基于综合判识与时变数值模拟的高渗条带定量描述方法

中高渗砂岩储层经过长期注水开发,局部区域会出现高渗透条带,造成大量注入水低效无效循环,使注水效率降低,研究高渗条带定量描述方法可改善特高含水油田开发效果,降低油田开发成本。从特高含水期高渗条带表征参数入手,分析各参数对高渗条带的影响作用,应用综合判识方法建立高渗条带综合判识指数计算模型,在时变地质模型以及数值模拟历史拟合的基础上,计算各网格的综合判识指数,结合矿场密闭取心井及动态监测资料确定高渗条带判识标准,最终实现了特高含水期各级别高渗条带定量描述。典型井描述结果与取芯结果一致,方法可靠。描述结果可为特高含水开发期剩余油挖潜对策的制定奠定基础。

基于无监督机器学习的流场分级方法研究——以D油田为例

目前我国大量老油田已进入特高含水期,储层在水驱过程中形成流场,流场内注入水存在大量的无效循环,驱油效率低,正确的流场评价成为高含水油藏挖潜措施之一。针对高含水油田长时间注入水冲刷导致储层物性时变这一现象,引入水相驱替通量,建立储层渗透率及相对渗透率随水相驱替通量变化的渗流模型,形成时变数值模拟技术。在考虑驱替效率及注入水冲刷程度的基础上,提出以油通比作为指标对流场进行分级评价。引入无监督机器学习算法,采用轮廓系数对分类数进行优选,确定流场分级的最佳分级类别及边界,克服人为主观影响。将建立的时变数值模拟及无监督机器学习流场分级方法应用于D油田,在确定流场分级的基础上,进一步制定产液结构调整策略,可有效提高油田采收率3.44个百分点。该方法为高含水油田流场评价及优势通道刻画提供了一种新思路。

高邮凹陷阜三段隐蔽油藏保幅处理方法及应用

高邮凹陷阜三段岩性油藏勘探潜力较大,但因阜三段主要为三角洲前缘亚相沉积环境,砂泥薄互层发育,阜三段地震反射特征的连续性差,反射能量弱,分辨率不够,常规的地震资料处理方法无法满足阜三段保幅成像的要求。针对这一问题,研究和应用曲波域保幅去噪、时变谱模拟反褶积两项关键技术,结合其他针对性处理技术,建立“三维一体”保幅处理框架和保幅评价方法,达到提高阜三段储层反射特征和分辨率的目的,取得了良好的勘探效果,具有在类似区块推广应用的前景。

Poststack reverse-time migration using a non-reflecting recursive algorithm on surface relief

Presently the research based on the accurate seismic imaging methods for surface relief, complex structure, and complicated velocity distributions is of great significance. Reverse-time migration is considered to be one of highly accurate methods. In this paper, we propose a new non-reflecting recursive algorithm for reverse-time migration by introducing the wave impedance function into the acoustic wave equation and the algorithm for the surface relief case is derived from the coordinate transformation principle. Using the exploding reflector principle and the zero-time imaging condition of poststack reverse- time migration, poststack numerical simulation and reverse-time migration with complex conditions can be realized. The results of synthetic and real data calculations show that the method effectively suppresses unwanted internal reflections and also deals with the seismic imaging problems resulting from surface relief. So, we prove that this method has strong adaptability and practicality.

Numerical modeling of the 2D time-domain transient electromagnetic secondary field of the line source of the current excitation

To effectively minimize the electromagnetic field response in the total field solution, we propose a numerical modeling method for the two-dimensional （2D） time- domain transient electromagnetic secondary field of the line source based on the DuFort- Frankel finite-difference method. In the proposed method, we included the treatment of the earth-air boundary conductivity, calculated the normalized partial derivative of the induced electromotive force （Emf）, and determined the forward time step. By extending upward the earth-air interface to the air grid nodes and the zero-value boundary conditions, not only we have a method that is more efficient but also simpler than the total field solution. We computed and analyzed the homogeneous half-space model and the fiat layered model with high precision--the maximum relative error is less than 0.01% between our method and the analytical method--and the solution speed is roughly three times faster than the total-field solution. Lastly, we used the model of a thin body embedded in a homogeneous half-space at different delay times to depict the downward and upward spreading characteristics of the induced eddy current, and the physical interaction processes between the electromagnetic field and the underground low-resistivity body.

