In recent years, extensive low-resistivity shale reservoirs have been discovered in the Sichuan Basin, especially in the Lower Cambrian Qzs Fm (Qiongzhusi Formation). However, significant variations in gas production from these low-resistivity reservoirs across different regions have posed challenges in selecting and predicting sweet spots for the exploration and development of shale gas. Therefore, the shale samples were subjected to the analysis of a series of experiments, including core resistivity measurements, thermal simulations, and Raman spectroscopy, in order to explore the genesis mechanisms behind low-resistivity shale reservoirs and analyze their response characteristics to pore structure. The results show that HMG-OM (highly mature graphitized organic matter) and formation water stored in pores and fractures provide more conductive pathways, which are the primary mechanisms driving the low-resistivity characteristics of shale within the study area. As graphitization increases, shale resistivity significantly decreases, while maturity increases. Additionally, there are notable changes in the shale mineral composition and pore structure, including quartz breakage, clay minerals transforming into quartz, feldspar, and other minerals, and the dissolution of calcite and pyrite, which leads to a significant increase in inorganic pores. Meanwhile, the graphitization of OM causes the continuous deformation, shrinkage, and collapse of OM pores, resulting in poor development of OM pores. In this study, we integrate theoretical analysis and the experimental results and identify the Weiyuan-Ziyang area in southwestern Sichuan as a key area for future shale development in the Qzs Fm, with the aim of providing theoretical guidance for the exploration and development of shale gas in the Sichuan Basin.

The Triassic marine gas reservoir in the Moxi Gas Field is one of the large gas fields initially discovered in the Sichuan Basin. However, the origin of its natural gas has long been debated. To study the genetic types and origin of natural gas, the light hydrocarbons (LHs) composition, carbon isotopes, chemical compositions, and stable carbon and hydrogen isotopic compositions were analyzed in the Triassic strata of Moxi gas field in the Sichuan Basin. The natural gases from the second member of the Jialingjiang Formation (T2j2) and the first member of the Leikoupo Formation (T2l1) have dryness coefficients higher than 0.997 and contain low content non−alkane gases such as CO2 and N2. The δ13C1 values of natural gas in the Moxi (MX) gas field range from −35.3‰ to −32.9‰, the δ13C2 values range from −34.0‰ to −30.3‰, and the δD1 values range from −144‰ to −120‰. As for light hydrocarbons composition, the C7 LHs are dominated by the methylcyclohexane (MCH), and the C6−C7 LHs have low normal alkane contents. The individual carbon isotopes of light hydrocarbons have the characteristics of δ13C > −28‰. The origin identification indicates that the natural gas in this area is oil−type gas that results from the secondary cracking of crude oil. Our results show that the natural gas in T2j2 of the MX gas field is sourced from the shale gas of the Є1q, the T2l1 gas is a mixed−source gas from different thermal evolution stages of the Є1q source rocks, shale gas and oil−cracking gas. The mixing effect is the main reason for the reversed phenomenon (δ13C1 > δ13C2).

[Background]In recent years,promising helium-rich natural gas shows have been discovered in the Dong-ping gas field.However,the helium resources in the gas field exhibit lateral heterogeneity and vertical differential accu-mulation in multiple sequences,which restrict the further exploration of these resources.[Methods]By analyzing the lat-eral and vertical distribution characteristics of helium in the Dongping gas field,this study explored its origin and sources,analyzed the differences in geological backgrounds between helium-rich and helium-deficient gas reservoirs,and systematically summarized the differential enrichment pattern across different blocks within the Dongping gas field.[Results and Conclusions]In the Dongping gas field,helium-rich gas reservoirs are predominantly distributed in the shallowly buried Dongping-3 well block,where there is a significant positive correlation between helium and nitrogen concentrations.In contrast,the Dongping-1 and Dongping-17 well blocks exhibit gas reservoirs with a low helium con-centration.Helium in the Dongping gas field is typically of the crustal origin,derived primarily from ancient basement rocks including granites and granitic gneiss.The differential helium enrichment is jointly controlled by multiple factors,including source rock availability,groundwater dynamics,natural gas charging intensity,and tectonic framework.The Dongping-3 well block is characterized by U-and Th-rich ancient granites,active groundwater circulation,relatively weak natural gas charging,and traps located in structurally high parts,and the basement exhibits the highest helium gen-eration intensity of 1.02×10-12 cm3/(a·g).In this well block,small traps located in the structurally high parts were formed by the large-amplitude tectonic uplift during the Himalayan period.These traps are conducive to the upward migration of ancient formation water containing He and N2 at depth while also determining the small intensity of natural gas charging.Conversely,the Dongping-1 well block,despite its higher helium reserves,features weak groundwater hydrodynamics,intense natural gas charging,and traps in structurally low parts,which restrict helium migration and enrichment.The Dongping-17 well block shows the lowest helium concentration due to helium source rocks comprising schists,slates,and limestones with low U and Th concentrations and deeply buried traps.Based on research on differential helium en-richment in gas reservoirs with different basal lithologies and tectonic morphologies in the Dongping gas field,it is pre-dicted that the structurally high parts in the piedmont paleo-uplift and paleo-slope area of the Altun Mountain are poten-tially play fairways for helium enrichment.This prediction is expected to provide guidance for the subsequent helium ex-ploration and development work in the Qaidam Basin.

