Carbon isotopes of organic matter from the upper Jurassic oil shales from the Volgian-Pechora shale province and its accumulation mechanisms

The isotopic composition of carbon from the organic matter of late Jurassic oil shales from the Volgian-Pechora shale province is studied. The existence of a dependence between C_org content in the rock and the isotopic composition of kerogen carbon is ascertained. The content of the heavy carbon isotope increases with increasing C_org. This dependence is accounted for by the progressive accumulation of isotopically heavy hydrocarbons of the initial organic matter due to sulfurization. The data on the isotopic composition of individual n-alkanes of bitumen in the rocks and the data on the absence of isotopic fractionation between thermobitumen and the residual kerogen from oil shales from the Volgian-Pechora shale province obtained by treating shale in an autoclave in the presence of water are presented first in this paper.     

Molecular composition and organic petrographic characterization of Madbi source rocks from the Kharir Oilfield of the Masila Basin (Yemen): palaeoenvironmental and maturity interpretation

The upper part of Madbi Formation organic-rich shale is considered an important regional source rock in the Masila Basin, Yemen. Ten cutting samples from this Upper Jurassic organic-rich shale were collected from wells drilled in the Kharir Oilfield, Masila Basin in order to geochemically assess the type of organic matter, thermal maturity and depositional environment conditions. Results reveal that Upper Jurassic organic-rich shale samples contain high organic matter more than 2.0 wt.% TOC and have very good to excellent hydrocarbon potential. Marine algae organic matter is the main source input for the Upper Jurassic shale sequence studied. This has been identified from organic petrographic characteristics and from the n-alkane distributions, which dominated by n-C₁₄-n-C₂₀ alkanes. This is supported by the high value of the biomarker sterane/hopane ratio that approaches unity, as well as the relatively high C₂₇ sterane concentrations. A mainly suboxic depositional environment is inferred from pr/ph ratios (1.75–2.38). This is further supported by relatively high homohopane value, which is dominated by low carbon numbers and decrease towards the C₃₅ homohopane. The concentrations of C₃₅ homohopane are very low. The depositional environment conditions are confirmed by some petrographic characteristics (e.g. palynofacies). Detailed palynofacies analysis of Madbi shales shows that the Madbi shale formation is characterised by a mix of amorphous organic matter, dinoflagellates cysts and phytoclasts, representing a suboxic, open marine setting. The Upper Jurassic marine shale sequence in the Masila Basin is thermally mature for hydrocarbon generation as indicated by biomarker thermal maturity parameters. The 22 S/22 S + 22R C₃₂ homohopane has reached equilibrium, with values range from 0.58 to 0.62 which suggest that the Upper Jurassic shales are thermally mature and that the oil window has been reached. 20 S/(20 S + 20R) and ββ/(ββ + αα) C₂₉ sterane ratios suggest a similar interpretation, as do the moretane/hopane ratio. This is supported by vitrinite reflectance data ranging from 0.74% to 0.90%Ro and thermal alteration of pollen and spore. The thermal alteration index value is around 2.6–3.0, corresponding to a palaeotemperature range of 60–120°C. These are the optimum oil-generating strata. On the basis of this study, the Madbi source rock was deposited under suboxic conditions in an open marine environment and this source rock is still within the oil window maturity range.     

阿尔金山前下—中侏罗统页岩气成藏地质条件分析

阿尔金山前侏罗系出露大套厚层的暗色泥页岩,生烃潜力优越,具备陆相页岩气形成条件,是有利的勘探接替区。通过野外地质调查、样品采集和测试分析,研究下—中侏罗统泥页岩的沉积展布、有机地球化学特征及储集性能,并探讨了该区页岩气的勘探潜力。研究表明: 富有机质泥页岩主要处于滨浅湖—半深湖相、沼泽相沉积环境中,其在平面上呈NE向展布,单层厚度和累计厚度均较大; 泥页岩的有机质类型主要为Ⅱ₁、Ⅱ₂型干酪根; TOC含量为0.55%~10%,平均为2.28%; 镜质体反射率(R_o)为1.0%~1.6%,平均为1.269%,处于成熟—高成熟阶段,为页岩气藏形成提供良好的生烃条件; 其矿物特征表现为脆性矿物含量高,大于51%,有利于后期的水力压裂改造和页岩气开采; 通过扫描电镜观察,泥页岩储层发育微孔隙及微裂缝,为页岩气提供了良好的储集空间和运移通道。初步预测,后期改造相对较弱的月牙山地区为页岩气勘探的有利目标区。     

