Geochemical characteristics and source rock of Ordovician gas reservoir, Changqing Gasfleld

Carbon isotopic composition of methane in Ordovician gas reservoir in the Changqing Gasfield can reflect the dominance of Upper Paleozoic coal-type gas despite its high mature degree. The 12C-rich ethane in the Ordovician reservoir (δ13C2 < - 29‰), known as a marker as oil-type gas, does not indicate the Ordovician marine carbonate as main source rock, it is because of the relative less ethane content in coal-type gas than in oil-typed gas due to generation and migration. The way of Upper Paleozoic coal-type gas migrating into the Ordovician reservoir is widely through the unconformity instead of only through the erosion groove in the weathering crust.     

Identification of the Kukersite-type source rocks in the Ordovician Stratigraphy from the Tarim Basin, NW China

Due to the importance of the Gloeocapsomorpha Prisca （G. prisca）-enriched source rocks, which belong to Kukersite-type source rocks in the Lower Paleozoic Ordovician strata, it has received great attentions during the petroleum exploration as to whether there are the Kukersite-type source rocks developed in the major hydrocarbon source strata of the Upper and Middle Ordovician in the Tarim Basin. Using pyrolysis-gas chromatography-mass spectrography to analyse kerogens from source rocks in the lime- mud mound with moderate maturity, study reveals that there are the Kukersite-type source rocks in the Ordovician strata of the Tarim Basin. The pyrolysis products showed a low content of 〉n-C19 normal alkanes with a significant odd-even predominance between n-C13 and n-Cl7, long-chain alky substituted alkylbenzene and alkylthiophene isomers and distinctive distribution of 5-N- alkyl-1, 3-Benzenediol and its homologous. Based on the geographic environment characteristics of G. Prisca, the molecular dis- tributions of crude oil from the Lower Paleozoic petroleum systems in the Tarim Basin and characteristics of kerogen pyrolysis products from the Middle and Upper Ordovician source rocks, the results suggested that it is less possible to develop the G. Pris- ca-enriched Kukersite-type source rocks in the major hydrocarbon source rocks in the Middle and Upper Ordovician strata in the Tarim Basin. However, the benthic macroalga and planktonic algae-enriched source rocks are the main contributors.     

A breakthrough of researching reservoir adsorption gas and its significance

GC-C-MS on linear isotope analysis equipment makes it possible to measure the hydrocarbon gases at the level of 10 -3-10 -2 μL- By applying this technique the carbon isotopes of C1-C3 of the adsorbed gas from the Triassic oil sand bed of the Aican-l Well in the Turpan-Hami basin were analysed. The δ13C values of C1-C3, are -55.1‰, -38.6‰ and -35.0‰ respectively. In terms of geochemical characteristics of natural gases and crude oils, in combination with basinal geological backgrounds, it is considered that the reservoir adsorbed gas was formed by crude-oil biodegradation, absorbed by reservoir rocks and its oil-gas source is related with the Permain (perhaps including the Carboniferous). The adsorbed gas is obviously different from the Jurassic coal-generated oil and gas.     

Natural gas releasing simulation experiment of coal in process of temperature decreasing and decompression and preliminary application in Ordos Basin

Natural gas releasing simulation experiments were carried out in laboratory for researching the gas storage capacity in state of high temperature and high pressure and its gas releasing potential in process of temperature decreasing and decompression. The exiting phase state was studied through measuring gas adsorption of coal and PVT phase calculating of natural gas. Gas volume, gas molecular and isotope compositions in process of temperature decreasing and decompression were measured, natural-gas yields released from the Upper Paleozoic coal strata after later Cretaceous (K3) were calculated and the formation of the reservoir was studied combining with the geological background. The results indicate that natural gas stored in coal has still bigger releasing potential after the uplift of Upper Paleozoic strata. There exists a weak gas supply-effluent equilibrium in the reservoir of Ordos Basin, which is another possible evidence that the Upper Paleozoic gas reservoir may be a deep basin gas reservoir.     

