海拉尔盆地贝尔凹陷储层成岩与储渗结构特征

在对海拉尔盆地贝尔凹陷储层沉积学研究的基础上,探讨了储层物性与粘土矿物演化、有机质成熟过程、油气生成、新生矿物形成、次生孔隙发育程度等沉积成岩演化的关系;分析了储层孔隙的成因与分布;根据储层岩性、成岩结构与储层物性特征建立了贝尔凹陷5种储层的储渗结构类型,对研究区的油气运移与富集区带进行了预测。     

铜石金矿田金元素来源新认识

铜石金矿田位于鲁西中生代富碱次火山杂岩体--铜石岩体周围,该岩体侵入于燕山晚期,主要有闪长玢岩、二长斑岩和隐爆角砾岩组成.岩体与金矿田有密切的成因关系,目前一般认为铜石金矿田金元素来源于泰山群地层,岩体与金矿是衍生关系而非同源关系.但文章通过对铜石金矿田地质特征、流体包裹体成分、氢氧同位素证据、锶、氧和铅同位素比值、碲元素地球化学特征以及国内外成矿地质条件相似地区研究成果分析得出新的观点:铜石金矿田金元素来源于深部碱性玄武岩浆,矿体与岩体是同源而非衍生关系.该新认识对鲁西黄金找矿具有一定参考价值.     

Diagenesis and reservoir quality analysis in the Lower Cretaceous Qishn sandstones from Masila oilfields in the Sayun–Masila Basin,eastern Yemen

Lower Cretaceous sandstones of the Qishn Formation have been studied by integrating sedimentological, petrological and petrophysical analyses from wells in the Masila oilfields of eastern Yemen. These analyses were used to define the origin, type of diagenesis and its relation to reservoir quality. The sandstones of the Qishn Formation are predominately quartz arenite to subarkose arenite with sublitharenite and quartz wackes displaying a range of porosities, averaging 22.33%. Permeability is likewise variable with an average of 2844.2 mD. Cementation coupled with compaction had an important effect on porosity destruction after sedimentation and burial. The widespread occurrence of early calcite cement suggests that the sandstones of the Qishn Formation lost significant primary porosity at an early stage of its diagenetic history. In addition to poikilotopic calcite, several different cements including kaolinite, illite, chlorite and minor illite–smectite occur as pore‐filling and pore‐lining cements, which were either accompanied by or followed the development of the early calcite cement. Secondary porosity development occurred due to partial to complete dissolution of early calcite cements and feldspar grains. The new data presented in this paper suggest the reservoir quality of Qishn sandstones is strongly linked to their diagenetic history; hence, the reservoir quality is reduced by clay minerals, calcite and silica cements but is enhanced by the dissolution of the unstable grains, in addition to partial or complete dissolution of calcite cements and unstable grains. Copyright © 2015 John Wiley & Sons, Ltd.     

Apatite fission‐track analysis of Cretaceous alkaline rocks of Ponta Grossa and Alto Paranaíba Arches,Brazil

This work presents fission‐track ages and thermal history modelling of apatite samples from two Brazilian alkaline formations: Alto Paranaíba and Ponta Grossa Arches. The apatite fission‐track ages obtained for Alto Paranaíba Arch agree with those determined by other radiometric dating methods presenting higher closure temperatures. The ages given by the fission‐track thermochronometer suggest that no strong tectonic event has occurred after Alto Paranaíba Formation during Upper Cretaceous. This event is also supported by thermal history modelling of this arch, which is characterized by fast cooling followed by residence at lower temperatures. On the other hand, apatite fission‐track ages from Ponta Grossa Arch are systematically lower than other radiometric ages, suggesting that at least one tectonic event occurred after Ponta Grossa Formation, around 130 Ma. Copyright © 2015 John Wiley & Sons, Ltd.     

