On the modelling of sand bedforms using the semivariogram

This study shows the usefulness of the semivariogram for modelling sand ripples created by water flows of varied flow intensity. A combination of two mathematical functions is fitted to each sample semivariogram, that is an exponential (or stochastic) component and a periodic component. The parameters of each of these components have direct physical meaning. A non-dimensional ratio combining the two parameters of the exponential model is interpreted as a regularity index (which increases with the degree of regularity of bedform arrangement). This regularity index is inversely related to the Froude number of the flow. The non-dimensional wavelength, estimated from the dominant periodic function, is also inversely and closely related to the Froude number. The wave height, accurately estimated from properties of the two fitted components, is a direct function of flow velocity and is also proportional to the standard deviation of bed elevations. The bedform shape introduces a considerable discrepancy between the generally assumed normal frequency distribution and the empirical distributions of bed height. The series of bed elevations are generally characterized by a mixture of normal distributions having the same variance but different means. The calculation of a covariance assuming a constant and single mean (as in spectral analysis) can therefore be misleading and the problem may be avoided by using the semivariogram.     

依据密度测井资料评估煤层的含气量

煤层甲烷长期以来认为是对采煤工作的危害，只是近十多年来才被认为是一种潜在的能源。煤层不仅是甲烷的储层，而且是甲烷的源岩。煤的物理结构是一种双重孔隙结构，即煤层中含有由基质孔隙和裂缝孔隙组成的孔隙系统。煤层中的气（甲烷）主要吸附在基质孔隙的内表面，是吸附气，而不是存在于骨架粒间的孔隙空间内，因而传统的评价天然气储层含气量的方法虽然不能适合于评估煤层的气含量。本文利用密度测井资料和煤样煤质化验资料确定     

Migrating sand waves

A simple mathematical model is described, which reproduces the major features of sand waves' appearance and growth and in particular predicts their migration speed. The model is based on the linear stability analysis of the flat configuration of the sea bottom subject to tidal currents. Attention is focused on the prediction of the complex growth rate that bottom perturbations undergo because of both oscillatory fluid motions and residual currents. While the real part _r of controls the amplification or decay of the amplitude of the bedforms, the imaginary part _i is related to their migration speed. Previous works on the migration of the sand waves (Németh etal. 2002) consider a forcing tide made up by the M2 constituent (oscillatory period equal to 12 h) plus the residual current Z0 and predict always a downcurrent migration of the bedforms. However, field cases exist of upcurrent-migrating sand waves (downcurrent/upcurrent-migrating sand waves mean bedforms moving in the direction of the steady residual tidal current or in the opposite direction, respectively). The inclusion of a tide constituent characterized by a period of 6 h (M4) is the main novelty of the present work, which allows for the prediction of the migration of sand waves against the residual current Z0. Indeed, the M4 tide constituent, as does also the residual current Z0, breaks the symmetry of the problem forced only by the M2 tide constituent, and induces sand-wave migration. The model proposed by Besio etal. (2003a) forms the basis for the present analysis. Previous works on the subject (Gerkema 2000; Hulscher 1996a,b; Komarova and Hulscher 2000) are thus improved by using a new solution procedure (Besio etal. 2003a) which allows for a more accurate evaluation of the growth rate for arbitrary values of the parameter r, which is the ratio between the horizontal tidal excursion and the perturbation wavelength. Responsible Editor: Jens Kappenberg     

The First James K. Mitchell Lecture In situ soil testing: from mechanics to interpretation†

The current use of fundamental mechanics in developing rational interpretation methods for deriving soil properties from in situ test results is reviewed and evaluated. The focus is on some of the most widely used in situ test devices including cone penetrometers with and without pore pressure measurements (CPTU and CPT), self-boring and cone pressuremeters (SBPMT and CPMT), and flat dilatometers (DMT). In situ tests in both cohesive and frictional soils for measuring strength and stiffness properties, in situ state parameters, consolidation coefficients, stress history, and in situ stresses are considered in detail.     

Further Information of the Associated Li Deposits in the No.6 Coal Seam at Jungar Coalfield,Inner Mongolia,Northern China

Total 138 coal samples and 14 parting samples were taken from the No. 6 Seam of the Jungar Coalfield, Inner Mongolia. These samples were analysed by optical microscopy, sequential chemical extraction procedure (SCEP), inductively coupled plasma mass spectrometry (ICP-MS), X-ray powder diffraction (XRD), and scanning electron microscope in conjunction with an energy-dispersive X-ray spectrometer (SEM-EDX) analysis. The results indicate that the Li contents have reached the industrial grade of the coal associated Li deposit, and the total Li reserves have reached 2406600 tons, that is, 5157000 tons Li2O in the No. 6 seam in the Jungar Coalfield. The sequential chemical extraction procedure results suggest that the Li concentration is mainly related to inorganic matter. The minerals in the coals consist of kaolinite, boehmite, chlorite-group mineral, quartz, calcite, pyrite, siderite and amorphous clay material. Some Li could be absorbed by clay minerals in the Li-bearing coal seam. The chlorite phase?could be?most likely the host for a part of Li. The Yinshan Oldland should be the most possible source of Li of the coal.     

