step of modeling for all three cases, the initial tensile strength was the same. When formation rock was exposed to a cool wellbore fluid, tensile strength was maximum at initial stages and then decreased to the estimated value by the uncoupled approach. Rising wellbore fluid temperature causes an initial tensile instability shock (decrease in tensile strength) vanishing by time. Based on the results, average principal stress distribution in near wellbore zone intensely alters permeability distribution. The sensitivity of other parameters is less than permeability and can be neglected in further studies.

Laboratory measurement of Biot's coefficient and pore pressure influence on poroelastic rock behaviour

Understanding rock behaviour as a function of pore pressure and confining pressure is crucial for petroleum and geomechanical analysis. Indeed, deformation and local stress variations within hydrocarbon reservoirs and their surroundings occur due to pore pressure changes. Theoretically, pore pressure changes coupled with stress variations in hydrocarbon reservoirs are a function of the Biot’s coefficient, the elastic properties of the rock and the reservoir shape. Thus, in this study, the Biot’s coefficient was measured as a function of porosity, permeability, and volumetric strain for five Gosford sandstone samples. A triaxial loading system was used to measure rock volumetric strain while pore pressure and confining pressure were varied. The constant deformation technique was employed for these experiments; i.e. the variation of pore pressure created a volumetric strain, and the confining pressure required to restore the original volumetric strain was measured to calculate Biot’s coefficient. For the investigated samples, measured liquid permeabilities were in the range of 7–10 mD and Biot’s coefficients were 0.84–0.91. This is consistent with similar investigations by other researchers in which measured Biot’s coefficients were in the range of 0.65–0.90. This study thus illustrates how liquid permeability and the Biot’s coefficient decrease as a function of confining pressure.

Effective stress law for rock masses and its application in impoundment analysis based on deformation reinforcement theory

Reservoir impoundment is related to several hydraulic engineering concerns, including irreversible valley contractions, landslides and reservoir-induced earthquakes. However, these phenomena, such as valley contractions, are hardly to be explained by the conventional method. The scientific understanding of water effects during impoundment and their hazards to hydraulic structure are needed. The effective stress law for fissured rock masses is introduced in the elasto-plastic model employing the Drucker-Prager criterion and implemented in the three dimension (3D) nonlinear finite element method (FEM) program Three-dimensional FINite Element (TFINE). The slope deforms towards river-way during impoundment since the increasing pore pressure in fissures changes stress state and leads to additional plastic deformation in the rock materials. The value of Biot coefficient and the influence of water on rock materials are discussed in detail. Thus, the mechanism of slope deformation during the impoundment of Jinping-I arch dam is revealed, and the deformation is accurately measured. The application of the effective stress law provides a method to consider stress assessment, deformation evaluation and stability estimate of hydraulic structures during the impoundment process. This is a beneficial exploration and an improvement of hydraulic engineering design.

Capturing the two‐way hydromechanical coupling effect on fluid‐driven fracture in a dual‐graph lattice beam model

SummaryFluid‐driven fractures of brittle rock is simulated via a dual‐graph lattice model. The new discrete hydromechanical model incorporates a two‐way coupling mechanism between the discrete element model and the flow network. By adopting an operator‐split algorithm, the coupling model is able to replicate the transient poroelasticity coupling mechanism and the resultant Mandel‐Cryer hydromechanical coupling effect in a discrete mechanics framework. As crack propagation, coalescence and branching are all path‐dependent and irreversible processes, capturing this transient coupling effect is important for capturing the essence of the fluid‐driven fracture in simulations. Injection simulations indicate that the onset and propagation of fractures is highly sensitive to the ratio between the injection rate and the effective permeability. Furthermore, we show that in a permeable rock, the borehole breakdown pressure, the pressure at which fractures start to grow from the borehole, depends on both the given ratio between injection rate and permeability and the Biot coefficient.

A multimethod Global Sensitivity Analysis to aid the calibration of geomechanical models via time-lapse seismic data

Time-lapse seismic attributes are used extensively in the history matching of production simulator models. However, although proven to contain information regarding production induced stress change, it is typically only loosely (i.e. qualitatively) used to calibrate geomechanical models. In this study we conduct a multimethod Global Sensitivity Analysis (GSA) to assess the feasibility and aid the quantitative calibration of geomechanical models via near-offset time-lapse seismic data. Specifically, the calibration of mechanical properties of the overburden. Via the GSA, we analyse the near-offset overburden seismic traveltimes from over 4000 perturbations of a Finite Element (FE) geomechanical model of a typical High Pressure High Temperature (HPHT) reservoir in the North Sea. We find that, out of an initially large set of material properties, the near-offset overburden traveltimes are primarily affected by Young's modulus and the effective stress (i.e. Biot) coefficient. The unexpected significance of the Biot coefficient highlights the importance of modelling fluid flow and pore pressure outside of the reservoir. The FE model is complex and highly nonlinear. Multiple combinations of model parameters can yield equally possible model realizations. Consequently, numerical calibration via a large number of random model perturbations is unfeasible. However, the significant differences in traveltime results suggest that more sophisticated calibration methods could potentially be feasible for finding numerous suitable solutions. The results of the time-varying GSA demonstrate how acquiring multiple vintages of time-lapse seismic data can be advantageous. However, they also suggest that significant overburden near-offset seismic time-shifts, useful for model calibration, may take up to 3 yrs after the start of production to manifest. Due to the nonlinearity of the model behaviour, similar uncertainty in the reservoir mechanical properties appears to influence overburden traveltime to a much greater extent. Therefore, reservoir properties must be known to a suitable degree of accuracy before the calibration of the overburden can be considered.

