影响气层中途测试资料解释准确性的因素分析

由于天然气的可压缩性及含硫化氢高等特点 ,气井的测试资料往往会因为井筒效应大而出现曲线变化复杂 ;或者含硫气井测试受时间限制而出现曲线不完整的情况 ;这些情况 ,会影响对油藏模型的诊断和资料解释的精度。针对以上问题 ,文章主要介绍如何区分双对数曲线中的变井筒效应和复杂模型的方法 ,以及如何正确处理含硫气井测试时间短和取全原始资料的之间的矛盾 ,另外 ,文中分析了针对气井测试的拟时间法 ,这种方法的使用与否会影响对气层解释的准确性。

NUMERICAL SIMULATIONS OF EVOLUTIONS FROM WALL PULSE TO TURBULENT COHE RENT STRUCTURES

The high order compact d if ference method is developed for solving the perturbation equations based on Navi er Stokes equations, and is used in studying complex evolution processes from w all negative pulse to the turbulent coherent structure in the channel flow. Th is method contains three dimensional coupling difference scheme with high accur acy and high resolution, and the high order time splitting methods. Compared with the general spectral method, the method can be used to research turbule nt coherent structure under more general boundary conditions and in flow domains . In this paper, the generation and evolution of the turbulent coherent structur es ind uced by wall pulse in the channel flow are simulated, and the basic characterist ics and rules of the turbulent coherent structure are shown. Computational r esults indicate that a wall negative pulse is more convenient than the resonant three wave model.

Three-dimensional numerical modeling of fullspace transient electromagnetic responses of water in goaf

The full-space transient electromagnetic response of water-filled goaves in coal mines were numerically modeled. Traditional numerical modeling methods cannot be used to simulate the underground full-space transient electromagnetic field. We used multiple transmitting loops instead of the traditional single transmitting loop to load the transmitting loop into Cartesian grids. We improved the method for calculating the z-component of the magnetic field based on the characteristics of full space. Then, we established the full- space 3D geoelectrical model using geological data for coalmines. In addition, the transient electromagnetic responses of water-filled goaves of variable shape at different locations were simulated by using the finite-difference time-domain （FDTD） method. Moreover, we evaluated the apparent resistivity results. The numerical modeling results suggested that the resistivity differences between the coal seam and its roof and floor greatly affect the distribution of apparent resistivity, resulting in nearly circular contours with the roadway head at the center. The actual distribution of apparent resistivity for different geoelectrical models of water in goaves was consistent with the models. However, when the goal water was located in one side, a false low-resistivity anomaly would appear on the other side owing to the full-space effect but the response was much weaker. Finally, the modeling results were subsequently confirmed by drilling, suggesting that the proposed method was effective.

Direct fitting measurement of gas content in coalbed and selection of reasonable sampling time

In this study, we selected 9 typical coal samples with different metamorphic grades as the study subjects,measured their initial 30-min gas desorption at 30℃ and different pressure using a self-developed gas adsorption/desorption device. Based on the characteristics of gas desorption from coal samples, we proposed a direct fitting method for measurement of gas content in coalbed, analyzed the effects of sampling time on the measurement results and determined the reasonable sampling time of coal samples with different metamorphic grades at different gas adsorption pressure at equilibrium. The results show that (1)the error of gas contents obtained using the direct fitting method relative to that obtained using indirect method is less than 10%, which meets the actual on-site requirements and verifies the feasibility of the direct fitting method;(2) when the relative error is controlled within ±10%, the reasonable sampling time of coal samples is linearly related to the gas adsorption pressure at equilibrium;(3) the reasonable sampling time of coal samples with the same metamorphic grade exhibits a shortening trend with increasing gas adsorption pressure at equilibrium;(4) for coal samples with similar gas adsorption pressure at equilibrium, the reasonable sampling time of coal samples displays a shortening trend with increasing metamorphic grade. Overall, the study provides a basis for improving the measurement accuracy of gas content in coalbed.

An improvement to the simulation of phase-change heat-transfer during soil freezing and thawing

A new variable time step method,which is called the backwards calculating time step method,is presented in this paper.It allows numerical simulation of soil freezing and thawing while avoiding "phase change missing and overflowing".A sensitive heat capacity model is introduced through which the calculation errors are analyzed.Then the equation using the self-adjusted time step is presented and solved using finite differences.Through this equation,the time needed for a space cell to reach the phase change point temperature is calculated.Using this time allows the time step to be adjusted so that errors caused by "phase change missing and overflowing" are successfully eliminated.Above all,the obvious features of this method are an accelerated rate for adjusting the time step and simplifing the computations.An actual example proves that this method can accurately calculate the temperature fields during soil freezing and thawing.It is an improvement over traditional methods and can be widely used on complicated multi-dimensional phase change problems.

