ABSTRACTIn Sichuan Basin, uranium (U) and thorium (Th) are more abundant in organic‐rich shale than in granitic rocks, suggesting that organic‐rich shale is a significant source rock for helium (He). However, the He generation potential of organic‐rich shale and He enrichment mechanisms in shale gas fields remain limited in understanding. Based on the He, U and Th concentration tests, fluid inclusion analysis in the Jiaoshiba shale gas field, it was found that the He concentrations in shale gas is 340–730 ppm. The helium‐rich shale gas (≥ 500 ppm) was primarily found in synclinal units. The biggest helium abundance area (0.27 m3/m2) is located at the core of the Jiaoshiba anticline. The He is not solely derived from Wufeng–Longmaxi shale itself, for the current helium abundance (0.15–0.27 m3/m2) exceeds its historical He generation intensity (0.063–0.104 m3/m2) calculated by the U and Th concentration of the shale. Low‐angle deep faults are more favourable for He capture than high‐angle deep faults. The generation intensity of hydrocarbon is 21,851–29,224 times greater than He, which indicates that the dilution of hydrocarbon to He in organic‐rich shale is more significantly than in common source rocks (3000 times). The He enrichment model in the study area includes three stages: continuous burial, fold‐dominated, and fault‐dominated stages. In the anticline zone, He is continuously accumulated as carrier gas migration. In the syncline zone, He is mainly accumulated as the migration of carrier gas along faults and the water flows the aquifer, at the fault‐dominated stage. He‐rich gas is preferentially accumulated in shallow gas reservoirs associated with deep faults, and the shale gas layers in synclinal zones adjacent to low‐angle deep faults.

Understanding helium migration in source rocks is critical to resolving constraints imposed by helium's weak sourcing on modern enrichment models. This work investigates the permeability behaviour of helium in granite and shale across the Sichuan Basin to elucidate their contrasting controls on helium accumulation. Basing on the permeability behaviour of helium and nitrogen in shale and granite in the southwest of Sichuan Basin, it is found: (1) Helium permeability decreases by 81.06%-98.03% under confining pressure escalation (2-60 MPa), exhibiting negative correlations with rock strength/water saturation and a positive correlation with porosity. (2) Single-phase helium systems maintain higher permeability than two-phase gas-water pore systems, where dissolution/exsolution cycling governs flow. At > 60% water saturation, gas properties no longer exert a dominant control over the sample's permeability. When water saturation > 60%, gas-phase dominance ceases-granites show solubility-driven permeability evolution, while shales remain compaction-controlled. (3) Granite permeability plunges about 95.7% when heated from 25 degrees C to 85 degrees C, attributed to thermal grain expansion reducing pore-throat volumes. (4) Subsurface helium transport progresses through three stages. In shallow burial stages, it is dominated by groundwater-driven dissolved helium migration. In the middle/deep burial stages, flow decelerates due to the Jamin effect and aqueous phase trapping, with permeability increasingly controlled by dissolution/exsolution cycling in both lithologies. (5) In the Weiyuan gas field, helium accumulation derives from water-dissolved migration during granite burial. Shales indirectly control enrichment through (i) post-maturation migration retardation via the Jamin effect/aqueous phase trapping and (ii) compartmentalisation of underlying helium-saturated aquifers. Bedding orientation governs shale permeability anisotropy, contrasting with granite's isotropic pore geometry.

