Maturity studies and source-rock potential in the southern Sverdrup Basin, Arctic Canada

The purpose of the study is to better understand the relationship between organic matter optical properties and the presence of potentially large oil and gas accumulations in Arctic Canada. The type and thermal maturity of the dispersed organic matter of the Mesozoic formations in the southern Sverdrup Basin, Melville Island, have been studied using organic petrology and Rock-Eval pyrolysis.All types of organic matter are present in the strata of Mesozoic age. Hydrogen-rich liptinite is dominated by alginite (Botryococcus and Tasmanites), dinoflagellate cysts and amorphous fluorescing matrix. Sporinite, cutinite, resinite and liptodetrinite made up the lesser hydrogen-rich exinite. Vitrinite reflectance in Cretaceous sediments ranges from 0.36 to 0.65% R_o; in Jurassic sediments it ranges from 0.40 to 1.0% R_o and in the Triassic from 0.45 to 1.30% R_o, showing an overall increase with depth of burial.Cretaceous sediments of the Deer Bay Formation are thermally immature and contain organic matter of terrestrial origin. The Upper Jurassic shales of the Ringnes Formation contain predominantly organic matter of liptinitic and exinitic origin with a considerable vitrinitic input. At optimum maturation levels, potential source beds of this formation would have a good hydrocarbon-generating potential. The hydrocarbon potential, however, would be limited to the generation of gases due to the leanness of the source rocks. Parts of the Lower Jurassic Jameson Bay Formation are organic-rich and contain a mixed exinitic/vitrinitic organic matter, Botryococcus colonial algae but visible organic matter is dominated by high plant remains (mainly spores). The Schei Point Group shales and siltstones contain organic matter of almost purely marine origin, whereas the predominantly higher plant-derived organic matter found in the Deer Bay, Jameson Bay and partly in the Ringnes formations have higher TOC. Among the Schei Point Group samples, the Cape Richards and Eden Bay members of the Hoyle Bay Formation are richer in TOC (>2.0%) than the Murray Harbour Formation (Cape Caledonia Member). This may reflect differences in the level of maturity or in the depositional environment (more anoxic conditions for the former).Regional variations in the level of thermal maturity of Mesozoic sediments in Sverdrup Basin appear to be a function of burial depth. The Mesozoic formations thicken towards the basin centre (NNE direction), reflecting the general pattern of increasing thermal maturity north of Sabine Peninsula. However, the regional thermal-maturation pattern of the Mesozoic is not solely a reflection of the present-day geothermal gradient, which indicates that anomalous zones of high geothermal gradient may have existed in the past, at least since when the Mesozoic sediments attained maximum burial depth. The contour pattern of the regional variation of maturity at the base of numerous Triassic formations is similar to that of the structural contours of the Sverdrup Basin, indicating that present-day maturation levels are largely controlled by basin subsidence.     

莺琼盆地中新统海相烃源岩地球化学特征及生烃潜力评价

通过有机碳测定、岩石热解分析、显微组分定量分析、饱和烃色谱、色谱-质谱等实验分析,对莺琼盆地中新统海相烃源岩的地球化学特征进行了研究,探讨了不同层位烃源岩的生烃潜力。结果表明：莺琼盆地中新统海相烃源岩有机质丰度总体较低,大部分烃源岩为中等烃源岩,有机质类型以Ⅱ2型和Ⅲ型为主,有机质热演化主要处于成熟阶段。烃源岩显微组分组成具有富含镜质组、壳质组+腐泥组次之、贫含惰性组的特征。烃源岩沉积环境主要为弱氧化-弱还原环境,具有陆生高等植物和低等水生生物生源混合输入的特征。莺歌海盆地梅山组烃源岩综合评价为中等烃源岩,生烃潜力相对较好,三亚组烃源岩综合评价为较差—中等烃源岩,具有一定的生烃潜力。琼东南盆地梅山组和三亚组烃源岩综合评价为中等烃源岩,具有相当的生烃潜力。     

An organic geochemical investigation on organic rich sediments from two Neogene formations in the Klias Peninsula area,West Sabah,Malaysia

Twenty organic rich outcrop samples from the Belait and Setap Shale formations in the Klias Peninsula area, West Sabah, were analysed by means of organic petrology and geochemical techniques. The aims of this study are to assess the type of organic matter, thermal maturity and established source rock characterization based primarily on Rock-Eval pyrolysis data. The shales of the Setap Shale Formation have TOC values varying from 0.6 wt%–1.54 wt% with a mean hydrogen index (HI) of 60.1 mg/g, whereas the shal...     

