Hydraulic Fracture Propagation Model Research Articles

The range of influence of the poroelastic effects in terms of dimensionless complexes for the radial hydraulic fracturing model

In our previous work the fully coupled model of the planar hydraulic fracture propagation in a poroelastic medium was developed. In present paper we simplify this model to the case of axisymmetric fracture propagation in order to find the conditions whereby the poroelastic effects are essential. We consider two dimensionless complexes responsible for the transition from 1D to 3D filtration and for the poroelastic influence on the fracture geometry. Analyzing a large set of case studies, we find the critical values for these parameters below which the aforementioned physical effects are not important. Particularly, we demonstrate that 1D pressure diffusion is preserved until the diffusion length scale is 2.4 times smaller than the fracture size. In turn, the diffusion scale plays a central role in the poroelastic stress influence on the fracture propagation. Also, we show that in case of low closure stress the pressure diffusion is dominated not by the filtration process but by the rock deformation with a slight impact on the fracture geometry.We believe that this study will become useful for the appropriate model selection in engineering practice.

A 3-D hydraulic fracture propagation model applied for shale gas reservoirs with multiple bedding planes

Rock layering, a critical factor in determining fracture height growth, is pervasive in Longmaxi shale formation in the southwest of China. This formation has characteristics of large burial depth, low porosity and multiple bedding layers that hamper reaching the target fracture height even after increasing the pumping rate and treatment size. Hence, it becomes much significant to develop a fracture propagation model considering the effect of bedding layers on fracture height growth. This paper introduces a coupled 3-D hydraulic fracture propagation model and investigates the influence of shear displacement discontinuities along bedding planes on fracture height growth. Our model addresses rock deformation and fluid flow. Rock deformation is governed by a fully three-dimensional displacement discontinuity method (3D DDM). The fluid flow model employs a finite difference method (FDM) being able to capture fluid movement along vertical fractures and bedding planes. Additionally, a propagation criteria determines whether the fracture would penetrate bedding planes. In this paper, we selected two different fracture geometries and analyzed profiles of fracture width, pressure and two types of shear displacement discontinuities. From numerical investigations, we found that the maximum width can be obtained at the junction after the vertical fracture penetrated the bedding planes as a result of the decrement of the compressive stress acting on the bedding planes. As the fracture penetrates the bedding planes, a certain amount of fluid would leak into the planes, which leads to fracture height containment. Moreover, the slope utilized for characterizing the correlation between leak-off volume and fracture height, is regarded as a tool to identify the number of BPs that fracture penetrates through. This paper illustrates the potential application of our 3-D fracture propagation model for Longmaxi shale formation with multiple bedding layers. Shear displacements along bedding planes are regarded as a primary mechanism of fracture height containment.

Performance evaluation of synthetic and natural polymers in nitrogen foam-based fracturing fluids in the Cooper Basin, South Australia

Hydraulic fracturing is a well-known stimulation technique for creating fractures in a subsurface formation to achieve profitable production rates in low-permeability reservoirs. Slickwater has been widely used as a traditional fracturing fluid. However, it has multiple disadvantages, such as high consumption of water, clay swelling and low flowback recovery. Foam, as an alternative fracturing fluid, consumes less liquid and provides additional energy. However, foam bubbles are typically unstable due to the degradation of surfactants, particularly in high temperature reservoirs, which reduces their capabilities of carrying and placing proppants into fractures. The purpose of this study is to provide general guidelines for an optimised application of polymers to improve the foam stability in high temperature reservoirs while increasing the proppant placement and water usage efficiencies. In this paper, the effects of natural hydroxypropyl guar (HPG) and synthetic polyacrylamide (PAM) polymers on the rheological properties of nitrogen foam-based fluids were examined by laboratory experiments conducted using temperatures up to 110°C. Then, a 3D hydraulic fracture propagation model was developed to study the fracturing performance of HPG-foamed and PAM-foamed fluids in the Toolachee Formation, Cooper Basin. It was found that synthetic PAM polymers were more effective than natural HPG polymers in stabilising foam viscosity under high temperature conditions. The simulation results indicate that foam-based fluids totally outperform slickwater in the field case application. This paper emphasises the significance of crosslinkers, foam quality and thermal stability on the performance of foams in high temperature environments.

