湘中坳陷涟源凹陷烃源岩油气地球化学特征

湘中坳陷涟源凹陷烃源岩类型复杂,包括碳酸盐岩、泥岩和煤层。根据涟源凹陷大量露头样品的残余有机碳含量、氯仿沥青“A”、镜质体反射率和包裹体等地球化学实验数据,分析了泥盆系-二叠系烃源岩的有机质丰度、类型及热演化程度。结果表明涟源凹陷的烃源岩总体演化程度均已达到过成熟阶段,油气资源以干气为主。针对烃源岩样品的热演化程度高、丰度低的特征,在了解烃源岩地球化学特征及其与构造运动匹配关系的基础上,探讨了涟源凹陷二次生烃的可能性,最终认为涟源凹陷泥盆系-二叠系烃源岩具有中等级别的生烃能力,并在二叠系的龙潭组煤层有二次生烃的可能。     

ORGANIC FACIES VARIATIONS AND HYDROCARBON GENERATION POTENTIAL OF PERMIAN GONDWANA GROUP COALS AND ASSOCIATED SEDIMENTS,BARAPUKURIA AND DIGHIPARA BASINS,NW BANGLADESH

In the Barapukuria and Dighipara coal basins, NW Bangladesh, the Basement Complex is overlain by the coal‐bearing Permian Gondwana Group. In the present study, 36 core samples collected from five boreholes in these two basins were analysed using organic geochemical and organic petrological methods. Based on the results of biomarker analyses (TIC, m/z 191 and m/z 217 fragmentograms) and maceral composition (proportions of vitrinite, liptinite, inertinite), three organic facies were identified: coals, carbargillites and mudstones. Together with other evidence, cross‐plots of HI versus T_max and Pr/nC₁₇ versus Ph/nC₁₈ indicate that the coals, as expected, were dominated by terrestrial organic matter (OM). The carbargillites contained a mixture of terrestrial and probable Type II aquatic OM, and the mudstones contained mostly terrestrial OM. Accordingly the coals, carbargillites and mudstones are interpreted to have been deposited in swamp‐dominated environments in a delta‐plain setting which was subject, in the case of carbargillites, to periodic flooding. Suboxic conditions were indicated by very high Pr/Ph ratios and a high content of inertinite macerals. All the samples analysed were immature or early mature for hydrocarbon generation, as indicated by mean vitrinite reflectance (%R_o) of 0.60–0.81%, Rock‐Eval T_max of 430–439°C, and biomarker ratios (hopane C₃₂ 22S/(22S+22R)) of 0.57–0.60. Carbargillites showed potential for both liquid and gaseous hydrocarbon generation; coals were mainly gas‐prone with minor liquid hydrocarbon potential; and mudstones were dominantly gas‐prone. The oil‐prone nature of the samples was attributed to the presence of resinite, cutinite, bituminite and fluorescent vitrinite. The presence of exsudatinite within crack networks, solid bitumen and oil droplets as well as bituminite at early oil‐window maturities suggests that the organic matter may have expelled some hydrocarbons.     

鄂尔多斯盆地延X井烃源岩有机地球化学特征

以石油有机地球化学理论为指导,并结合有机岩石学、构造地质学及沉积学等学科,通过对岩石热解、有机物抽提、族组份分离、镜质体反射率、有机元素等相关地球化学参数的研究,从暗色泥岩厚度、有机质的丰度、有机质的类型和有机质成熟度等方面对延X井上古生界烃源岩进行了研究。综合评价认为石盒子组、石千峰组、山西组、太原组生烃能力逐渐增强。上古生界太原组和山西组烃源岩有机质丰度高,干酪根类型以腐殖型为主,有机质处于过成熟阶段,气态烃生成能力较强。     