Despite over 60 years of helium development in the Sichuan Basin, the mechanism of helium enrichment remains poorly understood. Helium-rich gas is primarily found as gas composition analysis in the fields. This study explores the relationship between helium distribution and two regional shale formations (the Qiongzhusi and Wufeng-Longmaxi formation), basing on the spatial distribution of these shales, structural profiles, and reported helium concentrations. Our findings indicate a typical trend of helium enrichment within the Sichuan Basin, where helium concentrations generally increase from the basin margins toward its center. The R/Ra ratios in the natural gas are consistently below 0.1, indicating that the helium mainly originates from the granite basement. The Wufeng-Longmaxi Formation is absent from central to western parts of this basin. The hydrocarbon generation intensity of this shale is 3,627.26 m³/m2, which is 25,896.7 times greater than its helium generation intensity (0.14 m³/m2). Its helium capture time is short (237 Ma). There is no obvious correlation between the distribution of helium concentration and Wufeng-Longmaxi shale. The Qiongzhusi shale extends across the entire Sichuan Basin. Its hydrocarbon generation intensity is approximately 57 m³/m2, which is 267.4 times greater than its helium generation intensity (0.27 m³/m2). Beneath this shale, the Pre-Sinian granite exhibits a helium generation intensity exceeding 0.51 m³/m2, acting as the primary helium source rock in the basin. The helium capture time of Qiongzhusi shale is 435 Ma. Helium concentration increases as the burial depth of the Qiongzhusi shale decreases, and helium becomes isotopically lighter in the direction of fluid potential drop. This indicates that helium enrichment in the Sichuan Basin is predominantly influenced by the Qiongzhusi shale. From maximum burial depth to present, helium solubility in water has decreased by approximately 63.6% and 54.3% in the Wufeng-Longmaxi and Qiongzhusi shale respectively, suggesting that uplift processes contributed to helium degassing into gas reservoirs. The regional shale influenced the long-distance migration of helium, although faults can alter this pathway. Faults may either promote helium accumulation in shallow gas fields, such as the Jinqiu gas field, or lead to helium loss, as observed in the southeastern region of the Sichuan Basin.

Abstract The Late Ordovician-Early Silurian period witnessed the second largest Phanerozoic mass extinction, Hirnantian glaciation and volcanic events. Wufeng, Guanyinqiao and Longmaxi formations were developed in South China across the Ordovician-Silurian transition.To infer the weathering conditions, provenance, tectonic setting of the source area in western South China during this period, we measured the mineralogical and geochemical characteristics of 42 samples of Wufeng-Longmaxi formations taken from Xindi No. 1 well, south west of Sichuan Basin. These shales and argillaceous limestones mainly consist of quartz, clay mineral, carbonate, feldspar, and minor amounts of pyrite. Geochemically, the rocks from three formations are enriched in CaO and MgO and slightly depleted in SiO2, Al2O3 and K2O. Chondrite-normalized rare earth elements (REE) patterns display a negative Eu anomaly, a slight enrichment in LREE and a flat HREE. Paleoweathering indices (CIA and PIA) and Th/U ratios indicate that the sediments experienced moderate-intense to weak chemical weathering in the source area. CIA values of the lower Wufeng Formation range from 64.88 to 70.88, indicating a warm and humid climate. Upward the CIA values on the top of Wufeng Formation decrease from 62.56 to 62.93, the CIA values of the Guanyinqiao and lowest Longmaxi formation are consistently low values (58.48-67.12) , suggesting a cold and dry climate which is consistent with Gondwana glaciation in Hirnantian period. Geochemical discrimination diagrams revealed that the rocks of the three formations were derived from felsic igneous source rocks and deposited in an active continental margin setting.

Although almost all the shale gas in China is exploited from marine shale (Wufeng–Longmaxi Formation) in Sichuan Basin and several prolific wells, it has also been obtained in Jurassic lacustrine shale. However, the reservoir conditions of the lacustrine shale are not well understood, which has impeded a breakthrough regarding lacustrine shale gas in Sichuan Basin. To probe the reservoir conditions of the lacustrine shale in Sichuan Basin, we take the Wufeng–Longmaxi shale and Dongyuemiao shale sampled from wells and outcrops as examples. A series of experiments were conducted, including TOC, XRD, FE-SEM, N2 adsorption, Micro-CT, vitrinite reflectance and bitumen reflectance. The results show that the pores in marine shale are mainly composed of organic-matter-hosted pores (OM pores). However, in the lacustrine shale, the pores are mainly composed of dissolution pores and intergranular pores. The marine shale is characterized by small-caliber and large-volume pores in which cluster pores are levitated in the shale as kites and connected by past channels. However, in the lacustrine shale, the cluster pores and the past channels are mainly arranged according to the flow channels in the vertical direction. The arrangement of the pores in the marine shale is obviously deformed by compaction. The lacustrine shale is characterized by under-compaction. It can be deduced that the sweet spots for lacustrine shale gas are likely located at the areas characterized by under-compaction resulting from fluid pressure conducted upward, such as the hinge zone of syncline or the core of anticline overlap on the gas reservoirs.