Paleocene-Eocene potential source rocks in the Avengco Basin,Tibet: Organic geochemical characteristics and their implication for the paleoenvironment

The Avengco Basin is located in the western part of the Tibetan Plateau and is similar to the Nima Basin in the central part of the plateau and the Lunpola Basin in the eastern part in terms of sedimentary characteristics and tectonic settings, which are well known to provide a good source rock potential. However, the organic geochemical characteristics of the Paleocene-Eocene potential source rocks in the Avengco Basin have been under debate. Thirty-four marl and mudstone outcrop samples of the Niubao Formation in the Avengco Basin were collected and subjected to the following analyses: total organic carbon (TOC), Rock–Eval pyrolysis, stable carbon isotopes of kerogen, gas chromatography (GC) and gas chromatography–mass spectrometry (GC–MS). Here, we present the results indicating the organic matter of the upper Niubao Formation is mainly composed of Type II kerogen with a mixed source, which is dominated by algae. However, the lower Niubao Formation has the less oil-prone Type II–III kerogen, and the sources of the organic matter are mainly terrestrial plants with less plankton. In addition, the samples are thermally immature to marginally mature. The Niubao Formation was deposited in an anoxic–oxic environment which was brackish with an imperceptible stratified water column. The upper Niubao Formation has a medium to good hydrocarbon-generating potential. However, the lower Niubao Formation has a zero to poor hydrocarbon-generating potential.     

辽宁北部秀水盆地秀D1井烃源岩评价

基于有机碳、热解等有机地球化学资料,从有机质丰度、类型及成熟度3个方面对辽宁北部秀水盆地秀D1井钻遇的九佛堂组和义县组暗色泥岩进行评价.结果表明：秀D1井义县组上部泥岩为中等-好烃源岩,有机质类型为Ⅱ1~Ⅱ2型;九佛堂组泥岩处于未成熟-低成熟阶段,义县组泥岩为低成熟-成熟阶段.该评价结果为秀水盆地下一步油气资源勘探提供了基础资料.     

Organic matter from the Callovian (Middle Jurassic) deposits of Lithuania: Compositions,sources and depositional environments

This study presents the first organic geochemical and petrographical investigation of the Callovian deposits of the eastern part of the Central European Basin. It is shown that in both the terrigenous Papil? Formation (Lower Callovian) and shallow- to deeper-marine facies of the Papartin? and Skinija formations (Middle and Upper Callovian, respectively), terrestrial organic matter predominates. This is reflected by the carbon preference index values higher than 1.2 for all samples and in some cases higher than 2, as well as the occurrence of characteristic higher plant biomarkers like cadalene, dehydroabietane, simonellite and retene. Moreover, in the case of the Papil? Formation, sugiol – a natural product terpenoid produced by distinct conifer families, has been detected in clay sediments. The occurrence of such a biomolecule in the Middle Jurassic clays is reported for the first time. Its occurrence is probably connected with the presence of small wood debris in the clay sediments. In samples of the Papil? Formation, charcoal fragments co-occurring with unsubstituted polycyclic aromatic hydrocarbons were detected, indicating that wildfires took place during the Early Callovian of Lithuania and/or neighbouring areas. In the Middle and Upper marine Callovian sediments of Lithuania there is no evidence of anoxic conditions occurring in the water column. However, periodic anoxic or strongly dysoxic episodes may have occurred, most probably below the photic zone, during the deepest phase of the Late Callovian transgression, as is evidenced from pyrite framboid diameter distribution and general impoverishment of benthic fauna. Huminite reflectance (R_r) values for the investigated area are in the range of 0.21–0.31%, suggesting the occurrence of immature organic matter. Such values indicate that these investigated deposits were close to the surface during their whole diagenetic history, and the thickness of younger cover did not exceed ca. 500 m. This is also supported by a biomarker analysis in which less thermally stable ββ-hopanes and hopenes significantly dominated.     