从有机质成熟度看四川盆地下古生界油气勘探

从回顾有机质成熟度检测研究现状入手，论证认为镜质体反射率至今仍是有机质成熟度研究的最佳参数。以此为据，编绘了四川盆地上二叠统有机质成熟度图；通过对其与下伏产层油气属性关系的分析，探讨了四川盆地下古生界因缺乏镜质体作为检测对象而被迫选用其他参数用于有机质成熟度划分所存在的可变因素；最后借用四川盆地上二叠统有机质成熟度演变趋势分析结果，确认川东-川东北有机质过成熟地区的高陡构造仍不失为该区天然气勘探的目标区。     

合肥盆地寒武系底部烃源岩沉积环境和地球化学特征

合肥盆地海相油气的勘探逐渐受到重视。盆地西部发现的寒武系底部海相泥质烃源岩具有重要的现实意义,对其沉积环境和地球化学特征的研究是进一步油气勘探的基础。层序地层学及有机地球化学研究表明,其沉积构造环境为拉张裂陷向移离扩张的过渡阶段,盆地性质属于内裂谷盆地向被动大陆边缘盆地的过渡类型,对于烃源岩的形成和保存极其有利。该套烃源岩有机碳平均含量为6.46%,有机质类型为I型,R_o(2%～3.5%)与T_max(500～600℃)反映的成熟度已进入过成熟早期乃至晚期阶段。生物标志物反映该套烃源岩在强还原高盐度的环境中形成,生源为菌藻类低等生物,其演化程度处于生油阶段。两类有机地化指标反映的成熟度差异,可能是各自代表的有机质不同。R_o和T_max主要反映烃源岩主体的成熟度,而生物标志物可能主要反映岩石包体有机质的成熟度。综合研究认为,该套烃源岩不仅处于生气高峰期,并具有生油的可能。该套烃源岩沉积环境和地球化学的研究,为合肥盆地勘探下古生界天然气藏提供了理论依据。      

中上扬子北缘中古生界海相烃源岩特征

中上扬子北缘中古生界海相层系有机地球化学剖面的研究表明,中古生界海相层系烃源岩主要发育于下寒武统、上奥陶统五峰—下志留统龙马溪组底部和二叠系。其中下古生界烃源岩以泥质岩为主,有机质丰度高,有机质类型好,多属好—最好的烃源岩;上古生界(P)烃源岩以碳酸盐岩为主,泥质岩为辅,前者有机碳一般<1%,多属较好的烃源岩,后者有机质丰度高,多属好—最好的烃源岩;二叠系碳酸盐岩和泥质烃源岩有机质类型复杂多样,以Ⅱ₁型为主。3套烃源岩热演化程度普遍较高,等效镜质体反射率R_o一般>2.0%,区内油气结构以天然气为主。烃源岩可溶有机质有机地球化学特征研究表明,下古生界烃源岩正构烷烃呈单前峰型,而二叠系烃源岩正构烷烃有3种类型。在甾、萜烷生物标志化合物方面,二叠系烃源岩以较低的C₂₁三环萜烷/C₂₃三环萜烷、C₂₇规则甾烷/C₂₈₊₂₉规则甾烷等为显著特征而区别于下寒武统烃源岩,五峰组—龙马溪组烃源岩则介于其间。      

十万大山盆地古油藏沥青地球化学特征及来源

根据沥青产状、族组成、饱和烃色谱、生物标志化合物、碳同位素以及沥青热演化程度等,对广西十万大山盆地北缘的老虎山古油藏、上屯古油藏二叠系灰岩中固体沥青的地球化学特征进行了系统分析,并结合有关烃源岩地球化学特征及油气成藏研究成果对其来源和成因进行了探讨.结果表明,古油藏沥青抽提物含量低,族组成中芳烃和非烃含量高,饱和烃含量低,芳烃含量最高可达58.60%.饱和烃气相色谱分析表明,沥青具还原环境、以低等水生生源为主的母质来源及较高的热演化程度.沥青稳定碳同位素为-27.8‰~-28.7‰,反映其生烃母质以低等生源为主.沥青中的甾、萜烷含量很低,且以低分子量化合物占绝对优势,其中甾烷系列中具很高的孕甾烷含量,萜烷则以三环萜烷为主,反映其高热演化特征.沥青几乎不含芳香甾烷,与本区上二叠统泥质烃源岩特征相似;沥青反射率为1.9%~2.5%,结合本区生烃成藏演化史分析结果,反映其经历过230℃高温.最后结合相关烃源岩地球化学特征及有关油气成藏信息,综合认为古油藏沥青与上二叠统泥质烃源岩有较好的亲缘关系,是古油藏早期原油高温裂解的产物之一,即焦沥青.      

