Hydromechanical Process Research Articles

Stress field behavior induced by hydraulic fracture in shale reservoirs: A practical view on cluster spacing

Hydraulic fracturing is a complicated hydro-mechanical process, which is used to stimulate reservoir volume, where a pressurized fluid drives fracture propagation in a solid, or porous medium. This process changes the initial state of stress in the reservoir as the applied hydraulic pressure develops discontinuity throughout the media. As the fracture network propagates, it achieves a greater surface contact area with the producing formation and the wellbore, allowing for a greater rate of oil and gas migration in ultra-low permeability reservoirs (e.g. shale reservoirs). This process greatly enhances production, but may lead to instability within surrounding discontinuities or changes to the local stress distribution, which may cause unfavorable events such as hydraulic fracture cluster merging.Hydraulic fracture design is not recommended when only complicated numerical simulation and modeling techniques are used without verification through accompanying field data. Often times, comparing with field data, complicated mathematical simulation models are altered to better correlate the simulation results to real-time or post-treatment field data. This raises uncertainty in whether the physics of the hydraulic fracturing are being captured correctly or not using commercial numerical simulators. Many times this leads to a trial and error based approach for fracture treatment operations, which are backed by physical results, such as microseismic, or production data. Unfortunately, in initial field or well completion design scenarios, there is significant uncertainty associated with stimulation treatment designs. Observations of treated wells are required to corroborate the simulated data using scientific evidence.The Theory of Critical Distance (TCD) was developed as a quick analysis method to determining material failure; most often to notched type cases of non-propagating crack fatigue (Taylor, 2007). This theory demonstrates the ability to predict failure based upon the stress concentrations surrounding the notch (Yin, 2014; Louks, 2014). In a similar fashion this methodology is derived and applied to a dynamic pressurized fluid front within a fracture in order to predict stress concentrations surrounding the fracture (Lajtai, 1971; Ito, 1991). The premise of modifying TCD theory is nothing new as this has been done for various cases, however it has yet to be used in this type of application concerning dynamic loading and hydraulic driven fracture propagation.The application of a modified TCD theory displays the possibility of using a simple technique to predict hydraulic fracture cluster spacing by precisely defining the dynamics of the failure envelope around the fracture tip and surrounding fracture geometry and also to optimize injection pressure required for propagation but eliminate interference between clusters. In this paper Von Mises stress has been calculated and used to analyze the multi-fracture interactions. This behavior can be idealized such that the maximum Von Mises stress emanates from the fracture tip creating a critical angle with the fracture plane or fracture tip. The angle and magnitude of stress can be used to justify the stability of the reservoir or to interpret stress reorientations that are seen surrounding propagating fractures. These reorientations can affect the geometry and relative stress distributions surrounding adjacent fracture propagation by either easing or impeding the ability of the fracture to propagate.As a result of this study, the modified TCD theory provides a tool for the determination of these stress interactions in order to make quick decisions in the field to modify stimulation treatment plans during injection, which would typically require complicated modeling and simulation results.

Analysis of energy flows in systems of different physical nature of electrically driven of turbomachines

A method of the energy flows in the different physical nature systems’ electrically driven turbomachines analysis has been offered. Energetic relationship between the Bond Graph models of the induction motor and centrifugal pump has been established. The study of a single electro hydro mechanical process of turbomachines work has been conducted. At the current stage of scientific progress, solving the complex technical systems’ operational calculation and optimization problem of mostly carried out by computer simulation. Therefore, the necessity of the electrically driven turbomachines computer-based models' development such modeling techniques that would not require special skills in the programming and made it possible to analyze the mutual influence of the different physical nature subsystems' components of the object's dynamic behavior have been arisen. As a result of the research, numerical set and graphical depending on the instantaneous values of the electric motor power, mechanical shaft power of the hydraulic machine and hydraulic power on the pump discharge pipe have been received. The efficiency of energy conversion in each individual area of the turbomachine, based on the obtained results, has been analyzed. In the future, it will enable to develop and implement energy saving measures in the electrical complexes of the industrial enterprises .

