Energies

Research

18 pages, 9925 KiB

Open AccessArticle

Numerical Study of Elasto-Plastic Hydraulic Fracture Propagation in Deep Reservoirs Using a Hybrid EDFM–XFEM Method

by Wenzheng Liu, Qingdong Zeng, Jun Yao, Ziyou Liu, Tianliang Li and Xia Yan

Energies 2021, 14(9), 2610; https://doi.org/10.3390/en14092610 - 02 May 2021

Cited by 6 | Viewed by 1952

Rock yielding may well take place during hydraulic fracturing in deep reservoirs. The prevailing models based on the linear elastic fracture mechanics (LEFM) are incapable of describing the evolution process of hydraulic fractures accurately. In this paper, a hydro-elasto-plastic model is proposed to [...] Read more.

Rock yielding may well take place during hydraulic fracturing in deep reservoirs. The prevailing models based on the linear elastic fracture mechanics (LEFM) are incapable of describing the evolution process of hydraulic fractures accurately. In this paper, a hydro-elasto-plastic model is proposed to investigate the hydraulic fracture propagation in deep reservoirs. The Drucker–Prager plasticity model, Darcy’s law, cubic law and cohesive zone model are employed to describe the plastic deformation, matrix flow, fracture flow and evolution of hydraulic fractures, respectively. Combining the embedded discrete fracture model (EDFM), extended finite element method (XFEM) and finite volume method, a hybrid numerical scheme is presented to carry out simulations. A dual-layer iterative procedure is developed based on the fixed-stress split method, Picard iterative method and Newton–Raphson iterative method. The iterative procedure is used to deal with the coupling between nonlinear deformation with fracture extension and fluid flow. The proposed model is verified against analytical solutions and other numerical simulation results. A series of numerical cases are performed to investigate the influences of rock plasticity, internal friction angle, dilatancy angle and permeability on hydraulic fracture propagation. Finally, the proposed model is extended to simulate multiple hydraulic fracture propagation. The result shows that plastic deformation can enhance the stress-shadowing effect. Full article

(This article belongs to the Special Issue Petroleum Geomechanics)

► Show Figures

Figure 1

32 pages, 8983 KiB

Open AccessArticle

Particulate Modeling of Sand Production Using Coupled DEM-LBM

by Siavash Honari and Ehsan Seyedi Hosseininia

Energies 2021, 14(4), 906; https://doi.org/10.3390/en14040906 - 09 Feb 2021

Cited by 10 | Viewed by 2616

Abstract

Sand production is a complex phenomenon caused by the erosion of borehole walls during the extraction of hydrocarbons. In this paper, the sanding process in a typical Thick-Walled Hollow Cylinder (TWHC) test is numerically simulated. The main objective of the study is to [...] Read more.

Sand production is a complex phenomenon caused by the erosion of borehole walls during the extraction of hydrocarbons. In this paper, the sanding process in a typical Thick-Walled Hollow Cylinder (TWHC) test is numerically simulated. The main objective of the study is to model the particulate mechanism of sand production in granular assemblies with different bonding conditions and examine the effects of parameters such as stress level and cavity size on the sanding model. Due to the discrete nature of sand particles, the Discrete Element Method (DEM) is chosen to model solid particles, and the Lattice-Boltzmann Method (LBM) is implemented to simulate fluid flow through the solid particulate medium. A computer program is developed using the Immersed Moving Boundary (IMB) approach to couple the two methods and model fluid–solid interactions. After the program is validated, the simulations were conducted on 2D models representing cross-sections of TWHC samples under radial fluid flow. The results show that the developed program is able to capture complicated stages of sand production already observed in experiments. The program also proves to be a promising tool in the parametric study of sand production. It successfully simulates different aspects of the sanding phenomenon, including the scale effect, the extension of failure zones in samples under incremental stress, and the stress relaxation during rapid particle erosion. Full article

(This article belongs to the Special Issue Petroleum Geomechanics)

► Show Figures

Graphical abstract

17 pages, 12604 KiB

Open AccessArticle

Geomechanics in Depleted Faulted Reservoirs

by Nikolaos Markou and Panos Papanastasiou

Energies 2021, 14(1), 60; https://doi.org/10.3390/en14010060 - 24 Dec 2020

Cited by 5 | Viewed by 2329

Abstract

This paper examines the impact of the effective stresses that develop during depletion of a faulted reservoir. The study is based on finite element modeling using 2D plane strain deformation analysis with pore pressure and elastoplastic deformation of the reservoir and sealing shale [...] Read more.