鄂尔多斯盆地中部气田奥陶系风化壳天然气成藏分析

根据地质和地球化学资料,并结合前人研究成果,研究了鄂尔多斯盆地古生界烃源岩生气中心及生气高峰,探讨了中部气田天然气的成藏期次、成藏过程和成藏模式.鄂尔多斯盆地中部气田位于烃源岩生气中心及其附近,可以获得充足的气源;天然气成藏主要有2期,即晚三叠世末和早白垩世末;成藏过程包括4个演化阶段:储集层孕育阶段(O1-C1)、圈闭形成阶段(C2-P)、天然气运聚成藏阶段(T3-K1)和气藏调整/定型阶段(K2-Q);奥陶系风化壳天然气成藏存在上古生界天然气穿层运移至奥陶系顶风化壳聚集和下古生界天然气自生自储型2种成藏模式.     

Zircon U-Pb and Hf isotopes of volcanic rocks from the Batamayineishan Formation in the eastern Junggar Basin

An internal structural study was conducted to investigate U-Pb age, trace elements and Hf isotopes of basaltic zircons from the Batamayineishan Formation. The basalt was obtained from drill well San-Can 1 on the eastern Luliang uplift within the Junggar Basin. Trace element data of zircons show that all samples are magmatic, with similar REE patterns, including positive Ce (δCe=5.06–134), but negative Eu (δEu=0.06⦒0.55) anomalies and enrichment in heavy rare earth elements. Among 25 grains, the concordant ages were subdivided into three groups; ages of 300.4±1.3 Ma (n=11), 339.2±2.7 Ma (n=3) and 392.0±1.7 Ma (n=8). Three remaining grains were nearly concordant, with ²⁰⁶Pb/²³⁸U ages of 510±7, 488±6 and 453±6 Ma, respectively. The youngest concordant age (i.e., 300.4±1.3 Ma) could be interpreted as the formation age of the studied basaltic rock; this is consistent with the sampling position at the upper part of the Batamayineishan Formation. On the other hand, ages such as Ordovician and early Devonian are consistent with the ages of island-arc volcanic rocks (enrichment in Pb) or ophiolites around the basin. Moreover, the positive ɛ _Hf(t) values of the early and middle Paleozoic zircons (+3.6–+10.5) may suggest that the basement traversed by the studied volcanic rocks may be Paleozoic in age, formed from the residual oceanic crust and island-arc complex. The ɛ _Hf(t) values (+4.2–+17.1) of the late Paleozoic (∼300.4 Ma) zircons suggest that the basaltic magmas were derived from partial melting of the asthenospheric mantle or depleted lithospheric mantle. These magmas were slightly contaminated by the existence of early-middle Paleozoic materials. The late Carboniferous basalts represent direct eruption of mantle-derived magmas at the upper crustal level during a post-collisional tectonic setting. We therefore consider that extensive vertical growth of the continental crust to have occurred before the late Carboniferous.     

鄂尔多斯盆地北部上古生界深盆气成藏剖析

鄂尔多斯盆地北部上古生界气藏为一典型的深盆气藏,其成藏要素主要包括平缓的单斜、充足的气源、渐变的储层、低渗透储层与气源岩的紧密接触及良好的封闭条件.成藏事件的研究表明上古生界储盖配套、圈闭形成与油气生成和运聚匹配,具有较好的成藏基础.成藏模式的划分指出了该区今后油气勘探方向,即在气带范围内寻找大型地层圈闭及岩性圈闭是天然气勘探的关键,在水带内的背斜圈闭和背斜-岩性复合圈闭是天然气勘探的有利靶区.     

