Hydrocarbons generation potential of the Jurassic–Lower Cretaceous Formation, Ajeel field, Iraq

Organic geochemical analysis and palynological studies of the organic matters of subsurface Jurassic and Lower Cretaceous Formations for two wells in Ajeel oil field, north Iraq showed evidences for hydrocarbon generation potential especially for the most prolific source rocks Chia Gara and Sargelu Formations. These analyses include age assessment of Upper Jurassic (Tithonian) to Lower Cretaceous (Berriasian) age and Middle Jurassic (Bathonian–Tithonian) age for Chia Gara and Sargelu Formations, respectively, based on assemblages of mainly dinoflagellate cyst constituents. Rock-Eval pyrolysis have indicated high total organic carbon (TOC) content of up to 18.5 wt%, kerogen type II with hydrogen index of up to 415 mg HC/g TOC, petroleum potential of 0.70–55.56 kg hydrocarbon from each ton of rocks and mature organic matter of maximum temperature reached (T_max) range between 430 and 440 °C for Chia Gara Formation, while Sargelu Formation are of TOC up to 16 wt% TOC, Kerogen type II with hydrogen index of 386 mg HC/g TOC, petroleum potential of 1.0–50.90 kg hydrocarbon from each ton of rocks, and mature organic matter of T_max range between 430 and 450 °C. Qualitative studies are done in this study by textural microscopy used in assessing amorphous organic matter for palynofacies type belonging to kerogen type A which contain brazinophyte algae, Tasmanites, and foraminifera test linings, as well as the dinoflagellate cysts and spores, deposited in dysoxic–anoxic environment for Chia Gara Formation and similar organic constituents deposited in distal suboxic–anoxic environment for Sargelu Formation. The palynomorphs are of dark orange and light brown, on the spore species Cyathidites australis, that indicate mature organic matters with thermal alteration index of 2.7–3.0 for the Chia Gara Formation and 2.9–3.1 for the Sargelu Formation by Staplin's scale. These characters have rated the succession as a source rock for very high efficiency for generation and expulsion of oil with ordinate gas that charged mainly oil fields of Baghdad, Dyala (B?aquba), and Salahuddin (Tikrit) Governorates. Oil charge the Cretaceous-Tertiary total petroleum system (TPS) are mainly from Chia Gara Formation, because most oil from Sargelu Formation was prevented passing to this TPS by the regional seal Gotnia Formation. This case study of mainly Chia Gara oil source is confirmed by gas chromatography–mass spectrometry analysis for oil from reservoirs lying stratigraphically above the Chia Gara Formation in Ajeel and Hamrine oil fields, while oil toward the north with no Gotnia seal could be of mainly Sargelu Formation source.     

Hydrocarbon generation potential of the uppermost Jurassic—basal Cretaceous Sulaiy formation, South Iraq

Organic geochemical analysis, palynology, and PetroMod software for the organic matters of subsurface Tithonian to Valanginian Sulaiy formation of six wells in Basrah Region, South Iraq showed evidences for hydrocarbon generation potential. These analyses include quantitative studies such as pyrolysis, fluorescence spectroscopy, and total organic carbon (TOC), while the qualitative studies are the textural microscopy used in evaluating amorphous organic matter for palynofacies analysis leading to hydrocarbon assessments. High TOC content of up to 7.3 wt.%, kerogen type II of mesoliptinic type with hydrogen index of up to 466 mg HC/g TOC, and mature organic matter along with dysoxic–anoxic environment and stratigraphic framework have rated the succession as a source rock for oil with ordinate gas, not only in Iraq but also in neighboring Kuwait and Saudi Arabia. This case study is also inferred for hydrocarbon generation and expulsion by PetroMod software which confirmed the source potential.     