This paper examines the impact of the effective stresses that develop during depletion of a faulted reservoir. The study is based on finite element modeling using 2D plane strain deformation analysis with pore pressure and elastoplastic deformation of the reservoir and sealing shale layers governed by the Drucker–Prager plasticity model. The mechanical properties and response of the rock formations were derived from triaxial test data for the sandstone reservoirs and correlation functions for the shale layers. A normal fault model and a reverse fault model were built using seismic data and interpretation of field data. The estimated tectonic in-situ stress field was transformed to the plane of the modeled geometry. Sensitivity studies were performed for uncertainties on the values of the initial horizontal stress and for the friction of the fault surfaces. It was found that the stress path during depletion is mainly controlled by the initial lateral stress ratio (LSR). The developed effective stresses with depletion are influenced by the fault geometry of the compartmentalized blocks. Plastic deformation develops for low LSR whereas for high values the system tends to remain in the elastic region. When plastic deformation takes place, it affects mainly the region near the fault. The reservoir deformation is dominated by vertical displacement which is higher near the fault region and nearly uniform in the remote area. The volumetric strain is dominated by compaction. More volatile conditions in relation to change of the friction coefficient and LSR were found for the normal fault geometry. Full article

(This article belongs to the Special Issue Petroleum Geomechanics)

► Show Figures

Figure 1

19 pages, 8713 KiB

Open AccessArticle

Frictional Properties and Seismogenic Potential of Caprock Shales

by Bahman Bohloli, Magnus Soldal, Halvard Smith, Elin Skurtveit, Jung Chan Choi and Guillaume Sauvin

Energies 2020, 13(23), 6275; https://doi.org/10.3390/en13236275 - 28 Nov 2020

Cited by 7 | Viewed by 2052

Abstract

Fractures and faults are critical elements affecting the geomechanical integrity of CO₂ storage sites. In particular, the slip of fractures and faults may affect reservoir integrity and increase potential for breach, may be monitored via the resulting seismicity. This paper presents an [...] Read more.

Fractures and faults are critical elements affecting the geomechanical integrity of CO₂ storage sites. In particular, the slip of fractures and faults may affect reservoir integrity and increase potential for breach, may be monitored via the resulting seismicity. This paper presents an experimental study on shale samples from Draupne and Rurikfjellet formations from the North Sea and Svalbard, Norway, using a laboratory test procedure simulating the slip of fractures and faults under realistic stress conditions for North Sea CO₂ storage sites. The motivation of the study is to investigate whether the slip along the fractures within these shales may cause detectable seismic events, based on a slip stability criterion. Using a direct shear apparatus, frictional properties of the fractures were measured during shearing, as a function of the shear velocity and applied stress normal to the fracture. We calculated the friction coefficient of the fractures during the different stages of the shear tests and analysed its dependency on shear velocity. Information on velocity-dependent friction coefficient and its evolution with increasing slip were then used to assess whether slip was stable (velocity-strengthening) or unstable (velocity-weakening). Results showed that friction coefficient for both Draupne and Rurikfjellet shales increased when the shear velocity was increased from 10 to 50 µm/s, indicating a velocity-strengthening behaviour. Such a behaviour implies that slip on fractures and faults within these formations may be less prone to producing detectable seismicity during a slip event. These results will have implications for the type of techniques to be used for monitoring reservoir and caprock integrity, for instance, for CO₂ storage sites. Full article

(This article belongs to the Special Issue Petroleum Geomechanics)

► Show Figures

Figure 1

28 pages, 6410 KiB

Open AccessArticle

Elastic and Frictional Properties of Fault Zones in Reservoir-Scale Hydro-Mechanical Models—A Sensitivity Study

by Torben Treffeisen and Andreas Henk

Energies 2020, 13(18), 4606; https://doi.org/10.3390/en13184606 - 04 Sep 2020

Cited by 3 | Viewed by 1994

Abstract

The proper representation of faults in coupled hydro-mechanical reservoir models is challenged, among others, by the difference between the small-scale heterogeneity of fault zones observed in nature and the large size of the calculation cells in numerical simulations. In the present study we [...] Read more.