阿尔金山前下—中侏罗统页岩气成藏地质条件分析

阿尔金山前侏罗系出露大套厚层的暗色泥页岩,生烃潜力优越,具备陆相页岩气形成条件,是有利的勘探接替区。通过野外地质调查、样品采集和测试分析,研究下—中侏罗统泥页岩的沉积展布、有机地球化学特征及储集性能,并探讨了该区页岩气的勘探潜力。研究表明: 富有机质泥页岩主要处于滨浅湖—半深湖相、沼泽相沉积环境中,其在平面上呈NE向展布,单层厚度和累计厚度均较大; 泥页岩的有机质类型主要为Ⅱ₁、Ⅱ₂型干酪根; TOC含量为0.55%~10%,平均为2.28%; 镜质体反射率(R_o)为1.0%~1.6%,平均为1.269%,处于成熟—高成熟阶段,为页岩气藏形成提供良好的生烃条件; 其矿物特征表现为脆性矿物含量高,大于51%,有利于后期的水力压裂改造和页岩气开采; 通过扫描电镜观察,泥页岩储层发育微孔隙及微裂缝,为页岩气提供了良好的储集空间和运移通道。初步预测,后期改造相对较弱的月牙山地区为页岩气勘探的有利目标区。     

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 rock potential evaluation of the Late Paleocene Patala Formation,Salt Range,Pakistan: Organic geochemical and palynofacies approach

Organic geochemical and palynofacies analyses were carried out on shale intervals of the Late Paleocene Patala Formation at Nammal Gorge Section, western Salt Range, Pakistan. The total organic carbon content and Rock-Eval pyrolysis results indicated that the formation is dominated by type II and type III kerogens. Rock-Eval \({T}_{\mathrm{max}}\) vs. hydrogen index (HI) and thermal alteration index indicated that the analysed shale intervals present in the formation are thermally mature. \(S_{1}\) and \(S_{2}\) yields showed poor source rock potential for the formation. Three palynofacies assemblages including palynofacies-1, palynofacies-2 and palynofacies-3 were identified, which are prone to dry gas, wet gas and oil generation, respectively. The palynofacies assessment revealed the presence of oil/gas and gas prone type II and type III kerogens in the formation and their deposition on proximal shelf with suboxic to anoxic conditions. The kerogen macerals are dominated by vitrinite and amorphinite with minor inertinite and liptinite. The kerogen macerals are of both marine and terrestrial origin, deposited on a shallow shelf. Overall, the dark black carbonaceous shales present within the formation act as a source rock for hydrocarbons with poor-to-moderate source rock quality, while the grey shales act as a poor source rock for hydrocarbon generation.     

海陆相泥页岩气体生成的半封闭模拟实验

明确不同沉积环境下页岩气生成机理的差异性对于页岩气成因机理及页岩气地球化学特征研究具有重要意义.选择低演化阶段的海相（中元古界洪水庄组）和陆相（三叠统延长组长7段）泥页岩进行了半封闭热模拟实验,对其气体产物进行了组分和碳同位素分析.结果表明,洪水庄组页岩产气量要远远低于同温度条件下长7段泥岩的产气量.同时,长7段泥岩气体产物二次裂解程度比较高.洪水庄组页岩有机质母源以生油性为主,长7段泥岩沉积过程受到陆源混入,有机质母源以相对偏生气性为主.热模拟实验条件下黄铁矿转化成磁黄铁矿的过程也可能促进长7段泥岩烃类气的生成.热模拟实验中所用样品的状态,即柱状样或颗粒样,也可能会对气体的裂解行为产生影响.在这种情况下,南方地区页岩气高的甲烷产率以及碳同位素倒转可能与厚层页岩高的油气滞留率有关.      

松辽盆地农安地区上白垩统油页岩含油率影响因素

农安油页岩含矿区地处松辽盆地东南隆起区,主要发育于上白垩统青山口组一段、嫩江组一、二段。油页岩有机质的干酪根类型为Ⅰ-Ⅱ₁型,质量较好,处于成岩的未成熟阶段。油页岩含油率与有机碳和氢元素含量间存在明显的线性正相关关系,当有机碳质量分数＞6％或氢质量分数＞1％时构成油页岩。此外,有机质干酪根的显微组分可以反映有机质的类型,与含油率之间也存在一定的相关性。青山口-嫩江组沉积时期,该区温暖湿润的古气候条件、大规模的海侵和缺氧事件影响了油页岩中有机质的丰度和类型,从而影响了油页岩的含油率。     