Helium is a very important strategic resource. As our helium gas external dependency has been more than 95%, the contradiction between the supply and demand of helium resources is very prominent. Thus the related helium resource evaluation needs to be carried out as soon as possible. In this paper, the authors summarized the present situation of helium gas exploration and the helium resources in the Sichuan basin and its surrounding areas. As the Sichuan Basin is the first region to realize the commercial utilization of helium gas in China. The helium-bearing natural gas is widely distributed in Sichuan Basin and its surrounding areas horizontal and vertically. The highly radioactive shale formation, basement granite, and uranium rock are developed, which have the common basis as helium source rock. Finally, the helium gas resource potential in the Sichuan basin and its adjacent areas were analyzed in this paper. And the main problems for helium gas exploration were summarized. Based on the characteristics of helium gas enrichment, the future focus in the study of helium gas was also given. The authors suggested investigating and analyzing the characteristics of helium in conventional gas fields and Paleozoic shale gas reservoirs in and around the Sichuan basin, investigating the distribution characteristics of helium, and comprehensively analyzing the mechanism of helium enrichment by establishing the helium-bearing natural gas features data set, and exploring the genesis and distribution of helium. These works would help to lay a firm foundation for future helium exploration and exploitation.

The permeability characteristics of natural fracture systems are crucial to the production potential of shale gas wells. To investigate the permeability behavior of a regional fault that is located within the Wufeng Formation, China, the gas permeability of shale samples with natural micro-fractures was measured at different confining pressures and complemented with helium pycnometry for porosity, computed micro-tomographic (µCT) imaging, and a comparison with well testing data. The cores originated from a shale gas well (HD-1) drilled at the Huayingshan anticline in the eastern Sichuan Basin. The measured Klinkenberg permeabilities are in the range between 0.059 and 5.9 mD, which roughly agrees with the permeability of the regional fault (0.96 mD) as estimated from well HD-1 productivity data. An extrapolation of the measured permeability to reservoir pressures in combination with the µCT images shows that the stress sensitivity of the permeability is closely correlated to the micro-fracture distribution and orientation. Here, the permeability of the samples in which the micro-fractures are predominantly oriented along the flow direction is the least stress sensitive. This implies that tectonic zones with a large fluid potential gradient can define favorable areas for shale gas exploitation, potentially even without requirements for hydraulic fracture treatments.

Pliensbachian-Toarcian lacustrine shales in the Sichuan basin is characterized by two organic matter-rich layers (Dongyuemiao and Da ' anzhai members) interlayered with an organic matter-poor layer (Ma'anshan member). These are promising target layers for shale oil and gas in China, and they are also a terrestrial sedimentary record for the Toarcian Oceanic Anoxic Event (T-OAE). Previous studies have mainly focused on this lacustrine shale only in the single inheritance sub-sag. Here, we studied the depositional environmental changes and their correlation with organic matter accumulation in the Pliensbachian-Toarcian lacustrine shale on the subaqueous paleo-uplift in the Sichuan basin based on lithofacies and geochemical analysis. We concluded that lake stratification and oxygen deficiency were gradually strengthened upward from Pliensbachian Dongyuemiao member to late Toarcian Da ' anzhai member. However, primary productivity is reduced. Chemical weathering was strongest during the early Toarcian stage (Ma'anshan member). The organic matter accumulation in these lacustrine shales is closely related to environmental changes caused by the Sichuan basin's tectono-sedimentary evolution and depositional conditions. The Pliensbachian Dongyuemiao member is consistent with high primary productivity and low terrigenous detrital input. In the case of the deposition of early Toarcian Ma'anshan member, the organic matter was difficult to preserve due to the high sedimentation rate and the lack of anoxic water conditions. However, the late Toarcian Da'anzhai member was primarily composed of chemical precipitation that was closely correlated with the climate changes during T-OAE. The organic matter accumulation in this member was positively correlated with salinity-induced stratification and elevated CO2 concentration.