银额盆地拐子湖凹陷北部烃源岩特征及控制因素

针对拐子湖凹陷勘探程度较低、有效烃源岩分布及控制因素不明确的问题,运用有机地球化学、沉积层序及构造演化分析方法,对温1井烃源岩特征及主控因素展开研究。研究结果表明:研究区烃源岩有机质丰度整体较低,受沉积层序、构造综合影响,高位体系域有利于有机质富集;有机质类型为腐泥腐殖型和腐殖型;有机质热演化程度差异较大,富泥质岩类的发育可促进早期的热演化进程,构造的后期抬升使局部生烃时间大幅缩短,故有机质成熟度从未成熟至高成熟均有分布;烃源岩展布受断裂及沉积演化控制明显。该研究可为拐子湖凹陷北部下一步勘探提供参考。     

中国西北地区侏罗纪煤系油气形成（之三）

西北地区侏罗纪煤系中主要成烃显微组分是孢子体、角质体、藻类体、沥青质体、碎屑类脂体和基质镜质体等，木栓质体和树脂体等早期成烃组分含量极低。侏罗纪煤系有机质成烃演化特征与一般湖相有机质稍有差异，但基本上仍然遵循一般有机质热降解成熟生油模式，主要生油阶段的Ｒｏ值为０．７％～１．２％，生油高峰Ｒｏ值约为０．９５％。目前西北地区侏罗纪煤系烃源岩Ｒｏ值一般为０．４％～１．３％，多数地区成熟度较低，在山前深坳陷地区成熟度较高，烃源岩Ｒｏ值大于０．７％，进入大量生油阶段，西北地区主要煤系含油气盆地油气田均分布于这些地区，烃源岩成熟度对油气田形成有明显的控制作用。西北地区侏罗系有利的生烃区域基本分布在侏罗纪是沉降、沉积中心而后续埋藏又较深的山前坳陷。图４表１参４５（王孝陵摘）     

A RE-CONSIDERATION OF THE "OIL WINDOW" FOR HUMIC COAL AND KEROGEN TYPE III SOURCE ROCKS

Based on natural data-sets and several hydrous-pyrolysis experiments on immature humic coals, the conventional "oil window" (0.5–0.6%R₀ to 1.3–1.35%R₀) for humic coals is re-considered. A worldwide coal data-set comprising coals of Carboniferous - Tertiary age and having vitrinite reflectances from 0.32%R₀ to 3.6%R₀ indicates that initial liquid hydrocarbon generation commences at a vitrinite reflectance of 0.5%R₀ to 0.6%R₀, and that a significant liquid hydrocarbon build-up occurs from approximately 0.6%R₀ to 0.85%R₀. The start of the "oil window" corresponds to a vitrinite reflectance of 0.85%R₀; however, the start of the "oil window" can vary significantly for individual coal series, and it may range up to a vitrinite reflectance of 1.15%R₀. Liquid hydrocarbon generation is negligible at a vitrinite reflectance of approximately 1.8%R₀, and at 2.0%R₀ the hydrocarbon generative potential is exhausted. A vitrinite reflectance of 1.8%R₀ corresponds to the end of the "oil window", and for general use a vitrinite reflectance range of 0.85–1.8%R₀ is suggested to define the "oil window" for humic coals and kerogen type III. The end of the "oil window" at 1.8%R₀ is supported by published data, indicating a much higher thermal stability of nC₁₅₊ hydrocarbons than is generally accepted, and therefore limited oil-to-gas cracking at 1.3%R₀. The re-considered "oil window" between 0.85–1.8%R₀ has significant implications for evaluating the prospectivity of basins dominated by terrestrial organic matter, such as coals.     

