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...     

复杂地质条件输水隧洞冻结施工段支护控制研究

穿越含水疏松砂岩层的深埋输水隧洞围岩稳定和支护控制问题是长距离输水生命线工程中的难点,其施工开挖和支护控制方法目前尚不完善。结合某深埋输水工程疏松砂岩层的支护工程实践,分析了疏松砂岩层冻结施工过程及解冻后土体力学性质的演化以及围岩支护联合受力机制,采用有限元法揭示了冻融过程下围岩的变形规律及支护受力演化特征,并提出疏松砂岩层冻结施工及分步联合支护的设计理念和支护方案。研究结果表明,采用分步联合支护方法能够得到较理想的支护效果,冻结施工段进行支护结构刚度设计和数值验证时应考虑冻融过程对围岩的扰动弱化,让各种支护手段在时间和空间上实现有效结合,使围岩和支护结构紧密结合,形成受力机制明确的联合受力体。     

Origin of Carboniferous sandstones fringing the northern margin of the Wales‐Brabant Massif: insights from detrital zircon ages

A study of detrital zircon age populations in Namurian–Westphalian (Carboniferous) sandstones in the southern Central Pennine Basin of the UK has revealed considerable complexity in their provenance history. The Pendleian–Marsdenian Morridge Formation, which is known to have been derived from the Wales‐Brabant Massif to the south on the basis of palaeocurrent and petrographic information, is dominated by zircons ultimately derived from the Caledonian belt to the north. These zircons were recycled from sandstones of northern origin that had been previously deposited over the massif during Middle to Late Devonian times. The Morridge Formation also includes Late Neoproterozoic zircons of local Wales‐Brabant Massif origin. The south lobe of the Yeadonian Rough Rock has been previously interpreted as having a complex provenance including sediment of northern origin interbedded with sediment ascribed to a Wales‐Brabant Massif source. However, the zircon spectrum lacks a Late Neoproterozoic component that would have been diagnostic of input from the Wales‐Brabant Massif, and the provenance history of the Rough Rock south lobe therefore remains enigmatic. The Langsettian Ludgbridge Conglomerate is dominated by Late Neoproterozoic zircons of Wales‐Brabant Massif origin, but even in this evidently proximal deposit, the provenance is complex since the main zircon group (ca. 640 Ma) cannot be matched with known local Neoproterozoic basement sources. The data either indicate the presence of hitherto‐unknown magmatic rocks of this age adjacent to the South Staffordshire coalfield or indicate that the zircons were recycled from sediment with a more distal origin. Finally, the Duckmantian Top Hard Rock contains zircons that can be reconciled with a source in the Irish Caledonides, consistent with the palaeocurrent evidence, supplemented by zircons derived from the Wales‐Brabant Massif, possibly including the Monian Composite Terrane of Anglesey. The study reinforces the important message that failure to recognize the presence of recycled zircon could lead to erroneous reconstructions of sediment provenance and transport history. Copyright © 2014 John Wiley & Sons, Ltd.     

鄂尔多斯盆地镇泾区块延长组长81储层成岩作用特征及其对储集物性的影响

鄂尔多斯盆地镇泾区块上三叠统延长组长81储层具有成分成熟度低,结构成熟度中等到好的特点,岩性以岩屑长石砂岩和长石岩屑砂岩为主.长81砂岩属于特低孔特低渗储层,以次生溶蚀粒间孔为主要储集空间.目前储层正处于中成岩阶段A期,主要发育压实、胶结、溶解和交代4种成岩作用类型.机械压实作用是造成长81储层埋深小于2000 m砂岩...     

利用数字岩心技术评价含黏土砂岩导电模型

黏土附加导电性使得岩石导电机理复杂化,影响了测井解释中饱和度计算的准确性。随着石油勘探的发展,测井解释研究者针对特定地区和储层条件的饱和度求解提出了多种导电模型。本文基于贝雷砂岩的数字岩心,构建多种含黏土的砂岩数字岩心,利用有限元方法模拟岩心饱和水时的电导率C₀,并将数值模拟C₀与5种模型计算C₀对比,分析各种导电模型的适用情况。结果表明,黏土体积分数越小,黏土的阳离子交换容量越小,岩石孔隙度越大,公式计算C₀越接近数值模拟C₀。Doll公式和Indonesia公式计算C₀与数值模拟C₀接近,基本适用于不同孔隙度、黏土体积分数和阳离子交换容量的情况。     

K–Ar dating of authigenic minerals in siliciclastic sequences: an example from the south Sanfranciscana Basin (Western Minas Gerais,Brazil)

K–Ar dating was applied on authigenic potassic minerals which are abundant in sandstones from the south of the Sanfranciscana Basin, Western Minas Gerais State, central Brazil. The Quintinos Member fluvial sandstones (Três Barras Formation, Areado Group) contain significant amounts of authigenic K‐feldspar as microcrystals of adularia and sanidine habits. The ages of these microcrystals cluster into three groups: 106.1 ± 2.2, 89.9 ± 1.9 and 88.8 ± 1.8 Ma (from Albian to Coniacian). The older age of 106.1 ± 2.2 Ma was obtained from the coarse fraction analysed (10–20 µm) that can contain a mixture of detrital potassic minerals (K‐feldspar, muscovite, biotite and illite) and different authigenesis of K‐feldspar (overgrowths and microcrystals). Thus, only the younger ages were interpreted as precipitation of K‐feldspar microcrystals during the Late Cretaceous into the Quintinos Member sandstones. Moreover, these ages can document the formation of microcrystals within a few million years after deposition of the sandstones. The ages of authigenic illite from the Capacete Formation epiclastic sandstones (Mata da Corda Group) range from 88.5 ± 1.9 to 71.5 ± 1.9 Ma (Coniacian–Campanian). These results suggest the timing of the illitization event in these sandstones as well as a synchrony with K‐feldspar authigenesis in the Quintinos Member sandstones. These results are well constrained and are in agreement with stratigraphic, biostratigraphic and radiometric ages previously reported for the Sanfranciscana Basin. Copyright © 2014 John Wiley & Sons, Ltd.     

