Comparison of relative permeability–fluid saturation–capillary pressure relations in the modelling of non-aqueous phase liquid infiltration in variably saturated,layered media

The characteristic functions relating relative permeabilities and capillary pressures to fluid saturations (k_r–S–P_c models) are of great importance for the modelling of sub-surface multi-phase flow and transport. In order to test their performance and to identify their important parameters, four well-known three-phase k_r–S–P_c models have been tested against published experimental data on non-aqueous phase liquid (NAPL) migration in the unsaturated zone. Both homogenous systems and systems with embedded heterogeneities have been analysed.     

Variable-density flow and transport in porous media: approaches and challenges

We review the state of the art in modeling of variable-density flow and transport in porous media, including conceptual models for convection systems, governing balance equations, phenomenological laws, constitutive relations for fluid density and viscosity, and numerical methods for solving the resulting nonlinear multifield problems. The discussion of numerical methods addresses strategies for solving the coupled spatio-temporal convection process, consistent velocity approximation, and error-based mesh adaptation techniques. As numerical models for those nonlinear systems must be carefully verified in appropriate tests, we discuss weaknesses and inconsistencies of current model-verification methods as well as benchmark solutions. We give examples of field-related applications to illustrate specific challenges of further research, where heterogeneities and large scales are important.     

Sealing law of far-field spectra based on observed parameters of the specific barrier model

A set of acceleration source spectra is constructed using the observed parameters of the specific barrier model of Papageorgiou and Aki. The spectra show a significant departure from the ²-model at the high frequency range. Specifically, the high frequency spectral amplitudes of seismic excitation are higher as compared to the level predicted by the ²-model. This is also supported by other observational evidence. The high frequency amplitudes of acceleration scale proportionally to the square root of the rupture areaS, to the rupture spreading velocityv, and to the local strain drop (/) (=strain drop in between barriers). The local strain drop in between barriers is not related in a simple way to the global strain drop, which is the strain drop estimated by assuming that it is uniform over the entire rupture area. Consequently, the similarity law does not apply. Using the source spectra which we constructed, we derive expressions for high frequency amplitudes of acceleration such asa _rms anda _max. Close to the fault both are independent of fault dimensions and scale as (/µ)(f)^1/2, while away from the fault plane they scale asW ^1/2(/µ)(f)^1/2, whereW is the width of the fault and f is the effective bandwidth of the spectra.     

基于速度-状态摩擦本构定律的三维DDA方法

原有三维非连续变形分析(DDA)方法采用常摩擦系数的Mohr-Coulomb定律作为切向破坏准则,然而当描述更大尺度构造块体的运动与变形时,常摩擦系数不再适用.速度-状态摩擦本构定律能够定量描述地震周期各阶段断层面剪应力变化,解释发震断层行为.本文将速度-状态摩擦定律与三维DDA方法相结合,首先推导了计算摩擦系数的实用公式,随后通过滑动-保持-滑动实验与速度步进实验算例对改进的三维DDA方法进行了验证.结果表明,应用速度-状态摩擦本构定律的三维DDA方法能够比较准确地模拟静摩擦的时间依赖性与动摩擦的速度依赖性,解决了将三维DDA方法在地学中应用的基本问题.     

论地理规律对流域过程模拟并行计算的指导作用

流域过程模拟是地理学研究和流域科学管理的有效工具。在应用需求的推动下,长时段、高空间分辨率的多过程综合模拟逐渐兴起,流域过程模拟所需的计算量越来越大,亟需借助并行计算技术来提高效率。流域过程模拟并行计算的现有研究,大多为针对特定模型的个例研究,缺乏对指导各类流域过程模型并行计算的共性思路和原则进行讨论和梳理。首先,对可指导流域过程模拟并行计算的地理规律进行了分析,从空间、子过程和时间3 个角度,探讨了空间等级层次结构、空间相互作用、子过程间依赖关系、时空动态变化等地理规律,对流域过程模拟并行计算的指导作用;然后,根据地理规律在并行计算中所发挥作用和适用范围的不同对其分类;最后,结合2 个实例,对地理规律的流域过程模拟并行计算进行了分析和验证,旨在对流域过程模拟并行计算理论和方法的发展与应用提供借鉴。     

