The origin of rhythmic sulphide bands from the Permian sandstones (Weissliegendes) in the footwall of the Fore-Sudetic “Kupferschiefer” (Poland)

Rhythmic copper sulphide bands occur in the Weissliegendes sandstones, in the footwall of the Kupferschiefer in the mining district of SW Poland. The δ ³⁴S values of sulphides vary from −39 to — 44‰ (6–7‰ lighter than Kupferschiefer sulphides). The copper sulphides are represented mainly by digenite and chalcocite. According to microprobe results their Pb, Ni, Zn and Ag contents are similar to those in the Kupferschiefer. The bands are assumed to be formed by diffusion of bacterially produced hydrogen sulphide from the Kupferschiefer into the porous volume of the white sandstones containing dissolved copper. The sulphides were precipitated in almost equidistant bands, from top to bottom, probably according to the Ostwald-Prager supersaturation theory. The increase of isotopically heavier sulphur towards the lower levels in the sandstone might be explained by closing of the bacterial sulphate reduction system. Contribution to the IGCP Project No. 254     

Evaluation of weathering-resistance classes in clastic rocks on the example of Polish sandstones

The scope of the paper is an attempt at the identification of the weathering-resistance classes within clastic rocks by means of analysis of capillary pressure saturation curves. The porosimetric parameters corresponding to the cementing character and the grains’ mineralogical content are very important features of stone building materials, because of the weathering processes. The analysed rocks were Polish sandstones and muddy sandstones used for building purposes, collected from different geological units of Poland (i.e. Sudety Mts. Carpathian Mts. and Holy Cross Mts.) The results indicate the usefulness of sandstone materials for building purposes. They could also be used in conservation procedures and for the reconstruction of existing buildings and monuments. Basing on the parameterisation, with the van Genuchten function, of cumulative capillary pressure saturation curves, it was possible to distinguish four groups of the sampled rocks. The lithological features and weathering sustainability within the groups are quite uniform, what allow identifying the weathering resistance classes. Taking into account the complicated nature of all the factors influencing weathering processes, it is supposed that the presented parameterisation could be a useful tool for weathering-resistance classification of clastic rocks. The classification could be useful in building industry and in conservation of historical stone monuments.     

Evaluation of probabilistic flow in two unsaturated soils

A variably saturated flow model is coupled to a first-order reliability algorithm to simulate unsaturated flow in two soils. The unsaturated soil properties are considered as uncertain variables with means, standard deviations, and marginal probability distributions. Thus, each simulation constitutes an unsaturated probability flow event. Sensitivities of the uncertain variables are estimated for each event. The unsaturated hydraulic properties of a fine-textured soil and a coarse-textured soil are used. The properties are based on the van Genuchten model. The flow domain has a recharge surface, a seepage boundary along the bottom, and a no-flow boundary along the sides. The uncertain variables are saturated water content, residual water content, van Genuchten model parameters alpha (α) and n, and saturated hydraulic conductivity. The objective is to evaluate the significance of each uncertain variable to the probabilistic flow. Under wet conditions, saturated water content and residual water content are the most significant uncertain variables in the sand. For dry conditions in the sand, however, the van Genuchten model parameters α and n are the most significant. Model parameter n and saturated hydraulic conductivity are the most significant for the wet clay loam. Saturated water content is most significant for the dry clay loam. Electronic Publication     

Pore Characteristics and Factors Controlling Lacustrine Shales from the Upper Cretaceous Qingshankou Formation of the Songliao Basin,Northeast China: A Study Combining SEM,Low-temperature Gas Adsorption and MICP Experiments

To investigate pore characteristics and the factors controlling lacustrine shales,geochemical,mineralogical and petrophysical experiments were performed on 23 shale samples from the Qingshankou Formation of the Songliao Basin,China.A comparison of mercury injection capillary pressure (MICP) and low-temperature N2 adsorption pore-size distribution showed that MICP has a higher pore-size distribution (PSD) line in its overlapping pore diameter range,which may be elevated by the higher pressure of MICP.Therefore,in the overlapping range,low-temperature N2 adsorption data were preferred in pore characterization.Negative correlations were observed between pore volumes and TOC content,indicating organic matter pores are not well-developed in the studied samples.This may be related to their low grade of maturity and type I kerogens.There existed negative relationships between pore volumes and S1,which illustrated that liquid hydrocarbons occupied some pore space.Micropore volume had a better correlation with S1 than mesopore and macropore volumes,which suggests that liquid hydrocarbons preferentially occur in micropores.No obvious relationships between pore volumes and quartz or feldspar were observed,while pore volumes increased with the increasing clay mineral content.These relationships indicate that intraparticle pores in clay minerals represent the principal pore type.     