Numerical simulation of multistage fracturing optimization and application in coalbed methane horizontal wells

Multistage fracturing technology is critical to coalbed methane (CBM) production from horizontal wells. Further, optimizing the fracture parameters has a crucial influence on the stimulated reservoir volume and gas production. To investigate fracture parameter optimization, a stress interference model, hydraulic fracture propagation model, and a CBM productivity model are proposed. The effects of crack length and spacing for one to three fractures on the induced stress are calculated by implementing a static analysis MATLAB-developed program. The extended finite-element method is used to study the mechanism of simultaneous fracturing and sequential fracturing. In addition, the influences of cluster spacing and stage spacing on the stress field, formation pressure, fracture geometry, gas production, and reservoir pressure drop are comprehensively investigated by using Abaqus and COMET3 software. The simulation results indicate that with multiple fractures, fracture spacing of 80 m and fracture length of 160 m are conducive for dilating the secondary fracture system and producing a broader contact area in the coal seam. Moreover, an optimal cluster spacing of 15 m, a fracture interval of 80 m, and two cluster numbers per stage are better at forming a uniform fracture geometry with low injection pressure; within a given horizontal well section length of 500 m, fracture parameters with cluster spacing of 30 m, fracture spacing of 80 m, and two clusters per stage offer the best production performance. The simulation results are applied in well TP-07, and microseismic monitoring was conducted to monitor fracture propagation. The microseismic monitoring results are consistent with the numerical simulation.

Development of Proxy Model for Hydraulic Fracturing and Seismic Wave Propagation Processes

Characterization of discrete fracture networks is necessary for unconventional reservoir development, as they control the flow of fluids toward the hydraulically fractured well. Interpretation of microseismic data provides information about the discrete fracture network in the vicinity of a well. While microseismic interpretation is currently based on plotting the swarm of microseismic events, the inference of fracture-related information from such data is likely to be non-unique. To address this non-uniqueness, the presented workflow involves applying a forward model that produces a synthetic seismogram corresponding to a suite of natural fractured reservoir models. The characteristics of the generated seismograms can be compared with the observed seismogram to determine the suite of fracture models that best reflect the observed seismic signature. The available full physics models are computationally expensive and cannot be applied within this framework. Hence, a proxy model is developed that is computationally inexpensive so that it can be applied on a large ensemble of models within the Bayesian model selection framework described above. Seismic wave propagation during a fracturing job involves many intermediate processes such as diffraction and reflection. As analytical solutions for most of these processes exist, a coupled analytical model is proposed. Firstly, a hydraulic fracture propagation model is coupled with a model for the interaction between a hydraulic fracture and a natural fracture. This interaction results in slip events along natural fractures that in turn can trigger a seismic event. With knowledge of the location of the slip event, a Green’s function solution is applied to model the propagation of the seismic wave. Using the results from the slip event and Green’s function, a synthetic seismogram is generated. Finally, the seismic signature from multiple slip events along several natural fractures is combined. Validation of individual elements of the coupled proxy model to experiments is shown. A comparison of the developed proxy model with more computationally expensive models is also performed.

Postfracturing permeability prediction for CBM well with the analysis of fracturing pressure decline

AbstractHydraulic fracturing is a widely used reservoir stimulation technique to exploit CBM in China. Compared with the original permeability of coal reservoir, the postfracturing permeability is more critical for the productivity evaluation of CBM wells. Based on hydraulic fracturing, microseismics monitoring, and well test data of the CBM wells in Zhengzhuang block of Qinshui Basin, this paper proposes a simple method to obtain the fitting pressure by the classic fracturing pressure decline analysis theory under the condition of corrected dynamic overall leakoff coefficient. In addition, the postfracturing permeability of coal reservoir is predicted by the injection well testing theory. The morphology of hydraulic fractures in the study area is mainly determined by in‐situ stress, and most fractures are vertical ones propagating along the direction of the maximum principal stress. The fracturing curves of the study area can be classified into stable curves, stably fluctuating curves, descending curves, ascending curves, and fluctuating curves, where the stable and descending fracturing curves represent better fracturing effect. The length of hydraulic fractures is much greater than the height. The PKN model has been selected as the hydraulic fracture propagation model to analyze the fracturing pressure decline. The slope value of liner segment of G(δ,0) curve is proposed as the criterion for the fitting pressure calculation. The postfracturing permeabilities of coal reservoir range from 1.55 to 8.83 × 10−3 μm2, all of which are remarkably higher than that of the original reservoir.

