The Experts below are selected from a list of 25305 Experts worldwide ranked by ideXlab platform
S. Rahman - One of the best experts on this subject based on the ideXlab platform.
-
Effect of non-uniform pore pressure fields on hydraulic Fracture propagation
Journal of Petroleum Science and Engineering, 2017Co-Authors: Amin Gholami, Mohammad Ali Aghighi, S. RahmanAbstract:Abstract In elastic materials, it is evident that the path of a propagating Fracture is deflected from its normal course in presence of imperfections of the material or loading conditions. This paper aims at investigating hydraulic Fracture deviation induced by non-uniformity of pore pressure fields with the use of a fully coupled poroelastic model based on the finite element method. The model includes a poroelastic domain in which pressurized hydraulic Fractures are explicitly embedded, thus allowing to realistically model the fluid flow inside the Fracture and to intrinsically consider the fracturing fluid load on the Fracture walls as well as fluid leak-off into the formation. The latter process (fluid leak-off into the formation) controls both the length and the orientation of the Fracture by changing the local pore pressure which in turn leads to a change in magnitude and direction of local principal stresses around the Fracture Tip. An innovative method, Mean Rotation Angle (MRA) is utilised for post-processing of evolving stress data at the vicinity of the Fracture Tip. The MRA predicts the potential growth path of pressurized Fractures. In this paper pore pressure induced Fracture reorientation is studied for a single Fracture as well as closely spaced Fractures. Results of this study indicate that presence of a pore pressure anomaly changes the growth path of a hydraulic Fracture, towards or away from the anomaly. A higher than average pore pressure zone attracts the Fracture while a lower pressure anomaly zone repulses the growing Fracture. The Fracture growth direction depends on the differential pressure and the distance between the anomaly and the Fracture Tip. Also in case of two simultaneously growing transverse Fractures pressurized by injected fluid, it has been observed that the fluid leak-off controls the potential deviation angle of the Fractures through changing the local pore pressure distribution pattern. It is shown that there are three distinct trends for the change of potential deviation angle due to fluid leak-off and that these three trends are linked to three corresponding stages of hydraulic communication between the two Fractures. Furthermore, this study shows that change in matrix permeability, stress anisotropy, Fracture half-length, spacing and the rate of leak-off influence the timing of each of the stages to the extent to which the corresponding stage of hydraulic communication of the two Fractures are affected. This new understanding gives a better insight into the mechanism by which closely spaced hydraulic Fractures interact and help optimize the design of multi-stage hydraulic Fracture treatments.
-
Investigation of Fracture Tip Behaviour in Visco-Elastic/ Visco-Plastic Shale Rocks and Its Effect on Fracture Propagation
All Days, 2015Co-Authors: Huifang Song, Amin Gholami, Gamaliel Bazunu, S. RahmanAbstract:Abstract Most shale plays have to be hydraulically Fractured to acquire commercial production. Shales are typically characterised by varying quantities of clay, carbonate and organic material, therefore each shale type has different deformational properties, which lead to different outcomes with respect to hydraulic Fracture efficiency. Unconsolidated, high clay content or organic rich shales exhibit visco-elastic or visco-plastic behaviour, acoording to many researchers[1–3]. Although the effect of this time-dependent behaviour on Fracture propagation is considerable it has not yet received much attention. The aim of this paper is to address the time-dependent response of shale under hydraulic stimulation, more specifically, to monitor Fracture parameters change and deformation at crack Tip area depending on the lag time between stress and strain. In this paper, an innovative method to analyse time-dependent deformation of material at Fracture Tip and its effect on propagation of hydraulically induced Fractures by incorporating visco-elastic behaviour is presented. To characterise Fracture state, J integral is revised and implemented in the framework of finite element model. The Fracture is treated explicitly with refined mesh around the crack Tip in order to obtain detailed information in static state. During loading condition, visco-elasticity and visco-plasticity is not differentiated for practical purposes. The results show that under a centain hydraulic pressure a crack creeps rapidly and possibly propagates. It is shown that stress intensity factor and revised J integral has a rapid changing gradient at the beginning and becomes stable over time. The crack tends to be wider and shorter in creeping shale. Propagation process is hindered by viscous energy dissipation and successive cohesive force. In simulation the experimental data from US shale plays are used to study Fracture propagation behaviour under viscoelastic behaviour. Results of this study allow industry gain a better understanding of deformational behaviour of shale when fracturing. The know-how derived from this study will assist planning effective stimulation program in the development of shale gas reservoirs.
Itamar Procaccia - One of the best experts on this subject based on the ideXlab platform.