Comparison between control factors of high quality continental reservoirs in Bohai Bay basin and Ordos basin

Bohai Bay basin, a typical extensional rift basin, and Ordos basin, an intra-craton down-warped basin, represent two important basin types in China. Because of their respective features, the main control factors for their high quality reservoirs are different. In Bohai Bay basin, the sandbody shows great variety in types and severely separated distribution and its high quality reservoirs are mostly controlled by the vertical secondary pore and vertical abnormal pressure. On the other hand, the sandbody in Ordos basin features a relative lack of variety, good continuity, indistinct vertical zone, and its reservoirs are mainly controlled by the diagenetic differentiation caused by different sedimentation inside the sandbody. Therefore, in the Bohai Bay basin, the exploration should be based on the analysis of sedimentary facies and the favorable diagenetic zones and formations. The focus in Ordos basin, however, should be put on the relatively high permeability sandstones in a generally low permeable sandstone background. __________ Translated from Geoscience, 2007, 21(2): 376–386 [译自: 现代地质]     

Evidence of Multi—Stage Hydrocarbon Charging and Biodegradation of the Silurian Asphaltic Sandstonesin the Tarim Basin,China

Asphalts distributed widely in the Silurian sandstones of the Tarim Basin include dry asphalt, soft asphalt and heavy oil. These asphaltic sandstones underwent multi-episodic sedimentary and tectonic events, and their occurrence is diverse and complex, being mixed with normal oil usually. So far, very little work has been done on the asphaltic sandstone origin and hydrocarbon charging ages. After detailed study on the Silurian sandstones, the following highlights were obtained from the analytical results: distribution of the mixed asphalt, heavy oil and normal oil in the Silurian sandstones is the result of multi-stage hydrocarbon charging from the Lower Paleozoic marine source rocks; the characters of asphalts formed from oils of different charging ages are of difference; the most important process constraining the asphaltic sandstone origin is thought to be biodegradation. This paper was financially supported by funds of Petroleum & Natural Gas Exploration in the Tarim Basin from the “State 9th Five-Year Plan Period” Key Scientific Project (No. 96-111).     

Occurrence characteristics and controls over mobile fluids in a tight sandstone reservoir

Using nuclear magnetic resonance (NMR) technology, this paper proposes a new pore structure parameter called ‘effective mobile fluid saturation’, which can account for two factors that influence mobile fluids in pores: the stiction of hydrophilic particulates on the surfaces of pores and the constraints of tiny throats. The new parameter quantifies the effective content of the mobile fluids and compensates for the deficiencies using conventional parameters like ‘mobile fluid saturation’. Pore-throat connectivity is crucial for effective mobile fluid saturation, which reaches its highest point when the sorting coefficient is in the range of 1.5–2.0. Recognition of the pore-throat configuration is crucial in assessing the effectiveness of mobile fluids in tight sandstone reservoirs. Factors that influence the effectiveness of mobile fluids in three types of pore structures are discussed from a diagenetic perspective, including the development of microfractures and secondary pores, recrystallisation, clay mineral precipitation, and other micropore structure characteristics.     

鄂尔多斯盆地新安边地区长7致密油特征及控制因素

鄂尔多斯盆地在新安边地区首次探明了致密油储量超亿吨级的新安边大油田。为了弄清致密油富集规律, 在前人对沉积相、烃源岩、储层特征及致密化原因研究的基础上, 利用铸体薄片、高压压汞、扫描电镜、岩芯物性、微米CT等分析手段, 通过对烃源岩特征、储集砂体规模及其连通性、储层物性和源储接触关系等因素的研究, 明确了新安边地区致密油的主要特征以及大面积展布的主要控制因素。延长组长7₂储集砂体发育, 储层渗透率差, 储集空间以微米级孔隙为主, 微米孔隙及纳米喉道构成了由多个独立连通孔喉体构成的复杂孔喉网络, 相对较好的孔喉连通性为石油在微观储集空间内流动提供了保障。原油性质好, 具有低密度、低黏度、低凝固点、不含硫、可流动性强的特点。致密储层紧邻优质烃源岩, 厚层烃源岩与较厚砂层共生形成了近源聚集的有利配置关系, 生烃增压为石油运聚提供了充足动力, 连片叠置发育的砂体和裂缝是油气运移的主要通道, 原油充注程度高, 多因素叠合形成了大面积展布的致密油区。     