Investigation of Rupture and Slip Mechanisms of Hydraulic Fractures in Multiple-Layered Formations

SummaryWeak bedding planes (BPs) that exist in many tight oil formations and shale–gas formations might strongly affect fracture–height growth during hydraulic–fracturing treatment. Few of the hydraulic–fracture–propagation models developed for unconventional reservoirs are capable of quantitatively estimating the fracture–height containment or predicting the fracture geometry under the influence of multiple BPs. In this paper, we introduce a coupled 3D hydraulic–fracture–propagation model considering the effects of BPs. In this model, a fully 3D displacement–discontinuity method (3D DDM) is used to model the rock deformation. The advantage of this approach is that it addresses both the mechanical interaction between hydraulic fractures and weak BPs in 3D space and the physical mechanism of slippage along weak BPs. Fluid flow governed by a finite–difference methodology considers the flow in both vertical fractures and opening BPs. An iterative algorithm is used to couple fluid flow and rock deformation. Comparison between the developed model and the Perkins–Kern–Nordgren (PKN) model showed good agreement.I–shaped fracture geometry and crossing–shaped fracture geometry were analyzed in this paper. From numerical investigations, we found that BPs cannot be opened if the difference between overburden stress and minimum horizontal stress is large and only shear displacements exist along the BPs, which damage the planes and thus greatly amplify their hydraulic conductivity. Moreover, sensitivity studies investigate the impact on fracture propagation of parameters such as pumping rate (PR), fluid viscosity, and Young's modulus (YM). We investigated the fracture width near the junction between a vertical fracture and the BPs, the latter including the tensile opening of BPs and shear–displacement discontinuities (SDDs) along them. SDDs along BPs increase at the beginning and then decrease at a distance from the junction. The width near the junctions, the opening of BPs, and SDDs along the planes are directly proportional to PR. Because viscosity increases, the width at a junction increases as do the SDDs. YM greatly influences the opening of BPs at a junction and the SDDs along the BPs. This model estimates the fracture–width distribution and the SDDs along the BPs near junctions between the fracture tip and BPs and enables the assessment of the PR required to ensure that the fracture width at junctions and along intersected BPs is sufficient for proppant transport.

Investigation of multiple hydraulic fractures evolution and well performance in lacustrine shale oil reservoirs considering stress heterogeneity

Giant Ordos basin, which locating in the northern China, consists of Palaeozoic lacustrine stacked sandstone and shale deposits with characteristics of low-permeability matrix rock and less-developed natural fractures (NFs). Recognizing the successful exploration of shale gas reservoirs in United States, Changqing oilfield uses advanced fracturing technology to create multiple straight hydraulic fractures (HFs) in shale oil zones with large differential horizontal stress. This paper firstly describes a hydraulic fracture propagation model (HFPM) that couples fracture deformation and fluid flow to simulate the growth of multiple HFs in the horizontal wellbore. We then integrated an embedded discrete fracture model (EDFM) and commercial reservoir simulator to analyze well performance based on the provided data from Changqing oilfield. We calibrated the fracture propagation model with reservoir performance data. Shale oil deposits in the Changqing oilfield have a relatively high brittleness index (BI) and large differential horizontal stress. This is the reason why reservoir with less-developed NFs system in the Ordos basin has less opportunity of generating complex fracture networks. Large-scale physical simulation experiments were conducted to validate the possibility of fracture networks generation. Our model considers the stress heterogeneity and offers the capability to address HF propagation in the presence of less-developed NFs and adjusts dimensions and spacing of NFs to achieve a history match with production data. This paper emphasizes the extensive application of an integrated model for lacustrine shale oil deposits. Considering features of Ordos basin, our model can provide a guideline for HF treatment design and optimization of well performance.

Adapting the explicit time integration scheme for modeling of the hydraulic fracturing within the Planar3D approach

This work is devoted to the model of hydraulic fracture propagation in a layered medium based on the Planar3D approach. The key features of the proposed model are to reduce the system of partial differential equations to a dynamic system, as well as apply universal asymptotes for determining the position of the crack front. We compare calculations with published results of ILSA and EP3D models and discuss methods for accelerating calculations and the possibility of taking into account additional effects (proppant transfer, elastic modulus contrast).