Finite difference time domain method forward simulation of complex geoelectricity ground penetrating radar model

The ground penetrating radar(GPR) forward simulation all aims at the singular and regular models, such as sandwich model, round cavity, square cavity, and so on, which are comparably simple. But as to the forward of curl interface underground or “v” figure complex model, it is difficult to realize. So it is important to forward the complex geoelectricity model. This paper takes two Maxwell’s vorticity equations as departure point, makes use of the principles of Yee’s space grid model theory and the basic principle finite difference time domain method, and deduces a GPR forward system of equation of two dimensional spaces. The Mur super absorbed boundary condition is adopted to solve the super strong reflection on the interceptive boundary when there is the forward simulation. And a self-made program is used to process forward simulation to two typical geoelectricity model.

Calculation of all-time apparent resistivity of large loop transient electromagnetic method with very fast simulated annealing

In large loop transient electromagnetic method(TEM),the late time apparent resistivity formula cannot truly reflect the geoelectric model,thus it needs to define the all-time apparent resistivity with the position information of measuring point.Utilizing very fast simulated annealing(VFSA) to fit the theoretical electromagnetic force(EMF) and measured EMF could obtain the all-time apparent resistivity of the measuring points in rectangular transmitting loop.The selective cope of initial model of VFSA could be confirmed by taking the late time apparent resistivity of transient electromagnetic method as the prior information.For verifying the correctness,the all-time apparent resistivities of the geoelectric models were calculated by VFSA and dichotomy,respectively.The results indicate that the relative differences of apparent resistivities calculated by these two methods are within 3%.The change of measuring point position has little influence on the tracing pattern of all-time apparent resistivity.The first branch of the curve of all-time apparent resistivity is close to the resistivity of the first layer medium and the last branch is close to the resistivity of the last layer medium,which proves the correctness of the arithmetics proposed.

Characteristics of gas explosion flow fields in complex pipelines

The explosion flow field in five straight pipes with different diameters and one bending pipe selected from a domestic coal mine are studied by the method of numerical simulation. And the results show that,both in the straight and bending pipes, the pressure wave and velocity wave are accelerated by the rising of reaction rate. As the explosion progressed, with the temperature reaching approximately 3000 K, only one pressure wave and one reaction rate wave were observed, while several velocity waves were found.The larger diameter presented the highest relative pressure as well as the largest velocity increase and subsequent decrease inside the tube. The bent pipes caused both turbulence and kinetic energy to increase, resulting in the acceleration of the reaction rate. The burning time was 7.4% shorter than the burning time observed for the straight pipe. Based on these results, designing one explosion resistance device, and in the practical engineering applications, it was to be proved to meet the security requirements fully.

Moving collocation methods for time fractional differential equations and simulation of blowup

A moving collocation method is proposed and implemented to solve time fractional differential equations. The method is derived by writing the fractional differential equation into a form of time difference equation. The method is stable and has a third-order convergence in space and first-order convergence in time for either linear or nonlinear equations. In addition, the method is used to simulate the blowup in the nonlinear equations.

Flow computations of multi-stages by URANS and flux balanced mixing models

The quasi-steady methods based on mixing models have been widely applied to flow computations of turbomachinery multi- stages in aerospace engineering. Meanwhile, the unsteady numerical simulation has also been used due to its ability in obtaining time-dependent flow solutions. In the paper, two different mixing treatments and the corresponding flux balanced ones are presented to exchange the flow solutions on the interfaces between adjacent blade rows. The four mixing treatments are then used for flow computations of a subsonic 1.5-stage axial turbine and a quasi-l.5-stage transonic compressor rotor. The results are compared with those by unsteady numerical method, which is implemented by using the sliding mesh technique. The effects of the quasi-steady and unsteady computation methods on the conservation of flow solutions across the interfaces are presented and addressed. Furthermore, the influence of mixing treatments on shock wave and flow separation of the transonic compressor rotor is presented in detail. All the results demonstrate that the flux balanced mixing treatments can be used for multi-stage flow computations with improved performance on interface conservation, even in the complex flows.

Three-dimensional finite element analysis of lumbar vertebra loaded by static stress and its biomechanical significance

Objective： To explore the mechanical behavior of lumbar spine loaded by stress and provide the mechanical basis for clinical analysis and judgement of lumbar spine fracture classification, mechanical distribution and static stress. Methods： By means of computer simulation method, the constructed lumbar spine three-dimensional model was introduced into three-dimensional finite element analysis by software Ansys 7.0. The lumbar spine mechanical behavior in different parts of the stress loading were calculated. Impact load is 0-8000 N. The peak value was 8000 N. The loading time is 0-40 minutes. The values of the main stress, stress distribution and the lumbar spine unit displacement in the direction of main stress were analyzed. Results： The lumbar spine model was divided into a total of 121 239 nodes, 112 491 units. It could objectively reflect the true anatomy of lumbar spine and its biomechanical behavior and obtain the end-plate images under different stress. The stress distribution on the lumbar intervertebral disc （L3-L4） under the axial, lateral flexion and extension stress, and the displacement trace of the corresponding processus articularis were analyzed. Conclusion： It is helpful to analyze the stress distribution of lumbar spine and units displacement in static stress loading in the clinical research of lumbar spine injury and the distribution of internal stress.