Improved understanding of the petroleum systems of the Niger Delta Basin,Nigeria

Biomarker and n-alkane compound specific stable carbon isotope analyses (CSIA) were carried out on 58 crude oil samples from shallow water and deepwater fields of the Niger Delta in order to predict the depositional environment and organic matter characteristics of their potential source rocks. Using a source organofacies prediction approach from oil geochemistry, the presence in the western deepwater oils relatively abundant C₂₇ steranes, C₃₀ 24-n-propyl cholestane, low oleanane index, relatively low pr/ph ratios, gammacerane, and positive to nearly flat C₁₂–C₃₀ n-alkane compound specific stable carbon isotope profiles, suggests that the source facies that expelled these oils contain significant marine derived organic matter deposited under sub-oxic and stratified water column conditions. This contrasts with the terrigenous organic matter dominated source rocks accepted for shallow water Niger Delta oils. Oils in the shallow water accumulations can be separated into terrigenous and mixed marine-terrigenous families. The terrigenous family indicates expulsion from source rock(s) containing overwhelmingly higher plant source organic matter (average oleanane index = 0.48, high C₂₉ steranes) as well as having negative sloping n-alkane isotope profiles. Oxic source depositional conditions (pr/ph > 2.5) and non-stratified conditions (absence to low gammacerane content) are inferred for the terrigenous family. The mixed marine-terrigenous family has biomarker properties that are a combination of the deepwater and terrigenous shallow water oils. Bitumen extracts of the sub-delta Late Cretaceous Araromi Formation shale in the Dahomey Basin are comparable both molecularly and isotopically to the studied western deepwater oil set, but with an over all poor geochemical correlation. This poor geochemical match between Araromi shale and the western deepwater oils does not downgrade the potential of sub-delta Cretaceous source rock contribution to the regional oil charge in the deepwater Niger Delta.     

Organic‐geochemical characteristics of the Miocene Lycian Basin,western Taurides,Turkey

In the Lycian Basin (SW Turkey), the Miocene Karabay?r and Karaku?tepe formations consist of algal limestone, conglomerate, sandstone, shale and limestone. Total organic carbon (TOC) analysis of the Miocene units show that these formations are poor in organic matter. TOC values are generally between 0.02 and 0.51%, but reach 3.47% in the Karabay?r Formation. Hydrogen indices (HI) are mostly below 600 mgHC/gTOC, increasing to 1200 mgHC/gTOC in the Karabay?r Formation. S₂ vs. TOC diagrams are used to evaluate the sedimentary environments and hydrocarbon potential of the Lower–Middle Miocene sediments (the Isparta, Bucak and Korkuteli‐Elmal? areas). The organic material contains about 63 (type I), 35 (type II) and 29 (type II/III) pyrolysable hydrocarbons, respectively. The dominant organic matter is type II kerogens, and hydrocarbon generating potential is quite low. A positive x‐intercept has been calculated in analysed samples according to S₂ vs. TOC diagrams; this value shows a rock‐matrix effect. Clay is the main agent of adsorption. Biomarker characteristics also verify these results. Isoprenoid rates are Pr/Ph: 2, Pr/n‐C17: 1.9, and Pr/n‐C18: 0.5, and a high Pr/Ph ratio (pristane/phytane) indicates an oxic environment; the terpane C29 NH/C30 H ratio is >1 for the Karabay?r Formation, and this value indicates a carbonate lithology. On the other hand, the C25 NH/C30 H ratio is <1 for the Karaku?tepe Formation; this indicates that the hydrocarbons were derived from terrestrial organic matter. According to m/z 191 mass fragmentograms, the Miocene units contain oleanane, indicating a Tertiary age. The abundance of sterane C29>C28>C27 shows that the kerogens formed from algal organic matter.     

