Journal of Natural Gas Geoscience最新文献

{"title":"Hydrocarbon-generating potential of the Middle Permian Lucaogou source rocks in the Gucheng Sag, Junggar Basin, China","authors":"Deyu Gong ,&nbsp;Yan Han ,&nbsp;Tanguang Fan ,&nbsp;Xinning Li ,&nbsp;Chuanmin Zhou ,&nbsp;Shoqing Wang ,&nbsp;Ruiju Wang ,&nbsp;Wei'an Wu ,&nbsp;Yihao Miao","doi":"10.1016/j.jnggs.2025.03.002","DOIUrl":"10.1016/j.jnggs.2025.03.002","url":null,"abstract":"<div><div>A billion-ton mega shale oil field has been discovered in the Jimsar Sag, located in the Eastern Uplift of Junggar Basin, which reveals the good hydrocarbon-generating potential of the source rocks in the Middle Permian Lucaogou Formation. This paper systematically evaluates the hydrocarbon-generating potential and formation environment of the Lucaogou source rocks in the Gucheng Sag, which is adjacent to the Jimsar Sag, and draws the distribution range of the source kitchen, and compares them with those of the Lucaogou source rocks in the Jimsar Sag. The results show that the kerogen type of Lucaogou source rocks in the Gucheng Sag is mainly of type II/III–III, dominated by good–excellent source rocks, and the type and abundance are slightly inferior to those in the Jimusar Sag. In the Middle and Late Jurassic, the Lucaogou source rocks in the Gucheng Sag entered the hydrocarbon-generating threshold, and now, the area entering the main oil-generating window reaches 212 km². Although both of them are lacustrine deposits, the Lucaogou source rocks in the Gucheng Sag have slightly higher Pr/Ph, Ts/(Ts + Tm), C₁₉/C₂₁ tricyclic terpane, C₂₄ tetracyclic terpane/C₂₆ tricyclic terpane ratios, and somewhat lower C₂₈ regular sterane content than the Jimsar Sag, suggesting that Lucaogou source rocks were deposited in an oxidizing–reducing transitional environment of a specific salinity in the Gucheng Sag. There was a certain amount of terrestrial higher plant input in addition to the contribution of algal and microbial biota in the Lucaogou source rocks in the Gucheng Sag^. The Lucaogou source rocks have developed four centers with a thickness greater than 160 m in the Gucheng Sag, covering a total area of about 420 km². In the southern part of the sag, three hydrocarbon-generating centers with an oil-generating intensity greater than 2000 × 10³ t/km² have developed, covering a total area of 130 km². The research results further strengthen the resource base of the Middle Permian petroleum system in the Junggar Basin and lay the foundation for the next step of petroleum exploration in the Gucheng Sag.</div></div>","PeriodicalId":100808,"journal":{"name":"Journal of Natural Gas Geoscience","volume":"10 2","pages":"Pages 87-100"},"PeriodicalIF":0.0,"publicationDate":"2025-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143869153","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Application of carbon and hydrogen isotopes in the study of natural gas origins","authors":"Yunyan Ni ,&nbsp;Jinchuan Zhang ,&nbsp;Limiao Yao ,&nbsp;Guoliang Dong ,&nbsp;Yuan Wang ,&nbsp;Li Wang ,&nbsp;Jianping Chen","doi":"10.1016/j.jnggs.2025.02.001","DOIUrl":"10.1016/j.jnggs.2025.02.001","url":null,"abstract":"<div><div>Different types of natural gas exhibit distinct carbon and hydrogen isotopic compositions, making these isotopic compositions crucial indicators for identifying gas origins. With ongoing advancements in natural gas exploration technology and the increasing volume of exploration data, our understanding of natural gas origins and sources continues to deepen, and how to update and verify the existing data to ensure the applicability of gas genetic diagrams has become crucial. This study comprehensively analyzes the stable carbon and hydrogen isotope characteristics of different genetic types of natural gases in Sichuan, Tarim, Ordos, Turpan-Hami, Songliao, Northern Jiangsu, Sanshui, Qaidam, and Bohai Bay basins in China, together with abiotic gases from the Lost City of the Middle Atlantic Ridge, and the genetic diagrams related to commonly used carbon and