Finite element simulations of interactions between multiple hydraulic fractures in a poroelastic rock

A fully coupled three-dimensional finite-element model for hydraulic fracturing in permeable rocks is utilised to investigate the interaction between multiple simultaneous and sequential hydraulic fractures. Fractures are modelled as surface discontinuities within a three-dimensional matrix. This model simultaneously accounts for laminar flow within the fracture, Darcy flow within the rock matrix, poroelastic deformation of the rock, and the propagation of fractures using a linear elastic fracture mechanics framework. The leakoff of fracturing fluid into the surrounding rocks is defined as a function of the pressure gradient at the fracture surface, the fluid viscosity, and the matrix permeability. The coupled equations are solved numerically using the finite element method. Quadratic tetrahedral and triangle elements are used for spatial discretisation of volumes and surfaces, respectively. The model is validated against various analytical solutions for plane-strain and penny-shaped hydraulic fractures. Several cases of simultaneous fracturing of multiple hydraulic fractures are simulated in which the effects of the various parameters (the in situ stresses, the distance between fractures, the permeability of the matrix, the Biot poroelastic coefficient, and the number of the fractures in a group) are investigated. The results show that the stress induced by the opening of the fractures, and the stress induced by the fluid leakoff, each have the effect of locally altering the magnitudes and orientations of the principal stresses, hence altering the propagation direction of the fractures. Opening of a fracture induces excessive compression (also known as the “stress shadow”) that causes adjacent fractures to curve away from each other. This excessive compression competes against the differential in situ stresses, which tend to cause the fracture to grow in the plane normal to the minimum in situ stress. The stress shadow effect is reduced by increasing the distance between fractures, and is increased by increasing the leakoff, which may be due to increased permeability of the rock, or an increase in the Biot coefficient.

Thermo-mechanical Properties of Upper Jurassic (Malm) Carbonate Rock Under Drained Conditions

The present study aims to quantify the thermo-mechanical properties of Neuburger Bankkalk limestone, an outcrop analog of the Upper Jurassic carbonate formation (Germany), and to provide a reference for reservoir rock deformation within future enhanced geothermal systems located in the Southern German Molasse Basin. Experiments deriving the drained bulk compressibility C were performed by cycling confining pressure p c between 2 and 50 MPa at a constant pore pressure p p of 0.5 MPa after heating the samples to defined temperatures between 30 and 90 °C. Creep strain was then measured after each loading and unloading stage, and permeability k was obtained after each creep strain measurement. The drained bulk compressibility increased with increasing temperature and decreased with increasing differential pressure p d = p c − p p showing hysteresis between the loading and unloading stages above 30 °C. The apparent values of the indirectly calculated Biot coefficient α ind containing contributions from inelastic deformation displayed the same temperature and pressure dependencies. The permeability k increased immediately after heating and the creep rates were also temperature dependent. It is inferred that the alteration of the void space caused by temperature changes leads to the variation of rock properties measured under isothermal conditions while the load cycles applied under isothermal conditions yield additional changes in pore space microstructure. The experimental results were applied to a geothermal fluid production scenario to constrain drawdown and time-dependent effects on the reservoir, overall, to provide a reference for the hydromechanical behavior of geothermal systems in carbonate, and more specifically, in Upper Jurassic lithologies.

Impact of material properties on caprock stability in [formula omitted] geological storage

In this study, thermo-hydro-mechanical coupled simulations are performed to investigate caprock stability under cooling and pressurization during the injection of carbon dioxide. It is shown that failure potential of caprock increases with a higher value of the material parameter R which is defined as a ratio of material properties (the thermal expansion coefficient and the elastic properties) of caprock and aquifer. The study also underlines that the consideration of the Biot coefficient of the aquifer is essential for properly estimating aquifer examination. The analysis shows that the cooling of caprock is mainly transferred by conduction, and the temperature drops with time t at a rate of erfc12Dt, where the rate increases if caprock has a higher thermal diffusivity D.

