Fluid Pressure Research Articles

Dynamic stress response in reservoirs stimulated by fluctuating fluid pressure during pulsating hydraulic fracturing

Determining the most effective scheme for fracturing operations depends on accurate calculations of reservoir stress. Traditional fracturing theories usually focus on stable fluid injection modes, which employ static assumptions in modelling and analysis. However, pulsating hydraulic fracturing (PHF) introduces fluctuating fluid pressure to stimulate reservoirs, which requires considering dynamic factors and exploring the dynamic stress response within the reservoir. Furthermore, reservoirs are often classified as homogeneous continuous or porous media materials, but the boundaries between these classifications are sometimes apparent. This paper investigated the development of both an elastodynamics model and a poroelastodynamics model for calculating dynamic stress responses during PHF. The staggered grid finite difference method addressed these models, with the outer boundary employing the perfectly matched layer (PML) method to simulate an infinite reservoir. The numerical simulation results were extensively verified and compared with analytical solutions, and the differences between various models and their relevant conditions were thoroughly analyzed. Analyzing fluid pressure fluctuation parameters revealed noteworthy insights into reservoir stress response characteristics. Results indicate that as the Biot coefficient and permeability increase, the disparities between the elastodynamics and poroelastodynamics models become prominent. In practical terms, high Biot coefficient or high permeability reservoirs necessitate using the poroelastodynamics model for accurate reservoir stress analysis. As the frequency of fluid pressure fluctuation increases, the amplitude of response of reservoir circumferential stress also increases, while the response amplitude of radial stress and fluid pressure decreases. These findings offer valuable theoretical guidance for parameter design in engineering applications during PHF.

A discontinuous Galerkin method for a coupled Stokes–Biot problem

The interaction between fluid and poroelastic structure is a complex problem that couples the Stokes equations with the Biot system. In this work, we rewrite the poroelastic equations using three fields (displacement, fluid pressure, and total pressure) to account for locking phenomenon in fluid–structure interaction and the oscillation of numerical solutions. Then, in order to solve the coupled system, we use the weighted discontinuous Galerkin finite element method for spatial discretization and propose a semi-discrete scheme. In addition, we propose a fully discrete scheme using the backward Euler’s method for temporal discretization. In the framework of the Galerkin approximation, the stability and errors of semi- and fully discrete schemes are analyzed using the theory of differential algebraic equations and weak compactness arguments. Through numerical experiments, we validate the theoretical rate of convergence, explain the behavior of the method in modeling the interaction between surface and groundwater hydrological systems, investigate the robustness of the method with respect to physical parameters, and simulate channel filtering. In particular, the numerical results are free of locking features, reducing non-physical numerical oscillations.

Comprehensive corrosion failure analysis of HAl77-2 alloy tubes serving in a low temperature multi-effect distillation plant: From feature analysis to corrosion mechanisms

Premature perforation and leakage of HAl77-2 alloy heat exchanger tubes occurs after 2.5 years of service in the largest low temperature multi-effect distillation (LT-MED) plant in China. The root reasons of perforation and leakage of tubes were investigated through macroscopic morphology, chemical composition, metallographic structure, seawater quality, flowing simulation and microstructure characterization. The results show that the HAl77-2 alloy tubes with perforation leakage meet the standard requirements. And the failure of the tubes was mainly attributed to the synergistic effect of serious pitting corrosion and stress cracking caused by the high fluid pressure and polluted seawater with Fe2+/Fe3+, sulfide and NH4+. Especially, the velocity and pressure spatial distribution of liquid film on the outside of horizontal tubes well verified the interesting observation that corrosion pits concentrating in one strip on the top of the tube. Moreover, corrosion mechanism was proposed that the loose corrosion products of Cu2S, FeS and Cu2(OH)3Cl lead to the formation of some defect points on the homogeneous protective Cu2O layer. For these defect points, the direct expose of the alloy matrix to corrosive substances such as Cl− and NH4+, significantly accelerates the dissolution of Cu in form of CuCl2− and Cu(NH3)2+ from the alloy. Finally, the tube occurs pitting corrosion and even perforates under the strong hydraulic erosion after long-terms of operation.

Natural MOF-Like Photocatalytic Nanozymes Alleviate Tumor Pressure for Enhanced Nanodrug Penetration.

