BIB-SEM characterization of pore space morphology and distribution in postmature to overmature samples from the Haynesville and Bossier Shales     

《Marine and Petroleum Geology》2015

Four Haynesville Shale and four Bossier Shale samples were investigated using a combination of Scanning Electron Microscopy (SEM) and Broad Ion Beam (BIB) polishing. This approach enables the microstructure and porosity to be studied down to the mesopore size (<50 nm) in representative areas at the scale of the BIB cross-sections. The samples vary in mineralogy, grain size and TOC and the maturity ranges from 2.42 to 2.58 VR_r in the Haynesville Shale to 1.79–2.26 VR_r in the Bossier Shale. This variety within the samples enabled us to study controls on the porosity distribution in these shales. Visible pores exist as intraparticle pores mainly in carbonate grains and pyrite framboids and as interparticle pores, mainly in the clay-rich matrix. Pores in organic matter show a characteristic porosity with respect to the type of organic matter, which mainly consists of mixtures of amorphous organic matter and minerals, organic laminae and discrete macerals. A clear positive trend of organic-matter porosity with maturity was found. Pore sizes are power law distributed in the range of 4.4 μm to at least 36 nm in equivalent diameter. The differences in power law exponents suggest that a more grain supported, coarse-grained matrix may prevent pores from mechanical compaction. Porosities measured in the BIB cross-sections were significantly lower in comparison to porosities obtained by Mercury Intrusion Porosimetry (MIP). This difference is mainly attributed to the different resolution achieved with BIB-SEM and MIP and type of pore network. Extrapolation of pore size distributions (PSDs) enables the BIB-SEM porosity to be estimated down to the resolution of the MIP and thus to upscale microstructural observation at the confined space of the BIB-SEM method to bulk porosity measurement. These inferred porosities are in good agreement with the MIP determined porosities, which underpins the assumption that pores segmented in BIB-SEM mosaics are representative of the MIP methodology.  相似文献   

An insight into crack density,saturation rate,and porosity model of the 2001 Bhuj earthquake in the stable continental region of western India     

《Journal of Asian Earth Sciences》2014

The 2001 Bhuj earthquake (Mw 7.6) source zone is examined in the light of crack density (ε), saturation rate (ξ) and porosity parameter (ψ) using new data set derived from a large aftershock sequence recorded by the Gujarat seismic network (GSNet) during November, 2006–December, 2009. Processes of rupture initiations of the mainshock and its aftershock sequence are better understood by synthesizing the dynamic snapshots of the source zone using the new dataset. Pattern of crustal heterogeneities associated with high-ε, high-ξ and high-ψ anomalies at depths varying from 20 km to 25 km is similar to those of earlier study by Mishra and Zhao (2003). The anomalous zone is found extended distinctly by 50–60 km in the lateral direction, indicating the reinforcement of cracks and fractured volume of rock matrix due to long aftershock sequence since 2001 Bhuj earthquake in the source area. It is inferred that the presence of a fluid-filled fractured rock matrix with super saturation may have affected the structural and seismogenic strengths of the source zone and is still contributing significantly to the geneses of earthquakes in and around the source zone. Anomalous pattern of high-ε with wider distribution of high-ξ indicates the existence of micro-cracks in the lower crust, while high-ψ suggests the cementation of cracks through permeation of residual magma/metamorphic fluids into the hypocenter zone. The results suggest that the existence of residual fluids in the fractured rock matrix in the mid to lower crust might have played a key role in triggering the 2001 mainshock and is still responsible for its continued long aftershock sequences.  相似文献   

Petrophysical properties of bioclastic platform carbonates: implications for porosity controls during burial     

Delphine Croizé  Stephen N. Ehrenberg  Knut Bjørlykke  François Renard  Jens Jahren 《Marine and Petroleum Geology》2010

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Hydrodynamic performance of a dual cylindrical caisson breakwater     