鄂尔多斯盆地中部奥陶系风化壳天然气的运移特征

鄂尔多斯盆地中部奥陶系风化壳天然气运移是迄今研究比较薄弱的重要问题 .在前人工作的基础上 ,依据实际的地质和地球化学资料 ,分析了鄂尔多斯盆地中部奥陶系风化壳天然气的运移特征 .研究认为 ,以靖边为中心的中部气区是天然气运移的有利区 .奥陶系风化壳天然气的运移较为复杂 ,既有奥陶系来源天然气的侧向运移 ,又有上覆石炭—二叠系来源天然气的穿层运移 .这与研究区的构造演化、古流体等研究结果相吻合     

鄂尔多斯盆地西北部奥陶系“三元”主控成藏规律

通过对鄂尔多斯盆地西北部奥陶系烃源岩、储集层及天然气展布规律的研究,探讨其天然气成藏规律。奥陶系烃源岩主要分布在上统乌拉力克组和拉什仲组,以海相泥岩为主;储层主要发育在中统克里摩里组和桌子山组,依据岩石类型、孔隙结构,可分为岩溶孔洞型储层和白云岩晶间溶孔型储层;天然气藏的形成受烃源岩、储层和圈闭的"三元"主控,具有有效烃源岩控制天然气区域分布、优质储层控制天然气聚集带展布、有效圈闭控制气藏分布特征。鄂尔多斯盆地西北部的西侧气藏主要为油型气,东侧主要为煤型气,均为上生下储的成藏模式。     

塔中地区油气资源评价

系统评价了塔里木盆地塔中地区的烃源岩,采用盆地数值模拟方法定量计算了塔中地区的生、排烃数量。研究表明,塔中地区的油气运移聚集主要发生于早古生代和晚古生代的几次构造运动期间,聚集的油气曾遭受过严重的破坏,塔中地区的构造演化对塔中地区的油气聚集起着至关重要的作用。寒武系和下奥陶统烃源岩生排油时间较早,因此对现今已发现的油藏贡献不大,而晚排出的天然气有利于聚集;中上奥陶统烃源岩生排油延续时间较长,对塔中的油气聚集有实质性的贡献。     

CO<Subscript>2</Subscript> gas emplacement age in the Songliao Basin: Insight from volcanic quartz <Superscript>40</Superscript>Ar-<Superscript>39</Superscript>Ar stepwise crushing

Due to a lack of suitable minerals, the gas/oil emplacement ages have never been accurately obtained before. CH₄-CO₂-saline- bearing secondary inclusions are found in quartz from the volcanic rocks of the Yingcheng Formation, the container rocks of the deep CO₂ gas reservoir in the Songliao Basin. The inclusion fluid was trapped into microcracks in quartz during the gas emplacement and accumulation, providing an optimal target for the ⁴⁰Ar-³⁹Ar stepwise crushing technique to determine the CO₂ gas emplacement age. ⁴⁰Ar-³⁹Ar dating results of a quartz sample by stepwise crushing yield a highly linear-regression isochron with an age of 78.4±1.3 Ma, indicating that the accumulation of the deep CO₂ gas reservoir in the Songliao Basin occurred in the late Cretaceous. This is the first time to report an exact isotopic age for a CO₂ gas reservoir, which indicates that the ⁴⁰Ar-³⁹Ar dating can serve as a new technique to date the oil/gas emplacement ages.     

The genesis of H2S in the Weiyuan Gas Field, Sichuan Basin and its evidence

The Sinian Dengying Formation gas pool in Weiyuan is the oldest large-scale sulfur-bearing gas field in China, which has a H2S content ranging from 0.8% to 1.4%. The Cambrian Xixiangchi Formation gas pool discovered recently above the Dengying Formation contains gas geochemical behaviors similar to those of Dengying Formation but different in sulfur isotopes of H2S. Investigations show that though these two Sinian and Cambrian gas pools are separate ones, they share the same Cambrian source rock. The higher dry coefficient, heavier carbon isotopes, sulfur isotopes of sulfide, lower filling of gas pools, formation water characteristics, reservoir properties and H2S distribution, indicate that H2S in both the Sinian and Cambrian gas pools originates from TSR. The sulfur isotopes of sulfates have shown that H2S was formed in respective pools, namely hydrocarbons charged into the pools reacted with the Dengying Formation and the Xixiangchi Formation gypsum （TSR）, respectively, to form H2S. Compared with sulfur isotopes of sulfates in each pool, δ^34S values of H2S are 8‰ lighter for the Dengying Formation pool and 12‰ lighter for the Xixiangchi Formation pool, respectively, which is attributed to the difference in temperatures of TSR occurrence. The reservoir temperature of the Xixiangchi Formation pool is about 40℃ lower than that of the Dengying Formation pool. Temperature plays a controlling role in both the sulfur isotopic fractionation and amounts of H2S generation during TSR.     

