页岩气地质—工程可压度评价方法研究及应用

针对目前页岩气水平井部分压裂段簇产量贡献率低,且与相应的地质甜点与工程甜点评价结果吻合程度低的问题,提出应用与压裂后产量相关性更强的甜度概念深化以往甜点研究的不足,在此基础上提出由地质甜度与工程甜度计算的综合甜度即可压度来表征可压性程度的方法。研究及应用结果表明:基于提出的页岩气地质甜度与工程甜度新理念,利用可压度表征可压性的理念与技术方法,增强了水平井分段压裂设计与施工的科学性与实用性;无效段簇占比由33%降至13%~20%,平均单井产量提高35.6%,单簇裂缝改造体积提高约15%,可压度大于0.5时,压裂效果较好。建议进一步加大页岩气可压度评价体系的应用力度,特别是在常压与深层页岩气中的应用与验证,并在应用中进一步完善与迭代升级。

页岩储层可压性调研及新发现

如何高效经济开采页岩气引起国内研究人员的重视。开采页岩气常用的方法就是水力压裂法,压裂最重要的是形成网状裂缝,研究表明页岩可压性随着外界因素的变化而呈现出一定的规律,于是在提出了"可压度"这个概念来评价储层可压性,页岩气储层的可压度与脆性指数呈正相关,与断裂韧性呈负相关,可压度可以由脆性指数和断裂韧度之比来表征,可压度越大,可压性越好,可压度可以更好地评估储层开采效果。

Temperature distribution for controlled-dwell extrusion of γ-TiAl

Ti-47Al-2Cr-2Nb-0.15B alloy （atom fraction） was extruded at temperatures（Tα） of 1250 and 1330 ℃, respectively. The method of adding a thermal insulating layer was used to overcome the problem associated with the flow stress mismatch between the can and the billet during extrusion. Effects of two kinds of insulations, ZrO2 powders and silica fibers, on the quality of extrude bar along the radial direction were studied, and the process parameters were optimized by combining with finite element method （FEM）. Tensile properties of the extruded alloy at room and elevated temperature were tested. The results show that the silica fibers has better thermal insulating property than ZrO2 powders. The temperature distribution in radial is more homogeneous using silica fibers. The alloy has a good balance of yield strength and room temperature ductility and the values are 680MPa and 3.5%, respectively.

Ultra-High Strength Concrete Mixtures Using Local Materials

This paper presents the development of ultra high strength concrete （UHSC） using local materials. UHSC mixture proportions were developed using local materials so that UHSC may be made more affordable to a wider variety of applications. Specifically, local sand with a top size of 600 um, and locally available Type I/II cement and silica fume were used in this research. Each of these material selections is seen as an improvement in sustainability for UHSC. Two mixtures （one with and one without fibers） were recommended as the UHSC mixtures. The greatest compressive strengths obtained in this study were 165.6 MPa for UHSC with steel fibers and 161.9 MPa for UHSC without fibers. The compressive and flexural strengths obtained from the UHSC mixtures developed in this work are comparable to UHSC strengths presented in the literature. Producing this innovative material with local materials reduces the cost of the material, improves sustainability, and produces mechanical performance similar to prepackaged, commercially available products.

Numerical Simulation of Viscoelastic Extrudate Swell Through Elliptical Ring Die

The numerical simulation of extrudate swell is significant in extrusion processing.Precise prediction of extrudate swell is propitious to the control of melt flow and the quality of final products.A mathematical model of three-dimensional（3D）viscoelastic flow through elliptical ring die for polymer extrusion was investigated.The penalty function formulation of viscoelastic incompressible fluid was introduced to the finite element model to analyze 3D extrusion problem.The discrete elastic viscous split stress（DEVSS）and streamline-upwind PetrovGalerkin（SUPG）technology were used to obtain stable simulation results.Free surface was updated by updating the streamlines which needs less memory space.According to numerical simulation results,the effect of zero-shear viscosity and elongation parameter on extrudate swell was slight,but with the increase of volumetric flow rate and relax time the extrudate swell ratio increased markedly.Finally,the numerical simulation of extrudate swell flow for low-density polyethylene（LDPE）melts was investigated and the results agreed well with others’work.These conclusions provided quantitative basis for the forecasting extrudate swell ratio and the controlling of extrusion productivity shape.