Palynofacies, palaeoenvironment, and source rocks evaluation of Ratawi Formation, Southern Iraq

Palynological analysis were done on 12 rock samples for Ratawi Formation from Rumailah well 131 and eight samples for the same formation from Zubair well 47, South Iraq, to extract sedimentary organic matters. Microscopic examination led to diagnose large numbers of spores, pollen, dinoflagellates (proximat, cavate, and chorate), foraminifera, melanogen, hylogen, and amorphogen. Three palynological facies were determined on the bases of percentages of sedimentary organic matter and palynomorphs from two sections. Analysis of these palynofacies clarified Ratawi Formation as deposited from environments ranging from delta and lagoon (suboxic–dysoxic) to shelf facies (anoxic near the shore–suboxic) with the presence of some layers deposited from semideep open marine environment (bathyal). Organic geochemical analysis of total organic carbon and Rock Eval pyrolysis were done to determine quantity, quality, and degree of maturation of the kerogen. Poor to medium proportion of total organic carbon of kerogen types II and III within a catagenesis stage are recorded in these rocks, and hence, poor hydrocarbon generation could be suggested for these strata.     

Cretaceous petroleum system of the Khasib and Tannuma oil reservoir, East Baghdad oil field, Iraq

Gas chromatography, palynomorph constituents, and maturation are analyzed for oil samples of the Campanian Khasib and Tannuma Formations in the wells of East Baghdad oil field for biomarker studies, while palynomorph constituents and their maturation, Rock Eval pyrolysis, total organic carbon (TOC) analysis are carried on for the Upper Jurassic and the Cretaceous Formations of core samples from the same wells for dating and evaluation of the source rocks. The gas chromatography of these oils have shown biomarkers of abundant ranges of n-alkanes of less than C₂₂(C₁₇–C₂₁) with C₁₉ and C₁₈ peaks to suggest mainly liquid oil constituents of paraffinic hydrocarbons from marine algal source of restricted palaeoenvironments in the reservoir as well as low nonaromatic $ {\hbox{C}}_{15}^{+} $ peaks to indicate their slight degradation and water washing. Oil biomarkers of $ \Pr ./{\hbox{Ph}}{.} = {0}{.85,}{{\hbox{C}}_{31}}/{{\hbox{C}}_{30}} < 1.0 $ , location is in the triangle of C₂₇–C₂₉ sterane, C28/C29 of 0.6 sterane, oleanane of 0.01, and CPI = 1.0, could indicate anoxic marine environment with carbonate deposition of Upper Jurassic–Early Cretaceous source. The recorded palynomorph constituents in this oil and associated water are four miospore, seven dinoflagellates, and one Tasmanite species that could confirm affinity to the Upper most Jurassic–Lower Cretaceous Chia Gara and Ratawi Formations. The recorded palynomorphs from the reservoir oil (Khasib and Tannuma Formations) are of light brown color of $ {\hbox{TAI}} = 2.8 - 3.0 $ and comparable to the mature palynomorphs that belong to Chia Gara and Lower part of Ratawi Formations. Chia Gara Formation had generated and expelled high quantity of oil hydrocarbons according their TOC weight percent of 0.5–8.5 with ${S_2} = 2.5 - 18.5\,{\hbox{mg}}\,{\hbox{Hc/g}}\;{\hbox{rock}} $ , high hydrogen index of the range 150–450 mg Hc/g Rock, good petroleum potential of 4.5–23.5 mg Hc/g rock, mature ( $ {\hbox{TAI}} = 2.8 - 3.0 $ and $ {\hbox{T}}\max = 428 - 443{\hbox{C}} $ ), kerogen type II, and palynofacies parameters of up to 100 amorphous organic matters with algae deposited in dysoxic–anoxic to suboxic–anoxic basin, while the palynomorphs of the rocks of Khasib Formation are of amber yellow color of TAI = 2.0 with low TOC and hence not generated hydrocarbons. But, this last formation could be considered as oil reservoir only according their high porosity (15–23%) and permeability (20–45 mD) carbonate rocks with structural anticline closure trending NW-SE. That oil have generated and expelled during two phases; the first is during Early Palaeogene that accumulated in traps of the Cretaceous structural deformation, while the second is during Late Neogene’s.     

