Pressure Solution Research Articles

New Green’s Function Method for Solving Underground Oil Seepage Problems

Abstract Compared with the variables separation method and integral-transform method, Green’s function method is much more applicable and thus of great practical significance. Based on the general steps of Green’s function method, a new method is originally raised to get Green’s function in oil and gas flow problems through underground formations. After that, the transient pressure solution is get for flow in a spherical reservoir by using this method. This case enlarged the application of Greenʼs method function, and this work can also be a good foundation for the solution of more and more complicated flow problems in oil and gas reservoirs.

Neural network surrogate for flow prediction and robust optimization in fractured reservoir systems

Embedded discrete fracture models are widely used to model flow in naturally fractured systems. These models are, however, time-consuming to simulate, and this limits their use for computationally demanding applications such as optimization. In this work we present a deep-learning-based surrogate model for fast prediction of time-varying well flow rates over multiple fracture realizations, for given well bottom-hole pressure schedules. Our surrogate model applies convolutional and recurrent neural networks. The convolutional neural network is used to capture the spatial variability of fractures in different realizations, though the direct input of the fracture geometry is not feasible because structured data are required. We show, however, that the use of the single-phase steady-state pressure solution defined on the structured rock-matrix grid, for each realization, provides the requisite input to the convolutional neural network. The resulting proxy is shown to give accurate flow rate predictions for different discrete fracture realizations. The proxy is then applied for robust optimization (expected net present value computed over an ensemble of realizations is optimized) subject to nonlinear output constraints. Proxy-based optimization provides an 18% improvement in net present value, with an overall speedup of ∼500 relative to simulation-based optimization. The optimized solutions are validated through comparison to simulation results, and agreement is within 1%.

Wormhole formation in massive gravity: an analytic description

The present study analyses the wormhole solution both in the dRGT-f(R, T) massive gravity and Einstein massive gravity. In both the models, the anisotropic pressure solution in ultrastatic wormhole geometry gives rise to the shape function that involves massive gravity parameters gamma and Lambda . However, the terms consisting of gamma and Lambda acts in such a way that the spacetime loses asymptotic flatness. Similar to the black hole solution in massive gravity, this inconsistency arises due to the repulsive effect of gravity which can be represented by the photon deflection angle that goes negative after a certain radial distance. It is investigated that the repulsive effect induced in the massive gravitons push the spacetime geometry so strongly that the asymptotic flatness is effected. On the other hand, in this model, one can have a wormhole with ordinary matter at the throat that satisfies all the energy conditions while the negative energy density is sourced by massive gravitons. Finally, using the TOV equation, it is found that the model is stable under the hydrostatic equilibrium condition.

Pressure solution-assisted diagenesis and thrusting-related deformation of Mesozoic platform carbonates

Depositional and diagenetic processes profoundly control the structural evolution of shallow-water carbonates through time. We focus on the Lower Jurassic platform carbonates pertaining to the southern Apennines fold-and-thrusts belt, Italy, by performing 3D digital outcrop modeling, field structural analysis, and microstructural investigation. Results show that pressure solution of the platform carbonates was affected by the grain size of single beds. Since early diagenesis, pressure solution localized within the coarser-grained carbonate beds, forming wave-like solution surfaces. Crosscutting relations among blocky cements, bed-parallel solution surfaces and high-angle veins show that pressure solution occurred during burial diagenesis with formation of wave-like solution surfaces, and during Late Miocene tectonic burial with formation of seismogram-like solution surfaces. The tectonic burial postdated the thrusting-related flexural slip folding and small-scale thrusting of the platform carbonates. Small scale thrusting took place by means of shearing of the bed-parallel heterogeneities, and formation of bed-oblique slickolites resulting in the development of back thrusts characterized by flat-ramp-flat geometries. The main results of this work are synthesized in a six-stage synoptic scheme reporting the structural evolution of the platform carbonates. Outcomes are helpful for the better assessment of geofluid production/storage from/in fractured platform carbonates pertaining to fold-and-thrust belts.