华北盆地中南部早古生代沉积特征及油气成藏条件

华北盆地下古生界分布广泛,沉积厚度较大。虽然其沉积沉降中心不断迁移,但其迁移性主要受板缘构造活动带影响,板内并未发生构造变形(褶皱、断裂),故沉积环境和沉积厚度差异不大,总体表现为浅水、高能、盆内碎屑丰富的陆表海沉积环境。沉积岩的有机质丰度低,基本无有效生油岩发育。统计了1500余个沉积岩有机质丰度资料,总结了有机质丰度与岩性、沉积相的关系,下古生界碳酸盐岩孔洞型储集层的形成机理及其与构造运动的关系表明,加里东期古岩溶主要发生在太康—开封古斜坡,印支期古岩溶主要发生在郯庐断裂西侧的褶皱和推覆构造带,可形成有工业意义的碳酸盐岩储集层。     

潮水盆地和民和盆地中侏罗统青土井组煤系烃源岩有机地球化学特征及其意义

随着非常规油气资源开采技术进步以及勘探范围日益扩大,煤系烃源岩日益获得重视。潮水盆地和民和盆地作为甘肃陇中、河西地区的典型侏罗系含煤沉积代表,其生烃能力及其差异性特征研究相对欠缺,为此对两地区煤系烃源岩展开综合有机地球化学参数特征及其对比研究。生物标志物特征指示:潮水盆地青土井组煤系烃源岩有机质来源以混合输入为主,处于低熟-成熟阶段,沉积环境上段为弱氧化-弱还原滨、浅湖相,下段为弱咸化半深湖-深湖相,出现高伽马蜡烷优势,指示水体出现分层现象;民和盆地窑街组煤系烃源岩有机质来源上段以低等水生生物输入为主,下段为陆相高等植物优势输入,有机质处于低熟-成熟阶段,沉积环境倾向于典型沼泽相煤系沉积。有机质丰度和类型数据揭示:潮水盆地烃源岩有机质类型主要为Ⅱ型;民和盆地烃源岩有机质类型Ⅰ型、Ⅱ型及Ⅲ型均有出现。综合分析各项有机地球化学参数,指示潮水盆地和民和盆地均具有一定生烃潜力,相对来说以低等水生生物输入为主的民和盆地煤系烃源岩可能具有相对较大的生液态烃潜力。     

BURIAL AND THERMAL HISTORY MODELLING OF THE MURZUQ AND GHADAMES BASINS (LIBYA) USING THE GALO COMPUTER PROGRAMME

The GALO computer programme was used to model the thermal and burial histories of the Murzuq and Ghadames Basins, Libya. The model was based on recent drilling and seismic data from the basins, and used published deep temperature and vitrinite reflectance measurements. The model provides more accurate results than previous studies which were based on constant geothermal gradients during the basins' histories, and variations in heat flux at the base of the sedimentary cover were chosen so that calculated values of vitrinite reflectance coincide with those observed. The Murzuq Basin and Libyan part of the Ghadames Basin contain similar source rock units but have different burial histories. In the Murzuq Basin, maximum present‐day burial depths of Cambrian sediments range from 2200 to 2800 m and only locally reach 3000 – 3600 m; in the Ghadames Basin, however, burial depths can exceed 4–5 km. The burial history of the Murzuq Basin includes several periods of intense erosion and lithospheric heating which produced significant lateral variations in thermal maturity, leading in places to unexpected results. For example, relatively shallow‐buried Lower Silurian source rocks in the A‐76 area on the flank of the Murzuq Basin have a thermal maturity of R_o = 1.24% which is higher than the maturity of the same interval in more deeply buried areas (wells D1‐NC‐58 or J1‐NC101). In the central part of the Ghadames Basin, the modelling suggests a higher level of thermal maturity for organic matter in Silurian strata (R_o 0.8 to 1.3%), confirming the generation potential of Lower Silurian “hot shales”. Significant hydrocarbon generation began here in the Late Carboniferous and continues at the present day. Modelling of the Late Devonian (Frasnian) Aouinat Ouinine Formation “hot shales” suggests limited hydrocarbon generation depending strongly on burial depth, with the main phase of hydrocarbon generation taking place during the final episode of thermal activation in the Cenozoic. In the wells studied in the Ghadames Basin, the “oil window” extends over a considerable part of the present‐day sedimentary column.     