Hydro-mechanical modeling of hydraulic fracture propagation and its interactions with frictional natural fractures

Hydraulic fracturing is a key technique to activate natural fracture networks aiming at increasing permeability of non-conventional reservoirs. In order to design effective stimulations, it is necessary a good understanding of the hydraulic fracture propagation and its interaction with natural fractures. A robust methodology was developed using the finite element method to study the mechanisms that influence the activation of natural fractures and the subsequent process of hydraulic fracture propagation. An innovated mesh fragmentation technic is developed to simulate hydraulic fracture propagation with arbitrary paths. The behavior of the hydraulic fracture is modeled using hydromechanical cohesive interface elements with progressive damage model. The Mohr-Coulomb criterion with tension cutoff is incorporated to represent the frictional behavior of natural fractures. The developed methodology is validated through literature data on experimental test results. The three main possibilities of interaction events (opening, crossing and arrest) are predicted accurately. Subsequently, the effect of some primary parameters such as the angle of approach between hydraulic and natural fracture, the stress ratio between minimum and maximum horizontal stresses and the internal friction angle of the natural fracture were studied to provide a better insight of the propagation processes of the hydraulic fracture. An interaction response diagram is proposed combining the effects of those parameters to provide a good estimative of fracture interaction.

Numerical evaluation of shear and tensile stimulation volumes based on natural fracture failure mechanism in tight and shale reservoirs

Although many scholars have put forward the methods and models to predict the stimulated reservoir volume (SRV), the mathematical models do not reflect well the mechanism of SRV development. In addition, the effects of relative fracture treatment and reservoir parameters on different stimulation areas are not well understood. During the process of hydraulic fracture propagation, fracturing fluid leak-off from the main fracture due to the activation of natural fractures can elevate the reservoir pore pressure, resulting in shear slippage and tensile failure of the natural fractures and, finally, in microseismic events. Different stimulation regions, including tensile failure zone, shear failure zone, and swept region, may co-exist along the activated natural fracture. In this study, a new mathematical model was presented based on the shear slippage and tensile failure criterion of weakness plane, hydraulic fracture propagation model, mechanical conditions of natural fracture activation, fluid diffusivity equation, and using a shear dilation model to characterize the reservoir permeability variation after shear slippage of the natural fractures, so as to better describe the growth of SRV. The model was also verified by matching field microseismic monitoring data. Then, the effects of azimuth angle and horizontal principal stress difference on the shear and tensile failure pressure of natural fractures, permeability enhancement, and critical net pressure of main fracture to activate natural fractures were illustrated. The impacts of treatment fluid viscosity, natural fracture azimuth angle, and horizontal stress difference on the reservoir pore pressure, SRV shape distribution, different SRV sizes, and SRV bandwidth and length were also analyzed. The results indicated that increasing the horizontal stress difference decreased the tensile failure area but increased the shear slippage zone sharply. Both shear and tensile failure regions decreased on increasing the natural fracture azimuth angle from 30° to 50°. Increasing the fluid viscosity from 1 to 10 mPa·s expanded the size of the tensile failure zone but reduced the shear slip zone.

Numerical simulation of hydraulic fracture propagation in deep reservior

To investigate the large-scale yielding of rock in the process of the hydraulic fracturing in deep reservoir, the mathematical model of elasto-plastic hydraulic fracture propagation was established. Rock deformation was modeled with the Drucker-Prager yield criterion with associative flow rule. Fluid flow in the fracture was modeled by the lubrication theory. The cohesive zone model was used as the fracture propagation criterion. The problem was modeled numerically with the finite element method to obtain the solution. The correctness of mathematical model and algorithm were verified by comParing its results with the classic model. Research results showed that the created elasto-plastic hydraulic fracture was much shorter and wider than the elastic hydraulic fracture of the same volume of injecting fluid, and higher pressure was needed to propagate an elasto-plastic hydraulic fracture than an elastic hydraulic fracture. Elasto-plastic hydraulic fracture remained open after the applied load was released as a result of the presence of plastic strain. With the increase of the friction angle of the rock, the width of the elasto-plastic hydraulic fractures decreased and the required fluid pressure increased. The hydraulic fracture in the hardened rock was narrower than that in the ideal elasto-plastic rock, and higher pressure was needed to propagate a hydraulic fracture in the hardened rock than in the ideal elasto-plastic rock.

Numerical simulation of elasto-plastic hydraulic fracture propagation in deep reservoir coupled with temperature field

With the increasing demand of oil and gas resource, the development of deep reservoir has become an inevitable trend. To investigate the coupled effects of rock elasto-plastic deformation, fluid flow and heat transfer in the process of hydraulic fracturing of deep reservoir, the mathematical model of elasto-plastic hydraulic fracture propagation is established based on cohesive zone model (CZM) and embedded discrete fracture model (EDFM). The constitutive equation incorporating thermal stress is derived by using Drucker-Prager yield condition and the associated flow law. Fluid flow in the fracture is modeled with lubrication theory. The thermal non-equilibrium theory is employed to describe the heat exchange between rock matrix and fluid in the fracture based on EDFM. The CZM is used as fracture propagation criterion. The rock deformation equation is solved by finite element method. The temperature field and fluid flow in the fracture are discretized by finite volume method. Due to the non-linearity of flow equation, the iterative method is used to solve the coupled problem of stress, pressure and temperature fields. A Triangular-PEBI (Perpendicular Bisector) dual mesh system is presented for numerical implementation. The numerical model is validated against with analytical solution and other methods in the literature. The results show the significance of accounting for elasto-plastic deformation and heat transfer when simulating hydraulic fracture propagation in deep reservoir.