Coal seam gas distribution and hydrodynamics of the Sydney Basin,NSW, Australia

This paper reviews various coal seam gas (CSG) models that have been developed for the Sydney Basin, and provides an alternative interpretation for gas composition layering and deep-seated CO₂ origins. Open file CSG wells, supplemented by mine-scale information, were used to examine trends in gas content and composition at locations from the margin to the centre of the basin. Regionally available hydrochemistry data and interpretations of hydrodynamics were incorporated with conventional petroleum well data on porosity and permeability. The synthesised gas and groundwater model presented in this paper suggests that meteoric water flow under hydrostatic pressure transports methanogenic consortia into the subsurface and that water chemistry evolves during migration from calcium-rich freshwaters in inland recharge areas towards sodium-rich brackish water down-gradient and with depth. Groundwater chemistry changes result in the dissolution and precipitation of minerals as well as affecting the behaviour of dissolved gases such as CO₂. Mixing of carbonate-rich waters with waters of significantly different chemistries at depth causes the liberation of CO₂ gas from the solution that is adsorbed into the coal matrix in hydrodynamically closed terrains. In more open systems, excess CO₂ in the groundwater (carried as bicarbonate) may lead to precipitation of calcite in the host strata. As a result, areas in the central and eastern parts of the basin do not host spatially extensive CO₂ gas accumulations but experience more widespread calcite mineralisation, with gas compositions dominated by hydrocarbons, including wet gases. Basin boundary areas (commonly topographic and/or structural highs) in the northern, western and southern parts of the basin commonly contain CO₂-rich gases at depth. This deep-seated CO₂-rich gas is generally thought to derive from local to continental scale magmatic intrusions, but could also be the product of carbonate dissolution or acetate fermentation.     

新密市白石沟井田二1煤层充水因素分析

白石沟井田是近年来探明的大巾型井田,位于五指岭-白寨背斜东端之南翼,新密-新郑复向斜之北翼．岗亚腰断层和梁山断层之间的地垒构造上,其基本构造形态为-向东倾伏的宽缓背斜。二叠系下统山西组二1煤为主要开采煤层,探明二1煤资源量7206×10^7t。分析了井田含水岩组及其富水性,对断层带及其富水特征进行了研究,从矿床（二1煤层）充水的水源、通道、机理三个方面分析了矿床充水因素,指出二1煤层的主要充水水源为该煤层底板的石炭系岩溶裂隙-承压水,充水通道为断层带和灰岩的岩溶裂隙发育带,充水机理为矿压及高水头压力冲破煤层底板阻水层阻力,形成底鼓,迅速突水。认为该井田水文地质勘查类型为三类二型,提出了排除与隔离地表水体,预留防水安全煤柱,灌浆辅助采掘的井田突水防范措施。     

重庆市砚石台煤矿煤层流变特征及规律探讨

以构造变形强烈的重庆市砚石台煤矿为例,通过井下煤层的观测与煤标本的显微镜观察,分析了煤层中的宏观与微观流变特征,并结合煤层构造的发育特征,总结了煤层流变的控制因素、发育规律及其成因。研究结果认为,砚石台煤矿存在不同程度的煤层流变现象,煤层流变程度受控于层滑作用、煤层构造、煤层层位和煤层倾角等因素。受其影响,煤层流变强烈地段主要集中在4号煤层的地层产状平缓处,次级构造密集发育和层滑作用强烈地段。     

A sand-production control system for gas production from clayey silt hydrate reservoirs

Sand production is a crucial problem during the process of extracting natural gas from hydrate reservoirs. To deal with sand-production problems systematically, a sand-production control system (SCS) is first proposed in this paper, specialized for pore-distributed clayey silt hydrate reservoirs. Secondly, a nodal system analysis method (NSAM) is applied to analyze the sand migration process during hydrate exploitation. The SCS is divided into three sub-systems, according to different sand migration mechanisms, and three key scientific problems and advances in SCS research in China Geological Survey are reviewed and analyzed. The maximum formation sanding rate, proper sand-control gravel size, and borehole blockage risk position were provided for clayey hydrate exploitation wells based on the SCS analysis. The SCS sub-systems are closely connected via bilateral coupling, and coordination of the subsystems is the basis of maintaining formation stability and prolonging the gas production cycle. Therefore, contradictory mitigation measures between sand production and operational systems should be considered preferentially. Some novel and efficient hydrate exploitation methods are needed to completely solve the contradictions caused by sand production.© 2019 China Geology Editorial Office.     

Identification of Milankovitch Cycles and Calculation of Net Primary Productivity of Paleo-peatlands using Geophysical Logs of Coal Seams

Individual coal seams formed in paleo-peatlands represent sustained periods of terrestrial carbon accumulation and a key environmental indicator attributed to this record is the rate of carbon accumulation. Determining the rate of carbon accumulation requires a measure of time contained within the coal. This study aimed to determine this rate via the identification of Milankovitch orbital cycles in the coals. The geophysical log is an ideal paleoclimate proxy and has been widely used in the study of sedimentary records using spectral analysis. Spectral analyses of geophysical log from thick coal seams can be used to identify the Milankovitch cycles and to calculate the period of the coal deposition. By considering the carbon loss during coalification, the long-term average carbon accumulation rate and net primary productivity (NPP) of paleo-peatlands in coal seams can be obtained. This review paper presents the procedures of analysis, assessment of results and interpretation of geophysical logs in determining the NPP of paleo-peatlands.