Trace element characterisation of Cretaceous Orange Basin hydrocarbon source rocks

Trace elements in the kerogen fraction of hydrocarbon source rock samples from two wells obtained from the Cretaceous units of the Orange Basin, South Africa were determined using X-ray fluorescence spectrometry, in order to determine their distribution and geochemical significances. The concentrations of the elements (As, Ce, Co, Cu, Fe, Mo, Ni, Pb and V) determined ranged from 0.64 to 47,300 ppm for the samples analysed. The total organic carbon (TOC) values indicate that the samples are organic rich but did not show any trend with the distribution of the trace metals except Ce, Mo and Pb. Dendrogram cluster analysis discriminated the samples into three groups on the basis of their level of thermal maturity. Thermal maturity has a significant effect on the distribution of the trace metals. Cobalt/Ni and V/Ni ratios and cross plots of the absolute values of V and Ni indicate that the samples had significant marine organic matter input. The V and Ni contents and V/(V + Ni) ratio indicate that the organic matter of the source rocks had been deposited in reducing conditions. Despite the similarities in the organic matter source input and depositional environment of the organic matter of the samples from the two well, cross plots of Co/Ni versus V/Ni and Mo/Ni versus Co/Ni were able to reveal subtle differences. Cluster analysis of the samples was also able to reveal the subtle thermal maturity differences of the samples.     

藏北羌塘盆地油气地质勘探新进展

羌塘盆地是青藏高原最大的含油气盆地,也是中国潜在的石油战略后备区之一。新的油气地质调查发现,盆地内发育优质古生代烃源岩,主要为石炭系、二叠系的暗色泥岩,具有机碳含量高的特征,机质类型主要为Ⅱ2-Ⅲ型,Ro值大多为1.50%~2.40%,处于高成熟-过成熟阶段。前那底岗日组的古风化壳是盆地内新发现的潜在的储集层,其覆盖于二叠系以及前人已确定的三叠系肖茶卡组地层之上。新发现的上侏罗统-下白垩世白龙冰河组泥灰岩夹膏盐、页岩是区域上较好的盖层。盆地内近年来在地表发现油气显示250余处,其中最重要的是发现了现代天然气泄漏的泥火山,并采集到了天然气样品。综合考虑沉积相、烃源岩、储集层、盖层、保存条件等因素,优选了6个有利区块,其中,托纳木和半岛湖区块作为潜力目标区进行了勘探。     

四川盆地震旦系陡山沱组烃源岩地球化学特征与有机质富集机制

深层古老层系在油气勘探中的重要性正越来越受到重视，四川盆地震旦系陡山沱组是中国南方这一领域的潜在烃源岩层系，但过去因关注少而研究程度低。为加深对其理解，文章以样品条件较好的四川盆地东北缘城口明月乡剖面为例，采用岩石学、主、微量及稀土元素等综合分析的方法，系统探讨了陡山沱组泥页岩的地球化学特征和有机质富集机制。结果表明，陡山沱组发育了一套富有机质的泥页岩，主体沉积于次氧化—还原水体环境，显著的Eu 正异常表明沉积时受热液活动影响明显。烃源岩有机质富集显著受控于沉积环境，同时由于沉积时整体处于较低的沉积速率，使得自下而上随沉积速率增大，有机质逐渐富集。此外，热液活动促进了有机质富集。陡山沱组具有资源潜力，但非均质性发育，可能与冰期—间冰期的海平面升降有关。     

四川盆地震旦系陡山沱组烃源岩地球化学特征与有机质富集机制

深层古老层系在油气勘探中的重要性正越来越受到重视,四川盆地震旦系陡山沱组是中国南方这一领域的潜在烃源岩层系,但过去因关注少而研究程度低。为加深对其理解,文章以样品条件较好的四川盆地东北缘城口明月乡剖面为例,采用岩石学、主、微量及稀土元素等综合分析的方法,系统探讨了陡山沱组泥页岩的地球化学特征和有机质富集机制。结果表明,陡山沱组发育了一套富有机质的泥页岩,主体沉积于次氧化—还原水体环境,显著的Eu 正异常表明沉积时受热液活动影响明显。烃源岩有机质富集显著受控于沉积环境,同时由于沉积时整体处于较低的沉积速率,使得自下而上随沉积速率增大,有机质逐渐富集。此外,热液活动促进了有机质富集。陡山沱组具有资源潜力,但非均质性发育,可能与冰期—间冰期的海平面升降有关。     

Late Albian–Middle Cenomanian palynofacies and palynostratigraphy, Abu Gharadig-5 well, Western Desert, Egypt

