华北地台东部石炭系—二叠系优质煤储层形成分布控制因素

优质煤储层在此指厚度大、分布广、储集物性好的煤层。沉积相对优质煤储层的形成和分布有重要控制作用。通过浅海和泻湖淤积填平发育起来的潮坪环境和三角洲环境是最有利的优质煤储层形成环境,煤储层厚度大、分布广。沉积环境对煤储层中的灰分含量和镜质组含量有重要影响,而灰分含量和镜质组含量又直接影响煤储层的储集物性。灰分充填了煤储层中的孔隙,其含量越高,储集物性越差;镜质组有利于割理的形成,其含量越高,储集物性越好。由于在灰分含量、煤岩显微组分等方面的差异,潮坪环境沉积的煤储层的储集物性优于三角洲的煤储层,下三角洲平原沉积的煤储层优于上三角洲平原沉积的煤储层。海平面变化对优质煤储层的形成和分布也有重要控制作用。高位体系煤储层富集,单层厚度大,横向分布相当稳定,尤其是高位体系域晚期,是形成优质煤储层最有利的层位。而水进体系域煤储层稀少,单层厚度小,横向分布不稳定,不利于优质煤储层形成。     

高、低煤阶煤层气藏地质特征及控气作用差异性研究

高、低煤阶煤层气地质特征及控气作用差异性是研究煤层气富集成藏的重要组成部分,是煤层气勘探开发理论研究过程中重要的基础性研究领域之一。本文以中国沁水、阜新盆地和美国粉河盆地等典型的含气盆地为例,探讨了高、低煤阶煤层气的储层物性差异,分析了构造控气和水文地质控气作用的差异性。研究表明,高煤阶气藏含气量高,CH4百分含量高,δ13C1值大于-38.75‰,储层渗透率变化小,储层改造难,构造热事件对煤层气的生成、富集贡献大,持续的水动力使气藏遭到破坏,且破坏幅度大,现今地下水格局对气藏的形成具有一定的影响;低煤阶气藏含气量低,CH4百分含量低,δ13C1值大于-49.11‰,储层渗透率变化大,储层易改造,煤热演化史及煤阶影响着煤层气的生成、富集,在煤层气生成过程中活跃的水动力是甲烷生成的主要的水文地质条件之一,但持续的水动力使气藏遭到破坏,且破坏幅度小,而合适的地层水矿化度则是低煤阶煤层气生成的重要条件,地下水格局对气藏的调整和改造起到决定性的影响。     

Using ALSM to map sinkholes in the urbanized covered karst of Pinellas County,Florida—1, methodological considerations

Comparison of a database of interpreted sinkholes made using airborne laser swath mapping (ALSM) with databases of sinkholes made from interpretation of aerial photographs reveals substantial disagreement. The discrepancies involve the location, number, areas, and circularity of interpreted sinkholes. Methodological factors that contribute to the discrepancies include blockage of ALSM laser returns in thick vegetation, multi-path reflections, and misrepresentation of the true extent of sinkholes. Comparison of two ALSM-derived databases made (1) independently from versus (2) in combination with earlier air photo analysis in undeveloped regions had the following result: one-fourth of the sinkholes interpreted by using the composite method were missed by the independent analysis, and one-third of the sinkholes that were interpreted from the independent analysis were not interpreted as sinkholes using the composite method. Subjective interpretation leads to a high level of uncertainty such that the results of the remote sensing studies are suspect, if not invalid.     

Use of sinkhole and specific capacity distributions to assess vertical gradients in a karst aquifer

The carbonate-rock aquifer in the Great Valley, West Virginia, USA, was evaluated using a database of 687 sinkholes and 350 specific capacity tests to assess structural, lithologic, and topographic influences on the groundwater flow system. The enhanced permeability of the aquifer is characterized in part by the many sinkholes, springs, and solutionally enlarged fractures throughout the valley. Yet, vertical components of subsurface flow in this highly heterogeneous aquifer are currently not well understood. To address this problem, this study examines the apparent relation between geologic features of the aquifer and two spatial indices of enhanced permeability attributed to aquifer karstification: (1) the distribution of sinkholes and (2) the occurrence of wells with relatively high specific capacity. Statistical results indicate that sinkholes (funnel and collapse) occur primarily along cleavage and bedding planes parallel to subparallel to strike where lateral or downward vertical gradients are highest. Conversely, high specific capacity values are common along prominent joints perpendicular or oblique to strike. The similarity of the latter distribution to that of springs suggests these fractures are areas of upward-convergent flow. These differences between sinkhole and high specific capacity distributions suggest vertical flow components are primarily controlled by the orientation of geologic structure and associated subsurface fracturing.     

GIS-based colour composites and overlays to delineate heavy metal contamination zones in the shallow alluvial aquifers, Ankaleshwar industrial estate, south Gujarat, India

In an attempt to delineate heavy metal contamination precincts and to evaluate the extent and degree of toxic levels, besides their possible sources, 38 water samples from Ankaleshwar Industrial Estate, south Gujarat, India were analyzed. By clutching geochemical analyses and GIS-based colour composites areas depicting anomalously high concentration of heavy metals (Mo, Zn, Pb, Ni, Co, Cd, etc.) in the groundwater were revealed. The multicomponent overlays in grey-scale facilitated in identifying situates of heavy metal ‘hot spots’, and lateral protuberances of the contamination plume around defile stretch of the main stream Amla Khadi flowing through the area. The multiple pollution plumes emerging from other parts of the area further coincide with effluent laden streams and small channels indicating industrial establishments as major sources of groundwater contamination. Influent nature of the streams, accelerated infiltration process, high mass influx and shallow groundwater table are the factors conducive for easy access of heavy metals to the phreatic aquifers affecting over 20 km² area. On the basis of P/U ratios (concentration of metals in polluted water to unpolluted water), geogenic and anthropogenic sources have been identified. Very high levels of technogenic elements present in the ground water raise concerns about possible migration into food crops, as the area is an important horticultural locale and is highly cultivated.     