Experimental studies on hydro-mechanical properties of metamorphic rock under hydraulic pressures

The research on the hydro-mechanical coupling of metamorphic rock is of great importance in rock engineering. The main purpose of this study was to investigate the hydro-mechanical properties of metamorphic rock based on the experimental data from triaxial compression tests. Metamorphic rock samples taken from an underground oil storage facility were tested under different hydraulic pressures using a rock servo-controlled triaxial rheology test system. The results indicated that hydraulic pressure had impact on the strength, deformation and permeability of the metamorphic rock. Based on the test results, the stress–strain behaviour and permeability evolution of the rock samples show three stages. The mechanical properties of the metamorphic rock are presented in detail for the three stages in the whole stress–strain process. The derived mechanical parameters are correlated to the division of the phases. The relationship between hydraulic pressure and axial strain, lateral strain, volumetric strain and permeability are analysed and discussed, especially the influence of hydraulic pressure on various parameters in the hydro-mechanical process. The influence of the hydraulic pressure on the failure mode of the rock under coupled conditions is described.

Finite Element Analysis and Experimental Validation of Warm Hydromechanical Deep Drawing Process

This study intended to establish finite element analysis (FEA) model of warm hydro mechanical deep drawing process (WHMD) of cylindrical cups by means of commercial FEA package Ls-Dyna The validity of established FEA model is verified by means of WHMD experiments through several studies. It was noted that the established model successfully simulated the real process leading to significant cost and time spent on trial-error stage in hydromechanical deep-drawing of lightweight alloys.

An Application of Fuzzy Logic Control Algorithm in Hydro Mechanical Deep Drawing Process

Hydro mechanical deep drawing (HDD) process is an advanced sheet metal forming technology. The aim of this process is to form deep drawn cups without any kind of forming instability such as buckling, wrinkling or bursting (tearing). The most important parameters in achieving this goal are fluid pressure and blank holder force. So in this study, a fuzzy logic control algorithm was used with Ls-Dyna FEA subroutines to determine the optimum fluid pressure (P) and the blank holder force (BHF) since it requires a lot of time and cost to perform this work with trial and error experiments. Minimum element thickness, punch wall contact position and wrinkling height were used as input parameters in the control algorithm. But studies on determining the BHF with the wrinkling height parameters have not been carried out yet. This will be investigated in further studies.

Modelling of hydro-mechanical coupling and transport in densely fractured rock mass

A numerical model is presented to study hydro-mechanical coupling process based on the rigid body spring method and the discrete fracture network model. In order to realistically simulate the constitutive behaviours of fractures, a non-linear constitutive model is employed, in which non-linear normal stress deformation relationship, tangential slipping failure and dilation effects are considered. To investigate coupling effects on transport, a particle tracking procedure is also incorporated to account for solute movement. Stress effects on flow field and transport are studied on a typical fracture network provided by the DECOVALEX project. Results show that it is the non-linear normal deformation that mainly influences flow and transport when the confining stress is relatively low and the stress difference is not large. When the stress increases and stress difference becomes larger, dilation effect gradually becomes the governing mechanism. These results are compared with other researcher’s work and reasonable agreements are obtained.

Internal Erosion of Earth Structures as a Coupled Hydromechanical Process

The present paper describes a model of internal erosion of earth structures based on rigorous thermodynamic principles and the theory of porous media. The focus is concerned with the initial stage of internal erosion, prior to the formation of macroscopic channels, whenthe continuum approach is applicable. The soil skeleton saturated by a pore fluid is treated as the superposition of 3 continua in interaction ;the pore fluid itself consists of a mixture of water and eroded particles. The erosion kinetics is based on the shear stress developed at the solid-fluid interface. The applicability of the model is illustrated by a finite element simulation. The simulations show how the phenomenon of piping preferentially arises in regions where hydraulic gradients are critical. Effects of mechanical degradations due to internal erosion are demonstrated.