Permian volcanisms in eastern and southeastern margins of the Jiamusi Massif, northeastern China: zircon U-Pb chronology, geochemistry and its tectonic implications

LA-ICP-MS zircon U-Pb dating and geochemical data for the Late Paleozoic volcanic rocks from eastern and southeastern margins of the Jiamusi Massif are presented to understand the regional tectonic evolution. Zircons from eight representative volcanic rocks are euhedral-subhedral in shape and display striped absorption and fine-scale oscillatory growth zoning as well as high Th/U ratios （0.33-2.37）, implying a magmatic origin. The dating results show that the Late Paleozoic volcanic rocks in the study area can be divided into two stages, i.e., the Early Permian （a weighted mean 205^Pb/238^U age of 288 Ma） and the Middle Permian volcanisms （a weighted mean 205^Pb/238^U age of 268 Ma）. The former is composed mainly of basalt, basaltic-andesite, andesite and minor dacite. They are characterized by low SiO2 contents, high Mg^# （0.40-0.59）, enrichment in Na （Na2O/K2O = 1.26-4.25） and light rare earth elements （LREEs）, relative depletion in heavy rare earth elements （HREEs） and high field strength elements （HFSEs）, indicating that an active continental margin setting could exist in the eastern margin of the Jiamusi Massif in the Early Permian. The latter consists mainly of rhyolite and minor dacite with high SiO2 （77.23%-77.52%）, low MgO （0.11%-0.14%）, enrichment in 1（20 （Na2O/K2O ratios 〈 0.80） and Rb, Th, U and depletion in Eu, Sr, P and Ti, implying a crust-derived origin. Therefore, it is proposed that the Middle Permian volcanic rocks could have formed under the collision of the Jiamusi and the Khanka Massifs.     

Paleozoic sedimentary record of the Xing-Meng Orogenic Belt,Inner Mongolia: Implications for the provenances and tectonic evolution of the Central Asian Orogenic Belt

The Xing-Meng Orogenic Belt is the eastern extension of the Central Asian Orogenic Belt, which marks the boundary between the North China and Siberian blocks. Key information on the collision between these two blocks and the evolution of this orogenic belt at the end of the Paleozoic are preserved in the widely distributed Paleozoic sedimentary sequences. Petrographic studies of the clastic sedimentary rocks from the Ordovician to the Permian in this region have shown that the rocks are mainly greywackes and arkosic sandstones characterized by low maturity, poor sorting and a large number of lithic fragments. Provenances of Paleozoic sandstones are mainly newly accreted crustal materials. Nd model ages range from the Neoproterozoic to the Late Mesoproterozoic. These ages are very different from those of the North China Block, but the change of εNd(t) (from the initial εNd value) is similar to that of igneous rocks in the Xing-Meng Orogen. This result indicates that provenances of these Paleozoic sedimentary rocks mainly arise from the Xing-Meng Orogen itself. These clastic sedimentary rocks mainly consist of inputs of juvenile accreted crustal materials and limited recycled old crusts. Their provenance is controlled by the following three end members: a felsic basement, a partially melted mafic, and a mafic end member. From the point view of lithology, these three end members must have mixed in a ratio of 53:41:5 to form the average composition of the clastic sedimentary rocks. The depositional environment began to change from an arc to an orogen during the Permian, and therefore the collision was complete before the Triassic. This interpretation is consistent with the argument that the final collision time was at the end of the Permian or beginning of the Triassic.     