川南地区龙马溪组有机质特征及其对页岩气富集规律的影响研究

四川盆地南部（简称“川南”） 广泛发育多套下古生界海相泥页岩层系,其中龙马溪组为该区一套优良的烃源岩 层,具备优越的页岩气形成条件。根据长宁和威远页岩气探区的钻井岩心、露头样品分析资料,对川南地区下志留统龙马 溪组页岩有机质特征及其对页岩气富集规律的影响进行研究后表明,川南龙马溪组页岩的有机质类型为Ⅰ～Ⅱ1型,有机 碳含量较高（平均为2.52%）,热演化程度为2.0%～3.8%,达到了高-过成熟阶段;研究区的有机质特征对页岩气的富集具 有重要的影响,干酪根的类型决定着甲烷吸附能力强弱,有机质丰度和有机演化程度决定了页岩的生气量和含气量,同时 高TOC和Ro也能促进有机质微孔隙的发育,为页岩气的富集提供更多有利空间。因此,研究认为川南地区龙马溪组有机质 特征较好,有利于页岩气的富集成藏。     

北部湾盆地流二段油页岩地球化学特征及成因

北部湾盆地涠西南凹陷和乌石凹陷流二段普遍发育油页岩。有机地球化学分析表明,北部湾盆地流二段油页岩具有高的有机质丰度,油页岩的有机碳含量下限为3%,含油率介于3.5%~10%,达到中等和优质油页岩矿品级,同时属于优质烃源岩。全岩有机显微组分、干酪根镜检和热解等分析表明,北部湾盆地流二段油页岩藻类含量丰富,藻类是有机质的主要来源,有机质类型主要为腐殖—腐泥型,部分为腐泥型,以湖相腐殖—腐泥型油页岩为主,部分为湖相腐泥型油页岩。流二段油页岩中镍和钼等微量元素含量普遍较高,镍和钼的含量与有机碳含量之间存在很好的正相关关系,说明流二段油页岩形成时期北部湾盆地具有富营养湖泊特征。北部湾盆地流二段油页岩中还原硫含量高,普遍大于1%,流二段油页岩形成于还原的沉积环境,具有很好的有机质保存条件。高有机质生产力及湖侵体系域顶部和高位体系域底部的中深湖还原环境共同控制了北部湾盆地流二段油页岩的发育。     

川东焦石坝地区页岩气特征及其意义

焦石坝地区五峰组-龙马溪组页岩富集有大量的天然气,但针对页岩气地球化学特征研究还较薄弱,其蕴含的地质意义不甚明确.通过页岩气组分及其碳同位素特征和页岩干酪根的碳同位素特征分析,讨论了页岩气的来源、成因类型和完全倒转的碳同位素分布特征.五峰组-龙马溪组页岩具有很好的生烃能力、有机质丰度与含气量的关系有明显的正相关性、甲烷与干酪根相似的碳同位素特征、地层的超压特征等,综合表明研究区天然气应为页岩自生自储的页岩气;页岩气的甲烷含量均超过98%,其碳同位素平均为-29.93‰,反映了成熟度已经达到过成熟干气阶段;相对稳定的ln（C₁/C₂）和快速增大的ln（C₂/C₃）揭示其成因主要为二次裂解气;页岩气碳同位素完全倒转的分布特征主要受到在相对封闭环境中的原油裂解生气作用的影响,其完全倒转的碳同位素分布特征也反映了研究区良好的页岩气保存、富集条件.      

临兴地区海陆过渡相页岩及页岩气地球化学特征

为揭示鄂尔多斯盆地东缘上古生界海陆过渡相页岩及页岩气地球化学特征,选取临兴地区页岩样,开展薄片鉴定、全岩和黏土含量、扫描电镜、有机碳、岩石热解、干酪根显微组分和干酪根碳同位素测试,分析页岩解吸气的气体组分和碳同位素组成。结果表明:临兴地区过渡相页岩矿物组分主要是石英和黏土矿物,含少量方解石、斜长石、钾长石、白云石和黄铁矿等。受矿物成因、沉积环境等多方面的影响,不同矿物组分与有机质赋存方式各异。石英与有机质存在2种赋存方式,黏土矿物存在3种赋存方式,黄铁矿存在4种赋存方式。有机质类型为Ⅱ₂–Ⅲ型,有机碳含量平均值大于2.0%,干酪根碳同位素介于–24.5‰~–23.2‰。镜质体反射率介于0.92%~1.30%,t_max值介于427~494℃,有机质热演化达到成熟阶段。页岩气中烃类气以甲烷为主,含有少量乙烷、丙烷,总体属于干气。甲烷碳同位素均值为–40.0‰,介于海相页岩气和陆相页岩气甲烷碳同位素之间;乙烷碳同位素值介于–26.8‰~–22.56‰,均大于–29‰,整体呈现出δ13C₁＜δ13C₂＜δ13C₃正碳序列。研究认为,该区页岩具备大量生成页岩气的潜力,页岩气主要来源于上古生界偏腐殖型页岩,属于由干酪根裂解而生成的有机热成因煤成气。      