川东地区下侏罗统自流井组东岳庙段富有机质泥页岩发育,且在局部地区已获工业页岩油气流,但尚未实现规模开发,其页岩油气富集机理研究滞后于生产实践.本文在野外调查和测试分析的基础上,对其沉积环境演化及页岩油气地质条件进行分析,并探讨其页岩油气富集主控因素,以期为实现东岳庙段页岩油气突破提供有益借鉴.结果显示:川东地区东岳庙段发育一个完整的水进水退沉积旋回,富有机质泥页岩主要发育于中部半深湖相,厚约15～30m,TOC平均为1.79％,以II型有机质为主,热演化程度较高,达凝析油—湿气阶段.以黏土矿物粒间孔和有机质孔为主,脆性矿物含量中等,脆性指数平均为62.1％.平均孔隙度为8.85％,而渗透率极低,均值仅0.239mD,呈现出"高孔低渗"特征,层内油气以侧向运移为主.其页岩油气的富集主要受富有机质泥页岩分布、热演化程度和裂缝发育条件的控制.推论垂向富有机质泥页岩连续发育的现今油气低势区是川东地区东岳庙段潜在的页岩油气高产区.

奥陶—志留交替时期是地球历史时期中的关键时期,该时期华南地区沉积的五峰组—龙马溪组黑色页岩是现阶段我国页岩气勘探的重点层位,多套斑脱岩存在于黑色页岩内,指示该时期研究区经历过多期连续的火山活动.本文选取了四川盆地东部华地1井和武隆黄莺乡五峰组—龙马溪组剖面,以黑色页岩和斑脱岩为研究对象,通过野外考察、元素地球化学等分析方法,系统地分析了有机质富集的主控因素(陆源输入、古生产力、古氧化还原条件),并在此基础上分析斑脱岩与页岩有机质富集间的关系.结果显示,研究区五峰组—龙马溪组黑色页岩TOC呈高-低-高模式,氧化还原指标(V/V+Ni、V/Cr、Ni/Co)表明水体经历了厌氧-富氧-厌氧的过程,生产力指标(Cu、Babio、Sibio)、陆源输入指标(Ti/Al、Zr/Al、Th/Al)表明五峰和龙马溪组具较高的生产力和陆源输入,观音桥组较两者均低,三者与有机碳的相关关系反映氧化还原条件对有机质富集作用最大,生产力次之,陆源输入最弱.从斑脱岩发育特征与有机碳、生产力和氧化还原条件的关系看,频繁的火山活动可能对五峰和龙马溪组有机质的保存产生双促作用,一是为海洋提供营养物质,提升其生物生产力;二是火山灰飘落至海水表面阻止了部分光照进入,海底缺氧环境加剧,造成生物大量死亡并落入海底,作为有机质埋藏.

扬子地台内晚奥陶世末—早志留世初五峰—龙马溪组内沉积了多层钾质斑脱岩,但对于该时期扬子地台西缘钾质斑脱岩的研究报道相对较少.本文旨在通过对云南大关地区新地2井五峰—龙马溪组内沉积的钾质斑脱岩进行矿物学及地球化学分析,进一步确定扬子西缘该时期钾质斑脱岩原始岩浆类型及其所产生的构造环境.矿物学特征表明,钾质斑脱岩主要由黏土矿物和非黏土矿物组成,其中黏土矿物由伊利石和伊蒙混层组成,非黏土矿物以石英、长石、方解石、白云石和黄铁矿等为主.钾质斑脱岩主量元素以高K2O,低TiO2为特征,微量元素特征表现为富集Rb、Ba、Th、U等元素,Ti、P元素相对亏损,Ti/Th值指示了酸性火山灰的性质;ΣREE在(49.86～209.43)×10-6;与球粒陨石相比,轻稀土轻微富集、具Eu负异常,无Ce异常;在Nb/Y-Zr/TiO2图解中,数据点主要落在安山岩和粗面英安岩之间,表明钾质斑脱岩源岩浆性质为中酸性岩浆;依据微量元素特征和构造环境判别结果,初步认为原始岩浆可能形成于岛弧环境,其火山灰来源可能与扬子北缘早古生代秦岭洋闭合过程中的板块碰撞有关.