川中广安地区上三叠统须六段储层特征及控制因素分析

广安地区上三叠统须六段为辫状河三角洲平原分流河道的大套砂岩复合体沉积,以中—细粒长石岩屑砂岩、岩屑砂岩为主;孔隙度主要分布在3%~15%之间,渗透率主要分布在0.01×10-3~1×10-3μm2之间。主、次分流河道为该区有效储层,复合砂体内渗透层与致密层交互分布形成了复杂的储层分布特征。在此基础上,结合成岩作用分析储层物性的影响因素认为,物源成分的不同影响储层发育富集区的分布,沉积演化特征控制储层发育层段,沉积微相控制层内非均质性。在煤系地层酸性环境下,强烈压实作用是形成普遍低渗的主要原因。主分流河道沉积的中、粗粒长石岩屑砂岩次生孔隙较发育,是主要的储层岩石类型。     

羌塘盆地南坳陷布曲组白云岩储层孔喉结构及其分形特征研究

羌塘盆地中侏罗统布曲组白云岩为非均质性强的低孔、低渗储层,孔喉结构评价难度较大。选取南羌塘坳陷布曲组20件白云岩岩心样品,通过铸体薄片、扫描电镜观察,结合物性分析和常规压汞实验,研究其孔喉分布和分形特征,探索分形维数与白云岩储层物性参数、孔喉结构参数、孔隙成因之间的关系。结果表明：（1）研究区布曲组白云岩储集空间类型包括组构选择性孔隙、非组构选择性孔隙、裂缝3类,依据毛管压力曲线特征将其孔喉结构分为5种类型,其分形曲线具有明显的转折点,转折点为孔喉分布峰值,代表连通性好的大尺度孔喉向连通性差的小尺度孔喉的转变;（2）小尺度孔喉的层内非均质性较弱、层间非均质性强,大尺度孔喉的分形维数比小尺度孔喉小,但分布区间较宽,样品间差异明显,表明大尺度孔喉复杂多样,层间（整体）非均质性比小尺度强;（3）大尺度孔喉的分形维数与储层参数、孔喉结构参数相关性较好,可用于布曲组白云岩储层的孔喉结构定量表征,大尺度孔喉分形维数越小,储层物性越好,大尺度孔喉占比越多对储层整体渗透能力的贡献越大;（4）该套储层的储集空间与孔喉结构以沉积形成的碳酸盐沉积物孔隙为基础,白云石化作用和溶蚀作用共同控制了孔喉结构的差异性。     

西昌盆地白果湾组致密砂岩油气形成关键指标评价与有利区优选

综合钻井、大量实测剖面、样品测试分析和区域地质资料,对西昌盆地白果湾组烃源岩生烃强度、镜质体反射率、砂岩储层物性等关键指标进行了系统评价.西昌盆地上三叠统白果湾组主要油气储层类型为中-粗砂岩,有利层段主要发育在白果湾组一段、三段和四段,砂岩具有中孔低渗、区域分布广、厚度大等特征,ZD-1井揭示砂岩含油气性好.西昌盆地白...     

Salt weathering and experimental desalination treatment of building sandstone,Sydney (Australia)

Local sandstone used in nineteenth century buildings in Sydney has been affected by salt weathering and surface crust formation. This study trialled two approaches, namely washing-and-vacuuming and poulticing, to salt-removal treatment of weathered sandstone blocks from the Sydney Hospital and Australian Museum. Both treatments removed solutes from the stones in laboratory tests. ICP/titration of sampled scrapings at depths of 0–2, 2–5 and >50 mm showed substantial between-sample variation, with no significant difference being recorded in solute levels after treatment (Mann–Whitney U test), except for sulfur and sodium. Sulfur levels increased at the surface (0–2 mm) following washing-and-vacuuming but not poulticing for the Hospital and Museum samples. Sodium levels increased at the surface (0–2 mm) following poulticing but not washing-and-vacuuming for the Hospital samples. The presence of surface crusts may have contributed to some of the variation in desalination responses.     