Quantitative analyses of palynomorph assemblages, particulate organic matter (kerogen), and total organic carbon (TOC) have been made on samples of the Albian–Cenomanian Kharita and Bahariya formations encountered in the Abu Gharadig-5 well, Western Desert, Egypt. Two assemblage palynozones are defined: Assemblage Zone A (Kharita Formation) of late Albian–early Cenomanian age and Assemblage Zone B (Bahariya Formation) of early–middle Cenomanian age. Palynofacies of the Kharita Formation suggest that sedimentation of these strata took place in a warm, shallow, nearshore-marine environment. The deposition of the lower Bahariya Formation took place initially in similar conditions but subsequently further offshore in somewhat deeper water of the inner shelf. The relatively high percentage of Ephedripites, Afropollis and elaterate pollen in both formations indicates an arid climate. The Kharita Formation yields kerogen types III and IV whereas the assemblages recovered from the Bahariya Formation contain types II and III. The TOC is generally between 0.42 and 0.65% in the Kharita Formation, while it ranges between 0.42 and 0.80% in samples of the Bahariya Formation. The spores and pollen grains are pale in colour; hence little source potential for hydrocarbons is indicated.     

Study of the Factors Affecting the Abundance of Organic Matter in Jurassic Carbonate Rocks in Qiangtang Basin, Tibet

Field and laboratory analyses of carbonate rock samples from the Qiangtang Basin,Tibet, indicate that carbonate source rocks are mainly developed in the Middle Jurassic Xiali Formation and Upper Jurassic Suowa Formation. Comprehensive studies showed that the Suowa Formation carbonate source rocks have a favorable hydrocarbon-generating potential. The abundance of organic matter in the carbonate rocks is controlled mainly by sedimentary environment and inorganic compounds in the rocks, which is higher in the restricted platform facies than in the open platform facies. Organic carbon contents decrease with increasing CaO contents in the source rocks.     

Potential source rocks, organic geochemistry and thermal maturation in the southern depocenter (Kipourio–Grevena) of the Mesohellenic Basin, central Greece

The study area is the southern depocenter (depth > 4200 m) of the Mesohellenic Basin which extends between Kipourio and Grevena, central Greece. The Mesohellenic Basin is a Middle-Tertiary intramontane basin developed within the Hellenide orogen. Previous studies have focused on the depositional environments, configuration and hydrocarbon potential of the basin. In this paper we present additional geochemical and petrographic data from outcrop samples of the basin's southern depocenter, which is considered the most promising area, in terms of hydrocarbon prospectivity. A total number of thirty six samples were analysed: Rock-Eval pyrolysis, maceral analysis, vitrinite reflectance and thermal alteration index, bitumens extraction, liquid chromatography, and GC-MS. The samples were collected from deltaic deposits and submarine fan sediments of Late Eocene to Late Oligocene age. The TOC values of the analysed samples range between rich and very rich and the organic matter consists mainly of type III kerogen and the organic matter consider to be predominately gas prone. The thermal maturity assessed from T_max and vitrinite reflectance shows an immature stage of the organic matter along with the presence of layers having reached the very early mature stage. Vitrinite reflectance measurements and maturity calculations (applying the Lopatin modeling), reveal that the lower part of the depocenter sediments falls within the ‘oil window’. The extractable organic matter (EOM) (mg bitumens/g TOC) indicate the existence of samples (from deltaic deposits) with high ratio of transformation (EOM) (> 100 mg bitumen/g TOC). The GC and GC-MS analyses of the biomarkers indicate mainly the occurrence of terrestrial organic matter reflecting oxidizing conditions and both immature and very early mature stages. The results of the Rock-Eval pyrolysis and the distribution of the isoprenoids support the assumption of the input of an organic matter mixture.     