In oncological nanomedicine, overcoming the dual-phase high interstitial pressure in the tumor microenvironment is pivotal for enhancing the penetration and efficacy of nanotherapeutics. The elevated tumor interstitial solid pressure (TISP) is largely attributed to the overaccumulation of collagen in the extracellular matrix, while the increased tumor interstitial fluid pressure (TIFP) stems from the accumulation of fluid due to the aberrant vascular architecture. In this context, metal-organic frameworks (MOFs) with catalytic efficiency have shown potential in degrading tumor interstitial components, thereby reducing interstitial pressure. However, the potential biotoxicity of the organic components of MOFs limits their clinical translation. To circumvent this, a MOF-like photocatalytic nanozyme, RPC@M, using naturally derived cobalt phytate (CoPA) and resveratrol (Res) is developed. This nanozyme not only facilitates the decomposition of water in the tumor interstitium under photoactivation to reduce TIFP, but also generates an abundance of reactive oxygen species through its peroxidase-like activity to exert cytotoxic effects on tumor cells. Moreover, Res contributes to the reduction of collagen deposition, thereby lowering TISP. The concurrent diminution of both TISP and TIFP by RPC@M leads to enhanced tumor penetration and potent antitumor activity, presenting an innovative approach in constructing tumor therapeutic nanozymes from natural products.

Numerical analysis on the effects of hydrothermal development on the permeability of porous reservoir based on coupled THMC modeling

As a clean and renewable energy, geothermal is gaining widespread attention worldwide. The development of hydrothermal resources is accompanied by the coupling processes of thermo-hydro-mechanical-chemical (THMC) caused by production and injection, which have a complex effect on the porosity and permeability of reservoir. Exploring the effects of these processes on the changes in various physical fields within the reservoir is of great significance for the efficient and sustainable development of geothermal energy. Based on the fully coupled framework of fluid flow and transfer in TOUGH2, a method that considered both mechanical and chemical processes was proposed and taken in this study, to analyze the effects of long-term injection and production on reservoir porosity and permeability. The results show that the effective stress changes under fluid pressure and thermal stress, as well as mineral dissolution and precipitation under chemical action, jointly led to the variation of reservoir porosity and permeability. The overall variation trend was mainly controlled by the mechanical action, as the influence of fluid pressure was more obvious and rapid, which dominated the mechanical changes of the whole reservoir in the early stage of injection (within 3.5 years). With the continuous injection, thermal stress played a more obvious role around the cooling area. By 30 years, the significant change in effective stress has extended to the entire reservoir. In the later stage of operation (after 20 years), as the temperature field of the reservoir gradually stopped changing, porosity began to increase under the dominance of fluid pressure. The effect of chemical action was long-term and lag in time. Mineral precipitation only occurred near the injection well, and the precipitation range and amount increased gradually with the continuous injection. By 30 years, the precipitation of dolomite injected into the grid reached 0.06%.

Effect of orientation and hardness of rubber tread block on the friction coefficient under glycerol lubrication and its underlying mechanisms

This study examines the influence of orientation and hardness of rubber tread blocks on friction under glycerol lubrication, focusing on negative fluid pressure. Measurements of fluid pressure, film thickness, and friction coefficient were conducted at the contact interface. Results showed that when tread blocks aligned parallel to the sliding direction, the friction coefficient increased by 57–191 %, attributed to either reduced film thickness or enlarged real contact area from greater negative fluid pressure. Conversely, with a perpendicular orientation, decreased hardness led to increased friction, due to thinner fluid films from enhanced negative pressure.

A coupling concept for Stokes-Darcy systems: The ICDD method

We present a coupling framework for Stokes-Darcy systems valid for arbitrary flow direction at low Reynolds numbers and for isotropic porous media. The proposed method is based on an overlapping domain decomposition concept to represent the transition region between the free-fluid and the porous-medium regimes. Matching conditions at the interfaces of the decomposition impose the continuity of velocity (on one interface) and pressure (on the other one) and the resulting algorithm can be easily implemented in a non-intrusive way. The numerical approximations of the fluid velocity and pressure obtained by the studied method converge to the corresponding counterparts computed by direct numerical simulation at the microscale, with convergence rates equal to suitable powers of the scale separation parameter ε in agreement with classical results in homogenization.