Palynofacies and hydrocarbon generation potential of the upper Triassic Kurrachine Formation and lower part of the Baluti Formation, Mosul Block, Northwestern Iraq

Three exploration wells were selected near Mosul city (Az-29, Bm-15, and Kd-1) to study the palynozones and hydrocarbon generation potential of the Upper Triassic Baluti and Kurrachine Formations. This study was completed in two phases: The first was a study of palynofacies and their paleoenvironmental indications, degree of preservation, diversity of palynomorphs, and organic maturity of the rocks according to palynomorphs’ color using a refracted light microscope. More than 80 slides of organic matter were used for this study. Four palynofacies were tentatively recognized. (1) The first palynofacies is diagnostic of the Baluti Formation in the Az-29 and Kd-1 wells; (2) The second palynofacies appeared at different depths in the Kurrachine Formation in three wells. (3) The third was only found between the depths of 4,534 to 4,685 m in the well Az-29. (4) The fourth was only found between 3,500- and 3590-m depth in the well Bm-15. A distal coastal marine environment is suggested for the Baluti Formation and restricted lagoonal environment for the Kurrachine Formation. The second phase used organic geochemical analyses to confirm the suggested paleoenvironmental and hydrocarbon generation material. Three techniques were used, namely total organic carbon, pyrolysis, and pyrolysis gas chromatography, on more than 35 samples from different depths in three wells. The analyses proved that a sufficient quantity of organic matter occurs that and has suitable maturity for hydrocarbon generation potential of oil and gas.     

The potential of hydrocarbons generation in the Chia Gara Formation at Amadia area, north of Iraq

Sixteen rock samples of outcrop of Chia Gara Formations from the type locality area, south of Amadia, North Iraq showed evidences for hydrocarbon generation potential by palynological studies. These analyses include age assessment of Upper Jurassic (Tithonian) to Lower Cretaceous (Berriasian) age based on assemblages of mainly dinoflagellate cyst constituents. Qualitative studies are done in this study by textural microscopy used in assessing amorphous organic matter for palynofacies type belong to kerogen type A of Thompson and Dembiki (Int J Coal Geol 6:229–249, 1986) which contain brazinophyte algae, Tasmanites, and foraminifera test linings, as well as the dinoflagellate cysts and spores, deposited in dysoxic–anoxic environment. The palynomorphs are of dark orange and light brown, on the spore species Cyathidites australis, that indicate mature organic matters with thermal alteration index of 2.7–3.0 by Staplin’s scale. These characters and total organic carbon of 0.5–8.5 wt% have rated the succession as a source rock for high efficiency for generation and expulsion of oil with ordinate gas that charged mainly oil fields of Tawqi. Some oil is released from the Chia Gara Formation to charge the Cretaceous–Tertiary total petroleum system.     

Source rock characterization and hydrocarbon generation modeling of the Middle to Late Eocene Mangahewa Formation in Taranaki Basin,New Zealand

The Middle to Late Eocene Mangahewa Formation of Taranaki Basin, New Zealand, has been evaluated in terms of organic matter abundance, type, thermal maturity, burial history, and hydrocarbon generation potential. Mangahewa Formation reflects the deposition of marine, marginal marine, shallow marine, and terrestrial strata due to alternative transgressive and regressive episodes in Taranaki Basin. The sediments of the Mangahewa Formation contain type II (oil prone), types II–III (oil-gas prone), and type III kerogens (gas prone), with hydrogen index values ranging from 58 to 490 mg HC/g total organic content (TOC). Vitrinite reflectance data ranging between 0.55 and 0.8 %R_o shows that the Mangahewa Formation is ranging from immature to mostly mature stages for hydrocarbon generation. Burial history and hydrocarbon generation modeling have been applied for two wells in the study area. The models have been interpreted that Mangahewa Formation generated oil in the Mid Miocene and gas during Middle to Late Miocene times. Interpretations of the burial models confirm that hydrocarbons of Mangahewa Formation have not yet attained peak generation and are still being expelled from the source rock to present.     

Programed oil generation of the Zubair Formation, Southern Iraq oil fields: results from Petromod software modeling and geochemical analysis