Water and SnF2 Assisted Ultralow-Temperature Sintering of Mechanically Tough Y3Fe5O12 Composites for Magneto-Dielectric Antennas

Recently, the cold sintering process (CSP) has gained worldwide recognition from the scientific community as a green and innovative fabrication technique due to the substantial reduction of processing energy, time, and cost. The present work reports the preparation, fabrication, and properties of (1 – x)Y3Fe5O12–xSnF2 (x = 0.2, 0.3, 0.4, 0.5 volume fraction) ceramic composites for the first time through the cold sintering process under 150 °C, by applying 300 MPa uniaxial pressure for 30 min. The evolved microstructures of the cold-sintered composites suggest enhanced densification with increasing SnF2 concentration. The evolution of the microstructure, consequent densification, and hardness of the composites can be due to the combined effect of water as a transient solvent and the relatively low melting point of SnF2. The main mechanism behind the densification in the SnF2-based system can be the liquid phase formation followed by pressure solution creep and plastic deformation. At the optimum additive concentration, the measured microhardness of the composite is around 4.7 GPa and its moisture absorption lies below 0.1%. The (1 – x)YIG–xSnF2 ceramics have relative permittivity (εr) in the range of 7.1–11.3 and loss tangent of the order of 10–2 at a frequency of 900 MHz. Further, the real part of permeability and the corresponding loss tangent lie below 2 and 10–1, respectively, at 900 MHz. Herein, a microstrip patch antenna (MPA) is designed, simulated, and fabricated using the 0.5YIG–0.5SnF2 composite, which shows excellent performance at 5.29 GHz with a return loss of −17.9 dB and an impedance bandwidth of 780 MHz. Hence, cold sintering using SnF2-based additives is considered a sustainable, energy-efficient, and cost-effective tool for the densification of magneto-dielectric materials.

Analytical solution of wave-induced pore pressure under solitary waves

Analytical solution of wave-induced pore pressure under solitary waves

Deployment of an electrocorticography system with a soft robotic actuator.

Electrocorticography (ECoG) is a minimally invasive approach frequently used clinically to map epileptogenic regions of the brain and facilitate lesion resection surgery and increasingly explored in brain-machine interface applications. Current devices display limitations that require trade-offs among cortical surface coverage, spatial electrode resolution, aesthetic, and risk consequences and often limit the use of the mapping technology to the operating room. In this work, we report on a scalable technique for the fabrication of large-area soft robotic electrode arrays and their deployment on the cortex through a square-centimeter burr hole using a pressure-driven actuation mechanism called eversion. The deployable system consists of up to six prefolded soft legs, and it is placed subdurally on the cortex using an aqueous pressurized solution and secured to the pedestal on the rim of the small craniotomy. Each leg contains soft, microfabricated electrodes and strain sensors for real-time deployment monitoring. In a proof-of-concept acute surgery, a soft robotic electrode array was successfully deployed on the cortex of a minipig to record sensory cortical activity. This soft robotic neurotechnology opens promising avenues for minimally invasive cortical surgery and applications related to neurological disorders such as motor and sensory deficits.

A fully coupled thermo-poro-elastic model predicting the stability of wellbore in deep-sea drilling. Part A: Analytic solutions

Wellbore stability is important to deep-sea drilling (DSD) for exploiting offshore oil and gas resources. Accurate prediction of the mechanical behaviors of rock formation around the wellbore can effectively prevent wellbore failure via adjusting mud weight. In this paper, a fully coupled thermo-poro-elastic (THM) model is developed by combining fluid circulation in the wellbore and rock deformation in the reservoir. Transient heat transfer in the wellbore/reservoir and heat exchange between the tubing, annulus, riser, casing, cement, seawater and rock formation are considered. By decomposing the problem into axisymmetric and antisymmetric sub-problems, the analytical solutions for transient temperature, pressure and stress in the rock formation and fluid temperature changes in the drill pipe, annulus and seawater near the riser are obtained and validated against with the numerical solutions, existing fluid circulation model, field measurement data and the existing model without considering fluid circulation. After that, a typical case study is carried out to show the mechanical behavior around the wellbore. It is found that the proposed fully coupled THM model has a high accuracy with a relative error of around 1.2%. There is a large difference in the predicted bottomhole temperature (BHT) and thus the temperature in the reservoir between the models with and without considering fluid circulation in the wellbore. An assumption of constant temperature boundary condition may lead to overestimated or underestimated results depending on the selection of the assigned wellbore temperature. In the DSD case studied, the rock formation at the upper part of the reservoir (Z < 0.40) is continuously heated and the rock formation at the lower part (Z > 0.6) of the reservoir is continuously cooled during fluid circulation, which thus results in a complex heat transfer and thus mechanical behavior in the wellbore/reservoir system, especially near the wellbore. The bottomhole temperature (BHT) decreases by 38.9 K due to cold fluid circulation from 3.68 min to 25.68 days, which can lead to 14.59 MPa tensile stress that cannot be ignored for wellbore stability analysis. The proposed analytical model provides a useful tool to predict the mechanical behaviors such as the transient temperature, pressure, displacement and stresses in the wellbore/reservoir system during fluid circulation in DSD. It runs efficiently in terms of seconds per case study in a portable laptop computer and can also work a benchmark for other numerical methods. However, the fully coupled THM model and its analytical solution are based on several assumptions, such as the heat generated by the drill bit rotation is ignored and only the liquid phase is considered, which requires further investigation.