hydrogen isotopes are evaluated. The study yields the following four conclusions: (1) The carbon isotopic values of methane (δ¹³C₁), ethane (δ¹³C₂), propane (δ¹³C₃) and butane (δ¹³C₄) of natural gases from China are from −89.4‰ to −11.4‰ (average of −36.6‰), −66.0‰ to −17.5‰ (average of −29.4‰), −49.5‰ to −13.2‰ (average of −27.3‰), −38.5‰ to −16.0‰ (average of −25.6‰), respectively. (2) The hydrogen isotopic values of methane (δD₁), ethane (δD₂) and propane (δD₃) of natural gases from China range from −287‰ to −111‰ (average of −177‰), −249‰ to −94‰ (average of −158‰), and −237‰ to −75‰ (average of −146‰), respectively. (3) The carbon and hydrogen isotopic distribution patterns among methane and its homologues of natural gases in China are mainly in positive order (δ¹³C₁&lt;δ¹³C₂&lt;δ¹³C₃&lt;δ¹³C₄, δD₁&lt;δD₂&lt;δD₃). In most natural gas samples, the fractionation amplitude between methane and ethane is greater than that between ethane and propane (Δ(δ¹³C₂−δ¹³C₁) &gt; Δ(δ¹³C₃−δ¹³C₂), Δ(δD₂−δD₁) &gt; Δ(δD₃−δD₂)). (4) The δ¹³C₁–δ¹³C₂–δ¹³C₃, the δ¹³C₁–δD₁, δ¹³C₁–C₁/C₂₊₃, Δ(δ¹³C₂−δ¹³C₁)–Δ(δ¹³C₃−δ¹³C₂) and Δ(δD₂−δD₁)–Δ(δD₃−δD₂) diagrams, can be used to identify the gas origin in many different cases, and the combined application between different charts can enhance the identification effect.</div></div>","PeriodicalId":100808,"journal":{"name":"Journal of Natural Gas Geoscience","volume":"10 2","pages":"Pages 75-85"},"PeriodicalIF":0.0,"publicationDate":"2025-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143869152","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Geochemical characteristics and genesis of the Paleozoic natural gas in the southern Ordos Basin, China","authors":"Tao Zhang ,&nbsp;Xiaofeng Wang ,&nbsp;Kai Lu ,&nbsp;Yiran Wang ,&nbsp;Xiaoyan Chen ,&nbsp;Wen Zhang ,&nbsp;Xiaohui Jin ,&nbsp;Qingqiang Meng ,&nbsp;Juan Zhang","doi":"10.1016/j.jnggs.2025.03.001","DOIUrl":"10.1016/j.jnggs.2025.03.001","url":null,"abstract":"<div><div>The geochemical characteristics of the Paleozoic natural gas in the southern part of the Ordos Basin shows significant differences from those in the northern part. These differences lead to the increase in dryness coefficient and a heavier carbon isotope composition of methane attributed to the increase in organic matter maturity of the source rocks. Additionally, the Upper Paleozoic natural gas in the southern basin contains a higher carbon dioxide (CO₂) gas content, and exhibits a common phenomenon of methane and ethane carbon isotope composition inversions. This paper employs gas geochemistry as the principal analytical method to systematically compare the north-south differences in the Paleozoic natural gas composition and to explore its origin and source. The findings indicate that the Upper Paleozoic natural gas in the southern basin mainly composed of highly over-mature coal-type gas. However, certain gas geochemical indicators suggest the presence of lower paleomarine hydrocarbon sources in specific areas. The observed inversion of methane and ethane carbon isotope composition in the Upper Paleozoic natural gas in the southern basin is attributed to the mixing of different types of natural gas. Specifically, the varying degrees of mixing with the Lower Paleozoic oil-type gas—characterized by a higher ethane content and lighter ethane carbon isotope values—are identified as the primary cause of the inversion of carbon isotopes. Furthermore, geochemical indicators of natural gas in the lower Paleozoic in the southern basin strongly reflect typical marine hydrocarbon source characteristics. While these gases predominantly originate from marine source rocks, a minor contribution from the Upper Paleozoic coal-type gas cannot be entirely ruled out.