The use of diagenetic signatures to distinguish marine from continental deposits in Triassic-Jurassic sandstone reservoirs from the UK Central Graben     

《Marine and Petroleum Geology》2017

Poor biostratigraphic control for some Triassic-Jurassic successions in the North Sea Basin and sub-basins necessitates the use of alternative correlation methods. This study examines the use of diagenetic signatures to distinguish continenetal from marine sandstone successions (Triassic-Jurassic) in the UK Central Graben. The key diagenetic alterations encountered in these successions include kaolinitization of the framework grains and the development of sphaerosiderite and pyrite. The δ ¹³C_V-PDB values of siderite (−8.1 to −8.5‰) and of ankerite (−10.8 to −9.2‰), indicate a strong contribution of dissolved carbon from the decay of plant material in soil. However, marine water likely influenced diagenesis during periods of relative sea level rise by providing the dissolved sulfate (SO₄²⁻) required for the precipitation of pyrite. The presence of diagenetic alterations such as kaolinitization of framework grains and cementation by sphaerosiderite could indicate that the sediments were deposited in an overall continental setting. However, the occurrence of pyrite and scattered grains of deep-green colored glauconite suggests occasional marine influence. Such information on the changes of the diagenetic realm provides important clues for establishing a framework for stratigraphic correlations. Caution should be exercised when interpreting petrographic data as subsequent episodes of telodiagenesis can complicate petrographic interpretations.  相似文献   

Quantitative analyses of porosity evolution in tight grainstones: A case study of the Triassic Feixianguan formation in the Jiannan gas field,Sichuan Basin,China     

《Marine and Petroleum Geology》2017

Tight grainstones, although widespread throughout the Lower Triassic Feixianguan Formation in the Sichuan Basin, have received little attention, in part, due to their lower porosity and greater heterogeneity relative to their dolostone counterparts. Based on data from cores and thin sections, as well as petrophysical properties, the Feixianguan grainstones, representing a major gas reservoir in the Jiannan gas field were systemically analysed to better understand porosity evolution in tight carbonates that have experienced original oil accumulation and subsequent thermal cracking during progressive burial. The grainstones were divided into two types according to whether pyrobitumen was present, and their porosity evolutions were quantitatively reconstructed. Taking 40% as the original porosity, the grainstones without pyrobitumen, which were ineffective palaeo-oil reservoirs, lost 21.94% and 3.13% of their porosities through marine and burial calcite cementation, respectively, and 13.34% by compaction, and have a current porosity of 1.59%, thus allowing them to serve as major present-day gas reservoirs. Comparatively, pyrobitumen-bearing grainstones, which were once palaeo-oil reservoirs, lost 23.96% and 2.36% of their porosities through marine and burial calcite cementation, respectively; 11.4% by compaction, and 1.44% by pyrobitumen and have a current porosity of 0.84%, thus making them ineffective gas reservoirs. This study provides a quantitative understanding of the close association between porosity evolution and reservoir effectiveness for the palaeo-oil charge and present-day gas accumulation with respect to diagenetic history, which is useful for the future exploration in tight gas limestone reservoirs.  相似文献   