Deformation mechanisms and fluid conditions of mélange shear zones associated with seamount subduction

Lithologic heterogeneity and the presence of fluids have been linked to seamount subduction and collocated with slow earthquakes. However, the deformation mechanisms and fluid conditions associated with seamount subduction remain poorly understood. The exhumed Chichibu accretionary complex on Amami-Oshima Island preserves mélange shear zones composed of mudstone-dominated mélange and basalt–limestone mélange deformed under sub-greenschist facies metamorphism. The mudstone-dominated mélange contains sandstone, siliceous mudstone, and basalt lenses in an illitic matrix. The basalt–limestone mélange contains micritic limestone and basalt lenses in a chloritic matrix derived from the mixing of limestone and basalt at the foot of a seamount. The basalt–limestone mélange overlies the mudstone-dominated mélange, possibly representing a submarine landslide from the seamount onto trench-fill terrigenous sediments. The asymmetric S–C fabrics in both mélanges show top-to-SE shear consistent with megathrust-related shear. Quartz-filled shear and extension veins in the mudstone-dominated mélange indicate brittle failure at near-lithostatic fluid pressure and low differential stress. Microstructural observations show that deformation in the mudstone-dominated mélange was accommodated by dislocation creep of quartz and combined quartz pressure solution with frictional sliding of illite, whereas the basalt-limestone mélange was accommodated by frictional sliding of chlorite and dislocation creep of coarse-grained calcite, with possible pressure solution creep and diffusion creep of fine-grained calcite. The mélange shear zones formed in association with seamount subduction record temporal changes in deformation mechanisms, fluid pressure, and stress state during megathrust shear with brittle failure under elevated fluid pressure, potentially linking tremor generation near subducting seamounts.

Transient behavior of a plate partially immersed in the fluid subjected to impact loadings: Theoretical analysis and experimental measurements

This study aimed to investigate the transient behavior of a rectangular plate partially in contact with fluid subjected to a dynamic external force. To this purpose, a theoretical model was developed to analyze vibration characteristics and transient wave propagation. Based on superposition method, the dry mode shapes and natural frequencies of the plate under vacuum could be obtained. The dry mode shapes were treated as the fundamental function to construct the wet mode that describes the vibration behavior of the fluid-plate coupled system. The velocity potential and fluid pressure within a finite tank due to the plate deflection were derived using an equation governing the incompressible fluid. Based on the relationship between dry mode shape and wet mode shape, the fluid-plate coupled system's wet mode shape and resonant frequency could be determined from the frequency response function. Applying the normal mode method, the transient displacement of plate and fluid pressure can be obtained by solving a system of non-homogeneous differential equations. The theoretical predictions were verified by finite element method (FEM) and experimental measurements. Experiments were conducted using piezoelectric film sensors (polyvinylidene fluoride, PVDF) to measure the force history induced by a steel ball impact to quantitatively analyze the transient response. The comparison results proved that the theoretical predictions and experiments were in good agreement, including the transient responses of the displacement and in-plane strain of a plate partially submerged in the fluid. The results indicate that changes in water depth can induce resonance frequency shifts and wet mode shape distortions, which also illustrate that the vibrational properties of wet modes affect transient behavior. The proposed transient solution demonstrates an analytical approach that connects the physical significance of the dynamic behavior of the fluid-plate coupled system in time and frequency domains; it provides a connection between the transient behaviors and vibration characteristics.

Hamiltonian/Stroh formalism for reversible poroelasticity (and thermoelasticity)

Stroh’s sextic formalism represents the equilibrium equations of anisotropic elasticity in a particularly attractive form, that is most suitable for studying interface-dominated multilayered solids, composite materials and time-harmonic problems. Taking advantage of the fact that the Stroh formalism really amounts to the canonical form of the equations in the Hamiltonian sense, the case of Biot’s reversible (i.e. no fluid dissipation) poroelasticity is here addressed, in the absence of a fluid pressure gradient. This framework is the same as thermoelasticity of perfect conductors. Two Hamiltonian formulations are developed: the first describes both the solid and the fluid phases and it exhibits, besides energy conservation, momentum conservation, as a result of pressure uniformity (perfectly drained conditions). The second is restricted to the solid skeleton and perfectly parallels anisotropic elasticity, where the Stroh matrices refer to the effective stress tensor. The case of weak fluid–solid coupling is also considered and it produces a perturbation from anisotropic elasticity with the same structure as incompressibility, although in an “opposing” manner. This comparison suggests that the incompressibility limit introduced by Biot should be revised. The energy conservation integral and the edge impedance matrix are also illustrated.