</div></div>","PeriodicalId":100808,"journal":{"name":"Journal of Natural Gas Geoscience","volume":"10 2","pages":"Pages 101-109"},"PeriodicalIF":0.0,"publicationDate":"2025-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143869093","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Hydrate occurrence identification of shallow loose sediments in deep water and its saturation calculation","authors":"Jun Zhao ,&nbsp;Chao Zheng ,&nbsp;Jianxiang Pei ,&nbsp;Di Tang ,&nbsp;Jiang Jia","doi":"10.1016/j.jnggs.2025.03.003","DOIUrl":"10.1016/j.jnggs.2025.03.003","url":null,"abstract":"<div><div>The Chinese offshore area holds vast reserves of deepwater and shallow gas hydrates. However, due to the geological looseness of deepwater and shallow layers, the absence of tight sealing layers, and the high heterogeneity of gas hydrate reservoirs, identifying the occurrence state of gas hydrates remains challenging, greatly impeding the accurate prediction of gas hydrate saturation. Based on the acoustic-electric response characteristics of deepwater and shallow gas hydrates, this study employs the intersection method of resistivity and longitudinal wave velocity diagrams to identify the occurrence state of gas hydrates. The pore volume of gas hydrate reservoirs is calculated using a density formula corrected for mud content. Gas hydrate saturation in the YL target area of the Qiongdongnan (QDN) Basin is predicted using three methods: the mud-corrected resistivity method, the equivalent medium method, and the joint inversion method, finding the minimum combined error of acoustic and electric data. The results indicate that the predicted values using the joint inversion method in the YL target area of the QDN Basin are closest to the measured values obtained from the chloride ion concentration method, with prediction errors ranging from 0.09 % to 14.89 % and an average error of 6.85 %. These findings suggest that selecting an appropriate acoustic-electric joint inversion saturation calculation model, based on the determination of hydrate occurrence states, can significantly improve the accuracy of hydrate saturation prediction. This approach provides a realiable method for calculating hydrate saturation in the deepwater and shallow sediments.</div></div>","PeriodicalId":100808,"journal":{"name":"Journal of Natural Gas Geoscience","volume":"10 2","pages":"Pages 125-135"},"PeriodicalIF":0.0,"publicationDate":"2025-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143869761","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Geochemical and petrophysical characterization of the Midra Shale, Qatar","authors":"Syed Oubee Khadri ,&nbsp;Ahmed Hamza ,&nbsp;Ibnelwaleed A. Hussein ,&nbsp;Hamad Alsaad Alkuwari ,&nbsp;Fadhil Sadooni","doi":"10.1016/j.jnggs.2025.02.002","DOIUrl":"10.1016/j.jnggs.2025.02.002","url":null,"abstract":"<div><div>Shale gas is considered one of the promising unconventional gas reservoirs that would help meet the current demand for natural gas as a clean energy resource. Qatar has several shale gas reservoirs from diverse epochs, including the Eocene Midra Shale. Outcrop samples of Midra Shale were collected from the Umm Bab and Dukhan areas, and multiple measuring and geochemical analysis techniques were utilized to characterize the mineralogy, microstructure, and pores type. X-ray diffraction (XRD) mineralogy analysis and X-ray Fluorescence (XRF) indicated that palygorskite is the dominant clay in Midra Shale. The mineralogy of Midra Shale includes other minor minerals such as calcite, quartz, and halite, as well as low content of other clays, including sepiolite, smectite, and illite. Although the Midra Shale contains many elements, such as shark teeth and large foraminifera that support deposition under marine conditions, the existence horizons of laminated shale designate mixed marine continental depositional settings. Scanning electron microscope (SEM) images revealed various types of pores in Midra Shale, such as intragranular, intergranular, and organic pores. The geochemical analysis revealed that the Dukhan section is poor in organic matter and has low potential as a source rock for oil or gas. In contrast, the Umm Bab Section has a relatively high amount of organic carbon, making it a potential source rock.