THE ROLE OF OVERPRESSURE IN THE RETARDATION OF ORGANIC MATTER MATURATION

Abnormal profiles of organic matter maturation in overpressured sequences, which express the retardation of maturation, are a worldwide phenomenon; however, the cause of this retardation has not been explained satisfactorily. Clearly, the different types of pressure in an overpressured regime must be identified in order to determine their role in the retardation of organic matter maturation. Differential pressure is shown to have a marked influence on the maturation of organic matter through its effects on the thermal properties of the source-rock system. Vitrinite reflectance data from several wells in basins offshore NW Europe have been used to calibrate source-rock maturation against differential pressure and “effective temperature ” (i.e. observed temperature in an overpressured sequence corrected to the temperature at the same depth in a normally-pressured sequence). High correlation coefficients with vitrinite reflectance have been measured for both relationships. Differential pressure is a determining factor in porosity reduction. Temperature and porosity affect the thermal conductivity of a rock in both overpressured and normally-pressured sequences according to established formulae. Cumulative heat flow, the product of observed temperature and thermal conductivity, is an important value which is affected indirectly by differential pressure. A close linear correlation between cumulative heat flow and vitrinite reflectance is proved. Cumulative heat flow can be related to thermodynamic properties of source-rock systems, and it can be compared to the enthalpy of a system or the internal energy of a reaction. In overpressured sequences, conditions resemble those of constant pressure and constant volume reactions. As a result, cumulative heat flow can be taken as a measure of the final state of a reaction, corresponding in this discussion to the level of vitrinite reflectance. So it can be used as a guide to the state of source-rock maturation in both normally-pressured and overpressured sequences.     

THE CHAIDAM BASIN (NW CHINA): FORMATION AND HYDROCARBON POTENTIAL

The Chaidam Basin forms one of the deepest sedimentary basins in the world, with over 14kms of sediment deposited since the Oligocene. Basement rocks consist of: (i) pre-Sinian gneisses; (ii) Sinian and Lower Palaeozoic sediments folded by the Silurian - Devonian orogeny; (iii) Upper Palaeozoic molasse in a half-graben produced by the collapse of the Silurian mountain belt; (iv) Carboniferous terrestrial to shallow-marine facies sediments deposited on the margins of Palaeotethys; and (v) Permo-Triassic sediments deposited in a back-arc basin N of the Palaeotethyan subduction zone. Triassic back-are basin development was followed by thermal subsidence during the Jurassic to Eocene, with a low sedimentation rate, modified by flexural subsidence on the margins of the thickened and uplifted S Qilian Mountains. Gentle folds and SW-propagating thrusts were developed in Jurassic strata. The region was uplifted as a whole during Early Jurassic and Middle Cretaceous times. The main period of subsidence occurred from the Oligocene to the Recent, producing a deep hinterland basin in western and central Chaidam. Uplift along the Kunlun and the Aerjin Fault Zone provided a ready sediment supply. Basin subsidence throughout the Neogene probably reflects lithospheric flexure due to the loading of the Tibetan lithosphere, although the rapid increase of Sedimentation during the latest Tertiary and Quaternary must reflect rapid Recent uplift of the Tibetan Plateau. During the Pliocene and Pleistocene, there was inversion and shortening of the Basin, associated with reworking of the Mesozoic strike-slip and thrust faults. Thus, the Aerjin Fault Zone was reactivated to control the shortening direction across the Basin. Mesozoic thrusts were reactivated along the NE margin of the Basin during the Pliocene, but by Pleistocene times, WNW-trending folds developed throughout the western part of the Basin. There was differential uplift; the zone nearest the Aerjin Fault was uplifted most, causing tilting and variations in sediment thickness and facies from NW and SE. There are numerous source rocks formed by lacustrine facies sediments of Jurassic and Neogene age. The burial history and the timing and location of structural and stratigraphic traps has controlled the locations of the major hydrocarbon occurrences in western and NW Chaidam. An evaluation of hydrocarbon prospectivity is given in the light of the tectonic - stratigraphic framework and basin analysis.     