The proper representation of faults in coupled hydro-mechanical reservoir models is challenged, among others, by the difference between the small-scale heterogeneity of fault zones observed in nature and the large size of the calculation cells in numerical simulations. In the present study we use a generic finite element (FE) model with a volumetric fault zone description to examine what effect the corresponding upscaled material parameters have on pore pressures, stresses, and deformation within and surrounding the fault zone. Such a sensitivity study is important as the usually poor data base regarding specific hydro-mechanical fault properties as well as the upscaling process introduces uncertainties, whose impact on the modelling results is otherwise difficult to assess. Altogether, 87 scenarios with different elastic and plastic parameter combinations were studied. Numerical modelling results indicate that Young’s modulus and cohesion assigned to the fault zone have the strongest influence on the stress and strain perturbations, both in absolute numbers as well as regarding the spatial extent. Angle of internal friction has only a minor and Poisson’s ratio of the fault zone a negligible impact. Finally, some general recommendations concerning the choice of mechanical fault zone properties for reservoir-scale hydro-mechanical models are given. Full article

(This article belongs to the Special Issue Petroleum Geomechanics)

► Show Figures

Figure 1

24 pages, 9442 KiB

Open AccessArticle

The Use of Nanomaterials in Shaping the Properties of Cement Slurries Used in Drilling

by Marcin Rzepka and Miłosz Kędzierski

Energies 2020, 13(12), 3121; https://doi.org/10.3390/en13123121 - 16 Jun 2020

Cited by 3 | Viewed by 1927

Abstract

For several decades, constant research has been performed in the world in order to obtain more durable, tighter, or less environmentally harmful binding materials which could be used to seal casing strings in boreholes. There is an increasing search for innovative solutions allowing [...] Read more.

For several decades, constant research has been performed in the world in order to obtain more durable, tighter, or less environmentally harmful binding materials which could be used to seal casing strings in boreholes. There is an increasing search for innovative solutions allowing the production of the highest possible class of binding cements. Since the beginning of the 21st century, one thing which has become synonymous with development is nanotechnology—a dynamically growing branch of science involving both the design, production, and testing of structures with the size of billionths of a metre. Among other things, a set cement stone is made of the grains of hydrated calcium silicates and calcium aluminates, between which there are pore spaces. Fine grains of nanoparticles can successfully settle inside these spaces, causing a decrease in the porosity and permeability of cement matrix. The paper presents the results of laboratory tests performed for formulas of cement slurries containing between 0.5% and 1% of nanosilica, between 1% and 3% of nanosized alumina and approximately 0.1% of carbon nanotubes. The resulting slurries had a density of approximately 1830–1920 kg/m³ and zero water settling. The thickening times of slurries were selected in accordance with the given geological and technical conditions. Early compressive strength amounting to 3.5 MPa (based on a test using an ultrasound cement analyser) was achieved by slurries after times between approximately 7 and 14 h. Upon setting of samples, cement stones produced from slurries featured a very low share of capillary pores. After 28 days of hydration, the compressive strength of the resulting cement stones took on very high values, reaching even up to 50 MPa. Photographs of cement stones containing nanomaterials (taken by means of scanning microscopy) are a confirmation of the exceptionally compact microstructure of the resulting samples. Full article

(This article belongs to the Special Issue Petroleum Geomechanics)

► Show Figures

Figure 1

18 pages, 7935 KiB

Open AccessArticle

Analyzing the Validity of Brazilian Testing Using Digital Image Correlation and Numerical Simulation Techniques

by He Zhang, Fatick Nath, Prathmesh Naik Parrikar and Mehdi Mokhtari

Energies 2020, 13(6), 1441; https://doi.org/10.3390/en13061441 - 19 Mar 2020

Cited by 6 | Viewed by 4327

Abstract

Characterizing the mechanical behavior of rocks plays a crucial role to optimize the fracturing process in unconventional reservoirs. However, due to the intrinsic anisotropy and heterogeneity in unconventional resources, fracture process prediction remains the most significant challenge for sustainable and economic hydrocarbon production. [...] Read more.