Dickite‐ and kaolinite‐bearing sandstones and conglomerates in Illawarra Coal Measures of the Sydney Basin,New South Wales

The recent discovery of dickite, intimately associated with ordered and disordered kaolinite, in quartzose sandstones and conglomerates of the Illawarra Coal Measures is of interest since in terms of the phase rule the co‐existence of two or more of these polytypes is evidence of either an unstable or metastable assemblage. A study has, therefore, been undertaken of the host rocks and accompanying strata in an attempt to gain insight into the mechanism of formation of the dickite and the reason for its development in preference to either of the other generally more abundant polytypes. From the results it would appear that although much still remains unresolved, the dickite is authigenic and precipitated from migrating groundwaters. Due probably to unusually low concentrations of silica in the groundwaters the rate of precipitation was inordinately slow and this apparently facilitated growth of relatively coarse crystals and development of the most stable phase.     

洪水型季节性河流砂岩中碎屑黏土的岩石学特征及其研究意义

洪水型季节性河流砂岩以碎屑黏土含量高为特征。按照组构,碎屑黏土可划分为泥质内碎屑、机械渗滤黏土和成壤泥质凝聚体。泥质内碎屑主要分布于河道砂岩的底部。机械渗滤黏土包括脊状和桥状、示底组构、松散聚集、胶膜和块状聚集体5种类型,其空间分布受控于潜水面波动和河道下切或迁移。成壤泥质凝聚体往往分布于具有纹理或交错层理的砂岩或粉砂岩、滞留沉积、大型槽状层理砂岩与河道充填序列的顶部。机械渗滤黏土是导致河流相砂岩储层非均质性的重要因素之一,砒砂岩的侵蚀脆弱性可能与高含碎屑蒙皂石有关。     

Origin of Lower Cretaceous (‘Nubian’) sandstones of North‐east Africa and Arabia from detrital zircon U‐Pb SHRIMP dating

Lower Cretaceous sandstones of the type exposed in Israel, deposited over much of North Africa and Arabia as widespread sandstone sheets, typically are mineralogically and texturally mature. Previous petrographic examinations suggested that the Lower Cretaceous sandstones are at least partly a product of recycling and the present study supports this notion. The results of U‐Pb Sensitive High Resolution Ion Micro‐Probe (SHRIMP) dating of detrital zircons from the Lower Cretaceous section exposed in Israel indicate that they are dominated by detrital zircons of Neoproterozoic age, mainly concentrated in the 0·55 to 0·65 Ga interval, with various amounts of older (pre‐Neoproterozoic) zircons (of 0·95 to 1·10, 1·7 to 2·0 and 2·6 to 2·65 Ga age groups). The overall age signal is similar to detrital zircon age spectra previously obtained from the Cambrian–Ordovician sections of Israel and Jordan. Remarkably, the detrital zircon spectra remained almost unchanged for nearly 400 Myr. Thus, the most probable provenance of the Lower Cretaceous sandstone is the recycling of relatively proximal Palaeozoic sandstone. Since first unroofed from above pan‐African terranes closer to the secession of orogeny, the ensuing siliciclastics were recycled repeatedly throughout the Phanerozoic with little additional basement denudation. The Lower Cretaceous sandstone comprises quartz sand that was first eroded from above pan‐African orogens ca 400 Myr prior to deposition.     

Nature of sedimentary deposits in the western Makgadikgadi basin, Botswana

Quaternary sedimentation in the western Makgadikgadi basin of north central Botswana is evaluated on the basis of new evidence from satellite imagery and sedimentological analyses. Thematic Mapper imagery interpretation, combined with field evidence, has led to the identification of geomorphological features which are mainly composed of light grey calcareous sandstones (formerly calcretes) overlain by dark grey sands. The literature suggests that palaeolake Makgadikgadi I formed and developed intermittently after initial downwarping in the early–mid Pleistocene. The calcareous sandstones were formed when calcium carbonate precipitation took place in pre-existing Kalahari sands along the western shoreline of Makgadikgadi I. Field evidence, supported by X-ray diffraction and SEM analyses, indicates that CaCO₃precipitated mainly in marshy conditions around plant roots and stems and in association with bacteria in embayments along the lakeshore. The sandstones thickened and became partially indurated as a result of increasing palaeolake levels. Deposition was terminated by renewed tectonism which uplifted the shoreline zone relative to the lake basin, leading to falling palaeolake levels. Post-uplift reworking led to case hardening and pedogenic calcrete formation in the upper sections of the calcareous sandstones. Sedimentary conditions altered during the late Pleistocene. Extensive distributaries from the proto-Okavango system incised the shoreline ridge contributing to the filling of Makgadikgadi II. Satellite data suggest that the proto-Okavango rivers formed a series of fan deltas at this time along the western Makgadikgadi basin. Widespread dispersal of fluvial grey sands took place as a result of basin tilting which led to anastomosing channels flowing southward possibly around 18,000 B.P. These results, although preliminary in nature, augment previous geomorphological analyses by adding some detail in terms of depositional environments and by providing a tentative age and origin for the ubiquitous grey sands.