藏北羌塘盆地QK-1井中侏罗统烃源岩地球化学特征

QK-1天然气水合物钻探试验井位于西藏羌塘盆地毕洛错地区,主要钻遇中侏罗统夏里组粉砂质泥岩和布曲组灰岩。其有机质丰度、有机质类型、有机质成熟度等有机地球化学特征表明,南羌塘地区中侏罗统烃源岩的有机质丰度偏低,夏里组泥岩TOC介于0.26%~0.38%之间,达到差-中烃源岩标准,而布曲组灰岩TOC介于0.02%~0.08%之间,仅局部达到差烃源岩标准;两个组的烃源岩有机质类型主要为Ⅱ₂型及Ⅲ型,较利于天然气的生成,其中夏里组的生气能力优于布曲组;该区烃源岩热演化程度较高,Ro为1.31%~1.63%之间,均达到高成熟阶段,而夏里组有可能已进入干气阶段。基于冻土区天然气水合物成藏条件分析,综合考虑夏里组烃源岩及沉积厚度特征,认为中侏罗统夏里组具备良好的天然气水合物勘探前景。     

Palynofacies evidence of dysoxia and upwelling in the Turonian of the Sergipe Basin,Brazil

This paper presents the integrated results of palynofacies and geochemical analyses in Turonian carbonate strata from the Sergipe Basin, Brazil. Forty-three outcrop samples were analyzed from sections of the Cotinguiba Formation in the Votorantim and Rita Cacete quarries. Our results allow for the characterization of the organic matter and interpretation of the environments of deposition. Together with the existing geochemical data, the results allow for recognition of oxic and dysoxic intervals and inferences pertaining to local oceanographic conditions to explain these environmental changes. The palynofacies groups are dominated by marine palynomorphs and amorphous organic matter (AOM), with minor amounts of terrigenous palynomorphs and phytoclasts. The total organic carbon (TOC) and δ¹³C ratio are directly correlated with the dominant palynofacies elements, particularly AOM. The upper section in Rita Cacete quarry has the most complete data set, and the TOC, δ¹³C and marine-derived AOM in this section tend to decrease upsection and serve to differentiate the oxic and dysoxic intervals. The sections also contain abundant, low-diversity dinoflagellate assemblages composed primarily of Trichodinium boltenhagenii, Cribroperidinium? muderongense, Canningia reticulata and Xenascus plotei. The palynofacies and dinoflagellate assemblages indicate deposition in shallow marine to outer neritic environments. The dysoxic events are recognized by an increase in TOC and δ¹³C, high amounts of AOM, an abundance of the low-diversity dinoflagellate assemblages and the lowest amounts of terrestrial components. The changes in marine productivity seem to be related to periods of low-intensity upwelling, which likely decreased the levels of dissolved oxygen in the basin.     

Paleoenvironments, organic petrology and Rock-Eval studies on source rock facies of the Lower Maastrichtian Patti Formation, southern Bida Basin, Nigeria

The southern Bida Basin in central Nigeria forms a part of the larger Bida or Middle Niger Basin, which is contiguous with the south east trending (petroliferous) Anambra Basin. These basins were major depocenters for Campanian–Maastrichtian sediments in southern and central Nigeria prior to the build up of the Tertiary Niger delta. The successions in the southern Bida Basin consist of the basal Lokoja Formation, overlain by the Patti Formation and capped by the Agbaja Formation. The Lokoja Formation is a sequence of matrix supported conglomerates and sandstones overlying the Pre-Cambrian to Lower Paleozoic basement. Depositional environments are predominantly within fluvial systems of a continental setting. The Patti Formation consists of dark grey carbonaceous shales; mudstone and siltstones representing flood plains to shallow marine deposits with likely organic rich intervals. The overlying Agbaja Formation is made up of ferruginised oolitic and kaolinitic mudstone of a marginal marine environment. Twenty samples of shales of the Patti Formation were studied by incident light microscopy and geochemical analysis to determine the maceral components, geochemical type and potential yield of the pyrolysate. Maceral analysis indicate a large abundance of vitrinite (50–85%; mean = 66%); moderate abundance of liptinites (10–33%; mean = 18%) and lesser amounts of inertinite (9–40%; mean = 16%). Total organic carbon (TOC) values vary from 0.17 to 3.8 wt.% (mean = 2.1 wt.%) with most samples having greater than 2 wt.% TOC. Three of the samples yield greater than 2 kg_(HC)/ton of rock suggesting a fair source rock potential. Most of the samples are thermally immature to marginally mature with vitrinite reflectance ranging from 0.4 to 0.6% R_om and T_max values of 407–426 °C. Given the prevalence of the humic Type III kerogen, maturity and hydrocarbon potential yields, we conclude that the Patti Formation source rock facies have moderate to fair potential for gaseous hydrocarbons which have not yet been generated at the present day outcrop levels but could be important gas source where buried down-dip.     