Characterizing the mechanical behavior of rocks plays a crucial role to optimize the fracturing process in unconventional reservoirs. However, due to the intrinsic anisotropy and heterogeneity in unconventional resources, fracture process prediction remains the most significant challenge for sustainable and economic hydrocarbon production. During the deformation tracking under compression, deploying conventional methods (strain gauge, extensometer, etc.) is insufficient to measure the deformation since the physical attachment of the device is restricted to the size of the sample, monitoring limited point-wise deformation, producing difficulties in data retrieval, and a tendency to lose track in failure points, etc. Where conventional methods are limited, the application of digital image correlation (DIC) provides detailed and additional information of strain evolution and fracture patterns under loading. DIC is an image-based optical method that records an object with a camera and monitors the random contrast speckle pattern painted on the facing surface of the specimen. To overcome the existing limitations, this paper presents numerical modeling of Brazilian disc tests under quasi-static conditions to understand the full-field deformation behaviors and finally, it is validated by DIC. As the direct tensile test has limitations in sample preparation and test execution, the Brazilian testing principle is commonly used to evaluate indirectly the tensile strength of rocks. The two-dimensional numerical model was built to predict the stress distribution and full-field deformation on Brazilian disc under compression based on the assumptions of a homogenous, isotropic and linear elastic material. The uniaxial compression test was conducted using the DIC technique to determine the elastic properties of Spider Berea sandstone, which were used as inputs for the simulation model. The model was verified by the analytical solution and compared with the digital image correlation. The numerical simulation results showed that the solutions matched reasonably with the analytical solutions where the maximum deviation of stress distribution was obtained as 14.59%. The strain evolution (normal and shear strains) and displacements along the central horizontal and vertical planes were investigated in three distinguishable percentages of peak loads (20%, 40%, and 90%) to understand the deformation behaviors in rock. The simulation results demonstrated that the strain evolution contours consistently matched with DIC generated contours with a reasonable agreement. The changes in displacement along the central horizontal and vertical planes showed that numerical simulation and DIC generated experimental results were repeatable and matched closely. In terms of validation, Brazilian testing to measure the indirect tensile strength of rocks is still an issue of debate. The numerical model of fracture propagation supported by digital image correlation from this study can be used to explain the fracturing process in the homogeneous material and can be extended to non-homogeneous cases by incorporating heterogeneity, which is essential for rock mechanics field applications. Full article

(This article belongs to the Special Issue Petroleum Geomechanics)

► Show Figures

Figure 1

18 pages, 5908 KiB

Open AccessArticle

Effect of Slot Width and Density on Slotted Liner Performance in SAGD Operations

by Yujia Guo, Alireza Nouri and Siavash Nejadi

Energies 2020, 13(1), 268; https://doi.org/10.3390/en13010268 - 05 Jan 2020

Cited by 7 | Viewed by 4027

Abstract

Sand production from a poorly consolidated reservoir could give rise to some severe problems during production. Holding the load bearing solids in place is the main goal of any sand control technique. The only sand control techniques that have found applications in steam [...] Read more.

Sand production from a poorly consolidated reservoir could give rise to some severe problems during production. Holding the load bearing solids in place is the main goal of any sand control technique. The only sand control techniques that have found applications in steam assisted gravity drainage (SAGD) are some of the mechanical methods, including wire wrapped screens, slotted liners and more recently, punched screens. Slotted liner is one of the most effective mechanical sand control methods in the unconsolidated reservoir exploitation, which has proven to be the preferred sand control method in the SAGD operations. The main advantage of the slotted liners that makes them suitable for SAGD operations is their superior mechanical integrity for the completion of long horizontal wells. This study is an attempt to increase the existing understanding of the fines migration, sand production, and plugging tendency for slotted liners by using a novel large-scale scaled completion test (SCT) facility. A triaxial cell assembly was used to load sand-packs with specified and controlled grain size distribution, shape and mineralogy, on multi-slot sand control coupons. Different stress levels were applied parallel and perpendicular to different combinations of slot width and density in multi-slot coupons, while brine was injected from the top of the sand-pack towards the coupon. At each stress level, the mass of produced sand was measured, and the pressure drops along the sand-pack and coupon were recorded. Fines migration was also investigated by measuring fines/clay concentration along the sand-pack. The current study employed multi-slot coupons to investigate flow interactions among slots and its effect on the flow performance of liner under typically encountered stresses in SAGD wells. According to the experimental observations, increasing slot width generally reduces the possibility of pore plugging caused by fines migration. However, there is a limit for slot aperture beyond which the plugging is not reduced any further, and only a higher level of sanding occurs. Test measurements also indicated that besides the slot width, the slot density also influences the level of plugging and sand production and must be included in the design criteria. Full article