Molecular fossils and oil-source rock correlations in Tarim Basin, NW China

The distribution of "molecular fossils" (bio-markers) of steroid compounds in extracts from some spe-cific geologic age in the Tarim Basin have been analyzed andare used as the fingerprints for the oil-source rock correla-tion. Having been affected by maturation, migration, phasefractionation and biodegradation, not any molecular fossilsrelated to source and environment can be used as the finger-prints for oil-source rock correlation. Some special bio-markers widely existed in the extracts from Cambrian andOrdovician rocks in the Tarim Basin and showed obviousdifference in each stratum, including dinosteranes (C₃₀),4-methyl-24-ethyl-cholestanes (C₃₀) and their aromatizedsteroids, C₂₄-norcholestanes and C₂₈ steranes originated fromdinoflagellates and diatom. Few oils such as the heavy oildrilled in the Cambrian reservoir from Tadong 2 well (TD2)correlated well with the extracts from the Cambrian. Theamazing similarity of the relative contents of these com-pounds between the marine oils produced in Tazhong andTabei uplifts and the extracts from the Upper Ordoviciansuggests that the Middle-Upper Ordovician is the very likelymain source for the marine oils.     

Detrital zircon U–Pb geochronology and Hf isotopic compositions of Middle–Upper Ordovician sandstones from the Quruqtagh area,eastern Tarim Basin:implications for sedimentary provenance and tectonic evolution

Figuring out whether the sedimentary provenance regions of the thick deep-water turbidite systems deposited during Middle–Upper Ordovician in South Quruqtagh are the intracontinental uplifts or the peripheral orogenic belts is of great significance for us to understand the tectono-sedimentary nature of the northeastern Tarim Basin and basin-range coupling processes in the middle Paleozoic.This paper reports the in situ LA-ICP-MS U–Pb ages and Hf isotope data on detrital zircons from two Middle–Upper Ordovician sandstone samples which were collected from the Charchag Formation and the Zatupo Formation in South Quruqtagh,respectively.The results show that the studied two samples have extremely similar U–Pb age patterns and Hf isotopic compositions,reflecting multiphase tectonothermal events with age groups of 527–694,713–870 Ma(peaking at 760 Ma),904–1,090,1,787–2,094 Ma(peaking at 1,975 Ma)and 2,419–2,517 Ma.Combining previous studies,the presence of age groups of 713–1,090 and1,787–2,094 Ma,respectively,demonstrates that Tarim had ever been a part of Rodinia and Columbia supercontinent.Moreover,98%of 713–870 Ma detrital zircons are characterized by negative e Hf(t)values ranging from-38.07 to-0.61,which are highly consistent with those of Neoproterozoic granites from the Quruqtagh area.No Early Paleozoic ages(*470–500 Ma)signifying subduction or collision events in Altyn Tagh were detected in the two samples,indicating that the Middle–Late Ordovician sediments in South Quruqtagh and northern Mangar depression were mainly derived from intracontinental uplifts,i.e.,the North Quruqtagh uplift or the Tabei paleo-uplift,rather than the Altyn Tagh.In conjunction with regional sedimentary-tectonic background and previous studies,we proposed preliminarily that the northeastern Tarim remained as a passive continental margin in Late Ordovician and changed into an active-continental margin in Silurian due to the southward subduction of the South-Tianshan Ocean.     

Natural gas geochemistry of low evolutionary stage of medium- and small-sized basins in Yunnan Province, southwestern China