-
Dissipative viscoplastic deformation in dynamic Fracture: Tip blunting and velocity selection.
Physical review letters, 2006Co-Authors: Eran Bouchbinder, Anna Pomyalov, Itamar ProcacciaAbstract:Dynamic Fracture in a wide class of materials reveals a "Fracture energy" Gamma much larger than the expected nominal surface energy due to the formation of two fresh surfaces. Moreover, the Fracture energy depends on the crack velocity, Gamma=Gamma(upsilon). We show that a simple dynamical theory of viscoplasticity coupled to asymptotic pure linear elasticity provides a possible explanation to the above phenomena. The theory predicts Tip blunting characterized by a dynamically determined crack Tip radius of curvature. In addition, we demonstrate velocity selection for cracks in fixed-grip strip geometry accompanied by the identification of Gamma and its velocity dependence.
Dmitry I Garagash - One of the best experts on this subject based on the ideXlab platform.
-
multiscale Tip asymptotics in hydraulic Fracture with leak off
Journal of Fluid Mechanics, 2011Co-Authors: Dmitry I Garagash, Emmanuel M Detournay, Jose AdachiAbstract:This paper is concerned with an analysis of the near-Tip region of a fluid-driven Fracture propagating in a permeable saturated rock. The analysis is carried out by considering the stationary problem of a semi-infinite Fracture moving at constant speed V. Two basic dissipative processes are taken into account: fracturing of the rock and viscous flow in the Fracture, and two fluid balance mechanisms are considered ― leak-off and storage of the fracturing fluid in the Fracture. It is shown that the solution is characterized by a multiscale singular behaviour at the Tip, and that the nature of the dominant singularity depends both on the relative importance of the dissipative processes and on the scale of reference. This solution provides a framework to understand the interaction of representative physical processes near the Fracture Tip, as well as to track the changing nature of the dominant Tip process(es) with the Tip velocity and its impact on the global Fracture response. Furthermore, it gives a universal scaling of the near-Tip processes on the scale of the entire Fracture and sets the foundation for developing efficient numerical algorithms relying on accurate modelling of the Tip region.
-
plane strain propagation of a fluid driven crack in a permeable rock with Fracture toughness
Journal of Engineering Mechanics-asce, 2010Co-Authors: Dmitry I GaragashAbstract:A solution to the problem of a plane-strain fluid-driven crack propagation in elastic permeable rock with resistance to Fracture is presented. The Fracture is driven by injection of an incompressible Newtonian fluid at a constant rate. The solution, restricted to the case of zero lag between the fluid front and the Fracture Tip, evolves from the early-time regime when the fluid flow takes place mostly inside the crack toward the large-time response when most of the injected fluid is leaking from the crack into the surrounding rock. This transition further depends on a time-invariant partitioning between the energy expanded to overcome the rock Fracture toughness and the energy dissipated in the viscous fluid flow in the Fracture. A numerical approach is used to compute the solution for the normalized crack length and crack opening and net-fluid pressure profiles as a function of two dimensionless parameters: the leak-off/storage evolution parameter and the toughness/viscosity number. Relation of this solution to the various available asymptotic solutions is discussed. Obtained mapping of the solution onto the problem parametric space has a potential to simplify the tasks of design, modeling, and data inversion for hydraulic fracturing treatments and laboratory experiments.
David Durban - One of the best experts on this subject based on the ideXlab platform.
-
The Influence of Crack-Face Normal and Shear Stress Loading on Hydraulic Fracture-Tip Singular Plastic Fields
Rock Mechanics and Rock Engineering, 2018Co-Authors: Panos Papanastasiou, David DurbanAbstract:We investigated the singular plastic fields at the crack Tip of a Fracture that is loaded with normal and shear loads due to a viscous flow in a hydraulic fracturing. The level of the expected shear load in comparison with the normal load is examined. The lubrication flow and plastic deformation were decoupled assuming that the relation between applied shear load and normal load follows a linear friction-type relation. This assumption allows to investigate extreme bounds of the solution. Both the applied normal and shear loads are assumed to exhibit singular behavior near the Tip which is consistent at the Fracture surfaces with the plastic singular stress fields that are investigated. The Fractured material is assumed to obey a non-associative Drucker–Prager solid with power law hardening response. The singular values and the corresponding fields were determined over a range of material parameters. For both von Mises material and associative Drucker–Prager material, we found that the level of singularity is given by 1/ n where n is the power coefficient of the hardening relation. This level of singularity is stronger than the HRR value, 1/( n + 1), which has been determined for traction free crack surfaces. We found that the shear loading does not influence the level of singularity but it changes the shape of the developed plastic zones with the emergence of a boundary layer near the Fracture surface. Deviation from material associativity produces consistent small increases in the level of singularity. The near-Tip stress, strain and displacement profiles are illustrated for a few representative cases.