Multiphysics extension to physically based analyses of pipes with emphasis on frost actions

Pipes, especially buried pipes, in cold regions generally experience a rash of failures during cold weather snaps. However, the existing heuristic models are unable to explain the basic processes involving frost actions. This is because the frost action is not a direct load but one that causes variations in pipe-soil interactions resulting from the coupled thermo- hydro-mechanical process in soils. This paper developed and implemented a holistic multiphysics simulation model for freezing soils and extended it to the analysis of pipe-soil systems. The theoretical framework was implemented to analyze both static and dynamic responses of buried pipes subjected to frost actions. The multiphysics simulations reproduced phenomena commonly observed during frost actions, e.g., ice fringe advancement and an increase in the internal stress of pipes. The influences of im- portant design factors, i.e., buried depth and overburden pressure, on pipe responses were simulated. A fatigue cracking criterion was utilized to predict the crack initialization under the joint effects of frost and dynamic traffic loads. The frost effects were found to have detrimental effects for accelerating fatigue crack initialization in pipes.

Investigation of the Effect of Blank Shape on the Sheet Hydroforming Parameters

In the deep drawing processes, the use of an optimal blank shape not only saves the material but also it may reduce the occurrence of defects e.g. wrinkling and tearing. In addition, finding the desirable flange contour, eliminate the trimming step in the deep drawing of parts with flange. The main objective of this study is to optimize the blank shape in order to produce a cylindrical cup with desirable flange contour and investigation of its effect on important parameters. Presently, to overcome this issue, a very expensive and time consuming trial and error method is used. In this study, a systematic method based on sensitivity analysis has been used to find the optimal blank to obtain a desirable flange contour for a cylindrical cup by hydromechanical deep drawing process. With the aid of a well-known dynamic explicit analysis code ABAQUS; optimum initial blank shape has been obtained. With the predicted optimal blank, both computer simulation and experiment are performed and the effect of blank shape on the some parameters such as thickness distribution and forming pressure of the formed cups were investigated. It is shown that formed cup with an optimum blank shape has a better thickness distribution in the rolled direction.

The effects of proportional loading, plane stress, and constant thickness assumptions on hydro-mechanical deep drawing process

The goal of this study is to evaluate the effects of proportional loading, plane stress, and constant thickness assumptions on hydro-mechanical deep drawing (HDD) by developing analytical models. The main model includes no simplifying assumption, and then each of the mentioned assumptions is considered in a specific model. The interrelationships between geometrical and mechanical variables are obtained in the finite difference form based on the incremental strain theory, thereby being solved by Broyden algorithm. Published experimental and FE results are used for evaluation of the results obtained in the present work. The results of models under proportional loading, plane stress, and constant thickness conditions show more differences with the experimental data in strain distributions than the results of the main model. Thus, the analyses will be more accurate and the results more reliable without considering such assumptions.

Analysis of thermo–hydro–mechanical process in the engineered barrier system of a high-level waste repository

This paper presents a simulation of the KAERI's engineering scale experiment, KENTEX which is to study the thermal, hydrological and mechanical (THM) processes occurring in the engineered barrier system of a high-level waste repository. The simulation was performed by using the computer code, TOUGH2, which analyzes the multi-dimensional fluid and heat flows of multiphase, multicomponent fluid mixture in unsaturated medium. The detailed geometry of KENTEX was incorporated into the model, and the laboratory experiments were carried out to determine the thermal, hydrological and mechanical properties of bentonite, which were used as input parameters for the simulation. The calculated results on the temperature, water content, and total pressure distribution throughout the bentonite buffer were compared with the experimental ones.

Application of the geomechanical facies approach and comparison of exploration and evaluation methods used at Soultz-sous-Forêts (France) and Spa Urach (Germany) geothermal sites

Earth-reservoirs are increasingly exploited today with the extraction of resources, such as heat and hydrocarbons, and the large-scale emplacement of waste, such as CO2 sequestration. The characterization, site investigation, predictive modeling and long-term monitoring are dependent on the processes being investigated and modeled. In most cases complex coupled processes have to be addressed in a geologically complex rock mass system. In this paper we present a conceptual holistic framework known as geomechanical facies linking all the scales of investigation, characterization and reservoir development methods. We demonstrate this concept on the work undertaken during the design and development of the enhanced geothermal systems (EGS) systems at the forefront of European Hot-Dry-Rock (HDR) technology, Soultz-sous-Forets (France) and Spa Urach (Germany). Soultz-sous-Forets is situated within granitic rocks and an active tectonic graben system in the central part of the Rhine Graben. It presents conditions of lithology, temperature, stress, hydraulics and geochemistry that are very different from those at Spa Urach, located in a very dense gneiss formation in the South German crystalline complex. Spa Urach exhibits more elastic behavior and is set tectonically within an almost inactive strike-slip stress field described in more detail in Sects. “Drill core analysis” and “Hydraulic stimulation at Spa Urach”. This paper compares the exploration and field development methods used at these two sites against the back drop of the geomechanical facies concept. Issues addressed include the key parameters for flow and heat transport properties, coupled hydro-mechanical process identification, the success of the HDR reservoir as a heat exchanger and exploration techniques applicable to the different facies. Identification of the key geomechanical facies gives an indication as to which technologies will prove more efficient in the application of HDR technology. The results of this study will hopefully help in developing heat recovery schemes for the long-term economical operation of future HDR plants and EGS as well as assist in the understanding of engineered geosystems.