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.

Three-Dimensional Poroelastic Modeling of Multiple Hydraulic Fracture Propagation from Horizontal Wells

Numerical simulations of multistage hydraulic fracturing usually neglect poroelastic effects. However, in case of low permeability reservoirs, where hydraulic fracturing is usually carried-out using relatively low viscosity fluids and high injection rates, coupled poroelastic mechanisms need be included for better understanding of the fracturing process, which can involve rock failure and/or reactivation of natural fractures. In this paper, we present a fully coupled three-dimensional poroelastic analysis of multiple fracture propagation from horizontal wells. The numerical model uses the indirect boundary element method of displacement discontinuity for poroelastic response of the rock, the finite element method for fracture fluid flow, and the linear elastic fracture mechanics approach for fracture propagation. The model accounts for the mechanical interactions among multiple fractures, mixed-mode propagation, fluid diffusion into the reservoir matrix, and the effects of fluid diffusion on the rock mechanical response. The model is verified with analytical solutions, and numerical examples of simultaneous and sequential fracturing of single and multiple horizontal wells in the Niobrara Chalk formation are presented. The results show the created fracture network geometries are strongly influenced by the mechanical interactions among the fractures. It is also demonstrated that the poroelastic effect increases the net fracture pressure and causes a reduction in fracture volume. The poroelastic model illustrates the transient character of stress shadow, and is particularly useful for re-fracturing analysis since it readily calculates the stress variations due to reservoir depletion.

Influence of gravel on the propagation pattern of hydraulic fracture in the glutenite reservoir

The clear mechanism of hydraulic fracture propagation in glutenite reservoirs with high heterogeneity is still not obtained, thus it is difficult to carry out the design of fracturing plan effectively. Based on the characteristics of the glutenite reservoirs, a coupled flow-stress-damage (FSD) model of hydraulic fracture propagation with gravels is established. This model is experimentally verified and the research on the influence of rock physical parameters and gravel property on the hydraulic fracture propagation is conducted. It is shown that as the gravel tensile strength increases, the hydraulic fracture is prone to propagate around the gravel, where the fracture deflection always occurs; as the gravel Young's modulus increases, there is high probability that hydraulic fracture propagates around the gravel, with more obvious fracture deflection; the matrix permeability influences fracture propagating morphology when encountering gravel and total fracture length; the horizontal geostress difference seriously impacts the fracture deflection; as the fracturing fluids injection displacement increases, the fracture is prone to deflect when encountering gravel; the low viscosity fracturing fluids result in the shorter fracture; the larger gravel increases the possibility of fracture deflection; in case of smaller gravel sizes, the increasing gravel content has a big influence on fracture deflection, and the increasing content of large gravel complicates the fracture morphology, resulting in the fine branched fractures; for the well rounded gravel, the fracture propagation around the gravel is prone to occur, and the fracture is not prone to deflect. Compared with the conventional sandstone reservoir, the glutenite reservoirs have higher breakdown and extension pressures, which fluctuate due to the gravel; the larger gravel size results in higher extension pressure. In this paper, a simulation method of hydraulic fracture propagation in the glutenite reservoirs is introduced, and the result provides the theoretical support for prediction of fracture propagation morphology and plan design of hydraulic fracturing in the glutenite reservoirs.