CFD Investigation of Compressible Low Angles of Attack Flow over the Missile

In modem missile design, the operation of a missile aerodynamics with angles of attack is required to serve a demand on the maneuverability. The key aero-physics is the development of vortices and its interaction to the control surface such as wing and fins. This paper thus presents the investigation of the missile flow field at 4° and 8° degrees of angles of attack. The Mach numbers for both case were varied from 0.6 to 5.5. Here, the Steady Reynolds-Averaged Navier-Stokes （SRANS） equations with standard κ-ε turbulence model were selected. The numerical results of aerodynamics coefficients （both force and moment） were compared against semi-empirical data computed using Missile DatCOM. The results revealed the development of vortices observed and their interaction with fin at the rear part of the missile.

The Pressure Gradient Elastic Wave： Energy Transfer Process for Compressible Fluids with Pressure Gradient

The temperature separation was discovered inside the short vortex chamber （H/D = 0.18）. Experiments revealed that the highest temperature of the periphery was 465 ℃, and the lowest temperature of the central zone was -45 ℃ （the compressed air was pumped into the chamber at room temperature）. The objective of this paper is to proof that this temperature separation effect cannot be explained by conventional heat transfer processes. To explain this phenomenon, the concept of PGEW （Pressure Gradient Elastic Waves） is proposed. PGEW are kind of elastic waves, which operate in compressible fluids with pressure gradients and density fluctuations. The result of PGEW propagation is a heat transfer from area of low pressure to high pressure zone. The physical model of a gas in a strong field of mass forces is proposed to substantiate the PGEW existence. This physical model is intended for the construction of a theory of PGEW. Understanding the processes associated with the PGEW permits the possibility of creating new devices for energy saving and low potential heat utilization, which have unique properties.

Highly Efficient Lattice Boltzmann Model for Compressible Fluids:Two-Dimensional Case

We present a highly efficient lattice Boltzmann model for simulating compressible flows. This model is based on the combination of an appropriate finite difference scheme, a 16-discrete-velocity model [Kataoka and Tsutahara, Phys. Rev. E 69 （2004） 035701（R）] and reasonable dispersion and dissipation terms. The dispersion term effectively reduces the oscillation at the discontinuity and enhances numerical precision. The dissipation term makes the new model more easily meet with the yon Neumann stability condition. This model works for both high-speed and low-speed flows with arbitrary specific-heat-ratio. With the new model simulation results for the well-known benchmark problems get a high accuracy compared with the analytic or experimental ones. The used benchmark tests include （i） Shock tubes such as the Sod, Lax, Sjogreen, Colella explosion wave, and collision of two strong shocks, （ii） Regular and Mach shock reflections, and （iii） Shock wave reaction on cylindrical bubble problems. With a more realistic equation of state or free-energy functional, the new model has the potential tostudy the complex procedure of shock wave reaction on porous materials.

Theoretical investigation of micropolar fluid flow between two porous disks

The steady, laminar, incompressible and two dimensional micropolar flow between two porous disks was investigated using optimal homotopy asymptotic method(OHAM) and fourth order Runge–Kutta numerical method. Comparison between OHAM and numerical method shows that OHAM is an exact and high efficient method for solving these kinds of problems. The results are presented to study the velocity and rotation profiles for different physical parameters such as Reynolds number, vortex viscosity parameter, spin gradient viscosity and microinertia density parameter. As an important outcome, the magnitude of the microrotation increases with an increase in the values of injection velocity while it decreases by increasing the values of suction velocity.