Quantitative tests for stratigraphic cyclicity

Periodic Milankovitch (M-) orbital forcing provides an explanation for subjectively recognized short-term repetition of lithofacies-‘cycles’-in the stratigraphic record. Tests of this explanation often find no order in the lithofacies and/or no regularity in the recurrence of lithofacies. This does not disprove the influence of M-forcing, but a sedimentary response in terms of irregular M-forced ‘cycles’ is indistinguishable from one in which repetition of facies is not M-forced. Use of such cycles in time calibration is correspondingly suspect. Stricter, dimensional cyclicity invokes Sander's Rule, which suggests periodicity in sedimentation, for which M-forcing provides an obvious explanation. Time calibration on the basis of strict cyclicity thus appears more dependable. Objective tests for regular M-forced stratigraphic cyclicity commonly depend upon spectral analyses. Such tests are not unambiguous. Bilogarithmic thickness/frequency plots derived from objective layer thickness inventories (LTI) provide an alternative. Commonly, such plots show power-law relationships that preclude dimensional M-cyclicities. By contrast, a model data series that perfectly encodes the M-cyclic fluctuations in terrestrial insolation generates a strongly inflected, non-power-law LTI plot. Power-law plots result where the model data series is decimated by random hiatuses, with numbers and durations tuned to M-cycle frequencies. It seems improbable that natural data series record such tuning. The general absence of strict cyclicity in the M-frequency range is more likely to reflect the nonlinear response of sedimentary systems to cyclic M-forcing of insolation. Interestingly, when applied to the classically cyclic lacustrine Triassic sediments of the Newark Basin, USA, the LTI test suggests a decimated record, preserving some evidence of M-cyclicity. Copyright © 2008 John Wiley & Sons, Ltd.     

巴丹吉林最高沙山区CO2浓度与昼夜变化规律

为查明沙漠区CO₂浓度和对大气CO₂的影响以及在全球碳循环中的作用,利用红外CO₂监测仪,在2009年5月对全球最高大的巴丹吉林诺尔图东大沙山等进行了17个钻孔CO₂浓度的昼夜观测。结果表明,巴丹吉林大沙山不同观测点CO₂浓度差异较大,各观测点CO₂浓度变化在0.01%~0.075％之间;夜间沙层CO₂浓度低,白天CO₂浓度高;CO₂浓度昼夜变化明显,从早7时到次日7时1~5m各深度CO₂浓度均呈现由低到高再到低的变化规律;在24h内,沙层CO₂浓度变化存在4个转折点,分别出现在凌晨5时、11时、18时和21时左右。在沙层水分一定的条件下,昼夜温度变化是造成沙层CO₂浓度昼夜规律变化的主要原因,两者呈正相关关系;含水量较高的沙层CO₂浓度明显高于含水量较低的沙层;5m深度以上沙层CO₂浓度均高于地表空气CO₂浓度,表明极端干旱的高大沙山区是CO₂的来源区,也指示环境恶劣的裸露高大沙山区微生物活动产生的沙层CO₂浓度仍然超过了大气CO₂浓度。     

川中下侏罗统致密灰岩储层裂缝的主控因素与发育规律

天然裂缝是致密油储层重要的储集空间和主要的渗透通道,影响致密油气成藏、富集规律、单井产能及其开发效果。本文利用野外相似露头、岩心、薄片及成像测井资料,在研究四川盆地中部下侏罗统致密灰岩储层裂缝类型和发育特征的基础上,阐明了其裂缝分布的主控因素与发育规律。四川盆地中部下侏罗统致密灰岩储层普遍发育构造裂缝和成岩裂缝,其中以高角度构造剪切裂缝为主,大部分裂缝为有效裂缝。在同一区域应力场作用下,构造裂缝的分布主要受岩性、层厚及构造的控制。其中灰岩中裂缝最发育,随着泥质含量的增加,泥质灰岩、灰质泥岩和泥岩的裂缝密度依次降低。总体上,随着灰岩层厚的增加,裂缝间距增大,裂缝发育程度降低。大安寨致密灰岩储层可以分为4 种组合模式,不同组合模式的裂缝发育程度存在明显的差异,其中单层厚度为4～8 m 的介壳灰岩与单层厚度小于5 m 的泥页岩互层是形成裂缝的有利条件。不同构造部位的裂缝分布亦存在差异,其中断裂带附近与背斜轴部和转折端等构造高部位是裂缝发育的有利区域。