(This article belongs to the Special Issue Petroleum Geomechanics)

► Show Figures

Graphical abstract

14 pages, 4505 KiB

Open AccessArticle

Study on the Interaction Mechanism of Hydraulic Fracture and Natural Fracture in Shale Formation

by Heng Zheng, Chunsheng Pu and CHOE TONG IL

Energies 2019, 12(23), 4477; https://doi.org/10.3390/en12234477 - 25 Nov 2019

Cited by 14 | Viewed by 2462

Abstract

Hydraulic fracturing is an essential technique for the development of shale gas, due to the low permeability in formation. Abundant natural fractures contained in a formation are indispensable for the development of a fracture network. In this paper, a damage-stress-seepage coupled hydraulic fracture [...] Read more.

Hydraulic fracturing is an essential technique for the development of shale gas, due to the low permeability in formation. Abundant natural fractures contained in a formation are indispensable for the development of a fracture network. In this paper, a damage-stress-seepage coupled hydraulic fracture expansion model, based on the extended finite element method, is established. The simulation results show that shear failure occurs when the hydraulic fracture interacts with a frictional natural fracture, while tensile failure occurs when it interacts with a cement natural fracture. Low interaction angles and high tensile strength of the rock are beneficial for the generation of a complex fracture network. Furthermore, under the same geological conditions and injection parameters, frictional natural fractures are more beneficial for the generation of a complex fracture network, when compared with cement natural fractures. This can not only effectively increase the propagation length of the natural fracture, but also effectively reduce its reactive resistance. This research is of great significance for the efficient exploitation of unconventional oil and gas resources. Full article

(This article belongs to the Special Issue Petroleum Geomechanics)

► Show Figures

Graphical abstract

40 pages, 13345 KiB

Open AccessArticle

New Interface for Assessing Wellbore Stability at Critical Mud Pressures and Various Failure Criteria: Including Stress Trajectories and Deviatoric Stress Distributions

by Jihoon Wang and Ruud Weijermars

Energies 2019, 12(20), 4019; https://doi.org/10.3390/en12204019 - 22 Oct 2019

Cited by 8 | Viewed by 3167

Abstract

This study presents a new interface for wellbore stability analysis, which visualizes and quantifies the stress condition around a wellbore at shear and tensile failure. In the first part of this study, the Mohr–Coulomb, Mogi–Coulomb, modified Lade and Drucker–Prager shear failure criteria, and [...] Read more.

This study presents a new interface for wellbore stability analysis, which visualizes and quantifies the stress condition around a wellbore at shear and tensile failure. In the first part of this study, the Mohr–Coulomb, Mogi–Coulomb, modified Lade and Drucker–Prager shear failure criteria, and a tensile failure criterion, are applied to compare the differences in the critical wellbore pressure for three basin types with Andersonian stress states. Using traditional wellbore stability window plots, the Mohr–Coulomb criterion consistently gives the narrowest safe mud weight window, while the Drucker–Prager criterion yields the widest window. In the second part of this study, a new type of plot is introduced where the safe drilling window specifies the local magnitude and trajectories of the principal deviatoric stresses for the shear and tensile wellbore failure bounds, as determined by dimensionless variables, the Frac number (

F

) and the Bi-axial Stress scalar (

χ

), in combination with failure criteria. The influence of both stress and fracture cages increases with the magnitude of the

F

values, but reduces with depth. The extensional basin case is more prone to potential wellbore instability induced by circumferential fracture propagation, because fracture cages persists at greater depths than for the compressional and strike-slip basin cases. Full article

(This article belongs to the Special Issue Petroleum Geomechanics)

► Show Figures

Graphical abstract

21 pages, 9411 KiB

Open AccessArticle

Transient Stress Distribution and Failure Response of a Wellbore Drilled by a Periodic Load

by Xiaoyang Wang, Mian Chen, Yang Xia, Yan Jin and Shunde Yin

Energies 2019, 12(18), 3486; https://doi.org/10.3390/en12183486 - 10 Sep 2019

Viewed by 2068

Abstract

The poroelastodynamic failure of a wellbore due to periodic loading during drilling is an unsolved problem. The conventional poroelastic method to calculate the stress distribution around wellbore is for static loading cases and cannot be used for short-time dynamic-loading cases which result in [...] Read more.