辽宁省红庙子盆地烃源岩特征与生烃潜力研究——来自红地1井的证据

红庙子盆地是松辽外围东南部中生代沉积盆地之一,其油气基础地质研究程度极低,盆地内部烃源岩类型和有机地化特征及生烃潜力等均未知,制约着盆地油气资源研究和勘探部署。依据新近部署的红地1井钻探成果,系统采集岩心样品,进行了暗色泥岩有机质丰度、类型和成熟度测试。盆地内烃源岩主要由下白垩统下桦皮甸子组的黑色泥岩、粉砂质泥岩组成,黑色泥岩累计厚度101.16 m,单层最厚24.85 m,发现油气显示50层。实验结果表明,该区下桦皮甸子组烃源岩有机质丰度中等,类型以Ⅱ₂-Ⅲ型为主,局部含有Ⅱ₁和Ⅰ型;镜质体反射率为1.31%~1.84%,平均值1.53%,已进入高成熟阶段。扫描电镜分析揭示,该烃源岩矿物成分由黏土和脆性矿物组成,平均含量分别为58.4%和41.4%;泥晶间微孔隙发育,有利于储集空间和运移通道的改善,便于后期人工造缝,具有油气聚集和运移的成藏条件。综合研究认为,红庙子盆地烃源岩具有一定的生油气潜力,亟需持续深入地开展研究工作。      

THERMAL MATURITY AND SOURCE-ROCK POTENTIAL OF THE SEDIMENTARY SUCCESSION FROM THE DRAKE FIELD, SVERDRUP BASIN, ARCTIC CANADA

The thermal maturity and source-rock potential of the sedimentary succession in the Drake field, Melville Island, Arctic Canada, have been studied using reflected-light microscopy and Rock-Eval pyrolysis. The Mesozoic sediments are immature to mature (% Ro = 0.35-0.80). Vitrinite reflectance in Cretaceous sediments ranges from 0.35 to 0.56%; in Jurassic sediments, it ranges from 0.40 to 0.66%, and in Triassic sediments, from 0.50 to 0.80%. The Triassic Schei Point Group shales and siltstones contain organic matter of marine origin, whereas the predominantly plant-derived organic matter present in the Jameson Bay, Ringnes and Deer Bay Formations has higher TOC. Among the Schei Point Group sediments, the Eden Bay Member of the Hoyle Bay Formation has high TOC content (approx. 5.0%) and high HI values (in excess of 600 mg HC/g Corg). It is followed by the Cape Richards Member and the Cape Caledonia Member of the Murray Harbour Formation (approx. 5.0% TOC).
Regional variations in the level of thermal maturity of Mesozoic sediments in the Sverdrup Basin are mainly a function of burial depth. Thermal subsidence, uplift, erosion and heat associated with periods of diapiric and igneous intrusions may have been responsible for the thermal maturity pattern in the Drake field. The Jurassic Jameson Bay, Ringnes and Deer Bay Formations are immature to marginally mature, and have limited oil-generation potential due to their high terrestrial input. The organic matter is these formations has good gas potential.     