Coupled Thermo-hydro-Mechanical Effects on Caprock Stability During Carbon Dioxide Injection

This study presents a numerical investigation of the effects of coupled material properties on the caprock stability. A thermo-hydro-mechanical framework is proposed in order to reproduce the physical processes. The results indicate that for a given geometrical configuration and a given temperature difference between injected CO2 and reservoir, the potential for the caprock failure may increase or decrease. This contradictory behaviour mainly depends on the combination of the thermal-hydro-mechanical parameters, i.e., thermal expansion coefficient, stiffness and the Biot coefficient. Therefore, the coupled effects of material properties on the caprock stability should be addressed in a combined way for low-temperature CO2 injection problems.

Impact of water, nitrogen and CO2 fracturing fluids on fracturing initiation pressure and flow pattern in anisotropic shale reservoirs

Water-based fluids are currently main fracturing fluids but have some unavoidable limitation. Alternative options include nitrogen and CO2 in some new fracturing methods. However, the fracturing mechanism with water, CO2 and nitrogen has not been clear so far. This paper proposes a numerical model to investigate the impact of water, CO2 and nitrogen fluids on fracturing initiation pressure and seepage area of a shale reservoir. First, the governing equations for anisotropic deformation and anisotropic seepage are further extended for bedding shale. Second, a moving seepage boundary is used for fracturing fluid permeation. Third, a fracture initiation criterion is established based on the stress intensity factor of mode I crack. Fourth, a complex parameter is suggested to express the combined effect of shale permeability, fluid viscosity and pressurization rate. This numerical model is then verified with two sets of experimental data and numerical simulations available in literature. Finally, the impacts of the complex parameter, Biot's coefficient, confining pressure, and critical state on fracturing initiation pressure and seepage area are investigated. The permeability evolution during fracturing initiation process is discussed. It is found that this numerical model has the capability to simulate the hydraulic fracturing process with water, CO2 and nitrogen. Complex parameter, Biot's coefficient and confining pressure have significant impacts on fracturing initiation pressure and seepage area. The fracturing initiation pressure decreases with complex parameter and Biot's coefficient but increases with confining pressure regardless of fracturing fluid type. Water has the highest fracturing initiation pressure and the smallest seepage area. These differences are from the change of effective stress in seepage area, particularly nearby the permeation front. CO2 and nitrogen are good alternative fluids for hydraulic fracturing under the same condition of complex parameter, Biot's coefficient and confining pressure because they have lower fracturing initiation pressure and larger seepage area compared to water.

Evolution of permeability and Biot coefficient at high mean stresses in high porosity sandstone

A series of constant mean stress (CMS) and constant shear stress (CSS) tests were performed to investigate the evolution of permeability and Biot coefficient at high mean stresses in a high porosity reservoir analog (Castlegate sandstone). Permeability decreases as expected with increasing mean stress, from about 20 Darcy at the beginning of the tests to between 1.5 and 0.3 Darcy at the end of the tests (mean stresses up to 275MPa). The application of shear stress causes permeability to drop below that of a hydrostatic test at the same mean stress. Results show a nearly constant rate decrease in the Biot coefficient as the mean stress increases during hydrostatic loading, and as the shear stress increases during CMS loading. CSS tests show a stabilization of the Biot coefficient after the application of shear stress.

Stress redistribution and fracture propagation during restimulation of gas shale reservoirs

Restimulation of previously hydraulically-fractured wells can restore productivity to near original levels. Understanding the stress state resulting from the original hydraulic fracturing and subsequent depletion is vital for a successful refracuring treatment. The stress obliquity in the vicinity of the wellbore, due to production from a previously introduced hydraulic fracture, promotes a new concept – that of altered-stress refracuring which allows fractures to propagate into previously unstimulated or understimulated areas and therefore enhancing recovery. In this study, a coupled poromechanical model is used to define stress redistribution and to define optimal refrac timing as defined by maximizing the size of the stress reversal region. Key factors include the time dependency of the stress reorientation, the threshold stress ratio σhmax/σhmin and the influences of permeability anisotropy/heterogeneity, pressure drawdown and rock-fluid properties. The results show that stress reorientation develops immediately as the reservoir begins to produce. This stress reversal region extends to a maximum extent before retreating as the direction of the maximum principal stress gradually returns to the initial state. The optimal refrac timing and the size of the stress reversal region are positively correlated with pressure drawdown and Biot coefficient, negatively correlated with stress ratio σhmax/σhmin ratio and Poisson’s ratio and ambiguously correlated with permeability anisotropy. Permeability magnitude and porosity have no influence on the size of the resulting zone but are negatively and positively correlated to the timing, respectively. Permeability heterogeneity has no influence on the size nor the timing. Coupled fluid flow and damage-mechanics simulations follow fracture propagation under the effect of stress redistribution during refracturing treatments. These results define the evolving path of secondary refracture as it extends perpendicular to the initial hydrofracture and ultimately turns parallel to the hydrofracture as it extends beyond the stress-reversal region. This discrete model confirms the broader findings of the continuum model.