作为油气目标勘探的最主要技术手段,地震勘探具有资料覆盖面广、技术手段灵活多样、(储层)预测精度高等特点.地震解释的目的是为了从地震数据中提取更多的信息进行地下构造解释以及地层和岩性特征的描述.在构造地质理论的指导下,充分运用测井、地质、地震资料,综合利用地震解释方法,建立川东北地区构造圈闭识别技术流程,在广安地区五峰组构造圈闭识别中取得了较好的应用效果.

南羌塘拗陷中侏罗统布曲组结晶白云岩作为盆地最优质的储层是通过埋藏成岩过程中封闭条件下的白云石化作用形成的,岩石所具有的高孔隙度与封闭系统中白云石化反应有关.根据对羌资11井和羌资12井布曲组的岩石结构分类、碳氧同位素组成及温度计算、流体包裹体均一温度等分析结果,可以认为:结晶白云岩碳同位素值分布区间较窄(2.86‰ ～4.27‰),氧同位素值随着白云石晶体变粗(自形程度变差)逐渐偏负(-3.27‰ ～-8.17‰),显著低于保留原始组构的白云岩,表明结晶白云岩碳源来自于先驱灰岩中的碳,其白云石化作用应是在远离大气水的封闭成岩环境中进行;结晶白云岩流体包裹体均一温度主峰值区间为90～140℃,且随着白云石晶粒变粗(自形程度变差),均一温度呈升高的趋势,与氧同位素计算温度变化趋势一致,表明白云石化作用过程是在封闭的条件下进行,白云石随地热增温而生长,并非受外来流体的影响.开放系统中的白云石化作用对油气储集空间的形成没有实际意义,而埋藏成岩过程中封闭系统的白云石化是形成南羌塘拗陷优质储层最为重要的成岩机制.

Shale is a type of fracture-prone rock, but few regional faults are observed in shale strata. Here, we investigate a regional detachment fault in the Middle-Upper Yangtze (MUY) to understand the formation mechanism of a special regional fault in shale strata. Based on a lithological, mineralogical, and mechanical study as well as semi-quantitative model of displacement, we found that the formation of this detachment fault is closely related to the lithological association and flexural slip processes. The lithological association of this detachment fault is characterized by two thick competent layers separated by a thin weak interlayer at both the macroscopic and microscopic scales. When these layers are folded, the detachment fault zone is commonly present in a thin weak interlayer, namely, the Wufeng Formation at the macroscopic scale, and primarily along interfaces in laminar siliceous shales (LSS) and secondarily in K-bentonite interlayers within the LSS at the microscopic scale. The regional fault zone is characterized by parallel to strata surfaces and abrupt contacts with the protolith. The fabric of the fault core is obviously controlled by the flexural slip intensity and the number of slip events, as well as their direction and structural position. The natural shale gas obtained from Well HD-1 has proven that this regional detachment fault in shale strata is not only a migration pathway for hydrocarbons but also acts as an adsorption state reservoir for free gas from other areas. This regional detachment fault in shale strata is likely to advance the shale gas industry and to expand the exploration of conventional gas.