Safe mud weight window in wellbore with mud-cake: A simple solution and verification

Under overbalanced drilling co0ndition, a layer of particulates from drilling mud, called mud-cake or filter-cake, is often formed on the wellbore surface as the drilling fluid seeps through the surrounding geological formation. Mud-cake acts like a soft filter reducing the fluid pressure exerted on the wellbore surface by the fluid in the well. In this work, the safe mud weight window for wellbores with mud-cake is analytically derived by combining the long-term poroelastic wellbore stress solutions with steady-state flow solution for a two-layer cylindrical well. Parametric study on mud-cake permeability and thickness verifies that a wellbore with mud-cake transits smoothly from permeable wellbore to impermeable wellbore as the mud-cake accumulates. The new solution of breakdown pressure is also validated by a hydromechanical interaction numerical simulation.

Constraints on fracture connectivity from AVAz analysis

The analysis of seismic reflection amplitude variations with incidence angle and azimuth (AVAz) is a powerful tool for studying and characterizing fractured formations. There is evidence to suggest that wave-induced fluid pressure diffusion (FPD) within connected fractures can significantly affect the AVAz response. This, in turn, indicates that this seismic attribute may contain information on the connectivity degree of the fracture network, which represents a key hydraulic property of fractured formations. The assessment of the sensitivity of seismic reflectivity with respect to fracture connectivity accounting for FPD effects is so far limited to 2D models, which is mainly due to the complexity and the associated computational cost of modeling the effective properties of corresponding generically anisotropic 3D media. To overcome these issues, we employ a numerical upscaling procedure based on Biot’s theory of poroelasticity that allows us to obtain effective anisotropic representations of 3D fractured formations accounting for FPD effects. Using these effective properties, we then perform a plane-wave analysis to compute the reflection coefficients at the top of the corresponding fractured formation. The results of our numerical analyses extend previous 2D studies and demonstrate that seismic reflection coefficients are highly sensitive to the degree of connectivity of the fracture networks. The reflectivity responses of formations comprising connected and unconnected fractures show pronounced differences not only with respect to incidence angle, but also with respect to azimuth. Quite importantly, our results also demonstrate that crossplots of commonly used AVAz coefficients permit us to identify regions with higher or lower fracture connectivity.

Fatigue performance testing and life prediction of welded fuel pipes

The external piping system which connects power devices, valve control devices, actuators, etc. is an essential system on the aero engine. Under the combined effects of high fluid pressure and external vibration, multiaxial fatigue failure is the main factor that seriously affects the safety of the piping system. The objective of this paper is to establish the multiaxial fatigue life model for the typical welded fuel pipe of the piping system by combining fatigue testing, simulation and theoretical analysis which is of great guiding significance for the engineering application of the piping system. Firstly, the fatigue limits of welded fuel pipes under no and 13.5 MPa internal pressure are obtained by rotational bending fatigue tests using the up-and-down method. Three additional stress levels of rotational bending fatigue tests under no internal pressure are supplemented and then the S-N curve is further obtained by the group method. Since the corresponding fracture surface of the specimens locates at the weld toe near the fixed end, peak stress method is adopted to evaluate the fatigue performance of the weld toe on the pipe specimens. In addition, by comparing the fatigue limit with no and 13.5 MPa internal pressured pipes, it is obvious that the equivalent uniaxial stress corrected by Gerber formula is not applicable for the multiaxial fatigue condition which is caused by the combined effect of fluid pressure and displacement load. The local stress concentration factor caused by the weld toe is determined and based on Findley critical plane model, the multiaxial fatigue life model is established which simultaneously takes the local stress concentration effect, mean stress effect and multiaxial stress effect into consideration. The results of rotational bending fatigue tests under 13.5 MPa internal pressure are within the triple error dispersion band and the accuracy of the proposed life model are verified.