Asphaltene deposition during petroleum production presents persistent flow assurance challenges, necessitating advanced chemical solutions. This study elucidates the molecular mechanisms underlying asphaltene dispersion using acrylamide-based polymers through an integrated computational approach. Molecular dynamics simulations, geometric analysis, and density functional theory calculations were employed to investigate polymer-asphaltene interactions at multiple scales. A novel centroid triangle analysis method was developed to quantify dispersion efficiency, revealing that polyacrylamide (PAM) and chlorinated polyacrylamide (PAM-Cl) enhance asphaltene dispersion by 67.14 % and 94.49 %, respectively, at 298 K. Electronic structure analysis demonstrates that chlorine modification in acrylamide derivatives significantly alters molecular charge distribution, enhancing electrostatic interactions while reducing van der Waals forces. Quantum chemical calculations confirm that chloroacrylamide exhibits superior molecular activity, evidenced by a reduced HOMO-LUMO gap (5.18 eV vs. 4.94 eV) and increased electronegativity (3.249 vs. 2.673) compared to unmodified acrylamide. The findings establish electrostatic interactions as the dominant mechanism in asphaltene dispersion, providing fundamental insights for rational design of next-generation asphaltene inhibitors. This work advances our understanding of structure-activity relationships in asphaltene control chemicals, offering practical solutions for mitigating deposition-related challenges in petroleum operations.

Helium is a globally scarce strategic resource that is relevant to national economies and the development of high-tech industries, and China primarily depends on imported helium for its industrial applications. Therefore, there is an urgent demand for clarifying helium formation and enrichment patterns, searching for helium-rich fields, and realizing China's helium resource inventory and development potential. This article analyzes the reservoir characteristics and accumulation conditions of typical helium-rich fields in China, and clarifying the origin and source of helium as well as the main controlling factors of helium enrichment. It was recognized that helium in natural gas in China mainly comes from crustal sources. Relatively shallow buried ancient U–Th-rich granite basement or intrusion, large and stable ancient uplift or submarine formed in the early period, good overburden of huge thick paste-salt rock or mudstone cover, and channels connecting the basement and reservoir, were the main controlling factors of helium enrichment. Four types of helium-rich gas reservoirs, namely helium-rich conventional gas, helium-rich shale gas, helium-rich non-hydrocarbon gas, and helium-rich water-soluble gas, have been modeled and predicted to be helium-rich favorable exploration areas. Based on this analysis, the prospect of helium resource development in China has been analyzed. It was proposed that the exploration of helium-rich fields and the comprehensive development and utilization of medium- and low-abundance helium resources are important ways to increase the domestic helium production in China in the future.