Facies mosaic and diagenetic patterns of the early Devonian (Late Pragian–Early Emsian) microbialite‐dominated carbonate sequences,Qasr Member,Jauf Formation,Saudi Arabia

The Al‐Jawf area of northern Saudi Arabia provides spectacular outcrops of Early Devonian carbonate bioherms in the Wadi Murayr and Dumat Al‐Jandal areas. These carbonate bioherms belong to the Qasr Member of the Late Pragian–Early Emsian Jauf Formation (~405 Ma) and are surrounded by a bioclastic carbonate succession. The Qasr Member is the first major carbonate unit of the Palaeozoic succession in Saudi Arabia that mainly consists of microbialite carbonates and metazoan reefs exhibiting distinct mound features. These bioherm complexes and their associated carbonate facies are pervasively dolomitized. Stratigraphic, petrographic and geochemical analyses were conducted to determine the facies distribution and interpret their depositional and diagenetic processes. A total of 11 facies are identified from a range of depositional environments within a carbonate platform system, ranging from tidal flats, lagoon, shoal, patch reefs to reef front. The main diagenetic processes are carbonate cementation and dolomitization. Dolomitization occurred as both fabric preserved (mostly in grain‐dominated facies) and fabric destructive (mud‐dominated facies). The microbialites and coralline sponges facies show poor reservoir with visual porosity less than 5%, but this succession may have a potential to serve as a good source for the underlying and overlying facies. Ooid and peloidal grainstone facies show fair to good visual porosity that locally exceeds 10% with intergranular porosity as the dominant type. However, in the most studied samples, vuggy and intraparticle porosities are observed as the dominant type. Copyright © 2015 John Wiley & Sons, Ltd.     

Chert spheroids of the Monterey Formation,California (USA): early‐diagenetic structures of bedded siliceous deposits

Chert spheroids are distinctive, early‐diagenetic features that occur in bedded siliceous deposits spanning the Phanerozoic. These features are distinct in structure and genesis from similar, concentrically banded ‘wood‐grain’ or ‘onion‐skin’ chert nodules from carbonate successions. In the Miocene Monterey Formation of California (USA), chert spheroids are irregular, concentrically banded nodules, which formed by a unique version of brittle differential compaction that results from the contrasting physical properties of chert and diatomite. During shortening, there is brittle fracture of diatomite around, and horizontally away from, the convex surface of strain‐resistant chert nodules. Unlike most older siliceous deposits, the Monterey Formation still preserves all stages of silica diagenesis, thus retaining textural, mineralogical and geochemical features key to unravelling the origin of chert spheroids and other enigmatic chert structures. Chert spheroids found in opal‐A diatomite form individual nodules composed of alternating bands of impure opal‐CT chert and pure opal‐CT or chalcedony. With increased burial diagenesis, surrounding diatomite transforms to bedded porcelanite or chert, and spheroids no longer form discrete nodules, yet still display characteristic concentric bands of pure and impure microcrystalline quartz and chalcedony. Petrographic observations show that the purer silica bands are composed of void‐filling cement that precipitated in curved dilational fractures, and do not reflect geochemical growth‐banding in the manner of Liesegang phenomena invoked to explain concentrically banded chert nodules in limestone. Chertification of bedded siliceous sediment can occur more shallowly (< 100 m) and rapidly (< 1 Myr) than the bulk silica phase transitions forming porcelanite or siliceous shale in the Monterey Formation and other hemipelagic/pelagic siliceous deposits. Early diagenesis is indicated by physical properties, deformational style and oxygen‐isotopic composition of chert spheroids. Early‐formed cherts formed by pore‐filling impregnation of the purest primary diatomaceous beds, along permeable fractures and in calcareous–siliceous strata.     