1D petroleum system modeling was performed on wells in each of four oil fields in South Iraq, Zubair (well Zb-47), Nahr Umr (well NR-9), West Qurna (well WQ-15 and 23), and Majnoon (well Mj-8). In each of these fields, deposition of the Zubair Formation was followed by continuous burial, reaching maximum temperatures of 100°C (equivalent to 0.70%Ro) at depths of 3,344–3,750 m of well Zb-47 and 3,081.5–3,420 m of well WQ-15, 120°C (equivalent to 0.78%Ro) at depths of 3,353–3,645 m of well NR-9, and 3,391–3,691.5 m of well Mj-8. Generation of petroleum in the Zubair Formation began in the late Tertiary, 10 million years ago. At present day, modeled transformation ratios (TR) indicate that 65% TR of its generation potential has been reached in well Zb-47, 75% TR in well NR-9 and 55-85% TR in West Qurna oil field (wells WQ-15 and WQ-23) and up to 95% TR in well Mj-8, In contrast, younger source rocks are immature to early mature (<20% TR), whereas older source rocks are mature to overmature (100% TR). Comparison of these basin modeling results, in Basrah region, are performed with Kifle oil field in Hilla region of western Euphrates River whereas the Zubair Formation is immature within temperature range of 65–70°C (0.50%Ro equivalent) with up to 12% (TR?=?12%) hydrocarbon generation efficiency and hence poor generation could be assessed in this last location. The Zubair Formation was deposited in a deltaic environment and consists of interbedded shales and porous and permeable sandstones. In Basrah region, the shales have total organic carbon of 0.5–7.0 wt%, Tmax 430–470°C and hydrogen indices of up to 466 with S2?=?0.4–9.4 of kerogen type II & III and petroleum potential of 0.4–9.98 of good hydrocarbon generation, which is consistent with 55–95% hydrocarbon efficiency. These generated hydrocarbons had charged (in part) the Cretaceous and Tertiary reservoirs, especially the Zubair Formation itself, in the traps formed by Alpine collision that closed the Tethys Ocean between Arabian and Euracian Plates and developed folds in Mesopotamian Basin 15–10 million years ago. These traps are mainly stratigraphic facies of sandstones with the shale that formed during the deposition of the Zubair Formation in transgression and regression phases within the main structural folds of the Zubair, Nahr Umr, West Qurna and Majnoon Oil fields. Oil biomarkers of the Zubair Formation Reservoirs are showing source affinity with mixed oil from the Upper Jurassic and Lower Cretaceous strata, including Zubair Formation organic matters, based on presentation of GC and GC-MS results on diagrams of global petroleum systems.     

Palynostratigraphy and the assessment of gas and oil generation and accumulations in the Lower Paleozoic, Western Iraq

Palynological and organic geochemical analysis are performed in this study for 220 samples of cores and cuttings collected from the Ordovician Khabour, Silurian Akkas, and Upper Devonian Kaista Formations in wells Akkas/1-6, Khleisya/1, KH5/6, and KH5/1 of West Iraq. Their diagnostic organic matters are abundant acritarchs (134 species belonging to 54 genera, including marine algae of Tasmanites, Deflandstrum, and brazinophytes) and a few spores (21 species belonging to 16 genera) and Chitinozoa (43 species belonging to 12 genera) as well as scolecodonts, graptolite siculae, cuticles, and amorphous organic matters. On the basis of acritarchs with tentative selections of Chitinozoa and spores, this succession is subdivided into ten palynozones (PZ1–PZ10) within a stratigraphic framework and correlated with equivalent strata in Saudi Arabia and Libya. Beds of the Khabour and lower part of Akkas Formations were deposited in anoxic–dysoxic marine shelf environments northern Gondwana Continent with provincial acritarchs. These deposits were extending from outer to inner neritic with affects of local upwelling currents and lagoons, especially in boreholes Akkas/1, KH5/1, and KH5/6. Hydrocarbon generations potential are assessed by plotting organic matter types in palynofacies context of Bujaks (1970) graphical model with depths along with log of thermal maturation indices on the basis of the color changes of the acritarchs Diexallophasis denticulata–Orthosphaeridium ternatus and Baltisphaeridium constrictum as well as kerogen types and total organic carbon (TOC). These organic matters are up to 16% TOC, especially for the hot shale of the Lower Silurian Akkaz Formation, very low asphalting and sulfur, saturated and aromatic hydrocarbons of more than 96%, and high peaks of C2–C20 gas chromatography that could indicate predominant gas generation with some light oils. The associated gases are mainly methane and ethane of CH₄, C₂H₆, and C₃H₈. Accordingly, source potential for wet gas and condensates could be assessed for depth of 2,750–3,000 m and dry gas for depth of 3,570–3,650 m in well Akkas-1 only from the Ordovician Kabour Formation. Little oil might be generated from the lower Silurian Akkas formation in borehole Akkas-1 and KH5/6. These potential source rocks are extended toward Jordon, southwest Iraqi Desert and Syria. Accumulation sites of these generated gas and little oil could be within the sandstone porosities of 10–17% and permeability of 500 mD sealed by the non permeable shale's along closures of the structured anticline fold and fault of this field as well as along the unconformity boundary of the Upper Silurian Akkas Formation with the Upper Devonian Kaista Formation. Accordingly, Lower Paleozoic total petroleum system of generation, migration, and accumulations could be assessed for a basin includes West Iraq and their extensions in Jordon and Syria.     