Design, economic analysis, and environmental assessment of an innovative municipal solid waste-based multigeneration system integrating LNG cold utilization and seawater desalination

This paper presents a novel integrated solution for harnessing energy from biomass alongside liquefied natural gas cooling. The process is investigated and evaluated in various scenarios. This integrated system yields electricity, hydrogen, cold water, hot water, and fresh water. Thermodynamic analysis of the process is conducted under different scenarios. Moreover, the overall environmental damage effectiveness factor is calculated using exergo-environmental evaluation, revealing that heat exchanger E-103 exhibits the highest effectiveness factor of environmental damage, with an exergy efficiency of 37.3 %. Simulation results indicate an overall energy efficiency and overall exergy efficiency of 58.24 % and 31.97 %, respectively. Energy efficiencies of the process are found to be 32.15 %, 34.85 %, 36.71 %, and 58.24 % in single generation, combined heat and power, combined cooling, heating, and power, and multi-generation scenarios, respectively. The study evaluates the simultaneous effects of pressure and flow rate variations of liquefied natural gas fluid, input flow rate variations of municipal solid waste biomass, and cyclohexane working fluid pressure variations in the organic Rankine cycle on other variables. Finally, an economic evaluation of the new process outlines its annual cost and the levelized energy cost parameter under base design conditions, which amount to 9,383,042 $ and 0.092 $/kWh, respectively.

Modelling of water injection-induced shear stimulation and heat extraction in hot fractured reservoirs

Hydroshearing has been proposed as an effective technique for enhancing the permeability of fractured geothermal reservoirs. This approach involves complicated thermo-hydro-mechanical (THM) coupling, but the shear behaviour and its effect on flow and heat transfer are often simplified. In this study, Barton–Bandis (BB) joint behaviour is extended to include nonlinear rock joint deformation, shear dilation and post peak softening and healing behaviours. Two models of field-scale fractured geothermal reservoirs are considered. In addition, the widely used Mohr-Coulomb (MC) model is also incorporated into the THM coupled model for comparison. The results show that cold water injection-induced high-temperature rock contraction and fluid pressure increase, reducing the effective stress and promoting fracture shear deformation and irreversible slip. Moreover, shear dilation, shear softening, and nonlinear fracture opening notably alter reservoir permeability. The two models exhibit entirely different behaviours due to different pathway evolutions and consequent pressure build-up. The BB model displays a larger shear disturbance zone than the MC model, significantly enhancing the permeability and heat extraction within the fractured reservoirs. Accurate descriptions of the mechanical behaviour of rock fractures in hydroshearing models are crucial, suggesting the potential of these models to enhance fractured reservoirs and regulate fracturing for improved geothermal heat extraction.

Regulation of IFP in solid tumours through acoustic pressure to enhance infiltration of nanoparticles of various sizes

Numerous nanomedicines have been developed recently that can accumulate selectively in tumours due to the enhanced permeability and retention (EPR) effect. However, the high interstitial fluid pressure (IFP) in solid tumours limits the targeted delivery of nanomedicines. We were previously able to relieve intra-tumoural IFP by low-frequency non-focused ultrasound (LFNFU) through ultrasonic targeted microbubble destruction (UTMD), improving the targeted delivery of FITC-dextran. However, the accumulation of nanoparticles of different sizes and the optimal acoustic pressure were not evaluated. In this study, we synthesised Cy5.5-conjugated mesoporous silica nanoparticles (Cy5.5-MSNs) of different sizes using a one-pot method. The Cy5.5-MSNs exhibited excellent stability and biosafety regardless of size. MCF7 tumour-bearing mice were subjected to UTMD over a range of acoustic pressures (0.5, 0.8, 1.5 and 2.0 MPa), and injected intravenously with Cy5.5-MSNs. Blood perfusion, tumour IFP and intra-tumoural accumulation of Cy5.5-MSNs were analysed. Blood perfusion and IFP initially rose, and then declined, as acoustic pressure intensified. Furthermore, UTMD significantly enhanced the accumulation of differentially sized Cy5.5-MSNs in tumour tissues compared to that of the control group, and the increase was sevenfold higher at an acoustic pressure of 1.5 MPa. Taken together, UTMD enhanced the infiltration and accumulation of Cy5.5-MSNs of different sizes in solid tumours by reducing intra-tumour IFP.