</div></div>","PeriodicalId":100808,"journal":{"name":"Journal of Natural Gas Geoscience","volume":"10 2","pages":"Pages 111-124"},"PeriodicalIF":0.0,"publicationDate":"2025-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143869094","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Reservoir characteristics and geological implications of marine sandstone on the periphery of Awati Sag, Tarim Basin, China: Case study of Upper Ordovician-Lower Silurian Kepingtage Formation","authors":"Ronghu Zhang ,&nbsp;Chaofeng Yu ,&nbsp;Zhao Yang ,&nbsp;Ran Xiong ,&nbsp;Fengqin Zhi","doi":"10.1016/j.jnggs.2024.12.001","DOIUrl":"10.1016/j.jnggs.2024.12.001","url":null,"abstract":"<div><div>The marine-origin source rocks on the periphery of the Awati Sag in the western Tarim Basin hold significant potential for hydrocarbon resources. However, the developmental level of marine sandstone reservoirs remains a key factor limiting the hydrocarbon exploration across the Keping thrust nappe belt along the western margin of the Awati Sag. This study focuses on the Upper Ordovician-Lower Silurian Kepingtage Formation sandstone through a multi-factor comprehensive approach, integrating data from outcrops, drilling, seismic surveys, and experimental analyses. Is the study clarifies that the Kepingtage Formation in the western margin of the Awati Sag is predominantly characterized by an early tide-dominated sedimentary system transitioning into late littoral deposition, resulting in tight sandstone reservoirs of sufficient thickness. The Kepingtage Formation sandstone is mainly composed of lithic sandstone, followed by lithic quartz sandstone. It exhibits low compositional maturity but high textural maturity, with well-developed intergranular pores and structural fractures. Porosity generally generally ranges from 6% to 10%. Class-IV reservoirs dominate, followed by Class-III and a few Class-II reservoirs. Reservoir quality is mainly controlled by sedimentary microfacies and structural compression. The reservoir rocks of sufficient scales of the delta and foreshore sandstone are more developed in the backward-breaking zone of the thrust nappe belt and the western margin slope of the Awati Sag. In contrast, the northwestern margin slope of the Awati Sag tends to develop fault-block oil and gas reservoirs as well as updip pinch-out sandstone oil and gas reservoirs. The favorable play spans an area of approximately 4320 km², with the predicted oil and gas resources of 78.17 × 10⁶ t and 707.6 × 10⁹ m³, respectively. The deep to ultra-deep low-structural-compression zone at the front of the Keping thrust nappe structure are identified as strategic favorable field of exploration for structural-lithological oil and gas reservoirs.</div></div>","PeriodicalId":100808,"journal":{"name":"Journal of Natural Gas Geoscience","volume":"10 1","pages":"Pages 1-11"},"PeriodicalIF":0.0,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143529792","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Experimental and molecular dynamics evaluation of the effect of a sulfate surfactant on the shale’s methane sorption","authors":"Hamid Sharifigaliuk ,&nbsp;Vahid Khosravi ,&nbsp;Mansoor Zoveidavianpoor ,&nbsp;Syed Mohammad Mahmood","doi":"10.1016/j.jnggs.2024.11.002","DOIUrl":"10.1016/j.jnggs.2024.11.002","url":null,"abstract":"<div><div>Shale gas has shown a great potential for exploration and development via advanced horizontal drilling and multistage hydraulic fracturing. Slickwater is a major type of fracking fluid, containing various chemical additives, water, and sand. In this matter, surfactant additives play a significant role in regulating the optimal performance of slickwater. The implication of the change in gas adsorption/desorption behavior of shale rocks and their individual minerals has rarely been experimentally investigated. In this study, the effect of a sulfate surfactant on methane adsorption capacity of a Marcellus shale was evaluated. Molecular dynamics simulation was also applied for gas adsorption assessment on major minerals in shales. Accordingly, the