Organic geochemical characteristics and oil generating potential of the Upper Jurassic Safer shale sediments in the Marib-Shabowah Basin,western Yemen

The organic rich Safer shales exposed in the north-central part of onshore Marib-Shabowah Basin are evaluated and their depositional environments are interpreted. Total organic carbon contents (TOC) of the shales range from 1.02–16.8 wt%, and yield hydrogen index (HI) values ranging from 130 to 820 mg HC/g TOC, consistent with mainly Type II with minor contributions from Type I and mixed Types II–III kerogens. The Safer shale samples have vitrinite reflectance values in the range of 0.5–1.0 R_o%, indicating early mature to peak mature stage for oil generation. T_max values range from 429–438 °C, which are in reasonably good agreement with vitrinite reflectance data. Kerogen microscopy shows that the Safer shales are characterized by high amounts of organic matter, consisting predominantly of yellow fluorescing amorphous organic matter and alginite of marine origin. This is supported by their high content of hydrogen rich Type II and I oil-prone kerogen.The biomarker distributions of the Upper Jurassic Safer extracts are characterized by dominant low to medium molecular weight compounds (n-C₁₄ to n-C₂₀), low Pr/Ph ratio (<1.0), high phytane/n-C₁₈ ratios (0.82–2.68), and predominant regular sterane C₂₇. All biomarker parameters clearly indicate that the organic matter was derived from marine algal inputs and deposited under anoxic (reducing) conditions. Hypersaline conditions also prevailed during deposition of these sediments, as indicated by the presence of gammacerane.     

Kerogen based characterization of major gas shales: Effects of kerogen fractionation

Research into the origin and the mode of entrapment and expulsion of natural gas from unconventional plays requires the isolation and separation of kerogen in its purest and most intact form from the rock matrix. This study expands on the comparative analysis of the effects that isolation methods, conservative closed system versus conventional open system, have on kerogen’s elemental, isotopic and physical properties. Four major gas shales, including the Barnett, the Marcellus, the Haynesville and a Polish gas shale, were chosen. In addition, the Monterey shale, though not strictly a gas shale, was included to address the effects on sulfur rich, Type II-S kerogen.Results indicate that the kerogen residues from the conventional open system method showed lower recovery and higher mineral content than those from the conservative closed system method. Differences were manifested in the elemental analysis data, where kerogens isolated using the open system method showed a significant deficit in the organic C, H, O, S and N material balance. Furthermore, the recovered residues show different sulfur content and δ³⁴S composition, most likely attributable to differences in pyrite content. Nevertheless, the relative abundances of the various macerals in the kerogen residues from the same parent shale are not very different; neither was the bulk δ¹³C composition of the recovered residues. This is not particularly surprising, considering that in all the five cases examined in this study, the organic matter was fairly homogeneous.     

准噶尔盆地南缘柴窝堡凹陷泥页岩地球化学和矿物学特征研究

利用XRD、Rock-eval和气相色谱—质谱仪对准格尔南缘柴窝堡凹陷上石炭统、上二叠统及下侏罗统的泥页岩进行了地球化学和矿物学特征分析。有机地球化学实验结果指示,柴窝堡凹陷石炭纪至二叠纪经历了较长时期的淡水—微咸水沉积环境,有机质来源具有相似的母源输入特征,干酪根类型具有II型混合母质特征;有机质热演化特征表明,下侏罗统泥页岩处于低熟阶段,上石炭统与上二叠统泥页岩具有机质丰度较高、有机质类型丰富、热演化处于成熟—高成熟阶段等特点;矿物学特征显示,上二叠统泥页岩长石、石英等脆性矿物含量为73%,粘土矿物次之,指示其脆性指数较高,具有较好的可压裂性和粘土表面吸附性。结合前人认识,预测该段泥页岩中可能蕴藏着一定规模的页岩气资源,具有较好的页岩气资源前景和勘探潜力。     