Effect of swab and surge pressure on the time-dependent wellbore natural fracture development

Drilling engineers continue to grapple with the persistent challenge of maintaining wellbore stability. Throughout the drilling process, the wellbore pressure experiences fluctuations induced by various factors such as swab and surge pressure, leading to potential instability. This study employs a numerical approach, utilizing Abaqus software, to investigate the impact of swab and surge pressure on the natural fracture growth within the wellbore and the evolving pore pressure. A computational tool developed with MATLAB is then utilized to ascertain a safe operational mud window by assessing the time-dependent collapse and fracture pressures. The findings illustrated a notable increase in fracture width as a function of time in response to swab and surge pressure, with the most significant percentage increase reaching 69.92%. Notably, a 69.16% augmentation in fracture width is observed in the immediate vicinity of the wellbore following the application of swab and surge pressure. However, parameters such as fracture length, loss circulation rate, and pore fluid pressure exhibited marginal changes post-integration of swab and surge effects. The examination of the time-dependent wellbore stability after integration of swab and surge pressure indicated a narrowing of the initial mud window as a function of time, with a 14.33% increase in collapse pressure and a 13.80% decrease in fracture pressure. The numerical model verification against analytical solutions demonstrated good agreement, highlighting its potential utility in optimizing particle size for wellbore reinforcement and mitigating lost circulation through natural fracture sealing.

Effect of mineral dissolution on fault slip behavior during geological carbon storage

Geological carbon dioxide storage is one of the most effective technologies to reduce greenhouse gas emissions to the atmosphere. The mineral dissolution is inevitable during the long-term storage process, while the chemical effect on fault slip behavior remains poorly understood. In this paper, we present a hydro-chemical–mechanical coupled fault reactivation study using the unified pipe-interface element method (UP-IEM). The impact of chemical dissolution on stress redistribution is considered. The accuracy of the numerical method to simulate reactive solute transport and fault frictional slip are confirmed by analytical solution and numerical verification. Two different fault tectonic scenarios, of which fault locating in the caprock and fault crosscutting the reservoir and caprock, are designed to investigate the fault slip behavior induced by mineral dissolution. The effect of dissolved CO2 solute concentration, fault aperture, reservoir permeability and chemical reaction rate are discussed. Results show that fault locating in the caprock is easier to be activated. The chemical reaction has a more significant effect on fault slip behavior than fluid pressure during the long-term low-velocity CO2 leakage. The increase of CO2 solute concentration and reservoir reaction rate cause an obvious growth on fault slip displacement. The decrease of fault initial aperture results in the fault slip velocity slower and the slipping area smaller. The high-permeability reservoir keeps the fault more stable than low-permeability reservoir under the influence of mineral dissolution.

Design Calculation of Three Phase Separator

This research paper investigates the intricacies of design calculations involved in the development of three-phase separators in the oil and gas industry. Efficiently separating oil, water, and gas mixtures is crucial for maximizing production and ensuring compliance with environmental regulations. The paper explores the fundamental principles and equations used in the design of three-phase separators, including determining vessel dimensions, retention times, residence times, and separation efficiencies. Various factors influencing the design calculations, such as fluid properties, flow rates, pressure drops, and temperature gradients, are thoroughly analyzed. Additionally, the paper explores the importance of computational tools and simulation techniques in optimizing the design process and predicting separator performance under different operating conditions. Practical examples and case studies are provided to illustrate the application of design calculations in the successful implementation of three-phase separators in the oil and gas industry

Analysis of two discontinuous Galerkin finite element methods for the total pressure formulation of linear poroelasticity model

In this paper, we develop two discontinuous Galerkin (DG) finite element methods to solve the linear poroelasticity in the total pressure formulation, where displacement, fluid pressure, and total pressure are unknowns. The fully-discrete standard DG and conforming DG methods are presented based on the discontinuous approximations in space and the implicit Euler discretization in time. Compared to the standard DG method with penalty terms, the conforming DG method removes all stabilizers and maintains conforming finite element formulation by utilizing weak operators defined over discontinuous functions. The two methods provide locally conservative solutions and achieve locking-free properties in poroelasticity. We also derive the well-posedness and optimal a priori error estimates, which show that our methods satisfy parameter-robustness with respect to the infinitely large Lamé constant and the null-constrained specific storage coefficient. Several numerical experiments are performed to verify these theoretical results, even in heterogeneous porous media.