Georadiochemical evidence to weathering of mining residues of the Mansfeld mining district,Germany

Mining heaps are used as archives for the investigation of weathering processes. Aim of this work was to investigate the different weathering behavior of heap materials derived from Kupferschiefer mining with respect to environmental hazard. For this purpose, Kupferschiefer and slag material of two heaps of different age were examined regarding to the radionuclide distribution and geochemical composition. By measuring of the local dose rate, performing digital autoradiography and gamma spectrometry the radiological load of the heaps and the heap materials was determined. The geochemical characterization of the samples was performed by XRF, ICP–OES and ICP–MS. The results show a clear higher radionuclide load of the younger slag heap. A depletion of chalcophile and lithophile elements in the older slag was determined. Apart from a homogeneous radionuclide distribution, considerable radionuclide enrichments in fossil fragments could be proven. The results reveal a different weathering behavior of slag material in comparison to the Kupferschiefer depending on the chemical binding of the elements on organic and inorganic species. Natural organic matter as well as apatite in Kupferschiefer act as retention barrier for some metals.     

Quick-look assessments to identify optimal CO2 EOR storage sites

A newly developed, multistage quick-look methodology allows for the efficient screening of an unmanageably large number of reservoirs to generate a workable set of sites that closely match the requirements for optimal CO₂ enhanced oil recovery (EOR) storage. The objective of the study is to quickly identify miscible CO₂ EOR candidates in areas that contain thousands of reservoirs and to estimate additional oil recovery and sequestration capacities of selected top options through dimensionless modeling and reservoir characterization. Quick-look assessments indicate that the CO₂ EOR resource potential along the US Gulf Coast is 4.7 billion barrels, and CO₂ sequestration capacity is 2.6 billion metric tons. In the first stage, oil reservoirs are screened and ranked in terms of technical and practical feasibility for miscible CO₂ EOR. The second stage provides quick estimates of CO₂ EOR potential and sequestration capacities. In the third stage, a dimensionless group model is applied to a selected set of sites to improve the estimates of oil recovery and storage potential using appropriate inputs for rock and fluid properties, disregarding reservoir architecture and sweep design. The fourth stage validates and refines the results by simulating flow in a model that describes the internal architecture and fluid distribution in the reservoir. The stated approach both saves time and allows more resources to be applied to the best candidate sites.     

Seal integrity and feasibility of CO<Subscript>2</Subscript> sequestration in the Teapot Dome EOR pilot: geomechanical site characterization

This paper reports a preliminary investigation of CO₂ sequestration and seal integrity at Teapot Dome oil field, Wyoming, USA, with the objective of predicting the potential risk of CO₂ leakage along reservoir-bounding faults. CO₂ injection into reservoirs creates anomalously high pore pressure at the top of the reservoir that could potentially hydraulically fracture the caprock or trigger slip on reservoir-bounding faults. The Tensleep Formation, a Pennsylvanian age eolian sandstone is evaluated as the target horizon for a pilot CO₂ EOR-carbon storage experiment, in a three-way closure trap against a bounding fault, termed the S1 fault. A preliminary geomechanical model of the Tensleep Formation has been developed to evaluate the potential for CO₂ injection inducing slip on the S1 fault and thus threatening seal integrity. Uncertainties in the stress tensor and fault geometry have been incorporated into the analysis using Monte Carlo simulation. The authors find that even the most pessimistic risk scenario would require ∼10 MPa of excess pressure to cause the S1 fault to reactivate and provide a potential leakage pathway. This would correspond to a CO₂ column height of ∼1,500 m, whereas the structural closure of the Tensleep Formation in the pilot injection area does not exceed 100 m. It is therefore apparent that CO₂ injection is not likely to compromise the S1 fault stability. Better constraint of the least principal stress is needed to establish a more reliable estimate of the maximum reservoir pressure required to hydrofracture the caprock.     

Problems of soil and groundwater pollution in the disposal of “marble” slurries in NW Sicily

This work deals with disposal of slurries generated during the cutting and polishing processes of slabs of decorative sedimentary carbonate rocks in the north western Sicily. At present, they are used as fillers of dismantled quarries near the sawmills and, as a final step of reclamation, are covered with earth layers. In spite of such inexpensive solution, there is lack of knowledge about the composition of the waste. In order to assess if there is any threat for the environment and to suggest indications for alternative solutions, such as recycling or inactivation processes, the slurries were analysed by XR diffraction, simultaneous thermal analysis, ICP/MS, ionic chromatography, FTIR, UV-Vis, COD and TOC measurements, grain size analysis. Results indicate that the slurries can threaten the groundwater, because of the high chemical oxygen demand; furthermore they can modify the mechanism of groundwater recharge, because of their grain size distribution. Some laboratory tests show that, even in very aggressive conditions, the solid pollutants persist in the waste and slowly release into water the products of their degradation. The slurry therefore should be subjected to inactivation treatment before disposal or, alternatively, recycled as secondary raw material for a suitable process.