Structure of a silica diagenetic transformation zone: the Gjallar Ridge,offshore Norway

Three‐dimensional seismic data from the Gjallar Ridge were used together with X‐ray diffraction data, scientific boreholes and wireline logs to analyse the seismic structure of a silica diagenetic transformation zone. The following features were identified: (i) an interval some 150 to 300 m thick that contains anomalously high‐amplitude reflections; (ii) a strong reflection event at the top of this interval which cross‐cuts stratigraphy, interpreted as the transformation boundary between opal‐A‐rich and opal‐CT‐rich sediment; (iii) amplitude variations on stratigraphic reflections within the interval, attributed to variations in the proportions of opal‐A and opal‐CT; and (iv) a second, deeper, cross‐cutting reflection event within the interval, interpreted as the transformation boundary between opal‐CT‐rich and quartz‐rich sediment. The base of the interval containing the anomalously high‐amplitude reflections is interpreted as a stratigraphic reflection demarcating the base of the silica‐rich strata. On a stratigraphic reflection within the interval of high amplitudes, roughly circular regions of anomalously high amplitude with diameters of 0·8 to 2·5 km are separated by lower amplitude regions. This pattern is similar to the cells previously identified at the opal‐A to opal‐CT transformation boundary and probably results from more complete transformation of opal‐A to opal‐CT. All of these observations provide the first recognition from seismic data that silica diagenetic transformations are not always narrow boundaries represented by single cross‐cutting seismic reflection events, as implied previously, but can be heterogeneous and hundreds of metres in thickness, as observed at outcrop.     

Aragonite loss in a cold‐water coral mound: mechanisms and implications

Selective dissolution of aragonitic grains is emerging as a volumetrically significant process that affects a broad range of modern carbonate settings. This study explores mechanisms and implications of aragonite loss in Challenger Mound, a giant cold‐water coral (Lophelia pertusa) mound of Pleistocene age, which lies on the continental slope off south‐west Ireland. A comprehensive sampling scheme allowed the integration of petrographic data with geochemical analyses of sediment and pore water. The mound remains virtually unlithified and consists of stacked, fining‐upward cycles of silty coral floatstone–rudstone and bafflestone grading into wackestone. Whereas calcitic grains appear unaltered, aragonitic grains are corroded and fragmented. Aragonite dissolution is attributed to organic matter oxidation at/near the sediment–water interface and, at greater depths, to the initial stages of bacterially mediated sulphate reduction, when alkalinity production is outpaced by the generation of H⁺. Pore water profiles indicate that undersaturated waters are diffusing towards the mound interior from two centres of sulphate reduction: one located in the upper 10 m of the sediment column and a second that lies below an erosional unconformity which marks the base of the mound. Continued aragonite dissolution is expected to gradually lower the diagenetic potential of the Challenger Mound and delay lithification until deep burial, when solution‐compaction processes come into play. Despite a fundamental role in predestining the final taphonomic and textural characteristics of Challenger Mound, the processes described here are expected to leave little trace in the geological record due to a lack of cementation and calcitization. Assuming that similar processes have been active throughout the Phanerozoic, results imply that the understanding of diagenetic processes in carbonate systems may be incomplete.     

鄂尔多斯盆地余兴庄—子洲地区上古生界山_2~3储层砂岩成岩作用与成岩相

鄂尔多斯盆地余兴庄—子洲地区上古生界山23亚段岩石类型主要为石英砂岩、岩屑石英砂岩和岩屑砂岩,目前储层正处于晚成岩阶段B期甚至C期,储集层经历了压实、压溶、硅质胶结、碳酸盐胶结交代、高岭石胶结以及溶蚀等多种成岩作用。在成岩作用研究的基础上,通过大量的岩芯观察和薄片鉴定,结合阴极发光、X衍射、扫描电镜等方法,将研究区划分...     

四川盆地东北部地区长兴组碳酸盐岩成岩作用及储层孔隙演化

以四川盆地东北部长兴组碳酸盐岩为研究对象,应用薄片、铸体、阴极发光和X射线衍射等室内分析技术,对其成岩作用、成岩演化序列、储层孔隙演化及其特征进行了详细研究。研究区常见的成岩作用有：压实压溶作用、胶结作用、充填作用、交代作用、白云化作用、重结晶作用、溶蚀作用、破裂作用等成岩作用。其中对储层孔隙发育影响较大的主要是胶结作...