The annual output of shale gas from the Wufeng-Longmaxi formations in South China reached 15.4 × 109 m3 in 2019, which makes Sichuan basin the second-largest shale gas producing area in the world. Based on the data of more than 1000 shale samples of the Wufeng-Longmaxi formations taken from typical drilling and outcrop profiles in the Weiyuan, Changning, Fuling, and Wuxi areas in South China, the characteristics of differential enrichment of shale gas are analyzed and the main controlling factors are discussed. The study shows that the shale gas from the Wufeng-Longmaxi formations in South China has some differential enrichment characteristics in both vertical and lateral orientations. In vertical orientation, sweet-spot intervals of shale gas developed concentratedly sweet-spot. The key parameters (e.g., thickness, gas content, TOC content) in the sweet-spot intervals vary greatly in regional aspect, among which they are better in the Changning and Fuling areas. The gas contents and TOC contents of the Wufeng-Longmaxi shale in different areas have good positive correlations, indicating that the abundance of organic matters (TOC content) is a key factor that affects the degree of shale gas enrichment (gas content). The high primary productivity of marine surface water during the shale deposition period of the Wufeng-Longmaxi formations is an important prerequisite for the generation of large amounts of organic matters. However, in relatively stable tectonic zones with weak faults development, euxinic bottom water condition is the key factor controlling the formation of sweet-spot intervals of shale gas vertically and the distribution of sweet-spot area laterally, that is the key factor for the differential enrichment of Wufeng-Longmaxi shale gas.

由于缺乏对四川盆地西南缘永善-大关地区五峰组-龙马溪组生物地层的详细划分与对比,黑色页岩分布时限及其沉积背景不明确.对新地2井五峰组-龙马溪组黑色页岩岩心开展生物地层研究,识别出了从上奥陶统凯迪阶上部WF1 Dicellograptus complanatus带至志留系兰多维列统埃隆阶顶部LM8 Stimulograptus sedgwickii带的9个生物带和组合.新地2井与宁211井、焦页1井、威202井、巫溪2井黑色页岩生物地层对比结果显示,新地2井的顶界与宁211井、焦页1井黑色页岩笔石带相近,但与威202井、巫溪2井相比低了1个笔石带.结合TOC值标定,新地2井富有机质页岩沉积期为WF2-LM6笔石带,其顶界高于宁211井的LM4笔石带.在笔石生物地层框架内对比了各井黑色页岩的沉积厚度、沉积速率及TOC值,探讨了它们的沉积演化差异及构造背景.靠近古隆起或古陆的沉积区,海侵-海泛稳定期时间呈缩短的趋势,富有机质页岩上界可低至LM5笔石带或以下;远离古隆起或古陆的沉积区,富有机质页岩上界可达LM8-LM9笔石带.受沉积水体深浅差异及古隆起陆源碎屑输入的影响,威远、焦石坝及巫溪地区出现了沉积分异现象.阶段性的海退事件及古隆起的状态变化(隆升与扩大)是广西运动的构造响应.

晚奥陶世—早志留世之交是地球历史时期中的关键时段,该时段伴有全球生物大灭绝、冈瓦纳冰川以及火山事件.晚奥陶世末期的冰川事件历时相对较短,在中国尚未找到冰川存在的直接证据.为了更好地研究奥陶—志留纪交替时期是否存在古气候的变化,选取了川西南地区新地2井岩心中新鲜的上奥陶统五峰组—下志留统龙马溪组泥页岩样品,通过其主量、微量及稀土元素特征分析,采用多种化学风化指数判定源区风化作用强度及古气候条件.新地2井五峰—龙马溪组所有岩石样品成分变异指数(ICV)均大于1,表明源岩成分成熟度低,属构造活动时期的首次沉积.稀土元素表现为轻稀土富集、重稀土平坦并伴有明显的负Eu异常,配分模式与花岗岩相似,表明源岩以亲花岗岩、长英质为主;A-CN-K图解、主量元素Al2O3/TiO2值、微量元素Cr/Zr值和Th/Sc值也体现长英质成分为主的物源特征.化学蚀变指数(CIA)、化学风化指数(CIW)和斜长石蚀变指数(PIA)等多种化学风化作用指标均指示,晚奥陶世—早志留世古风化作用强度经历中等—低等—中等、古气候温暖湿润—寒冷干燥—温暖湿润的变化过程.CIA指数的低值指示的五峰组顶部(平均值64.14)、观音桥组(平均值61.7)和龙马溪组底部(平均值64.61)即赫南特期存在短暂的寒冷气候,间接证实了冈瓦纳冰川作用在中国华南地区存在相应的地球化学记录.