Improving the resolution of seismic traces based on the secondary time-frequency spectrum

The resolution of seismic data is critical to seismic data processing and the subsequent interpretation of fine structures. In conventional resolution improvement methods, the seismic data is assumed stationary and the noise level not changes with space, whereas the actual situation does not satisfy this assumption, so that results after resolution improvement processing is not up to the expected effect. To solve these problems, we propose a seismic resolution improvement method based on the secondary time-frequency spectrum. First, we propose the secondary time-frequency spectrum based on S transform （ST） and discuss the reflection coefficient sequence and time-dependent wavelet in the secondary time frequency spectrum. Second, using the secondary time frequency spectrum, we design a two- dimensional filter to extract the amplitude spectrum of the time-dependent wavelet. Then, we discuss the improvement of the resolution operator in noisy environments and propose a novel approach for determining the broad frequency range of the resolution operator in the time- fi＇equency-space domain. Finally, we apply the proposed method to synthetic and real data and compare the results of the traditional spectrum-modeling deconvolution and Q compensation method. The results suggest that the proposed method does not need to estimate the Q value and the resolution is not limited by the bandwidth of the source. Thus, the resolution of the seismic data is improved sufficiently based on the signal-to-noise ratio （SNR）.

Unsteady temperature field of surrounding rock mass in high geothermal roadway during mechanical ventilation

To explore the spatial-temporal evolution law of rock mass temperature in high geothermal roadway during mechar^ical ventilation, a series of experiments were conducted based on the physical simulation test system of thermal and humid environment in high geothermal roadway, which is a method independently developed by China University of Mining and Technology. The results indicate that during ventilation, the disturbed region of the temperature extends gradually from shallow area to deep area in the surrounding rock mass of the roadway. Meanwhile, the temperature increases as the exponential function from shallow area to deep, with steady decrease of the temperature gradient and heat flux. As the ventilation proceeds, the relationship between dimensionless temperature and dimensionless time approximately meets Hill function.

Movement of dispersed droplets of W/O emulsion in a uniform DC electrostatic field: Simulation on droplet coalescence

Considering the droplet coalescence, the motion of a group of dispersed droplets in W/O emulsion in a DC electric field is simulated. The simulation demonstrates the evolutions of droplet number, size as well as its distribution,local concentration distribution and droplet size-velocity relation with the applied time of electric field. The simulated average droplet size is roughly consistent with the experimental value. The simulated variation of droplet number with time under several applied voltages shows that increasing voltage is more effective for raising the rate of droplet coalescence than extending exerting time. However, with the further raise of applied voltage, the improvement in droplet coalescence rate becomes less significant. The evolution of simulated droplet size–velocity relationship with time shows that the inter-droplet electric repulsion force is very strong due to larger electric charge on the droplet under higher applied voltage, so that the magnitude and the direction of droplet velocity become more random, which looks helpful to droplet coalescence.

How Well does BCC_CSM1.1 Reproduce the 20th Century Climate Change over China?

The historical simulation of phase five of the Coupled Model Intercomparison Project （CMIP5） ex- periments performed by the Beijing Climate Center cli- mate system model （BCC_CSM1.1） is evaluated regard- ing the time evolutions of the global and China mean sur- face air temperature （SAT） and surface climate change over China in recent decades. BCC CSM1.1 has better capability at reproducing the time evolutions of the global and China mean SAT than BCC_CSM1.0. By the year 2005, the BCC_CSM1.1 model simulates a warming am- plitude of approximately I℃ in China over the 1961- 1990 mean, which is consistent with observation. The distributions of the warming trend over China in the four seasons during 1958-2004 are basically reproduced by BCC CSM1.1, with the warmest occurring in winter. Al- though the cooling signal of Southwest China in spring is partly reproduced by BCC_CSM1.1, the cooling trend over central eastern China in summer is omitted by the model. For the precipitation change, BCC_CSM1.1 has good performance in spring, with drought in Southeast China. After removing the linear trend, the interannual correlation map between the model and the observation shows that the model has better capability at reproducing the summer SAT over China and spring precipitation over Southeast China.

On-line Weighted Least Squares Kernel Method for Nonlinear Dynamic Modeling

Support vector machines (SVM) have been widely used in pattern recognition and have also drawn considerable interest in control areas. Based on rolling optimization method and on-line learning strategies, a novel approach based on weighted least squares support vector machines (WLS-SVM) is proposed for nonlinear dynamic modeling. The good robust property of the novel approach enhances the generalization ability of kernel method-based modeling and some experimental results are presented to illustrate the feasibility of the proposed method.