准噶尔盆地油气发现程度差别大,天然气探明率较低.石炭系火山岩是盆地内目前天然气储量最多的层系,勘探证实其天然气成藏特征非常复杂.依据盆地内克拉美丽气田、五彩湾气田、阜康凹陷、滴北凸起等地区井的岩心、薄片鉴定及分析化验数据,在重点研究主力烃源岩松喀尔苏组b段特征的基础上,结合盆地内火山岩储层特征及天然气来源,分析石炭系火山岩天然气的成藏特征及勘探潜力.结果表明:石炭系烃源岩在五彩湾凹陷、滴水泉凹陷及东道海子凹陷等地区广泛分布,其中泥岩有机碳含量平均为1.58％;石炭系烃源岩有机质类型以Ⅲ型为主,大部分达到高成熟阶段,且火山活动增加了有机质的生烃能力.优质储集体以爆发相和溢流相为主,孔隙和裂缝发育,与上覆二叠系或石炭系内部致密层段形成良好的储盖组合,靠近凹陷深部地区具备形成规模气藏的成藏条件,滴南凸起、滴北凸起、北三台凸起和车拐地区具有较大勘探潜力.

Shale gas is a green, low-carbon and clean unconventional natural gas energy. China is rich in shale gas resources. Accelerating shale gas exploration and development is of great practical significance to improve China's energy structure and achieve the goal of "2030 carbon peak and 2060 carbon neutralization". The Ordovician Wufeng Formation to Silurian Longmaxi Formation in Sichuan Basin is the key strata for shale gas exploration and development in China. Based on the experimental analysis of shale gas in Wufeng Formation to Longmaxi Formation in Weiyuan, Changning, Zhaotong, Fuling and Weirong areas of Sichuan Basin, this paper systematically analyzes the geochemical characteristics of shale gas in Wufeng Formation to Longmaxi Formation, discusses the genesis of shale gas, the causes of hydrocarbon isotope inversion and the source of shale gas, and looks forward to the exploration prospects of shale gas resources in the basin. It has important guiding significances for shale gas exploration and development in Sichuan Basin and even in China. The results show that: (1) The shale gas of Wufeng-Longmaxi Formations is a typical dry gas, and the hydrocarbon isotopes are distributed in negative sequence. The carbon isotopes of alkane gas in Changning, Zhaotong and Fuling areas are heavier and have a higher degree of thermal evolution than those in Weiyuan and Weirong areas, and the rare gas is of crustal origin. (2) Shale gas of Wufeng-Longmaxi Formations is a thermogenic oil-typed gas at high-over mature stage, which is mainly the mixture of crude oil cracking gas and kerogen cracking gas. The hydrocarbon isotope inversion of alkane gas is mainly caused by the mixing of crude oil cracking gas and kerogen cracking gas at high-over mature stage, the exchange between formation water and methane at high evolution stage and so on. (3) The carbon isotopic values of methane in shale gas of Wufeng-Longmaxi Formations match the carbon isotopic values of kerogen in mudstones of Longmaxi Formation of Lower Silurian, which conforms to the law of carbon isotopic fractionation δ13Ckerogen>δ13Coil>δ13Calkane gas. (4) The total amount of marine, marine continental transitional and continental facies shale gas resources in Sichuan Basin is about 41.5 × 1012 m3, with broad exploration prospects in resource potential.

The increased water consumption for hydraulic fracturing and the volume of wastewater generated from shale gas and tight oil exploration are major environmental challenges associated with unconventional energy development. Recycling of the flowback and produced water for hydraulic fracturing is one of the solutions for reducing the water footprint of hydraulic fracturing and removing highly saline oil and gas wastewater. Here we investigated the implications of recycling saline wastewater for hydraulic fracturing by monitoring the natural gas production, flowback water volume, and the water quality of generated flowback water in shale gas wells from Changning gas field in Sichuan Basin, China. A comparison of two sets of shale gas wells, with six wells in each sub-group, from the same location in Changning gas field shows lower (similar to 20%) natural gas production and higher flowback water volume (similar to 18%) in wells that were fracked with recycled saline wastewater relative to wells that were fracked with fresh water after a year of production. Geochemical analysis suggests that hydraulic fracturing with saline wastewater increases the salinity of the wastewater and reduces the magnitude of watershale rock interactions. In spite of the direct economic consequences in reduction in natural gas production from recycling of wastewater for hydraulic fracturing, in areas where water scarcity could become a limiting factor for future large-scale shale gas development, hydraulic fracturing with recycled flowback water can be more beneficial than utilization of limited freshwater resources, as long as the higher saline flowback water is fully recycled.