The geometry and organization of fluviodeltaic channel sandstones in the Jurassic Saltwick Formation, Yorkshire, England

Within the Middle Jurassic Saltwick Formation of Yorkshire, England, 65% of the fluvial channel sandstones (n= 22) have width to thickness ratios in the range 17–30. More than 90% lie in the range 17–67 and are classified as narrow sheet channel sandstones. A broad sheet channel sandstone (c. 15 m thick, 3 km wide, width to thickness ratio of 200) occurs at the base of the formation in the proximal part of the studied depositional system. The thicknesses of the channel sandstones are in the range 4 m to more than 22 m, with 90% in the range 4–12 m. The widths of the channel sandstone sections are in the range 100–800 m, with 80% between 100 and 400 m. In plan view the channel sandstones display relatively constant thicknesses across the main part (80%) of the channel body. Channel sandstones are usually multistorey. The storeys are separated by major scour surfaces, with depths of scour ranging from 2 m to 8–10 m. The individual storeys are 4–13 m thick, and transverse and oblique storey sections have lateral extents of 60–480 m. Vertical stacking of storeys is accompanied by a decrease in the width to thickness ratio of the channel sandstones, whereas lateral stacking of storeys is accompanied by an increase. Mudstones and siltstones within channel sandstone bodies occur at the top of storeys and were in most cases deposited during channel abandonment. The Saltwick Formation was deposited during increasing accommodation forming a transgressive systems tract. The channel sandstone to interchannel sediment ratio is highest in the lower parts of the transgressive systems tract. The quantitative geometry and architecture data from the Saltwick Formation may be useful for describing and modelling humid delta plain hydrocarbon reservoirs of transgressive systems tracts.     

The Mesoproterozoic Midsommersø dolerites and associated high-silica intrusions, North Greenland: crustal melting, contamination and hydrothermal alteration

The Midsommersø dolerites and the flood basalts of the Zig-Zag Dal Basalt Formation, eastern North Greenland, represent a major Mesoproterozoic (∼1,380 Ma) igneous event. The intrusive rocks form large sheets within a succession of feldspathic sandstones which underlie the basalts. The geochemistry of the basalts has recently been re-investigated and reported elsewhere in this Journal; here we present new trace element and Nd-, Sr- and Pb-isotopic data for the intrusive rocks. Unlike the basalts, the intrusions yield evidence of considerable interaction and contamination with upper crustal rocks, especially the sandstones. High-silica rocks (80–90 wt% SiO₂) occur in sheets, up to 60 m thick. They were formed by mobilisation of sandstones, and indicate a very high rate of emplacement of hot basic magma into the sandstones at depth. These mobilised sandstones (‘rheopsammites’) are among the most SiO₂-rich intrusive rocks on earth. Sheets of remobilised granitoid rocks from the crystalline basement (∼70% SiO₂) are also present. Hydrothermal activity, associated with the igneous event, significantly changed the compositions of the silicic rocks as well as that of many dolerites. Sheets of hydrothermally altered (‘red’) dolerites and silicic rocks invariably have borders of dark, fresh dolerite; this is interpreted to be the result of intrusion from zoned magma chambers. Nd isotope data confirm the crustal origin of the silicic rocks as well as the contamination of some dolerites by components derived from crustal sources, while Sr- and Pb-isotopic systems are strongly affected by the hydrothermal alteration, and give little information on the petrogenesis of the rocks. Recent loss of Sr from hydrothermally altered rocks further affected the Sr isotope systems, and earlier age determinations by the Rb–Sr whole-rock isochron method (1,230 Ma) have proved to be in error. The dolerites and the basalts are geochemically very similar, but most dolerites have moderately negative Eu anomalies that are not observed in the basalts. Eu anomalies in the dolerites could be related to contamination by sandstone at depth, but it is not clear why the basalts escaped a similar contamination.     

Palynodating of subsurface sediments,Raniganj Coalfield,Damodar Basin,West Bengal

The Gondwana sediments comprising fine-grained shales, carbonaceous shales, sandstones and the coal horizon in borecore RT-4 (approximately 547.00m thick) from Tamra block, Raniganj Coalfield, Damodar Basin, are analyzed palynologically. Based on the distribution pattern of marker palynotaxa, two assemblage zones are identified. In the Barren Measures Formation, dominance of enveloping monosaccate (Densipollenites) along with striate bisaccate (Striatopodocarpites, Faunipollenites) pollen taxa, and the FAD’s of Kamthisaccites and Arcuatipollenites observed at 30.75, have equated this strata (30.75–227.80 m thick) with the Raniganj Formation of Late Permian in age. Downwards in the Barakar Formation, between 423.80–577.70 m depths, an abundance of non-striate (Scheuringipollenites) and striate (Faunipollenites and Striatopodocarpites) bisaccate pollen taxa is observed, that dates late Early Permian in age.     