Real-time haptic model for soft tissue deformation in surgery simulation

The modelling and simulation of deformable objects is a challenging topic in the field of haptic rendering between human and virtual environment.In this paper,a novel and efficient layered rhombus-chain-connected haptic deformation model based on physics is proposed for an excellent haptic rendering.During the modelling,the accumulation of relative displacements in every chain structure unit in each layer is equal to the deformation on the virtual object surface,and the resultant force of corresponding springs is equivalent to the external force.The layered rhombus-chain-connected model is convenient and fast to calculate,and can satisfy real-time requirement due to its simple nature.Simulation experiments in virtual human liver based on the proposed model are conducted,and the results demonstrate that our model provides stable and realistic haptic feeling in real time.Meanwhile,the display result is vivid.

The Phase Transition during Post Annealing

We have studied why PA （post-annealing） takes a long time to restore damaged crystallinity, which corresponds to repeat 10 10 times of lattice vibrations. Using a MD （molecular dynamics） simulation, we monitored the time-series of the LRO （long-range order） parameter as LRO pattern, in the case of a type IIa diamond, from the beginning of ion impact by a sub-keV N2 beam implantation to a few nanoseconds, i.e., close to the feasible time limit for MD simulations. Due to the ion impact, the LRO parameter changed gradually from ＂LRO = 1＂ （crystal） to ＂LRO = 0＂ （amorphous）, showing the so-called critical slowing-down phenomenon. However, since PA was started the LRO pattern was not unique. The LRO patterns were grouped into more than three types of phases and the transition between them was also found. From the viewpoint of statistical dynamics, such chaotic variations in the LRO pattern may present that the system is a GCM （globally coupled map） of a complex system in a closed system. A GCM composed of coupled oscillators develops slowly to exhibit several different phases or ‘chaotic itinerancy＇ over time. Therefore, the long duration required for PA may be attributable to the nature of a complex system.

Interannual Climate Variability of the Past Millennium from Simulations

The interannual variability of global temperature and precipitation during the last millennium is analyzed using the results of ten coupled climate models participating in the Paleoclimate Modelling Intercomparison Project Phase 3. It is found that large temperature(precipitation) variability is most dominant at high latitudes(tropical monsoon regions), and the seasonal magnitudes are greater than the annual mean. Significant multi-decadal-scale changes exist throughout the whole period for the zonal mean of both temperature and precipitation variability, while their long-term trends are indistinctive. The volcanic forcings correlate well with the temperature variability at midlatitudes, indicating possible leading drivers for the interannual time scale climate change.

采用有限元法模拟旋转电机的一些技巧

尽管全世界做了努力并且目前进展很大，但是用有限元模拟电机计算上非常昂贵，尤其是如果需要采用三维模型时。这与速度提高过程有关。本文给出了线性起动永磁电动机和异步电动机的一些实例。

Impacts of wind stress on saltwater intrusion in the Yangtze Estuary

The observation at the Chongxi gauging station indicated the salinity of saltwater spilling over from the North Branch to the South Branch increased abnormally from November 10 to 12 in 2009 (during neap tide) and from February 11 to 12 in 2010 (during moderate tide).We found for the first time that the strong northerly wind was responsible for the above abnormal salinity increase.Previous studies indicated that the saltwater intrusion in the Yangtze Estuary is influenced mainly by the river discharge,the tide,and the wind stress,but the impacts of variations of wind speed and direction on it have not been investigated.In this study the impacts of wind stress on the saltwater intrusion were numerically simulated and the associated mechanisms were analyzed.The model results were consistent with the observed data obtained at six gauging stations during February and March in 2007 and four gauging stations in March 2008,and the abnormal salinity risings were well captured.Meanwhile,if the wind speed is reduced by half,the salinity there will be significantly decreased.Driven by the monthly mean river discharge of 11000 m 3 /s and northerly wind of 5 m/s from January to February,the model simulated the temporal and spatial variation of saltwater intrusion.The wind-driven circulation,as well as the net water and salt fluxes from the North Branch into the South Branch,was calculated and analyzed in the cases of different wind speeds and directions.The results indicated that the intensity of the saltwater intrusion in the Yangtze Estuary is significantly influenced by the wind speeds and directions.