四川盆地及周缘地区上奥陶统五峰组—下志留统龙马溪组富有机质页岩是我国页岩气勘探开发的主要层位,厚度20～60 m,该套富有机质页岩的时空展布差异明显.通过对重点剖面及钻井的岩芯观察、笔石生物地层划分、地化及矿物分析,明确了四川盆地及周缘不同地区富有机质页岩的时空展布特征,建立了3种富有机质页岩沉积演化模式:1)长宁—威远"三隆夹二洼"沉积演化模式:长宁地区富有机质页岩主要沉积于WF2—LM5,威远地区为LM1—LM8,隆起区域富有机质页岩沉积受到不利影响.2)黔渝地区的"渐进式"沉积演化模式:该区域呈现越靠近盆地内部,富有机质页岩沉积结束的时间越晚的趋势,焦石坝区域是富有机质页岩的沉积中心,其他区域厚度相对较薄.3)川东北地区的"稳定抬升型"沉积演化模式:位于盆地中心的巫溪2井区域的富有机质页岩厚度大,沉积持续时间长(WF2—LM9),盆地边缘区域富有机质页岩厚度明显变薄,区域呈现整体抬升趋势,随时间推移,富有机质页岩沉积范围越来越小.总体而言,富有机质页岩的沉积主要受广西运动的影响,富有机质页岩沉积中心有逐渐向北迁移的趋势,埃隆阶后仅威远和巫溪区域沉积富有机质页岩.研究成果对该地区页岩地层的精细对比具有重要的指导意义.

The Upper Ordovician Wufeng‐Lower Silurian Longmaxi and the Lower Cambrian Qiongzhusi shales are the major targets for shale gas exploration and development in China. Although the two organic‐rich shales share similar distribution ranges and thicknesses, they exhibit substantially different exploration and development results. This work analyzed the nanopore structures of the shale reservoirs in this region. Pore development of 51 shale samples collected from various formations and locations was compared using the petromineralogical, geochemical, structural geological and reservoir geological methods. The results indicate that the reservoir space in these shales is dominated by organic pores and the total pore volume of micropores, mesopores, macropores in different tectonic areas and formations show different trends with the increase of TOC. It is suggested that organic pores of shale can be well preserved in areas with simple structure and suitable preservation conditions, and the shale with smaller maximum ancient burial depth and later hydrocarbon‐generation‐end‐time is also more conducive to pore preservation. Organic pore evolution models are established, and they are as follows: ① Organic matter pore development stage, ② Early stage of organic matter pore destruction, and ➂ late stage of organic matter pore destruction. The areas conducive to pore development are favorable for shale gas development. Research results can effectively guide the optimization and evaluation of favorable areas of shale gas.

During the Paleogene–Neogene, the Qaidam Basin was a saline lacustrine basin so the biomarkers of hydrocarbon source rocks exhibited unique characteristics under the salinization conditions. Saturated hydrocarbons extracted from a large number of source-rock samples were analyzed using gas chromatography and mass spectrometry. The results showed that n -alkanes in the source rocks were evenly distributed between even and odd carbon numbers, isoprenoid alkenes were predominantly phytanes, and ratios of pristane to phytane (Pr/Ph) were low, mostly in the range from 0.2 to 0.8. Terpanes typically showed high contents of C 35 homohopane and gammacerane. Overall, the ratios of gammacerane to C 30 hopane (gammacerane/C 30 hopane) and C 35 –C 34 homohopane (C 35 /C 34 homohopane) exhibited a positive correlation. Differing concentrations of oleanane were detected. The relative content of C 27 and C 29 steranes in the hydrocarbon source rocks varied from 25 to 75%, and the relative content of C 28 sterane in a considerable number of samples was higher than 30%. C 27 –C 29 steranes generally showed an asymmetric V-shaped distribution, and the distribution of sterane/hopane and Pr/Ph ratios showed negative correlations. The salinity and reducibility indexes of the southern area of the Western Qaidam Basin were significantly higher than those of the northern area of the basin during the Oligocene–Miocene. Source rocks in the northern area were formed in a low-salinity and weakly reductive environment with type II 2 –III kerogen, whereas the hydrocarbon source rocks in the southern area formed in a high salinity and strongly reductive environment. The sedimentary water salinity and reducibility of the different areas were reduced in the following order: Hongliuquan, Yuejin, Shizigou, and Wunan–Lvcaotan. The best source rocks in this basin were developed in the Hongliuquan, Yuejin, and Shizigou areas with type II 1 –II 2 kerogen. This study lays a foundation for further understanding the geochemical distribution of the hydrocarbon source rocks and crude oil in addition to the characteristics of the oil source in Paleogene and Neogene.