微生物矿化作用改善不同孔隙砂岩抗冻融特性试验研究

砂岩是地质遗迹和石质文物最为常见的岩石类型,冻融循环导致的风化劣化是引起其发生地质灾害的主要原因。降渗加固是解决该问题的根本途径。文章引入国际上新型的岩土体加固技术—微生物诱导碳酸钙沉淀（MICP）,以中粒砂岩和微粒砂岩为例,通过开展MICP处理和冻融循环试验,研究其改善不同孔隙砂岩抗冻融特性的可行性,分析其改善机理。研究结果表明：（1）MICP作用能显著提高两类砂岩的抗冻融特性,主要改善机理是MICP过程生成的碳酸钙不仅填充了岩石孔隙,减小了孔隙水的体积和冻融损伤作用力,同时也加强了岩石颗粒之间的胶结强度,但孔隙因素对该过程有一定影响;（2）3轮次MICP处理后的岩样在冻融循环40次后未见明显表观破坏,而未经处理的岩样当冻融循环达到40轮次时在棱角处出现局部表观破坏且中粒砂岩破坏程度略大于微粒砂岩;（3）40轮次冻融循环作用后,中粒砂岩和微粒砂岩岩样孔隙率增加率从17.0%和14.8%降低到了4.4%和6.3%,质量损失率从0.22%和0.14%下降到了0.04%和0.02%,吸水率从6.8%和4.4%减小到了0.75%和1.5%,波速降低率从18.5%和12.4%降低到了7.3%和3.8%;（4）由于中粒砂岩孔隙大于微粒砂岩,其碳酸钙沉淀效率更高,有效处理深度更深,表层孔隙间距更大,从而在进行相同轮次MICP处理时,其孔隙率降低率、吸水率降低率、质量增长率、波速增长率均较大。     

Wetting weakening of tertiary sandstones—microscopic mechanism

The micromechanism accounting for wetting weakening of tertiary sandstones was studied. It was found that intragranular fracture prevails for all dry sandstones. However, when the sandstone is wet, intergranular fracture occurs for Type B sandstones. Therefore, one sandstone from Type A sandstones, MS1, and another from Type B, TK, were selected to further investigate the nature of the matrix. It was found that (1) for both sandstones, the major mineral components of the matrix are illite and kaolinite except that the MS1 sandstone has more chlorite; (2) leaching of matrix induced an increase of porosity and consequently results in leaching softening; and (3) among the mineral composition, chlorite is easiest to be dissolved and leached out and induces a more significant increase of porosity, which, in turn, results in a more significant leaching softening.     

南海北部白云深水区高变地温梯度砂岩渗透率定量预测

地温梯度如何影响砂岩成岩演化和储层物性变化是地学界的热点问题. 以具有高变地温梯度特征的白云深水区为例,通过分析大量不同地温梯度地区的样品,以地温梯度0.1~0.2 ℃/100 m为递进间隔,对比分析了不同地温梯度区间内不同粒度砂岩储层渗透率随埋藏深度变化的趋势,建立了砂岩渗透率的定量地质预测模型,展示了砂岩渗透率与地温梯度之间的内在联系. 结果表明,一定埋深范围内,随地温梯度升高,渗透率每下降一个数量级,砂岩埋深下限差异呈台阶式减少;相同地温梯度区间内,高成分成熟度、低塑性岩屑含量的含砾砂岩、粗粒砂岩、中粒砂岩和细粒砂岩的渗透率下降程度不同,相邻粒径砂岩等效渗透率埋深下限差异相近,随地温梯度增加,相邻粒径砂岩等效渗透率下限埋深差异呈规律性减小;低渗与特低渗砂岩储层的地层深度段随地温梯度升高而明显变小,粗粒砂岩特低渗储层的埋深下限可作为白云深水区常规油气勘探的极限深度. 研究成果对于揭示地温梯度对砂岩成岩演化作用的影响及物性演变效应具有重要的意义,对油气勘探有积极的指导作用.