Fractional derivative modelling for rheological characteristics of multilayered saturated porous rock with interfacial thermal contact resistance

AbstractIn this paper, the one‐dimensional rheological characteristics of multilayered saturated porous rock subjected to a ramp‐type heating is investigated. By introducing the fractional order parameter and material parameters, a viscoelastic constitutive model is proposed to describe the rheological characteristics of multilayered saturated porous rock. The general incomplete thermal contact model is established to predict the interfacial thermal contact resistance of multilayered saturated porous rock. Based on the coupled thermo‐hydro‐mechanical theory, the semi‐analytical solutions of the excess pore water pressure, temperature increment and displacement are obtained by using the Laplace transform method. The accuracy of the present solutions is verified by comparing with the classic elastic and viscoelastic models, and existing solutions. In addition, the influence of fractional order parameter, material parameter ratio, thermal contact transfer coefficient and thermal partition coefficient on the excess pore water pressure, temperature increment and displacement of multilayered saturated porous rock are investigated.

A research on excavation compensation theory for large deformation disaster control and a review on the multiphysical–multiscale responses of salt rock for underground gas storage

A research on excavation compensation theory for large deformation disaster control and a review on the multiphysical–multiscale responses of salt rock for underground gas storage

Analytical solutions of limit support pressure and vertical earth pressure on cutting face for tunnels

This paper focuses on theoretical analytical models to calculate the limit support pressure and vertical earth pressure on the cutting face for tunnels. The failure zone is divided into two parts: a sliding failure zone and an upper loosen zone, and the limit support pressure calculation equation is derived. To verify the rationality of the theoretical model, it was compared with the existing theory, numerical simulation, and centrifugal test, and then the parameter analysis was carried out. The results show that the results of this paper agree well with the existing theory, numerical simulation, and centrifugal test. The inclination angle of the proposed mechanism is determined based on the results of the existing centrifuge test, and the recommended inclination angle is between 52° + φ/2 and 54° + φ/2. The method is proven to be safe and accurate. It can provide a theoretical basis for similar projects.

Multiscale model to resolve the chemical environment in a pressurized CO2-captured solution electrolyzer

The community of electrochemical CO2 reduction is almost exclusively focused on gaseous CO2-fed electrolyzers. Here, we proposed a pressurized CO2-Captured solution electrolyzer to produce solar Fuel of CO (abbreviated “CCF”) without the need to regenerate gaseous CO2. Specifically, we developed an experimentally validated multiscale model to quantitatively investigate the effect of pressure-induced chemical environment and to resolve the complex relationship between this effect and the activity and selectivity of CO production. Our results show that the pressure-induced variation of the cathode pH has a negative effect on the hydrogen evolution reaction, whereas the species coverage variation positively affects CO2 reduction. These effects are more pronounced at pressures below 15 bar (1 bar = 101 kPa). Consequently, a mild increase in the pressure of the CO2-captured solution from 1 to 10 bar leads to a dramatic enhancement in selectivity. Using a commercial Ag nanoparticle catalyst, our pressurized CCF prototype achieved CO selectivity higher than 95% at a low cathode potential of −0.6 V versus reversible hydrogen electrode (RHE), comparable to that under the gaseous CO2-fed condition. This enables the demonstration of a solar-to-CO efficiency of 16.8%, superior to any known devices with an aqueous feed.