伦坡拉盆地渐新统丁青湖组油页岩特征及其地质意义

伦坡拉盆地丁青湖组油页岩呈北西-南东向断续分布,长约50 km,油页岩有18~22层,薄者0.10 m,厚者8.81 m,一般厚0.70~2.00 m。工业分析数据表明,油页岩属于高灰分、中低含油率、低发热量型。油页岩有机碳质量分数为2.40%~20.23%,平均值7.38%,丰度较高。干酪根镜检显示油页岩有机质类型为腐泥型（Ⅰ型）,镜质体反射率（R_o）值为0.43%~0.71%,平均值为0.52%,说明油页岩有机质处于未成熟-低成熟阶段。油页岩样品检测出丰富的正构烷烃、类异戊二烯烷烃、萜烷化合物和甾烷化合物。饱和烃色谱/质谱特征表明伦坡拉油页岩有机母质来源以水生浮游植物为主。通过生物标志物特征及野外地质观察,揭示了油页岩形成于一定盐度的缺氧还原半深湖-深湖环境。湖盆内各种水生浮游植物、藻类等为油页岩的形成提供了主要的有机母质来源,稳定的构造条件和缺氧的环境有利于有机质的堆积和保存。     

Comparative studies of organic matter petrography of the late palaeozoic black shales from Southwestern Poland

There are at least two sapropelic units associated with Late Palaeozoic black shales in Central Europe. The older unit, of Late Carboniferous age, is the lower part of the Anthracosia Shales in the Intrasudetic Basin, and the younger one is the well-known Zechstein Kupferschiefer in both the Foresudetic Monocline and the Northsudetic Basin. The first unit is of lacustrine origin, while the second one represents deposition in a shallow marine depositional environment. Both units contain high amounts of organic matter, thus being typical black shales.The organic matter dispersed in these shales was studied petrographically. In general, the vitrinite reflectance of the shales studied indicates variable, but moderate organic matter maturity (0.68–1.25%), equivalent to the oil window. Detailed microscopic studies of the organic material dispersed in the lower unit of the Anthracosia Shales showed that liptinite, especially alginite is the most abundant component. Secondary altered organic matter, i.e. solid hydrocarbons, rarely occurs. Organic components together with mineral matter constitute a lacustrine sapropelic association, a humic (terrestrial) association and an intermediary association. The character and predominance of alginite and lacustrine sapropelic association are indicative of an open-lacustrine depositional environment. In general, this organic composition is typical of type I kerogen.Microscopic analysis of the Kupferschiefer revealed a mixture of liptinite, vitrinite and inertinite macerals, and other organic components such as amorphous sapropelic mass (ASM) and solid bitumens. The most common organic components are liptinite macerals. Bituminite and alginite predominate, and are diagnostic macerals of this unit. The amount of bituminite locally exceeds 85 vol.%. Other liptinite macerals such as sporinite and liptodetrinite, are present in significantly lower amounts, one exception being ASM, which may be present in higher amounts. Humic constituents (vitrinite and inertinite) are rare, present in small amounts in the Kupferschiefer beds. The organic matter composition points to type II kerogen for this unit.     

下扬子皖南大隆组黑色岩系发育特征及油气资源潜力初探

下扬子地区上二叠统大隆组黑色岩系是区域潜在的烃源层,但过去关注较少。为加深对该问题的认识,本文以新近在皖南地区发现的3条剖面为例,通过详细的岩石学和有机地球化学综合研究,讨论了大隆组黑色岩系的发育特征及油气资源潜力。结果表明,宣城牛山、泾县蔡村和泾县昌桥三条剖面中大隆组黑色岩系均稳定发育,岩石类型包括硅质岩、钙质泥岩和硅质泥岩等。综合地层对比和沉积学研究结果,发现研究区在大隆期经历了一个完整的海进—海退的沉积旋回,黑色岩系主要发育于深水、还原滞留、欠补偿的海洋环境。岩石学和有机地球化学研究结果显示该地区大隆组黑色岩系的有机质丰度高,有机碳含量平均在2.0%左右,有机质类型以II_2和III型为主,并普遍进入高过成熟演化,因此区域勘探应以天然气勘探为主。对比研究区大隆组黑色岩系与中新生代火成岩的分布关系,推测大隆组黑色岩系中有机质的高过成熟演化可能与华南中新生代大规模的岩浆作用影响有关,因此在未受/少受影响的地区(例如泾县—广德一带),也可能存在一定的原油资源潜力。这些认识还可供区域黑色岩系基础地质研究参考。