Shale gas extraction through hydraulic fracturing and horizontal drilling is increasing in China, particularly in Sichuan Basin. Production of unconventional shale gas with minimal environmental effects requires adequate management of wastewater from flowback and produced water (FP water) that is coextracted with natural gas. Here we present, for the first time, inorganic chemistry and multiple isotope (oxygen, hydrogen, boron, strontium, radium) data for FP water from 13 shale gas wells from the Lower Silurian Longmaxi Formation in the Weiyuan gas field, as well as produced waters from 35 conventional gas wells from underlying (Sinian, Cambrian) and overlying (Permian, Triassic) formations in Sichuan Basin. The chemical and isotope data indicate that the formation waters in Sichuan Basin originated from relics of different stages of evaporated seawater modified by water-rock interactions. The FP water from shale gas wells derives from blending of injected hydraulic fracturing water and entrapped saline (Cl similar to 50,000 mg/L) formation water. Variations in the chemistry, delta O-18, delta B-11, and Sr-87/Sr-86 of FP water over time indicate that the mixing between the two sources varies with time, with a contribution of 75% (first 6 months) to 20% (>year) of the injected hydraulic fracturing water in the blend that compose the FP water. Mass-balance calculation suggests that the returned hydraulic fracturing water consisted of 28-49% of the volume of the injected hydraulic fracturing water, about a year after the initial hydraulic fracturing. We show differential mobilization of Na, B, Sr, and Li from the shale rocks during early stages of operation, which resulted in higher Na/Cl, B/Cl, Li/Cl, and Sr-87/Sr-86 and lower delta B-11 of the FP water during early stages of FP water formation relative to the original saline formation water recorded in late stages FP water. This study provides a geochemical framework for characterization of formation waters from different geological strata, and thus the ability to distinguish between different sources of oil and gas wastewater in Sichuan Basin.

Although there are many similarities between the shale of Cambrian Qiongzhusi Formation and Ordovician Wufeng Formation–Silurian Longmaxi Formation in South China, including total organic carbon content (TOC) and thickness, the drilling results of shale gas exploration are very different. One of the reasons is the difference of the nano-pores number developed in organic matter between them. In order to reveal the causes, the black shale of Upper Proterozoic Xiamaling Formation in North China, which is similar to the marine source rock in Sichuan basin, was selected for the thermal simulation experiment, and the pore size and volume of the samples before and after the experiment were acquired by scanning electron microscopy (SEM) and nitrogen adsorption isotherm measurement. Through the SEM photographs, we found that the sizes of the organic pores in algae, dispersed organic matter and organic matter associated with clay minerals get bigger with the increasing maturity. The total pore volume, micro-pore volume and meso-pore volume of the shale acquired by nitrogen adsorption isotherm measurement increase with the increasing maturity, too. However, under the overburden pressure, micro-pore volume decreases at high maturity stage, indicating the pores in organic matter might be compressed. It is considered that the pore volume in organic matter of the shale of Qiongzhusi Formation might be compacted under greater confining pressure, which may be the reason why the pore structures of the two sets of marine shale in South China are different.

Shale gas is likely to play a major role in China's transition away from coal. In addition to technological and infrastructural constraints, the main challenges to China's sustainable shale gas development are sufficient shale gas production, water availability, and adequate wastewater management. Here we present, for the first time, actual data of shale gas production and its water footprint from the Weiyuan gas field, one of the major gas fields in Sichuan Basin. We show that shale gas production rates during the first 12 months (24 million m3 per well) are similar to gas production rates in U.S. shale basins. The amount of water used for hydraulic fracturing (34,000 m3 per well) and the volume of flowback and produced (FP) water in the first 12 months (19,800 m3 per well) in Sichuan Basin are also similar to the current water footprints of hydraulic fracturing in U.S. basins. We present salinity data of the FP water (5000 to 40,000 mgCl/L) in Sichuan Basin and the treatment operations, which include sedimentation, dilution with fresh water, and recycling of the FP water for hydraulic fracturing. We utilize the water use data, empirical decline rates of shale gas and FP water productions in Sichuan Basin to generate two prediction models for water use for hydraulic fracturing and FP water production upon achieving China's goals to generate 100 billion m3 of shale gas by 2030. The first model utilizes the current water use and FP production data, and the second assumes a yearly 5% intensification of the hydraulic fracturing process. The predicted water use for hydraulic fracturing in 2030 (50-65 million m3 per year), FP water production (50-55 million m3 per year), and fresh water dilution of FP water (25 million m3 per year) constitute a water footprint that is much smaller than current water consumption and wastewater generation for coal mining, but higher than those of conventional gas production in China. Given estimates for water availability in Sichuan Basin, our predictions suggest that water might not be a limiting factor for future large-scale shale gas development in Sichuan Basin.