西峰油田延长组烃源岩生烃潜力评价

通过Rock—Eval岩石评价、显徽镜下观察、有机元素分析、镜质体反射率等分析，对鄂尔多斯盆地西峰油田延长组烃源岩进行了地球化学特征研究及生烃潜力评价。分析结果表明：①延长组长7段、长8段烃源岩有机质丰度普遍较高，其中，中等和好烃源岩所占比例分别为94％和77％，长8段烃源岩样品有机质丰度与生烃潜力均高于长7段烃源岩样品，董志区烃源岩样品高于白马区烃源岩样品；②长7段、长8段烃源岩有机质类型多为腐殖-腐泥型；③长7段、长8段烃源岩有机质热演化普遍处于成熟阶段，具有生成大量原油的有利条件，这对该区油气源对比和油气勘探具有重要的价值。     

THE CRETACEOUS SERIES IN THE CHAD BASIN, NE NIGERIA: SOURCE ROCK POTENTIAL AND THERMAL MATURITY

The Chad Basin is the largest intracratonic basin in Africa, and one-tenth of its surface area lies in NE Nigeria. Thermal maturation (mean vitrinite reflectance) and organic-geochemical (Rock-Eval pyrolysis) studies have been carried out on Cretaceous shales from the Bima Formation, Gongila Formation and Fika Shale Formation. Samples were derived from the Kanadi and Albarka exploration wells, which are located about 76 km apart in the Nigerian sector of the Chad Basin.
The organic matter is predominantly gas prone (Type III kerogen). Its thermal maturity, assessed from vitrinite reflectance and Tmax, indicates that the Gongila Formation and the Bima Formation are within the "oil window", while the Fika Shale Formation is only partly within it. The "oil window", deduced from the mean vitrinite reflectance profile, occurs between 1,270m - 2,600m in the Kanadi well, and between 1,985m -3,690m in the Albarka well, with respective maturation gradients of 0.52 log%Rm/km (0.41%Rm/km) and 0.41 log%Rm/km (0.34%Rm/km). Eroded thicknesses amount to about 1 km.
The upper part of the Fika Shale Formation has the best source-rock potential in terms of its organic carbon content, but has low thermal maturity. The Gongila Formation is poor in organic carbon and its hydrocarbon potential may already have been exhausted. The Bima Formation is well within the "oil window", but has only limited potential as a source rock, because of the presence of clastic and inert materials. The potential for gas accumulations, however, exists.     

延长气田上古生界烃源岩评价及生排烃特征

延长气田位于鄂尔多斯盆地一级构造单元陕北斜坡中南部,是一个新探明的天然气富集区,对烃源岩的研究评价工作相对较薄弱,制约了该区的油气勘探进展。为此,通过对大量新探井岩心样品的有机质丰度、有机质类型、有机质成熟度等资料的综合分析,探讨了该气田上古生界烃源岩的展布特征、地球化学特征和生排烃特征。结果表明:①煤岩为该区最好的烃源岩,其有机碳含量介于60.18%~86.89%,累积厚度介于6~18 m,是该区上古生界天然气最主要的烃源岩,而泥岩则是天然气的第二位供应者,其中山西组泥岩属中等—很好的烃源岩,太原组和本溪组泥岩为好很好的烃源岩;②烃源岩干酪根的类型主要为腐殖型,其R。多大于2.0%,已进入过成熟—干气阶段;③上古生界烃源岩在中晚侏罗世—早白垩世末处于大量生排烃期,现今生烃强度介于(25~65)×10~8m~3/km~2,现今排烃强度介于(15~60)×10~8m~3/km~2,煤的生排烃强度大干泥岩。