Low secondary compressibility and shear strength of Shanghai Clay

In order to investigate the compressibility, particularly the secondary compression behaviour, soil structure and undrained shear strength of Shanghai Clay, a series of one-dimensional consolidation tests （some up to 70 d） and undrained triaxial tests on high-quality intact and reconstituted soil specimens were carried out. Shanghai Clay is a lightly overconsolidated soil （OCR=1.2-1.3） with true cohesion or bonding. Due to the influence of soil structures, the secondary compression index Ca varies significantly with consolidation stress and the maximum value of C~ occurs in the vicinity of preconsolidation stress. Measured coefficients of secondary compression generally fall in the range of 0.2%-0.8% based on which Shanghai Clay can be classified as a soil with low to medium secondary compressibility. The effect of soil structures on the compressibility of Shanghai Clay is found to reduce with an increase in depth. Soil structure has an important influence on initial soil stiffness, but does not appear to affect undrained shear strength significantly. Undrained shear strengths of intact Shanghai Clay from compression tests are approximately 20% higher than those from extension tests.

On maximum power point tracking control strategy for variable speed constant frequency wind power generation

Based on the characteristic of AC-excited variable speed constant frequency(VSCF)wind power generation,the vector control technique was applied in a doubly fed induction generator(DFIG).Maximum wind energy or maximum output power point can be tracked by decoupling control of active power and reactive power.The research result shows that the net power of generation system delivered to grid in maximum wind energy tracking mode is not the most.We presented a novel maximum power point tracking(MPPT)control strategy by analyzing the DFIG mathematic model and power relations which delivered the maximum power to the grid.The maximum power point could be tracked automatically without measuring wind speed in the control strategy and the control was independent of optimal turbine power curve,which had excellent dynamic and static performances and robustness.Simulation and experimental results testify the accuracy and validity of the control strategy.

Effects of working parameters on gasoline engine exergy balance

To improve the energy utilization efficiency of internal combustion （IC） engine, exergy analysis was conducted on a passenger car gasoline engine. According to the thermodynamic theory of IC engine, in-cylinder exergy balance model was built. The working processes of gasoline engine were simulated by using the GT-power. In this way, the required parameters were calculated and then gasoline engine exergy balance was obtained by programming on computer. On this basis, the influences of various parameters on exergy balance were analyzed. Results show that, the proportions of various forms of exergy in gasoline engine from high to low are irreversible loss, effective work, exhaust gas exergy and heat transfer exergy. Effective exergy proportion fluctuates with cylinder volumetric efficiency at full load, while it always increases with break mean effective pressure （BMEP） at part load. Exhaust gas exergy proportion is more sensitive to speed, and it increases with speed increasing except at the highest speed. The lower proportion of heat transfer exergy appears at high speed and high load. Irreversible loss is mainly influenced by load. At part load, higher BMEP results in lower proportion of irreversible loss; at full load, the proportion of irreversible loss changes little except at the highest speed.

Computer Controlled High Precise, High Voltage Pules Generator

High precise, high voltage pulse generator made up of high-power IGBT and pulse transformers controlled by a computer are described. A simple main circuit topology employed in this pulse generator can reduce the cost meanwhile it still meets special requirements for pulsed electric fields (PEFs) in food process. The pulse generator utilizes a complex programmable logic device (CPLD) to generate trigger signals. Pulse-frequency, pulse-width and pulse-number are controlled via RS232 bus by a computer. The high voltage pulse generator well suits to the application for fluid food non-thermal effect in pulsed electric fields, for it can increase and decrease by the step length 1.

Research on the Correlation of the Fluctuating Density Gradient of the Compressible Flows

This work is to study a role of the fluctuating density gradient in the compressible flows tbr the computational fluid dynamics （CFD）. A new anisotropy tensor with the fluctuating density gradient is introduced, and is used for an invariant modeling technique to model the turbulent density gradient correlation equation derived from the continuity equation. The modeling equation is decomposed into three groups proportional to the mean velocity, proportional to the mean strain rate, and proportional to the mean density. The characteristics of the correlation in a wake are extracted from the results by the two dimensional direct simulation, and shows the strong correlation with the vortices in the wake near the body. Thus, it can be concluded that the correlation of the density gradient is a significant parameter to describe the quick generation of the turbulent property in the compressible flows.