The source of the Lower Paleozoic natural gas in the Ordos Basin has been a highly controversial issue. Using data obtained from newly drilled wells, we present the geochemical characteristics of Lower Paleozoic natural gas in various regions of the Ordos Basin. The Lower Paleozoic natural gas is dominated by hydrocarbons, of which methane accounts for 40.17%–97.24%, and the heavier gaseous hydrocarbon (C2+) ranges from 0.01% to 9.72%. Non-hydrocarbon gases in the Lower Paleozoic gas reservoir are mainly CO2 and N2, 2%–10% for CO2 and 0.04%–48.56% for N2, higher than those in the Upper Paleozoic gas reservoir. This observation showed that the high CO2 and N2 content was related to the Ordovician marine carbonate rock deposits. The carbon and hydrogen isotopes of the methane, ethane, and propane in the Lower Paleozoic natural gas of the Ordos Basin showed various degrees of reversal, indicating the mixing origin of natural gas. In the central–eastern Ordos Basin, coal-derived gas from the Carboniferous–Permian (C-P) coal measure and oil-associated from the Lower Ordovician Majiagou Formation marine source rocks gas coexist, as well as mixtures of these two gases. For the Lower Paleozoic natural gas from the western margin of the basin, coal-derived gas coexist with oil-associated gas, but no mixing gas, in which coal-derived gas originated mainly from the C–P source rocks and oil-associated gas from the Lower Ordovician Kelimoli Formation and Middle Ordovician Wulalike Formation source rocks in the western margin of the basin. The Lower Paleozoic natural gas in the southern part of the Ordos Basin was mixing gas, and the oil-associated gas is the dominant one. The natural gas was originated from the Lower Ordovician Majiagou Formation source rocks in the central–eastern Ordos Basin and the Pingliang Formation mudstone and argillaceous limestone at the southern margin of the basin.

Identification of natural gas genesis and source for high-matured multiple natural gases is a great challenge in the exploration of deep–ultra deep and unconventional natural gases. In this paper, the genesis identification method system of multiple natural gases is enriched through new experimental techniques and comprehensive analysis of geological data. New indexes and charts of genesis identification for multiple natural gases were determined to distinguish the sapropelic kerogen degraded gas and oil cracking gas, accumulated and scattered liquid hydrocarbon cracking gas in different evolution stages, nitrogen, carbon dioxide of organic and inorganic origins, inert gases of crustal and mantled origins, coal-formed gas and oil-typed gas by helium, nitrogen, carbon dioxide and mercury content in natural gas. These indexes and charts have been successfully applied in the Sichuan, Tarim and Songliao basins to identify the natural gas genesis and source for complicated gas reservoirs. The research results have provided effective supports for the natural gas exploration in the Sinian–Cambrian ancient carbonate formations in the Sichuan Basin, deep formations in the Kuqa depression of the Tarim Basin, and deep volcanic formations in the Songliao Basin.

There hasn't been a clear understanding of the lower limits of petrophysical parameters of tight sandstone gas reservoirs so far. However, it is an important question directly related to exploration and development strategies. Research methods of the lower limits of petrophysical parameters are reviewed. The new minimum flow pore throat radius method is used to determine the lower limit of flow pore throat radius. The relative permeability curve method, irreducible water saturation method, and testing method, are used to determine the lower limits of porosity, permeability, and gas saturation. After the comprehensive analysis, the lower limits of petrophysical parameters of the Upper Paleozoic tight sandstone gas reservoirs in Ordos Basin are thought as follows: the minimum flow pore throat radius is 0.02 μm, the lower limits of porosity are 3%, the permeability is 0.02 × 10−3 μm2 and the gas saturation is 20%. Besides, the influence of formation pressure on porosity and permeability, the tight sandstone gas filling mechanism, and reservoir characterization petrophysical parameters of tight sandstone reservoirs are further discussed.