Flow simulation with reactive transport applied to carbonate rock diagenesis     

《Marine and Petroleum Geology》2017

Significant volumes of the known hydrocarbon reserves are found in carbonate rocks, many of these dolomitized. The spatial distribution of diagenesis on these rocks is one of the main challenges in oil reservoir modeling. Reactive transport models can be a powerful tool to understand the active diagenetic processes and their effects on the quality of these reservoirs. In this study it was used, for the first time, the CMG-GEM simulator to model diagenetic evolution of a carbonate sequence, subjected to compaction-driven and geothermal flow in a simulated period of 200 thousand years. It was simulated carbonate cementation, dolomitization and dissolution, with and without presence of faults. Among the analyzed variables, the volume of circulating fluid was the most important factor. For both mechanisms, flow simulated velocities obtained had magnitudes smaller than 10⁻⁶ m/day. Diagenesis was insignificant for these low speeds at simulated time interval. Only dolomitized facies presented relevant diagenesis in form of calcite dissolution and dolomite precipitation. Simulations with flow rates of 1 m/day revealed a considerable increase in observed diagenesis, especially in carbonate cementation and in porosity enhancement. Diagenesis was more pronounced in more permeable sediments, highlighting the role of fluid flow in diagenetic reactions. Relative dissolution was greatly reduced during simulations performed with absence of dolomite and dolomitization reactions. The presence of faults strongly influences spatial distribution of diagenesis, especially relatively to dissolution. More permeable facies were more dissolved near fault, decreasing with increasing distance. Low permeability facies, as mudstones, are not dissolved, even near fault. Spatial distribution of diagenesis would then be dependent mainly on the quality of original pore structure, of fault presence and mineral composition of rock.  相似文献   

Reservoir quality along a homoclinal carbonate ramp deposit: The Permian Upper Dalan Formation,South Pars Field,Persian Gulf Basin     

《Marine and Petroleum Geology》2017

Permo-Triassic carbonate successions host some of the largest oil and gas reserves in the Arabian Plate, including the world's largest gas reservoirs of the Upper Dalan and the Kangan formations in the South Pars Gas Field, Persian Gulf Basin. Both formations are stratigraphically equivalent to the Upper Khuff Formation which has been long recognized as a major oil and gas reservoir in the Arabian Peninsula. The Permian Upper Dalan Formation is composed mainly of mixed carbonate-evaporite sequences that formed on a laterally continuous homoclinal carbonate ramp with significant variations in reservoir heterogeneity and quality. They can be grouped in 18 microfacies. High reservoir qualities are found within high-energy shoal environments with a tendency of the best reservoir quality to occur towards the basin in a mid-ramp setting. In contrast, low-energy tidal flat environments exhibit the poorest reservoir quality. Reservoir quality from lagoonal environments is diverse. Diagenesis has significantly affected reservoir properties by both enhancing and destroying original porosity and permeability. Bivariate plots of porosity and permeability values, combined with thin section petrography indicate that pore-filling “pervasive” and poikilotopic anhydrite cements had the greatest negative impact on the reservoir quality whereas dolomitization and dissolution of grains and cements played the most positive role. Two third-order sequence stratigraphic cycles link lithologies and depositional environments to sea-level fluctuations. HSTs are associated with better reservoir characteristics than TSTs.  相似文献   

Quantitative impact of diagenesis on reservoir quality of the Triassic Chang 6 tight oil sandstones,Zhenjing area,Ordos Basin,China     

《Marine and Petroleum Geology》2017

The Upper Triassic Chang 6 sandstone, an important exploration target in the Ordos Basin, is a typical tight oil reservoir. Reservoir quality is a critical factor for tight oil exploration. Based on thin sections, scanning electron microscopy (SEM), X-ray diffraction (XRD), stable isotopes, and fluid inclusions, the diagenetic processes and their impact on the reservoir quality of the Chang 6 sandstones in the Zhenjing area were quantitatively analysed. The initial porosity of the Chang 6 sandstones is 39.2%, as calculated from point counting and grain size analysis. Mechanical and chemical compaction are the dominant processes for the destruction of pore spaces, leading to a porosity reduction of 14.2%–20.2% during progressive burial. The porosity continually decreased from 4.3% to 12.4% due to carbonate cementation, quartz overgrowth and clay mineral precipitation. Diagenetic processes were influenced by grain size, sorting and mineral compositions. Evaluation of petrographic observations indicates that different extents of compaction and calcite cementation are responsible for the formation of high-porosity and low-porosity reservoirs. Secondary porosity formed due to the burial dissolution of feldspar, rock fragments and laumontite in the Chang 6 sandstones. However, in a relatively closed geochemical system, products of dissolution cannot be transported away over a long distance. As a result, they precipitated in nearby pores and pore throats. In addition, quantitative calculations showed that the dissolution and associated precipitation of products of dissolution were nearly balanced. Consequently, the total porosity of the Chang 6 sandstones increased slightly due to burial dissolution, but the permeability decreased significantly because of the occlusion of pore throats by the dissolution-associated precipitation of authigenic minerals. Therefore, the limited increase in net-porosity from dissolution, combined with intense compaction and cementation, account for the low permeability and strong heterogeneity in the Chang 6 sandstones in the Zhenjing area.  相似文献   