K. Sankarbabu  S.A. SannasirajV. Sundar 《Coastal Engineering》2008

The hydrodynamic performance of a dual cylindrical caisson breakwater (DCBW) formed by a row of caissons each of which consisting of a porous outer cylinder circumscribing an impermeable inner cylinder has been theoretically investigated. The theoretical formulation is based on the eigenfunction expansion method proposed by Spring and Monkmeyer (1974) which was further modified by Linton and Evans [Linton, C.M., Evans, D.V., 1990. The interaction of waves with arrays of vertical circular cylinders. Journal of Fluid Mechanics 215, 549–569] for an array of impermeable cylinders. The present formulation is an extension of the work of Wang and Ren [Wang, K.H., Ren, X., 1994. Wave interaction with a concentric porous cylinder system. Ocean Engineering 21(4), 343–360], wherein; the interaction of linear waves with a single concentric porous cylinder system was studied. In the present study, the formulation has been extended to the case of a group of porous dual cylinder system. Parametric studies are carried out to study the influence of porosity (G₀) on the outer caisson, width of the doughnut chamber (a/b) and the angle of wave incidence on the variation in the hydrodynamic loading, wave run-up, free-surface elevation in its vicinity as well as the transmission on its lee-side. The importance of the presence of the inner cylinder in achieving the required hydrodynamic performance in terms of either protection or providing tranquility on its lee side keeping higher stability for the breakwater system is highlighted.  相似文献   

鄂尔多斯盆地子洲气田上古生界山西组、下石盒子组储集层特征对比研究   总被引：2，自引：0，他引：2       下载免费PDF全文

王若谷  李文厚  廖友运  冯永玖  郭艳琴  马瑶  许星 《地质科学》2015,50(1):249-261

鄂尔多斯盆地子洲气田山西组山2~3段和下石盒子组盒8段是该区天然气的主力储集层,但其产能却存在很大差异。应用薄片鉴定、扫描电镜、高压压汞、恒速压汞及岩心分析资料,分别对该地区上古生界山西组山2~3段和下石盒子组盒8段储集层进行了研究。子洲气田山2~3储层以石英砂岩为主,孔隙类型多样,粒间孔、溶孔、晶间孔发育,喉道类别以微—细喉为主,属相对低孔高渗型储层;盒8储层则以岩屑砂岩为主,孔隙类型主要为岩屑溶孔和晶间孔,喉道类别以细—微喉为主,属于相对低孔低渗型储层。山2~3段和盒8段储集层岩石类型、孔隙结构差别巨大,造成了其储集性能的差异性。不同的沉积环境和成岩作用是造成其差异性的主要原因。  相似文献   

Diagenetic processes in cretaceous sandstones from occidental Brazilian Equatorial Margin     

《Journal of South American Earth Sciences》2015

Despite a great interest in Brazilian Equatorial Margin exploration, very little was published on the diagenesis of sandstones from that area. A wide recognition petrographic study was performed to identify the major diagenetic processes that impacted the porosity of Lower Cretaceous sandstones of the Pará-Maranhão, São Luís, Bragança-Viseu and Barreirinhas basins. Arkoses from the Pará-Maranhão Basin show neoformed or infiltrated clay coatings, mica replacement and expansion by kaolinite and vermiculite, and precipitation of grain-replacive and pore-filling quartz, kaolinite, albite, chlorite, calcite, dolomite, siderite, pyrite and titanium oxides. Compaction, quartz and calcite cementation were the main porosity-reducing processes. Barreirinhas Basin lithic arkoses and subarkoses display clay coatings, compaction of metamorphic fragments into pseudomatrix, and precipitation of grain-replacive and pore-filling kaolinite, quartz, albite, chlorite, calcite, dolomite, TiO₂ and pyrite. The main porosity-reducing processes were calcite cementation in the subarkoses, and compaction and quartz cementation in lithic arkoses. Quartzarenites from this basin were early- and pervasively cemented by dolomite. Arkoses and lithic arkoses of the São Luís and Bragança-Viseu basins show clay coatings, pseudomatrix from mud intraclasts compaction, and precipitation of pore-filling and grain-replacive kaolinite, vermiculite, smectite, quartz, albite, chlorite, illite, calcite, dolomite, hematite, TiO₂ and pyrite. Compaction of mud intraclasts and dissolution of feldspars and heavy minerals were the main porosity-modification processes. These preliminary results may contribute to the understanding of the spatial and temporal distribution of the diagenetic processes and their impacts on the porosity of the sandstones from these basins.  相似文献   