内蒙古拉布达林盆地烃源岩有机地球化学特征

在野外地质勘查、典型剖面实测、样品采集及实验分析基础上,对拉布达林盆地潜在的烃源岩的有机质丰度、类型、成熟度等有机地球化学特征进行了分析评价.结果表明：1）上石炭统新伊根河组有机碳含量和生烃潜力均较低,有机质类型为I型,普遍达到到高成熟-过成熟阶段,为差烃源岩;2）中侏罗统万宝组有机碳含量中等,生烃潜力偏低,有机质类型为I型和II₁型,处于低成熟阶段,为中等-差烃源岩;3）上侏罗统满克头鄂博组有机碳含量中等,生烃潜力较好,有机质类型为II₁型,处于低成熟阶段,为较好烃源岩;4）下白垩统大磨拐河组有机碳含量较高,生烃潜力较好,有机质类型为为II₁型和II₂型,处于低成熟-成熟阶段,为好烃源岩.     

Palynofacies characterization for hydrocarbon source rock evaluation in the Subathu Formation of Marhighat,Sirmaur district,Himachal Pradesh

This paper deals with the hydrocarbon source rock evaluation of the Subathu Formation exposed at Marhighat on Sarahan–Narag road in Sirmaur district of Himachal Pradesh. Hydrocarbon potential of these sediments is estimated on the basis of palynofacies analysis and thermal alteration index (TAI) values based on the fossil spores/pollen colouration. The analyses are based on the classification and hydrocarbon generation potential of plant derived dispersed organic matter present in the sediments. The palynofacies analysis of Subathu Formation in the area reveal moderate to rich organic matter, with amorphous organic matter constituting the bulk of the total organic matter, followed by charcoal, biodegraded organic matter, fungal remains, spores/pollen and structured terrestrial organic matter. The TAI value for the organic matter in these sediments has been ascertained as 3.00. A dominance of the sapropelic facies (amorphous organic matter) and the measured TAI values for the Subathu sediments in the Marhighat area suggests a good source-rock potential for the hydrocarbon generation.     

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.     

Hydrocarbon source potential of the Jurassic sediments of Salam-3X borehole,Khalda Concession,Northern Western Desert,Egypt

A total of 51 samples, collected from the Jurassic sediments (Ras Qattara, Yakout, Khatatba, Masajid, and Alam El Bueib (member 6) formations) of Salam-3X well, were subjected to organic geochemical analysis. Of the samples, nine have been subjected to palynofacies investigation. Based on the sedimentary organic matter, these sediments show only one palynofacies type, indicating the presence of gas- and oil-prone source rocks and reflecting deposition under marginal dysoxic–anoxic to shelf-to-basin transition conditions. The total organic content of the samples analyzed is characterized by a wide range of content, including fair, good, very good, and excellent. The organic matter quality of these samples is concentrated around types III (gas prone), III–II (gas and oil prone), and II (oil prone), reflecting gas- and oil-prone sediments, with a tendency to generate gas rather than oil; the result matches with the palynological analysis data. The temperature of maximum pyrolytic hydrocarbon generation of analyzed samples are ranging between 440 and 457 °C, reflecting thermally mature organic matter.     