The poroelastodynamic failure of a wellbore due to periodic loading during drilling is an unsolved problem. The conventional poroelastic method to calculate the stress distribution around wellbore is for static loading cases and cannot be used for short-time dynamic-loading cases which result in wave propagation in the formation. This paper formulates a poroelastodynamic model to characterize dynamic stress and pressure wave due to periodic loadings and to analyze the transient failure of the suddenly drilled wellbore in a non-hydrostatic stress field. The fully coupled poroelastodynamic model was developed based on the equations of motion, fluid flow and constitutive equations to reflect stress and pressure waves that resulted from a periodic stress perturbation at the wellbore surface. The model was analytically solved by means of field expansions of the solutions, by performing a Laplace transform as well as some special techniques. Simulation results show that the pressure and stress responses inside the formation resemble a damped oscillator where the amplitude decays as the distance to wellbore increases. Especially the potential shear failure zone around the wellbore was computed and plotted. Influences of poroelastic parameters, in-situ stress and periodic load parameters on the shear failure responses were analyzed in a detailed parametric study, and the results provide fundamental insights into wellbore stability maintenance in different reservoirs. Full article

(This article belongs to the Special Issue Petroleum Geomechanics)

► Show Figures

Graphical abstract

20 pages, 4812 KiB

Open AccessArticle

An Investigation into the Effects of Weak Interfaces on Fracture Height Containment in Hydraulic Fracturing

by Yongxiang Zheng, Jianjun Liu and Bohu Zhang

Energies 2019, 12(17), 3245; https://doi.org/10.3390/en12173245 - 22 Aug 2019

Cited by 16 | Viewed by 2794

Abstract

Hydraulic fracturing is an effective method for developing unconventional reservoirs. The fracture height is a critical geometric parameter for fracturing design but will be limited by a weak interface. Fracture containment occurs when fracture propagation terminates at layer interfaces that are weaker than [...] Read more.

Hydraulic fracturing is an effective method for developing unconventional reservoirs. The fracture height is a critical geometric parameter for fracturing design but will be limited by a weak interface. Fracture containment occurs when fracture propagation terminates at layer interfaces that are weaker than the surrounding rock. It always occurs in multilayer formation. Therefore, the mechanism of fracture height containment guides fracture height control in hydraulic fracturing. In order to study the fracture containment mechanism, this paper first calculates the propagation behaviour of the fracture in 3D under the influence of a weak interface through a block discrete element method and analyzes the geometric characteristics of the fracture after it meets the weak interface. Then, the induced stress of the hydraulic fracture on the weak interface is calculated by fracture mechanics theory, and the mechanism of blunting at the fracture tip is explained. Then, two kinds of interface slippage that can lead to blunting of the fracture tip are discussed. Based on the behavior of shear slippage at the interface, a control method for multilayer fracturing in thin sand-mud interbed and pay zone fracturing in shale is proposed. The results show that the fracture height is still limited by the weak interface in the formation without the difference of in-situ stress and rock properties. Interface slippage is the main factor impeding fracture propagation. Fracture height containment can be adjusted and controlled by changing the angle between the hydraulic fracture, the interface, and the stress state to strengthen and stiffen the interface. This study has a certain guiding significance for fracture height control in the design of hydraulic fracturing of shale or thin sand-mud interbed reservoirs. Full article

(This article belongs to the Special Issue Petroleum Geomechanics)

► Show Figures

Figure 1

Journal Menu

Journal Browser

Petroleum Geomechanics

Share This Special Issue

Special Issue Editor

Special Issue Information

Keywords

Published Papers (12 papers)

Research

Further Information

Guidelines

MDPI Initiatives

Follow MDPI