Influence of deformation bands on sandstone porosity: A case study using three-dimensional microtomography     

《Journal of Structural Geology》2015

This study presents a qualitative and quantitative analysis of porosity in deformation bands by applying X-ray micro-computed tomography in conjunction with microstructural analysis. Samples of compactional cataclastic bands and shear compactional bands identified in Early Cretaceous aeolian sandstones of the Paraná Basin were analyzed. The application of X-ray micro-computed tomography expanded the view of features in the porous framework of each type of deformation band studied and provided information that are not clear or was not observable with optical microscopy. The compactional cataclastic bands and shear compactional bands differ in geometry, thickness, microstructures and, mainly, in the distribution, shape and orientation of the remaining pores. Porosity analysis was also performed by comparing values of porosity (total, open and closed pores) of the parental rock and the deformation band in each sample. Results of these analyses show a reduction of total porosity and open pores and therefore an increase in the amount of closed pores in all types of deformation bands in relation to parental rock. In addition, it is observed that changes in porosity characteristics are related to the effect of different deformation mechanisms that operated in each type of deformation band.  相似文献   

Surface area, porosity and water adsorption properties of fine volcanic ash particles   总被引：1，自引：1，他引：0  

Pierre Delmelle  Frédéric Villiéras  Manuel Pelletier 《Bulletin of Volcanology》2005,67(2):160-169

Our understanding on how ash particles in volcanic plumes react with coexisting gases and aerosols is still rudimentary, despite the importance of these reactions in influencing the chemistry and dynamics of a plume. In this study, six samples of fine ash (<100 m) from different volcanoes were measured for their specific surface area, a_s, porosity and water adsorption properties with the aim to provide insights into the capacity of silicate ash particles to react with gases, including water vapour. To do so, we performed high-resolution nitrogen and water vapour adsorption/desorption experiments at 77 K and 303 K, respectively. The nitrogen data indicated a_s values in the range 1.1–2.1 m²/g, except in one case where a a_s of 10 m²/g was measured. This high value is attributed to incorporation of hydrothermal phases, such as clay minerals, in the ash surface composition. The data also revealed that the ash samples are essentially non-porous, or have a porosity dominated by macropores with widths >500 Å. All the specimens had similar pore size distributions, with a small peak centered around 50 Å. These findings suggest that fine ash particles have relatively undifferentiated surface textures, irrespective of the chemical composition and eruption type. Adsorption isotherms for water vapour revealed that the capacity of the ash samples for water adsorption is systematically larger than predicted from the nitrogen adsorption a_s values. Enhanced reactivity of the ash surface towards water may result from (i) hydration of bulk ash constituents; (ii) hydration of surface compounds; and/or (iii) hydroxylation of the surface of the ash. The later mechanism may lead to irreversible retention of water. Based on these experiments, we predict that volcanic ash is covered by a complete monolayer of water under ambient atmospheric conditions. In addition, capillary condensation within ash pores should allow for deposition of condensed water on to ash particles before water reaches saturation in the plume. The total mass of water vapour retained by 1 g of fine ash at 0.95 relative water vapour pressure is calculated to be ~10^–2 g. Some volcanic implications of this study are discussed.Editorial responsibility: J. Gilbert  相似文献   

Collisional disruption experiments of porous targets     

Akiko M. Nakamura  Kensuke Hiraoka  Nagisa Machii 《Planetary and Space Science》2009,57(2):111-118