南黄海盆地二叠系烃源岩孢粉相特征及其形成环境

以沉积环境控制烃源岩发育理论为指导,应用孢粉相分析方法,以南黄海盆地二叠系大隆组、龙潭组和栖霞组烃源岩层段为研究对象,对典型钻井剖面的孢粉及沉积有机屑进行系统的分析。根据沉积有机屑的丰度特征和组分类型,探讨三套烃源岩的形成环境,初步评价其生烃潜力。研究结果表明,利用孢粉相分析方法,可以有效地对高成熟海相烃源岩的生烃潜力和形成环境进行客观评价:栖霞组为缺氧远陆架沉积环境,以无定形有机质为主,水体分层缺氧,是烃源岩形成的有利环境;大隆组为缺氧和少氧的陆架环境,也较有利于烃源岩的形成,生烃潜力较栖霞组差;龙潭组煤质型有机质较为丰富,为充氧的陆架区,以陆源输入为主,沉积区水体较浅,含氧量高,不利于富氢烃源岩的形成。     

Organo-petrographic and geochemical characteristics of Gurha lignite deposits,Rajasthan,India:Insights into the palaeovegetation,palaeoenvironment and hydrocarbon source rock potential

The sedimentary sequence containing lignite deposits in Gurha quarry of the Bikaner-Nagaur Basin(Rajasthan)has been investigated.The samples from lignite and allied shale horizons were evaluated for petrographical,palynological,palynofacies and organic geochemical inferences,to depict the source flora and to reconstruct the palaeodepositional conditions prevailed during the sedimentation.An assessment for the hydrocarbon generation potential of these deposits has also been made.The results revealed the dominance of huminite macerals and phytoclasts organic matter(OM) indicating the existence of forested vegetation in the vicinity of the depositional site.A relatively high terrigenous/aquatic ratio(TAR) and the carbon preference index(CPI) are also suggesting the contribution of higher plants in the peat formation.However,the n-alkane distributions,maximizing at n-C17 and n-C29,showed inputs from the algal communities along with the higher plant derived organic matters.Recovered palynomorphs of the families Onagraceae,Meliaceae,Arecaceae,Rhizophoraceae,Rubiaceae,Ctenolophonaceae, etc.together with oleanene and ursane types of triterpenoids suggest the contribution from angiosperms source vegetation.Interestingly,the presence of Araucareaceae and Podocarpaceae pollen grains shows the existence of gymnosperms vegetation.Further,the presence of tetracyclic diterpanes;demethylated entbeyerane,sandaracopimarane,pimarane,and Kaurane type of compounds confirms the contribution of conifers.The variation in the values of the coefficient of non-equality(H:0.68%-7.56%),the standard deviation(8:0.04%-0.16%) and the coefficient of variability(V:16.10%-46.47%),also shows the heterogeneity in the source organic matter.The various petrographical indices,palynological entities,and geochemical parameters indicate that the peatforming vegetation was accumulated under a mixed environment and fluctuating hydrological settings.The interpretation of palynofacies data on APP(Amorphous organic matter-Phytoclast-Palynomorphs) diagram suggests that the accumulation of organic matter occurred in a dysoxic-suboxic condition in a proximal(to land)setting with the shift to an anoxic condition in distal setting towards the termination of sedimentation.The huminite(ulminite) reflectance(R_r) values(av.0.28%) showed a good relationship with average T_(max) value(414℃),suggesting the immaturity.The TOC content ranges of 13-59 wt.%,and HI values vary between 101 and 546 mg HC/g TOC in the studied samples.Collectively,the studied lignite and shale samples have the admixed kerogens(Type Ⅲ-Ⅱ) and exhibit the ability to generate the gaseous to oil hydrocarbons upon maturation.     

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.     

Palynofacies,organic geochemical analyses and hydrocarbon potential of some Upper Jurassic-Lower Cretaceous rocks,the Sabatayn-1 well,Central Yemen