Novel combined standard hydromechanical sheet hydroforming process

Sheet hydroforming techniques are widely used in industries for the production of different components with specific characteristics. Despite the advantages of the conventional sheet hydroforming techniques, they have their own limitations. In this paper, to increase the application and to overcome the limitations of conventional deep drawing, a new sheet hydroforming technique is proposed that is a combination of the standard and the hydromechanical sheet hydroforming processes. The proposed method has the advantages of conventional processes but eliminates their limitations. This technique is used in forming a cylindrical cup and a complex industrial part. After applying the appropriate pressure path, the products are formed successfully in one stage without any defects. It is also shown that the required forming pressure in the proposed process is low compared with other sheet hydroforming processes. It is demonstrated that because of the low internal pressure required in the present method, pre-bulging does not have any significant effect on the thickness distribution of the product. It is concluded that in this process increasing the friction coefficient between punch and blank can reduce the sheet thinning.

Tooling design and development of set-up for hydro-mechanical deep drawing

Hydro-mechanical deep drawing is a process for producing cup shaped parts with the assistance of a pressurised fluid. The design and development of tooling for hydro-mechanical deep drawing process is discussed in this paper. In the present work, an experimental set-up has been designed and fabricated for drawing cylindrical flat bottom cups. To overcome the limitation of a single action press and to provide variable blank holding pressure during the draw, a hydraulic blank holding system has been designed and developed. Design of the set-up for hydro-mechanical deep drawing requires detailed considerations than that of the forming of components with conventional deep drawing. The different aspects of the development are discussed in this paper.

Analysis of rupture instability in the hydromechanical deep drawing of cylindrical cups

This paper presents analyses of tensile instability in the hydromechanical deep drawing process of cylindrical cups. Analytical models are developed based on Barlat-Lian and Hill’s non-quadratic yield criteria and the maximum permissible fluid pressure, above which rupture occurs, is achieved, assuming plane strain tensile failure. The influences of process and material variables on this critical fluid pressure are investigated. The theoretical results are compared with results obtained from experiments to verify the validity of the proposed analytical approaches.

Parameter study of the axisymmetric hydromechanical deep drawing process

In this paper, hydromechanical deep drawing and the effect of process parameters on the process have been studied using the finite element (FE) method. In order to verify the results of FE simulations, a study has also been carried out using experimental tooling. Numerical results indicate a working zone with a maximum chamber pressure in which the maximum limit drawing ratio (LDR) can be achieved and where the effect of chamber pressure on the process can be shown. Also, the effect of parameters such as initial chamber pressure, die profile radius, blank thickness, and friction effect has been investigated. It is shown that initial chamber pressure has an optimum value in which the maximum LDR can be achieved. Increasing the die profile radius increases the LDR at lower chamber pressures but has no marked effect at higher pressures. The numerical result also shows that increasing the friction between blank and die or blank and blank-holder decreases the LDR value, while increasing the friction between blank and punch increases the LDR value.