Spectral Methods for Two Dimensional Incompressible Flow

We take the two dimensional vorticity equations as models to describe spectral methods and their combinations with finite difference methods or finite element methods, which are applicable to other similar nonlinear problems. Some numerical results and error estimates of these methods are given.

Compressibility dependence on grain size distribution and relative density in sands

A framework of continuum breakage mechanics was used to investigate the dependence of compressibility on grain size distribution(GSD)as well as relative density of sand.Compressibility dependence on GSD was considered by employing a GSD index and relative density dependence was reflected by varying the plastic-breakage coupling angle.Simulations of the experimental results including isotropic compression and one-dimensional compression of sands with different relative densities and GSDs revealed that sand compressibility increased with the increasing GSD index and plastic-breakage coupling angle.The coupling angle decreased with increasing relative density,indicating that grains would break more in sand with comparatively high relative density.

Weak-strong uniqueness for the compressible Navier-Stokes equations with a hard-sphere pressure law

We consider the Navier-Stokes equations with a pressure function satisfying a hard-sphere law.That means the pressure,as a function of the density,becomes infinite when the density approaches a finite critical value.Under some structural constraints imposed on the pressure law,we show a weak-strong uniqueness principle in periodic spatial domains.The method is based on a modified relative entropy inequality for the system.The main difficulty is that the pressure potential associated with the internal energy of the system is largely dominated by the pressure itself in the area close to the critical density.As a result,several terms appearing in the relative energy inequality cannot be controlled by the total energy.

Global well-posedness of 3-D density-dependent Navier-Stokes system with variable viscosity

Given initial data(ρ0, u0) satisfying 0 < m ρ0≤ M, ρ0- 1 ∈ L2∩˙W1,r(R3) and u0 ∈˙H-2δ∩ H1(R3) for δ∈ ]1/4, 1/2[ and r ∈ ]6, 3/1- 2δ[, we prove that: there exists a small positive constant ε1,which depends on the norm of the initial data, so that the 3-D incompressible inhomogeneous Navier-Stokes system with variable viscosity has a unique global strong solution(ρ, u) whenever‖ u0‖ L2 ‖▽u0 ‖L2 ≤ε1 and ‖μ(ρ0)- 1‖ L∞≤ε0 for some uniform small constant ε0. Furthermore, with smoother initial data and viscosity coefficient, we can prove the propagation of the regularities for such strong solution.

Supersonic-Subsonic Transition in Relatively Narrow Channels

The flow structure in relatively narrow channels has a strong three-dimensional character with complex flow phenomena, including regions of localized separation, various vortical smictures, etc., all of which have to be considered when dealing with the problem of supersonic-subsonic transition. In this paper only the following three problems are considered: 1. the effect of channel width on transition from supersonic to subsonic velocities, 2. transition from supersonic to subsonic velocities in a system of shock waves - pseudoshock wave, 3. transition from subsonic to supersonic velocities in a critical cross section at the end of a duct with fully developed turbulent channel flow. Problems connected with vortical structures and flow separation were discussed by the same author elsewhere (see References).

Temperature Distribution on Inclined Plate Caused by Interaction withSupersonic Jet

The Phenomena of the interaction between a supersonic jet and an obstacle is a very interesting and important problem relating to the industrial engineering. This paper aims to investigate the characteristics of the two-dimensional temperature distribution on an inclined plate surface and the relation between the temperature distribution and some shock waves formed in the flow field. In this study, the measurement of temperature distribution on an inclined plate surface and the now visualization has carried out for various conditions using the thermo-sensitive liquid crystal sheet and the schlieren method. The two dimensional temperature distribution on the plate surface is clearly obtained by the thermo-sensitive liquid crystal sheet. The relation between the temperature distribution on an inclined plate surface and some shock waves reached at a plate surface is discussed. In this paper, the characteristics of the temperature distribution and the maximum temperature, and some other experimental evidences are presented.