Dependence of Slippery and Elastic Properties of Thin Polymer Films on the Grafted Flexible Sidechain Amount

In modern life, people face a wide number of sticky problems when adhesion is highly undesirable: water and dirt stick to clothes, useful materials stick to the walls of their containers and cannot be fully used, water sticking and freezing on airplane wings affects handling and can be dangerous, biological liquids can stick and form clots inside medical devices threatening patients' lives, etc. Slippery liquid-infused porous surfaces (SLIPSs) with pressure stable omniphobicity could help to solve these issues. Lubricant depletion from porous surface and subsequent degradation of omniphobic properties is the major problem for SLIPS. It could be resolved by attaching flexible, liquid-like sidechains to the polymer matrix. Understanding the relationship between the structure of such polymer films and wetting effects is therefore of great importance. The present work is devoted to the study of droplet pinning on crosslinked polydimethylsiloxane (PDMS) polymer films with varied amounts of attached flexible PDMS sidechains and clarification of the relationship between slippery and viscoelastic properties of the films. An one-stage approach to the synthesis of such slippery coatings on smooth and porous substrates in "eco-friendly" pressurized CO2 solutions is proposed. Pinning force and Young's modulus (E) of the films on silicon substrates with variation of the grafted sidechains amount (x) are measured. The non-monotonic dependence of the pinning force on the amount of sidechains is obtained: the pinning force decreases at small x values (region I) and starts to increase at higher x (region II). The effects of the grafted sidechains amount, as well as matrix softening, are discussed for each case. It is demonstrated that the proposed method of film synthesis allows one to obtain thin, uniform coatings on fabrics without gluing the fibers. Such coatings with an optimal amount of PDMS sidechains demonstrate decreased sliding angles for droplets of water and aqueous alcohol solutions, as compared to PDMS coatings without grafted sidechains. The proposed technique may be of interest for deposition of coatings on porous surfaces having a complex morphology, such as textiles, aerogels, porous electrodes, etc.

Forward Osmosis for Metal Processing Effluents under Similar Osmotic Pressure Gradients.

Water recovery from aqueous effluents in the mining and metals processing industry poses a unique challenge due to the high concentration of dissolved salts typically requiring energy intensive methods of treatment. Forward osmosis (FO) is a lower energy technology which employs a draw solution to osmotically extract water through a semi-permeable membrane further concentrating any feed. Successful FO operation relies on using a draw solution of higher osmotic pressure than the feed to extract water while minimizing concentration polarization to maximize the water flux. Previous studies employing FO on industrial feed samples commonly used concentration instead of osmotic pressures for feed and draw characterization; this led to misleading conclusions on the impact of design variables on water flux performance. By employing a factorial design of experiments methodology, this study examined the independent and interactive effects on water flux by: osmotic pressure gradient, crossflow velocity, draw salt type, and membrane orientation. With a commercial FO membrane, this work tested a solvent extraction raffinate and a mine water effluent sample to demonstrate application significance. By optimizing with osmotic gradient independent variables, water flux can be improved by over 30% without increasing energy costs or compromising the 95-99% salt rejection of the membrane.

Burst Pressure Solutions of Thin and Thick-Walled Cylindrical Vessels

Abstract Pressure vessels (PVs) are widely used in the energy industry. Accurate burst pressure is critical to structural design and safe operation for both thin and thick-walled PVs. The traditional strength theories utilized a single-parameter material property, such as the yield stress or the ultimate tensile stress (UTS) to develop failure models for determining the yield or ultimate pressure carrying capacity in the PV design. The UTS-based Barlow formula is a typical burst pressure model developed from the Tresca strength theory that provides the basis for developing regulation rules and failure models for different industry design codes, such as ASME BPVC, ASME B31.3, and ASME B31G, among others. In order to reduce the conservatism of the Tresca strength model, ASME BPVC recently adapted failure models developed from the von Mises strength theory for the PV design and analysis. It has been commonly accepted that the burst pressure of pipelines depends on the UTS and strain hardening exponent, n, of the pipeline steel. An average shear stress yield theory was thus developed, and the Zhu-Leis solution of burst pressure was obtained as a function of UTS and n for thin-walled line pipes. Experiments showed that the Zhu-Leis solution provides an accurate, reliable prediction of burst pressure for defect-free thin-walled pipes. In order to extend the Zhu–Leis solution to thick-walled cylindrical PVs, this paper defined three new flow stresses, modified the traditional strength theories, and obtained three new burst pressure solutions that are valid for both thin and thick-walled cylindrical vessels. The proposed flow stresses are able to describe the tensile strength and the plastic flow response of PVs for a strain hardening steel. The associated strength theories were then developed in terms of the Tresca, von Mises, and Zhu-Leis yield criteria. From these new strength theories, three burst pressure solutions were obtained for thick-walled cylinders, where the von Mises solution is an upper bound prediction, the Tresca solution is a lower bound prediction, and the Zhu-Leis solution is an intermediate prediction of burst pressure for thick-walled cylinders. Finally, the proposed burst pressure solutions were evaluated and validated by two large datasets of full-scale burst tests for thick-walled tubes and for thin-walled pipes.