Finite Element Analysis of the Hydro-Mechanical Punching Process

This paper investigates the characteristics of a hydro-mechanical punching process. The hydro-mechanical punching process is divided into two stages: the first stage is the mechanical half piercing in which an upper punch goes down before the initial crack is occurred; the second stage is the hydro punching in which a lower punch goes up until the final fracture is occurred. Ductile fracture criteria such as the Cockcroft et al., Brozzo et al. and Oyane et al. are adopted to predict the fracture of a sheet material. The index value of ductile fracture criteria is calculated with a user material subroutine, VUMAT in the ABAQUS Explicit. The hydrostatic pressure retards the initiation of a crack in the upper region of the blank and induces another crack in the lower region of the blank during the punching process. The final fracture zone is placed at the middle surface of the blank to the thickness direction. The result demonstrates that the hydro-mechanical punching process makes a finer shearing surface than the conventional one as hydrostatic pressure increases.

Interaction Swelling Bitumen – Host Formation: Scoping Calculations

ABSTRACTThe Eurobitum bituminised waste product (BWP) from the former EUROCHEMIC reprocessing plant in Mol-Dessel (Belgium) contains a lot of salts, mainly NaNO3 and CaSO4. In contact with pore water in an underground repository, the dehydrated salts in the BWP will rehydrate, resulting in swelling and, possibly, a swelling pressure build-up. A high swelling pressure might impede the integrity and the safety of the repository by creation of preferential pathways for radionuclide migration. In Belgium, the Boom Clay is studied as a reference host formation.The interaction between the swelling BWP and the host formation is a very complicated hydromechanical process. It depends not only on the hydromechanical behaviour of the Boom Clay, but also on that of the BWP. The hydromechanical constitutive law of Eurobitum is not yet established. We have therefore realised scoping calculations to assess the stress redistribution and deformation due to the recompression of the clay around a disposal gallery caused by a swelling pressure. Sensitivity studies have evidenced some important influencing factors.The scoping calculations showed that the swelling pressure exercised to the Boom Clay should be limited to 7 - 8 MPa. Beyond this limit, the Boom Clay host formation will be subject to important deformation, and the risk of preferential paths for radionuclide transport becomes very high. The convergence during the excavation of the disposal galleries is of primary importance for a safe waste disposal system design. Indeed, excess convergence may result in a higher damaged zone before disposal of the bituminised waste.

Comparison of Simulation and Experimental Axial Loadings for Hydromechanical Bulge Forming of Copper Cross-Joints

Hydromechanical bulging is applied mainly to the series production of hydraulic installation and sanitary facilities including tubes with a changeable diameter, T-pipes and cross-joints. The process consists in placing a tube segment in a die-cavity, pouring some liquid over it and sealing the faces. As a result the liquid pressure rises and the pipe is upset. The basic parameters of the hydromechanical process of bulge forming are: liquid pressure and axial loading. The simulations of hydromechanical bulge forming were performed using MSC Marc software based on the finite element method. The calculation results were compared with the experimental data especially to study axial loading for different ratios d/D, so/D and for different variations of internal pressure. The results of numerical simulations of axial loading are in good agreement with the experimental data for established = 0,15.

Rapid wave-driven advective pore water exchange in a permeable coastal sediment

In this study we present in-situ measurements of pore water flow velocities in a coastal sandy sediment (permeability=3.65×10 −10 m 2). The advective pore water flows were driven by the interaction of oscillating boundary flows with sediment wave ripples, (amplitude=7 cm, wavelength=30 to 50 cm). The measurements were carried out in the Mediterranean Sea at 50 to 70 cm water depth during a phase of very low wave energy (max. wave amplitude=10 cm). An optode technique is introduced that permits direct pore water flow measurements using a fluorescent tracer. Near the sediment surface (0.5 cm depth) pore water reached velocities exceeding 40 cm h −1. Thus, advective transport exceeded transport by molecular diffusion by at least 3 orders of magnitude. Based on the pore water velocity measurements and ripple spacing, we calculate that 140 L m −2 d −1 are filtered through the sediment. Pore water visualisation experiments revealed a flow field with intrusion of water in the ripple troughs and pore water release at the ripple crests. The wave-driven water flow through the sediment, thus, was directly linked to the wave-generated sediment topography, and its spatial dimensions. These results show that surface waves cause water filtration through permeable sediments at water depths smaller than half the wavelength. We conclude that surface gravity waves constitute an important hydromechanical process that may convert large areas of the continental shelves into expansive filter systems. Surface gravity waves thereby could affect suspended particle concentration and cycling of matter in the shelf.