Delimiting Ecological Space and Simulating Spatial-temporal Changes in Its Ecosystem Service Functions based on a Dynamic Perspective: A Case Study on Qionglai City of Sichuan Province, China

Delimiting ecological space scientifically and making reasonable predictions of the spatial-temporal trend of changes in the dominant ecosystem service functions(ESFs) are the basis of constructing an ecological protection pattern of territorial space, which has important theoretical significance and application value. At present, most research on the identification, functional partitioning and pattern reconstruction of ecological space refers to the current ESFs and their structural information, which ignores the spatial-temporal dynamic nature of the comprehensive and dominant ESFs, and does not seriously consider the change simulation in the dominant ESFs of the future ecological space. This affects the rationality of constructing an ecological space protection pattern to some extent. In this study, we propose an ecological space delimitation method based on the dynamic change characteristics of the ESFs, realize the identification of the ecological space range in Qionglai City and solve the problem of ignoring the spatial-temporal changes of ESFs in current research. On this basis, we also apply the Markov-CA model to integrate the spatial-temporal change characteristics of the dominant ESFs, successfully realize the simulation of the spatial-temporal changes in the dominant ESFs in Qionglai City’s ecological space in 2025, find a suitable method for simulating ecological spatial-temporal changes and also provide a basis for constructing a reasonable ecological space protection pattern. This study finds that the comprehensive quantity of ESF and its annual rate of change in Qionglai City show obvious dynamics, which confirms the necessity of considering the dynamic characteristics of ESFs when identifying ecological space. The areas of ecological space in Qionglai city represent 98307 ha by using the ecological space identification method proposed in this study, which is consistent with the ecological spatial distribution in the local ecological civilization construction plan. This confirms the reliability of the ecological space identification method based on the dynamic characteristics of the ESFs. The results also show that the dominant ESFs in Qionglai City represented strong non-stationary characteristics during 2003–2019,which showed that we should fully consider the influence of the dynamics in the dominant ESFs on the future ESF pattern during the process of constructing the ecological spatial protection pattern. The Markov-CA model realized the simulation of spatial-temporal changes in the dominant ESFs with a high precision Kappa coefficient of above 0.95, which illustrated the feasibility of using this model to simulate the future dominant ESF spatial pattern. The simulation results showed that the dominant ESFs in Qionglai will still undergo mutual conversions during 2019–2025 due to the effect of the their non-stationary nature. The ecological space will still maintain the three dominant ESFs of primary product production, climate regulation and hydrological regulation in 2025, but their areas will change to 32793 ha, 52490 ha and 13024 ha, respectively. This study can serve as a scientific reference for the delimitation of the ecological conservation redline, ecological function regionalization and the construction of an ecological spatial protection pattern.

Seismic safety of arch dams with aging effects

Arch dams suffer time-varying external loadings and harsh environment that harm their physical properties. With the aging of such dams, damage accumulates and concrete degradation inevitably appears. In this paper, a model is proposed for simulating concrete degradation with aging because of chemo-mechanical damage. The seismic response of an arch dam with aging effects is analyzed using the proposed model. The results show that the damage caused by the aging of arch dams may result in an increase in tensile cantilever stresses during earthquakes. Meanwhile, the dynamic displacement and joint opening also clearly increase in comparison with those without damage. Thus, the seismic safety of arch dams is reduced by aging effects.

Venus round trip using solar sail

Trajectory optimization and simulation is performed for Venus round trip (VeRT) mission using solar sail propulsion. Solar gravity is included but atmospheric drag and shadowing effects are neglected in the planet-centered escape and capture stages. The spacecraft starts from the Geostationary orbit (GEt) at a predetermined time to prepare a good initial condition for the Earth-Venus transfer, although the launch window is not an issue for spacecraft with solar sails. The Earth-Venus phase and the return trip are divided into three segments. Two methods are adopted to maintain the mission trajectory for the VeRT mis- sion and then compared through a numerical simulation. According to the first approach, Planet-centered and heliocentric ma- neuvers are modeled using a set of blended analytical control laws instead of the optimal control techniques. The second pro- cedure is the Direct Attitude Angle Optimization in which the attitude angles of the solar sail are adopted as the optimization variables during the heliocentric transfer. Although neither of the two methods guarantees a globally optimal trajectory, they are more efficient and will produce a near-optimal solution if employed properly. The second method has produced a better result for the minimum-time transfer of the VeRT mission demonstrating the effectiveness of the methods in the preliminary design of the complex optimal interplanetary orbit transfers.

The effect of diffusion loss on the time-varying giant Panda population

It has been certificated that corridors can help giant pandas to keep their habitat from fragmenting. However there are still losses during the process of moving along corridors. In this study, a mathematical model with Allee effect is carried out to describe the diffusion of giant pandas between n patches. Some criteria are obtained to keep the system persisting. It is proved that the system has a unique positive w-periodic solution which is globally asymptotically stable. The ecological meanings of these findings are discussed following the results. And some numerical simulations in the Qinling Mountain giant panda nature reservation area are also presented in the end.