The Late Ordovician-Early Silurian transition was a critical interval in Earth's history, marked by mass extinction, the Gondwana glaciation and volcanic events. Here, we present mineralogical and geochemical characteristics across the Ordovician-Silurian boundary (Wufeng, Guanyinqiao and Longmaxi formations) from the Huadi No. 1 well, in the Sichuan Basin, in order to explore the paleoweathering, provenance, tectonic setting and paleoclimatic conditions of the source area. Thin sections, XRD (X-ray diffraction) data and major element results reveal that the rocks were abundant in clay minerals, quartz, minor feldspar, pyrite and carbonate minerals. The samples have similar chondrite-normalized REE patterns to those of PAAS, which are characterized by slight LREE enrichments and accompanied by flat HREE trends with weakly negative Eu anomalies. Paleoweathering indices (CIA and PIA) suggest that the sediments experienced weak to moderate chemical weathering in the source area. CIA values in the lower Wufeng formation range from 67.11 to 72.17, indicating a warm and humid climate, the CIA values in the upper Wufeng formation decrease from 70.35 to 66.15, and the CIA values in the Guanyinqiao and lower Longmaxi formation are persistently low (56.64–62.87), suggesting a cold and dry climate, which is consistent with the widespread presence of glaciation in the Hirnantian period. Further upward in the upper Longmaxi formation, the CIA returns to a high value (65.59), which may reflect that the climate started getting warm and glaciation had finished. Fluctuations in CIA values reflect that the climate shifted from warm to cold and then to warm again during the end Ordovician-early Silurian time period. The A-CN-K triangular diagram and SiO2-Al2O3/TiO2, TiO2-Zr, and La/Th-Hf bivariate diagrams indicate that the provenance of the rocks from the three formations was primarily felsic igneous rocks. Discriminant-function diagrams and La-Th-Sc, Th-Co-Zr/10 and Th-Sc-Zr/10 triangular diagrams show that the clastic sediments of the Wufeng-Longmaxi formations were derived most likely from an active continental margin. Finally, across the Late Ordovician-Early Silurian, tectonic activity and the end of the Ordovician glaciation dominantly controlled the deposition of black shales and siltstones in the Wufeng-Longmaxi formations of South China.

基于Xd2井和Ydd3井奥陶系五峰组-志留系龙马溪组岩心测试结果,结合邻区资料,总结滇东北地区木杆向斜黑色页岩岩性、分布规律、有机地球化学、储层及含气性特征,评价木杆向斜页岩气资源潜力.木杆向斜五峰组-龙马溪组一段主要为深水陆棚相黑色碳质泥页岩和粉砂质泥岩,其中龙马溪组一段可以分为1亚段、2亚段和3亚段,页岩优质段(总有机碳含量大于2.0％)厚40～70 m,平均有机碳含量为3.00％～3.61％,干酪根碳同位素值-30.21‰～-27.01‰,有机质含量高、类型好,等效镜质体反射率(VRo)为2.73％～2.79％.矿物组成具有较低含量的石英和长石,较高含量的碳酸盐岩和黄铁矿,由下至上,石英、碳酸盐岩和黄铁矿含量降低,长石和黏土含量增加.页岩孔隙度为2.39％～8.53％,横向渗透率(0.000 01～15.0) ×10-3 μm2,以中等孔隙为主,低-特低渗透率,孔隙类型主要为有机质演化形成的介孔和微孔.木杆向斜五峰组-龙马溪组页岩埋深约1 500～2300m,含气面积125.55 km2,资源量999.93×10s m3,主力含气层段位于五峰组上段-龙一段1亚段,厚度38～43 m,平均总含气量2.95～4.31 m3/t.木杆向斜五峰组-龙马溪组页岩厚度大,横向上和纵向上连续分布,埋藏适中,具有良好的页岩气资源潜力.