Facies effects on the behaviour of Nd and Sr isotope systems in turbidite mudrocks during diagenesis     

JANE A. EVANS  JAN A. ZALASIEWICZ†  ANNE CHOPEY-JONES† 《Sedimentology》2009,56(4):863-872

A detailed Sm/Nd, epsilon Nd and Rb/Sr profile through a 30-cm thick section of Silurian (Llandovery) interbedded turbiditic and hemipelagic mudrocks from the central Wales Basin shows well-marked chemical and isotopic trends. The variations reflect an interplay of depositional mode and diagenetic fractionation. Sm and Nd values are substantially higher and Sm/Nd ratios tend to be lower in the organic-rich hemipelagite layers due to diagenetic concentration in the hemipelagites. There is a corresponding depletion in the turbidite mudstones. Epsilon Nd values range from −0·8 to −7·1 and this is attributed to diagenetic modification of Sm/Nd ratios causing scatter in back-calculated epsilon values. Rubidium–strontium ratios in this succession fall within a narrow range, due to homogenization during diagenesis. By contrast, data from a hemipelagite-dominated (condensed) succession near the northern margin of the Welsh Basin show a lower range of epsilon Nd values and a higher scatter of Rb/Sr values, consistent with less fluid throughput during burial compaction and hence less diagenetic redistribution in these rocks. These patterns demonstrate the sensitivity of mudrock trace element and isotope compositions to both small-scale sedimentary structure and large-scale basin architecture.  相似文献   

From outcrop and petrographic studies to basin-scale fluid flow modelling: The use of the Albanian natural laboratory for carbonate reservoir characterisation   总被引：1，自引：0，他引：1  

Nadge Vilasi  Julien Malandain  Laurie Barrier  Jean-Paul Callot  Khalid Amrouch  Nicole Guilhaumou  Olivier Lacombe  Kristaq Muska  Franois Roure  Rudy Swennen 《Tectonophysics》2009,474(1-2):367

The Albanian fold-and-thrust belt and the Peri-Adriatic Depression are well documented by means of seismic reflection profiles, GPS reference points, potential data, wells and outcrops. The continuous Oligocene to Plio-Quaternary sedimentary records help to constrain both the burial history of Mesozoic carbonate reservoirs, the timing of their deformation, and the coupled fluid flow and diagenetic scenarios.Since the mid-90s, the Albanian foothills were used as a natural laboratory to develop a new integrated methodology and work flow for the study of sub-thrust reservoir evolution, and to validate on real case studies the use of basin modelling tools as well as the application of new analytical methods for the study petroleum systems in tectonically complex areas.The integration of the interactions between petrographic and microtectonic studies, kinematic, thermal and fluid flow basin modelling, is described in detail. The fracturing of the reservoir intervals has a pre-folding origin in the Albanides and relates to the regional flexuring in the foreland. The first recorded cement has a meteoric origin, implying downward migration and the development of an earlier forebulge in the Ionian Basin. This fluid, which precipitates at a maximum depth of 1.5 km, is highly enriched in strontium, attesting for important fluid–rock interaction with the Triassic evaporites, located in diapirs. From this stage, the horizontal tectonic compression increases and the majority of the fluid migrated under high pressure, characterised by brecciated and crack-seal vein. The tectonic burial increased due to the overthrusting, that is pointed out by the increase of the precipitation temperature of the cements. Afterwards, up- or downward migration of SO₄²⁻, Ba²⁺ and Mg²⁺-rich fluids, which migrated probably along the décollement level, allows a precipitation in thermal disequilibrium. This period corresponds to the onset of the thrusting in the Ionian Zone. The last stage characterised the uplift of the Berati belt, developing a selective karstification due likely to the circulation of meteoric fluid.The main results of the fluid flow modelling show that the Upper Cretaceous–Paleocene carbonate reservoirs in the Ionian zone have been charged from the Tortonian onward, and that meteoric fluid migration should have intensely biodegraded the hydrocarbon in place. Concerning the migration paths, it has been demonstrated that the thrusts act principally as flow barriers in Albania, mainly due the occurrence of evaporites (non-permeable), except in the foreland, where they do not occur.  相似文献   