Amin Gholami - One of the best experts on this subject based on the ideXlab platform.
-
Effect of non-uniform pore pressure fields on hydraulic Fracture propagation
Journal of Petroleum Science and Engineering, 2017Co-Authors: Amin Gholami, Mohammad Ali Aghighi, S. RahmanAbstract:Abstract In elastic materials, it is evident that the path of a propagating Fracture is deflected from its normal course in presence of imperfections of the material or loading conditions. This paper aims at investigating hydraulic Fracture deviation induced by non-uniformity of pore pressure fields with the use of a fully coupled poroelastic model based on the finite element method. The model includes a poroelastic domain in which pressurized hydraulic Fractures are explicitly embedded, thus allowing to realistically model the fluid flow inside the Fracture and to intrinsically consider the fracturing fluid load on the Fracture walls as well as fluid leak-off into the formation. The latter process (fluid leak-off into the formation) controls both the length and the orientation of the Fracture by changing the local pore pressure which in turn leads to a change in magnitude and direction of local principal stresses around the Fracture Tip. An innovative method, Mean Rotation Angle (MRA) is utilised for post-processing of evolving stress data at the vicinity of the Fracture Tip. The MRA predicts the potential growth path of pressurized Fractures. In this paper pore pressure induced Fracture reorientation is studied for a single Fracture as well as closely spaced Fractures. Results of this study indicate that presence of a pore pressure anomaly changes the growth path of a hydraulic Fracture, towards or away from the anomaly. A higher than average pore pressure zone attracts the Fracture while a lower pressure anomaly zone repulses the growing Fracture. The Fracture growth direction depends on the differential pressure and the distance between the anomaly and the Fracture Tip. Also in case of two simultaneously growing transverse Fractures pressurized by injected fluid, it has been observed that the fluid leak-off controls the potential deviation angle of the Fractures through changing the local pore pressure distribution pattern. It is shown that there are three distinct trends for the change of potential deviation angle due to fluid leak-off and that these three trends are linked to three corresponding stages of hydraulic communication between the two Fractures. Furthermore, this study shows that change in matrix permeability, stress anisotropy, Fracture half-length, spacing and the rate of leak-off influence the timing of each of the stages to the extent to which the corresponding stage of hydraulic communication of the two Fractures are affected. This new understanding gives a better insight into the mechanism by which closely spaced hydraulic Fractures interact and help optimize the design of multi-stage hydraulic Fracture treatments.
-
Investigation of Fracture Tip Behaviour in Visco-Elastic/ Visco-Plastic Shale Rocks and Its Effect on Fracture Propagation
All Days, 2015Co-Authors: Huifang Song, Amin Gholami, Gamaliel Bazunu, S. RahmanAbstract:Abstract Most shale plays have to be hydraulically Fractured to acquire commercial production. Shales are typically characterised by varying quantities of clay, carbonate and organic material, therefore each shale type has different deformational properties, which lead to different outcomes with respect to hydraulic Fracture efficiency. Unconsolidated, high clay content or organic rich shales exhibit visco-elastic or visco-plastic behaviour, acoording to many researchers[1–3]. Although the effect of this time-dependent behaviour on Fracture propagation is considerable it has not yet received much attention. The aim of this paper is to address the time-dependent response of shale under hydraulic stimulation, more specifically, to monitor Fracture parameters change and deformation at crack Tip area depending on the lag time between stress and strain. In this paper, an innovative method to analyse time-dependent deformation of material at Fracture Tip and its effect on propagation of hydraulically induced Fractures by incorporating visco-elastic behaviour is presented. To characterise Fracture state, J integral is revised and implemented in the framework of finite element model. The Fracture is treated explicitly with refined mesh around the crack Tip in order to obtain detailed information in static state. During loading condition, visco-elasticity and visco-plasticity is not differentiated for practical purposes. The results show that under a centain hydraulic pressure a crack creeps rapidly and possibly propagates. It is shown that stress intensity factor and revised J integral has a rapid changing gradient at the beginning and becomes stable over time. The crack tends to be wider and shorter in creeping shale. Propagation process is hindered by viscous energy dissipation and successive cohesive force. In simulation the experimental data from US shale plays are used to study Fracture propagation behaviour under viscoelastic behaviour. Results of this study allow industry gain a better understanding of deformational behaviour of shale when fracturing. The know-how derived from this study will assist planning effective stimulation program in the development of shale gas reservoirs.