层序地层格架下烃源岩地球化学研究:以尼日尔Termit盆地为例

如何利用有限的烃源岩样品的实验分析数据和地质资料尽可能地提高烃源岩评价和预测的精度,是当今烃源岩地球化学研究亟需解决的问题.采用层序地层学与油气地球化学相结合的方法,研究了非洲尼日尔Termit盆地基于层序地层格架下,上白垩统Yogou组烃源岩空间分布特征及有机质地球化学性质,初步展示了层序地层格架下烃源岩地球化学研究的方法、应用效果及优势.Termit盆地上白垩统Yogou组海相泥页岩是该盆地主要的烃源层,自下而上可划分为YSQ1、YSQ2和YSQ3共3个三级层序.根据层序/体系域发育特征、岩性录井和测井曲线响应特征,识别出外陆棚、内陆棚、三角洲、滨岸相泥岩及煤/炭质泥岩共5种不同沉积类型的烃源岩,不同层序与体系域具有不同的烃源岩纵向叠置关系和横向分布特征.不同类型的烃源岩有机质具有明显不同的地球化学性质:外陆棚和内陆棚泥岩有机质丰度中等-好,有机质生物来源中,低等水生生物贡献高,沉积于偏还原的沉积环境.滨岸和三角洲相泥岩有机质丰度高,具有低等水生生物和高等植物来源的双重贡献,沉积于偏氧化的沉积环境.三级层序或其体系域控制下的沉积相分布和演化导致不同类型烃源岩的发育和横向分布特征,同一沉积相类型的烃源岩具有相似的地球化学性质.与传统的以组、段为单元的烃源岩地球化学研究相比,层序地层格架下的烃源岩评价可以刻画不同层序、不同体系域和沉积相带烃源岩有机质地球化学性质的差异,提高资源评价和油-源对比的精度.      

Thermal maturity and hydrocarbon potential of the sedimentary succession from the Hecla field in Sverdrup Basin, Arctic Canada

The thermal maturity and source-rock potential of the Upper Palaeozoic and Mesozoic sediments in the Hecla field, Melville Island, Arctic Canada, have been studied using reflected-light microscopy and Rock-Eval pyrolysis. Approximately 250 polished whole-rock samples were examined and their reflectance (% R₀, random) measured. In addition, approximately 100 samples were subjected to Rock-Eval/TOC analyses.Hydrogen-rich organic matter in the Schei Point Group sediments is dominated by alginite (Tasmanales), dinoflagellate cysts with minor amounts of sporinite, cutinite, resinite and liptodetrinite in an amorphous fluorescing matrix. Vitrinite reflectance in Cretaceous sediments ranges from 0.41 to 0.54%; in Jurassic sediments it ranges from 0.43 to 0.64% and in Triassic sediments from 0.50 to 0.65%. The Triassic Schei Point Group calcareous shales and marlstones contain organic matter mainly of marine origin, whereas the predominantly terrestially-derived organic matter present in the Jameson Bay (Lower Jurassic) and in the Upper Jurassic to Lower Cretaceous Deer Bay formations have ower TOC. Only the Ringnes Formation has a TOC content of equivalent to or greater than Schei Point source rocks. Within the Schei Point Group, the Cape Richards and Eden Bay members of the Hoyle Bay Formation are slightly richer in TOC than the Murray Harbour Formation (Cape Caledonia Member). Higher average TOC contents (>3.0%) have been reported in the Cape Richards and Eden Bay members in almost all Hecla drillholes.Variations in the level of thermal maturity of Mesozoic sediments in the Hecla field are a function of burial depth. The stratigraphic succession thickens towards the main Sverdrup Basin depocentre located in a N-NE direction. The pattern of the isoreflectance contours at the top of the Triassic (Barrow Formation) is similar to that of formation boundary lines of the same formations, an indication that present-day maturation levels are largely controlled by basin subsidence.