白云岩埋藏成岩作用过程中的金属元素与同位素再分配规律与受控因素   总被引：2，自引：0，他引：2  

陈永权  周新源 《海相油气地质》2009,14(3):65-67

前人在白云岩岩石地球化学研究过程中注意到,在开放体系下埋藏成岩作用过程中白云石金属元素含量与同位素组成将发生再分配,然而到目前为止还没有系统的理论来解释这一现象。根据化学平衡原理,提出离子半径理论控制白云岩在埋藏过程中的金属元素与同位素组成再分配规律,基本概念为大半径离子含量减少,小半径离子含量升高。根据这一理论,结合Ca、Mg、Fe、Mn、Sr等+2价离子的离子半径数值得出推论,在埋藏压实成岩作用过程中白云石将向着有序度升高的方向转化,白云石中的Fe、Mn含量升高,Sr含量降低,同位素比值87Sr/86Sr升高。该结论与前人资料有着高度的一致性。  相似文献   

碎屑岩层序地层与成岩作用时空关系研究新进展   总被引：1，自引：1，他引：0  

周宗良  蔡明俊  石占中  朱敏 《新疆地质》2009,27(4)

成岩作用与层序地层学在沉积地质学内是两个分支学科.文章叙述了碎屑岩层序地层与成岩作用关系,指出层序、准层序界面、海(湖)侵和最大湖泛面附近,及在低位体系域、海(湖)侵体系域、高位体系域等地层层序条件下,成岩作用包括成岩自生矿物的形成组合(如方解石、白云石、菱铁矿、黄铁矿、高岭石、海绿石、磁绿泥石)、假基质形成、机械粘土充填、粒间孔隙演变等均有明显差异.原因主要是由于层序地层控制成岩作用的类型与时空分布:①碎屑组分.包括沉积盆地内外碎屑组分类型与比例;②孔隙水化学条件;③有机质存在与作用;④特定地球化学条件下沉积物存在的时间;⑤古气候条件.层序地层与成岩作用时空关系模式,将层序地层界面、体系域与成岩作用、储层性质的演化有机地结合在一起,扩大了预测砂岩储层能力,使储层预测更具准确性和实用性.  相似文献   

构造应变与砂岩成岩的构造非均质性——以塔里木盆地库车坳陷研究为例   总被引：6，自引：2，他引：4  

李忠  张丽娟  寿建峰  韩登林  沈杨  张惠良 《岩石学报》2009,25(10):2320-2330

孔隙性砂岩在应变过程中首先发生应变局域化并形成肉眼不易识别的变形条带(deformation band),这与低孔隙性的碳酸盐岩的应变效应迥然不同.实例分析说明,天山南缘库车坳陷后期构造变形强烈,自白垩纪以来构造应变具有南北分带、东西分异的显著特征.结合盆地构造格架以及砂岩物性分布特征,本文提出了该区六类砂岩储层改造的构造样式,并描述了其中砂岩的构造非均质性.其中深层卷入型(3类)主要发育于盆地西部,而浅层卷入型发育于盆地东部,其分布受基底构造、盐煤等滑脱层、近南北向的调节断裂、盆山边界接触方式的控制.除变形条带外,研究发现本区最大埋深大于6500～7000m的白垩系致密砂岩的应变属性亲近灰岩,其由于后期抬升或深层次构造应变将容易导致裂隙的发育,这一点在有效储层预测中值得重视.  相似文献