A parallel unstructured multi-color SOR solver for 3D Navier–Stokes equations on graphics processing units

In this paper, we develop a GPU parallelization technique to accelerate the pressure Poisson solver. We apply it in three-dimensional Navier–Stokes simulations with arbitrary geometries. The numerical method is based on a projection method, and the discretization is obtained by combining a second-order unstructured finite-volume method and a σ transformation. The pressure solution is responsible for this formulation’s most time-consuming computation tasks. This is because the Poisson equation must be approximated. This work proposes a GPU-based Multi-Color Successive Over-Relaxation (MC-SOR) method to solve the resulting sparse linear system. The proposed parallel finite-volume code is verified and validated by solving the Poisson problem. We employ analytical solutions and well-known benchmark problems with complex flows. These include the Taylor–Green vortex problem and the problem of turbulent flow around a circular cylinder.

Improved equations of ground pressure for shallow large-diameter shield tunnel considering multiple impact factors

Reasonable estimation of ground pressure is of vital importance for lining segments design in shield tunnelling. With the rapid development of the urban transportation, the diameter of the shield tunnel tends to become larger. The existing prediction of the ground pressure may overestimate the ground pressure of the shallow large-diameter shield tunnel and thus produce higher cost for the shield tunnel construction. To provide more reasonable solution for ground pressure surrounding the shallow large-diameter shield tunnel, a series of improved equations are proposed in this study. The two-stage method with non-uniform displacement pattern through numerical modelling is used to simulate the shield tunnelling at first. Secondly, the effect of multiple impact factors on horizontal and vertical ground pressure at tunnel vault, haunch and invert is analyzed and five key impact factors are determined. Thirdly, a series of improved equations are presented based on a large number of numerical modelling through nonlinear regression analysis. These improved equations can consider the effect of multiple impact factors and predict the ground pressure varying with position which is more realistic for the shallow large-diameter shield tunnel. Therefore, when compared with both the numerical modelling results and field measurements for 70 case histories, the improved equations show good performance. Also, the ground pressure of the above cases is calculated by traditional methods such as overburden pressure, Protodiaconov's formula and so on. By contrast to 7 traditional methods, the improved equations predict more reasonable result of ground pressure. At last, the influence of the tunnel axis depth, tunnel diameter, GAP parameter, ground classification and in-situ coefficient of lateral pressure at rest on the vertical ground pressure at tunnel vault is investigated through the improved equations. The results indicate that the tunnel size is of significant importance to the ground pressure as expected and thus special attention should be paid to shallow large-diameter shield tunnel. However, engineers may save the cost when tunnel diameter outweighs 15 m as ground pressure varies insignificantly. Furthermore, the initial stress as well as the GAP parameter which represents the shield tunnel construction details also play a vital role in ground pressure.

Slip-Line Solution for the Active Earth Pressure of Narrow and Layered Backfills against Inverted T-Type Retaining Walls Rotating about the Base

In this research, we used a slip-line method for a typical failure mechanism simulated with adaptive finite-element software to investigate the active earth pressure of narrow and layered backfills against inverted T-type retaining walls rotating around the base mode. The slip-line field calculation models for the inverted T-type retaining wall with narrow and layered backfills were established considering the effect of the heel bottom plate and the inverted T-type retaining wall characteristics. Subsequently, the limit equilibrium and finite difference methods were used to solve the stress state of each point. The earth pressure acting on the stem and the second failure surface can be obtained by converting the boundary conditions. The proposed method was verified by comparing its results with those from finite-element limit analysis and existing theoretical solutions. Furthermore, several extensive parametric studies have investigated the effects of backfill width, heel length, and interface strength. The results show that increasing interface strength and decreasing backfill width help reduce the earth pressure against the stem and second failure surface. The change in the length of the heel bottom plate exhibited a dual effect.

General variational solution for seismic and static active earth pressure on rigid walls considering soil tensile strength cut-off

General variational solution for seismic and static active earth pressure on rigid walls considering soil tensile strength cut-off

Carbonate diagenesis: A celebration of the work of John Anthony Dawson (Tony) Dickson

Carbonate diagenesis: A celebration of the work of John Anthony Dawson (Tony) Dickson