The current work investigates the hydrocarbon potentiality of the upper Jurassic–lower Cretaceous rocks in the Marib-Shabwah Basin, Central Yemen, through the Sabatayn-1 well. Therefore, palynological and organic geochemical analyses were carried out on 37 ditch cutting and 12 core samples from the well. Palynofacies analysis of the Madbi (late Oxfordian–early Tithonian) and Nayfa (Berriasian–Valanginian) Formations sediments indicates deposition of their organic-rich shale, calcareous shale and marl in middle to outer shelf environments under dysoxic–anoxic conditions, containing mainly kerogen of types II to III. However, the shales of the lower Sabatayn (Tithonian) Formation were deposited in an inner shelf environment of prevailing dysoxic–suboxic conditions, and show kerogen types III to II. Regional warm and relatively dry palaeoclimate but with local humid conditions developed near the site of the well is thought to have prevailed during deposition of the studied well sediments. The geochemical analyses of the Madbi Formation show higher total organic carbon content (TOC) than the overlying Sabatayn and Nayfa formations: it is varies between 1.2 and 7, and with average 4 wt% TOC, and the obtained S2 values (～3–10, average 7 mg HC/g rock) indicates that the Madbi Formation is mainly good source rock. It shows a good petroleum potential of 4–11 mg HC/g dry rock, and the Rock-Eval pyrolysis indicates mainly kerogen types II to III (oil to gas prone) of hydrogen index values (132–258, and only one sample from Lam Member is of 360 and average 215 mg HC/g TOC). The thermal maturation parameters as T _max (425–440 °C), production index (average 0.13 mg HC/g rock) and thermal alteration index (2 to 2+) reflected that this formation is present at margin of maturation to early mature stage oil window. So, the Lam Member (upper part) of the Madbi Formation is considered the main hydrocarbon (oil and gas) source rock in the Marib-Shabwah Basin. Accordingly, we predict that the Meem Member is an active source for gas and oil accumulations in the overlying sandstone reservoir of the Sabatayn Formation in the Sabatayn-1 well.     

Hydrocarbon source potential of the Proterozoic Sirban Limestone Formation,NW Himalaya,Jammu

The Proterozoic Sirban Limestone Formation (SLFm) crops out as detached allochthons in the northwest Himalaya (Jammu region, India) and has its coeval equivalents laterally disposed in the west in Salt Range, in the northwest in Abbotabad (Pakistan) and in southeast in Himachal Pradesh (India). The oil and gas occurrences have been reported from the Proterozoic successions globally and the hydrocarbon potential of the SLFm cannot be ruled out.The interbedded shales and algal laminated dolostones within the SLFm have yielded microflora comparable to those reported in the North African Neoproterozoic sandstones and the Late Proterozoic carbonates of the giant oil and gas fields of the Siberian Platform. The SLFm contains a rich and diverse biota comprising ~ 10% of the rock volume in thin section. The rich organic assemblage justified a hydrocarbon source potential analysis of the SLFm, tested in this study by Rock Eval (RE) pyrolysis.RE pyrolysis yielded a total organic carbon (TOC) content of 0.02 to 1 wt. % with very low Hydrogen Index (HI) values for the shales and TOC content averaging 0.02 wt. % for the dolostones. The organically lean shales and dolostones exhibit T_max values indicative of immature to post mature stage. But, since these values are for the samples with complex thermal and tectonic history the results may be unreliable. The highly altered organic matter and kerogen present in the SLFm had the potential to generate hydrocarbons and presently indicates no significant source potential. This study is important for understanding the hydrocarbon occurrences in the SLFm particularly in light of the recent oil and gas discoveries from the coeval Proterozoic successions.     

基于细粒岩石类型对玛湖凹陷下二叠统风城组烃源岩分类评价

准噶尔盆地玛湖凹陷风城组页岩油勘探取得巨大突破,但是按照普遍认可的页岩油烃源岩评价标准,本区的烃源岩品质并不理想。为了科学评价玛湖凹陷烃源岩品质特征,本文在系统的岩心观察和有机地球化学分析的基础上,揭示烃源岩的形成环境,并按照矿物组成对烃源岩分类评价。玛湖凹陷风城组细粒岩主要沉积于正常半深湖、咸化半深湖、半咸化半深湖、含热液半深湖和滨浅湖环境中,各环境中细粒岩的有机质特征存在一定区别,其中半咸化半深湖有机质较为富集,w(TOC)均值在1%左右。进一步结合有机质类型判别图解,表明咸化半深湖和含热液半深湖有机质来源以湖泊生物为主,而其他环境中存在湖泊和陆源混合有机质来源。基于有机质生烃潜力评价和成熟度(V_re=0.74%)估算,表明目前风城组烃源岩中有机质正处于大量排烃的成熟阶段,且确定了细粒岩中的烃类为原生烃。由于不同矿物组成的烃源岩吸附能力的差异,按照陆相泥质烃源岩和碳酸盐质烃源岩开展分类评价,结果表明风城组沉积了累计厚度近250 m的的有效烃源岩,且富含以藻类体为主的有机质。