Numerical simulation of horizontal well network fracturing in glutenite reservoir

Hydraulic fracturing is an economically effective technology developing the glutenite reservoirs, which have far stronger heterogeneity than the conventional sandstone reservoir. According to the field production experience of Shengli Oilfield, horizontal-well fracturing is more likely to develop a complex fractured network, which improves the stimulated volume of reservoir effectively. But the clear mechanism of horizontal-well hydraulic fracture propagation in the glutenite reservoirs is still not obtained, thus it is difficult to effectively carry out the design of fracturing plan. Based on the characteristics of the glutenite reservoirs, a coupled Flow-Stress-Damage (FSD) model of hydraulic fracture propagation is established. The numerical simulation of fracturing expansion in the horizontal well of the glutenite reservoir is conducted. It is shown that a square mesh-like fracture network is developed near the horizontal well in the reservoir with lower stress difference, in which fracture is more prone to propagate along the direction of the minimum principal stress as well. High fracturing fluids injection displacement and high fracturing fluid viscosity lead to the rise of static pressure of the fracture, which results in the rise of fracture complexity, and greater probability to deflect when encountering gravels. As the perforation density increases, the micro-fractures generated at each perforation gather together faster, and the range of the stimulated reservoir is also relatively large. For reservoirs with high gravel content, the complexity of fracture network and the effect of fracture communication are obviously increased, and the range of fracture deflection is relatively large. In the case of the same gravel distribution, the higher the tensile strength of the gravel, the greater fracture tortuosity and diversion was observed. In this paper, a simulation method of horizontal well fracture network propagation in the reservoirs is introduced, and the result provides the theoretical support for fracture network morphology prediction and plan design of hydraulic fracturing in the glutenite reservoir.

Mitigating lost circulation: A numerical assessment of wellbore strengthening

Drilling in complex geological settings often possesses significant risk for unplanned events that could potentially impede already cost-demanding operations. Lost circulation, a major challenge in well construction, refers to the loss of drilling fluid into formation during drilling operations. When excessive wellbore pressure appears, lost circulation is induced by tensile failure or reopening of natural fractures at the wellbore. Over years of research efforts and field practices, wellbore strengthening techniques have been successfully applied in the field to mitigate lost circulation and have proved effective in extending the drilling margin to access undrillable formations. In fact, wellbore strengthening contributes additional resistance to fractures so that an equivalent circulating density higher than the estimated fracture gradient can be exerted on the wellbore.In this study, a fully coupled hydraulic fracture propagation model based on the cohesive zone model is presented. By implementing the model, an extensive parametric study is conducted to investigate factors involved in lost circulation. The parametric influences emphasizing the mass balance within the fracture reveal mechanisms of lost circulation mitigation. Simulation studies on wellbore strengthening are conducted in two parts, hoop stress enhancement and fracture resistance enhancement. First, a near-wellbore stress analysis characterizes wellbore mechanical responses during lost circulation. The results show elevated hoop stress during fracture width development, which validates the hypothesis of hoop stress enhancement. Also, beneficial influences from poroelastic effect and high rock stiffness are demonstrated. Then, a novel method to simulate fracture sealing is introduced to quantify fracture gradient extension for field practices. With this method, a case study on fracture sealing investigates the roles of sealing permeability and sealing length. The results show inhibition of fracture repropagation and conclude that fracture tip protection is achieved through fracture sealing and fracture fluid dissipation. From the case study, operational insights on wellbore strengthening design are derived.

TOUGH–RBSN simulator for hydraulic fracture propagation within fractured media: Model validations against laboratory experiments

This paper presents coupled hydro-mechanical modeling of hydraulic fracturing processes in complex fractured media using a discrete fracture network (DFN) approach. The individual physical processes in the fracture propagation are represented by separate program modules: the TOUGH2 code for multiphase flow and mass transport based on the finite volume approach; and the rigid-body-spring network (RBSN) model for mechanical and fracture-damage behavior, which are coupled with each other. Fractures are modeled as discrete features, of which the hydrological properties are evaluated from the fracture deformation and aperture change. The verification of the TOUGH–RBSN code is performed against a 2D analytical model for single hydraulic fracture propagation. Subsequently, modeling capabilities for hydraulic fracturing are demonstrated through simulations of laboratory experiments conducted on rock-analogue (soda-lime glass) samples containing a designed network of pre-existing fractures. Sensitivity analyses are also conducted by changing the modeling parameters, such as viscosity of injected fluid, strength of pre-existing fractures, and confining stress conditions. The hydraulic fracturing characteristics attributed to the modeling parameters are investigated through comparisons of the simulation results.

Modeling of Hydraulic Fracture Propagation in Shale Gas Reservoirs: A Three-Dimensional, Two-Phase Model

A three-dimensional, two-phase, dual-continuum hydraulic fracture (HF) propagation simulator was developed and implemented. This paper presents a detailed method for efficient and effective modeling of the fluid flow within fracture and matrix as well as fluid leakoff, fracture height growth, and the fracture network propagation. Both a method for solving the system of coupled equations, and a verification of the developed model are presented herein.