More and more small bodies are found to be porous. Laboratory impact experiments of various porous materials have been performed, which increased our understanding of the impact process of porous bodies. In this review, we classify porous targets according to the internal structure, describe the physical properties that characterize these materials, and summarize some results of impact strength and the general tendency upon impact condition and material properties. The material property presented here includes a relation between applied load and distension although measured in static condition. Further investigation is required to clarify the role of crack growth and compaction in the time evolution of physical properties of porous materials upon impact. Laboratory experiments with detailed material properties will be useful as a database that can serve as a reference for numerical modeling and theoretical scaling considerations.  相似文献   

Mutual replacement reactions in alkali feldspars I: microtextures and mechanisms   总被引：5，自引：1，他引：4  

Ian Parsons  Martin R. Lee 《Contributions to Mineralogy and Petrology》2009,157(5):641-661

Intracrystal microtextures formed by a process of mutual replacement in alkali feldspars record fluid–rock reactions that have affected large volumes of the Earth’s crust. Regular, ≤1 μm-scale ‘strain-controlled’ perthitic microtextures coarsen, by up to 10³, by a dissolution–reprecipitation process, producing microporous patch or vein perthites on scales >100 μm. We have developed earlier studies of such reactions in alkali feldspar cm-scale primocrysts in layered syenites from the Klokken intrusion, South Greenland. We present new hyperspectral CL, SEM images, and laser ICPMS analytical data, and discuss the mechanism of such replacement reactions. The feldspars grew as homogeneous sodic sanidines which unmixed and ordered by volume diffusion during cooling into the microcline field at ~450°C, giving regular, fully coherent ‘braid’ cryptoperthite. At ≤450°C the crystals reacted with a circulating post-magmatic aqueous fluid. The braid perthite behaved as a single reactant ‘phase’ which was replaced by two product phases, incoherent subgrains of low albite and microcline, with micropores at their boundaries. The driving force for the reactions was coherency strain energy, which was greater than the surface energy in the subgrain mosaic. The external euhedral crystal shapes and bulk major element composition of the primocrysts were unchanged but they became largely pseudomorphs composed of subgrains usually with the ‘pericline’ and ‘adularia’ habits (dominant {110} and subordinate {010} morphology) characteristic of low T growth. The subgrains have an epitactic relationship with parent braid perthite. Individual subgrains show oscillatory zoning in CL intensity, mainly at blue wavelengths, which correlates with tetrahedral Ti. Regular zoning is sometimes truncated by irregular, discordant surfaces suggesting dissolution, followed by resumption of growth giving regular zoning. Zones can be traced through touching subgrains, of both albite and microcline, for distances up to ~500 μm. At ≤340°C, the microcline subgrains underwent a third stage of unmixing to give straight lamellar film perthites with periodicities of ~1 μm, which with further cooling became semicoherent by the development of spaced misfit dislocations. Sub-grain growth occurred in fluid films that advanced through the elastically strained braid perthite crystals, which dissolved irreversibly. Braid perthite was more soluble than the strain-free subgrain mosaics which precipitated from the supersaturated solution. Some volumes of braid texture have sharp surfaces that suggest rapid dissolution along planes with low surface energies. Others have complex, diffuse boundaries that indicate a phase of coherent lamellar straightening by volume diffusion in response to strain relief close to a slowly advancing interface. Nucleation of strain-free subgrains was the overall rate-limiting step. To minimise surface energy subgrains grew with low energy morphologies and coarsened by grain growth, in fluid films whose trace element load (reflected in the oscillatory zoning) was dictated by the competitive advance of subgrains over a range of a few tens of mm. The cross-cutting dissolution surfaces suggest influxes of fresh fluid. Removal of feldspar to give 2 vol% porosity would require a feldspar:fluid ratio of ~1:26 (by wt). The late reversion to strain-controlled exsolution in microcline subgrains is consistent with loss of fluid above 340°C following depressurization of the intrusion. A second paper (Part II) describes trace element partitioning between the albite and microcline subgrains, and discusses the potential of trace elements as a low-T geothermometer. This paper and the Part II are dedicated in memory of J.V. Smith and W.L. Brown, both of whom died in 2007, in acknowledgement of their unrivalled contributions to the study of the feldspar minerals over more than half a century.  相似文献