The biogenic gas and premature-low mature associated gases in some medium and small-sized basins of Yannan Province, such as Luliang, Yanglin, Baoshan and Jinggu basins, have beed researched. The results show that the biogenic-gas consists mainly of methane which is more than 99% in gasous hydrocarbons and of lighter carbon isotopic composition with δ13C1 values from -60.0‰ to - 75.4‰. The methane carbon isotopic compositions in the Baoshan Basin is relatively heavy (δ13C1 - 60‰- - 65‰), but those in Luliang and Yanglin basins are lighter (δ13C1, less than -70‰), which implies that the gas field of the Baoshan Basin formed earlier than the others. In the Jinggu Basin, where crude oil is premature-lower mature, the natural gas of associated oil relatively wet and the relative content of methane about 58%-95% in gasous hydrocarbons. Constituently the gas composition is much similar to associated one, but the methane carbon isotopic compositions from - 53.8‰ to - 57.8‰ are obviously richer in 12C than those of general oil fields and similarly characterize the biothermo-catalytic transitional zone gas. Their ethane carbon isotopic compositions from - 34.6‰ to -29.0‰ show that they may be derived from type Ⅰ or Ⅱ source rock. But for the associated gas from lower evolutionary stage, the heavier ethane carbon isotopic composition as well as the reversed order among the carbon isotopic composition of ethane, propylane and butane also implies that some gases from the type Ⅲ organic matter are mixed. The δ13CCo2 of the samples essentially less than - 10‰ may be generated from organic matter.     

Activation of northern margin of the North China Craton in Late Paleozoic: Evidence from U-Pb dating and Hf isotopes of detrital zircons from the Upper Carboniferous Taiyuan Formation in the Ningwu-Jingle basin

LA-MC-ICPMS U-Pb dating has been performed on detrital zircons from the Upper Carboniferous Tai-yuan Formation (N-8) in the Ningwu-Jingle Basin, west of the North China Craton (NCC). The ages of 72 detrital zircon grains are divided into three groups: 303―320 Ma (6 grains), 1631―2194 Ma (37 grains, peaked at 1850 Ma), 2318―2646 Ma (29 grains, peaked at 2500 Ma). Detrital zircons of Group 2 and Group 3 were likely derived from the basement of the NCC. Group 1 zircons exhibit 176Hf/177Hf ratios ranging from 0...     

辽河东部凸起C—P页岩气聚集地质条件

通过对辽河坳陷东部凸起已钻探井的录井、测井及岩芯资料的系统分析,结合目的层段样品的有机地化及实验测试结果分析,认为东部凸起上古生界石炭—二叠系暗色泥岩单层厚度较大,空间分布广泛稳定,有机质类型以III型干酪根为主,丰度指标高(TOC>2.0%),热演化程度高(Ro=1.5%～2.6%),具备形成页岩气藏的源岩条件;暗色泥岩有机碳含量高为吸附态页岩气提供了丰富的载体,微裂缝的发育为游离态页岩气提供了良好储集空间;同时泥岩石英矿物含量高(平均SiO2>40%),岩性较脆易形成裂缝,符合工程压裂条件要求,部分已钻探井在石炭系—二叠系暗色泥岩段普遍存在气测全烃异常,预示东部凸起上古生界石炭—二叠系具有较大的页岩气勘探潜力。     

鄂尔多斯北部杭锦旗探区上古生界烃源岩评价

鄂尔多斯盆地北部杭锦旗探区上古生界烃源岩问题争议大。通过有机地球化学分析、盆地模拟等方法手段对研究区上古生界烃源岩展开研究。结果表明,上古生界发育石炭系、二叠系两套烃源岩,煤层是最好的烃源岩,泥岩为差烃源岩。煤层有机碳的质量分数最高,平均值为61.32%;有机质类型好,以Ⅲ型干酪根为主,属于生气型源岩;有机质成熟度为0.8%~1.3%,已经进入生气高峰阶段。烃源岩生气强度为(0.1~1.3)×109m3/km2,具备为研究区天然气成藏提供物质基础的条件。盆地模拟结果表明山西组总生气量大于太原组,是主要的烃源岩层系。烃源岩从侏罗纪末进入大规模生烃阶段,生烃高峰为早白垩世。研究区石炭系和二叠系煤层是上古生界天然气成藏的主要气源岩,天然气组分中甲烷含量变化、天然气侧向运移距离等证据进一步佐证了上述观点,突出了研究区上古生界烃源岩的原地性特征。