南祁连盆地烃源岩的研究程度低,烃源岩分子地球化学方面的研究滞后.利用气相色谱、气相色谱—质谱联用技术研究了南祁连盆地石炭系与上三叠统尕勒得寺组烃源岩的生物标志化合物特征,详细分析了烃源岩有机质的沉积环境、母质来源和成熟度等方面的信息.伽马蜡烷/C30藿烷为0.09～0.12,伽马蜡烷/0.5C31αβ (22R+22S)为0 38～0.57,Pr/Ph为0.65 ～1.16,表明烃源岩有机质的沉积环境为微咸的弱还原—弱氧化环境.丰富的三环萜烷和以C29为优势的“V”字形分布的规则甾烷说明有机质母质为以陆源高等植物为主的混合来源.大多数成熟度参数均达到平衡值,而C29ααα-20S/ (20S+20R)的值发生“倒转”,说明有机质的成熟度处于高成熟—过成熟阶段.

The total components and isotopes of rare gases as well as hydrocarbon gases for Dabei gas field are analyzed firstly, then their geochemical characteristics and genesis are discussed respectively, finally gas source correlation and their contributions are evaluated. The research results show that: (1) In Dabei gas field, methane is the main component, accompanying with a few N2 and CO2, as well as extremely low rare gases. In total component contents of rare gases, the He content is from 56.0 to 60.4 ppm with an average of 57.8 ppm and generally 1 order of magnitude higher than the air content value, while the Ne, Ar, Kr, and Xe contents are generally 1–3 orders of magnitude lower than the corresponding air content values. (2) The δ13C1 value in Dabei gas field usually ranges from −31.9‰ to −29.4‰. The δ13C2 value generally ranges from −24.2‰ to −19.4‰, which is obviously heavier than −28.5‰, The natural gases in Dabei gas field can be identified as typical coal-formed gas. (3) The 3He/4He value in natural gases is generally from (6.31–11.24) × 10−8 with an average value of 8.42 × 10−8. The 20Ne/22Ne value is from 9.563 to 9.734, and the 21Ne/22Ne value is from 0.0298 to 0.0307. The 40Ar/36Ar value is usually from 390 to 858 with an average value of 552, and the 38Ar/36Ar value is from 0.1955 to 0.2035. The 129Xe is relative loss, while the 132Xe is relative surplus. The comprehensive genesis identifications of He, Ne, Ar, and Xe indicate that rare gases are crustal derived genesis, mainly originating from the decay of related radioactive elements in crust. (4) The gas source correlation indicates that the natural gases in Dabei gas field are originated from humic coal series source rocks of Triassic-Jurassic, mainly contributed by Jurassic in vertical strata and coal rocks in type, coal rocks accounting for 63% and mudstones accounting for 37%.

利用露头、钻井及岩心等资料,以地球化学、储层、气体成因以及构造保存条件等为重点研究对象,对湖南省常德地区牛蹄塘组页岩气的成藏条件开展了系统分析.研究表明:该区域牛蹄塘组富有机质页岩具有机碳含量高、厚度大、热演化程度普遍较高的特点;页岩的有效孔隙度为2％～5％,储集空间主要以基质孔隙为主,朗格缪尔体积分布于1～3.5m3/t之间;盖层厚度较大(＞200m),具备形成页岩气的生、储、盖条件.分析了常德1井产水产气的原因,指出所产气、水主要产自牛蹄塘组底部富有机质页岩中的封闭裂缝体系中,处于地层水交替阻滞带,所产烃类气体主要为原油裂解气,非烃类气体主要为过成熟阶段产物,并混入了部分大气,氦气为壳源无机成因.明确了常德地区页岩气成藏过程及散失模式,认为构造破坏、地层水散失和扩散作用是页岩气散失的主要途径,页岩的含气性主要受构造及保存条件控制.优选常德1井以西(地层水交替阻滞带以下)保存条件较好的区域为页岩气分布的有利区,具有较大的资源潜力.