significant alteration of the adsorption energy of illite, quartz, and calcite minerals treated by a surfactant was investigated. Conclusively, the methane sorption capacity of the treated shale sample was reduced and correspondingly, the gas diffusion coefficient increased. Experimentally, the methane sorption analysis showed that the diffusion of the surfactant resulted in significant methane desorption. Besides, the major mineral constituents of shale behaved differently as unveiled by molecular simulation. The methane adsorption energy of calcite was reduced more significantly than quartz and illite when treated with surfactant. And, at the molecular level, the number of adsorbed methane molecules on illite reduced by half after a sulfate surfactant treatment.</div></div>","PeriodicalId":100808,"journal":{"name":"Journal of Natural Gas Geoscience","volume":"10 1","pages":"Pages 59-74"},"PeriodicalIF":0.0,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143529720","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The Early Jurassic sedimentary records characteristics and geological significance in the northern margin of the Qaidam Basin, NW China: A study of Well Lengke-1","authors":"Dingshu Cheng ,&nbsp;Fei Zhou ,&nbsp;Chen Cheng ,&nbsp;Zhengwen Jiang ,&nbsp;Yushan Shen","doi":"10.1016/j.jnggs.2025.01.001","DOIUrl":"10.1016/j.jnggs.2025.01.001","url":null,"abstract":"<div><div>The Qaidam Basin began to accumulate continental deposits during the Early Jurassic period, when it was located at a geographical position of 8.8 °N latitude. The paleoclimate was characterized by a warm and humid climate zone, conducive to the formation of lakes and marshes. This ancient continental lake deposit record provides a robust indication of key paleoenvironmental and paleoclimatic information. According to the descriptions of rock debris in the basic geological research and oil &amp; gas exploration, the drilling coring and electrical measurement data confirm that Well Lengke 1 is drilled through the Early Jurassic Huxishan Formation, and the location of Well Lengke 1 is the center of the lake basin, which can well reflect the Early Jurassic sedimentary characteristics and paleoenvironment restoration in Qaidam Basin. This study utilizes rock dating, thin section identification, biomarker compounds, and spore-pollen analysis to investigate the Early Jurassic sediments of the cold lake in the Qaidam Basin. The results confirm: (1) The sedimentary environment was identified as the origin of the sediments from 400 to 450 Ma and 250 to 300 Ma, and the development of algal bodies, algal wall keratinites, sporophytes and other organisms was found in thin section identification. (2) Biomarker analysis confirmed various compounds indicating that the second member of the Early Jurassic Huxishan Formation was rich in terrestrial higher plants, followed by aquatic lower organisms, freshwater lakes developed, and the depositional environment was partial oxidation; The first member of Huxishan Formation indicates low biological bacteria and algae (<em>n</em>C₁₄), terrigenous organic matter (<em>n</em>C₂₁-₂₉), and mixed organic matter. Gamma-cerane and paleosalinity analysis of sedimentary water suggest that black shale was formed in freshwater environment. (3) The palaeoclimate was humid, hot and rainy, the terrain was flat, the plants were flourishing along the marshes and shallow lakes, the plant group was flourishing gymnosperms, the sporogenous assemblage was Coniferae with cysts - piceites - spines, and the fern types were relatively simple. (4) The deep strata in this area have the characteristics of Paleozoic strata, and brachiopods, foraminifera, grid bryozoa, echinodermata and other marine fossils are found in the rock debris.</div></div>","PeriodicalId":100808,"journal":{"name":"Journal of Natural Gas Geoscience","volume":"10 1","pages":"Pages 27-39"},"PeriodicalIF":0.0,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143529718","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Diagenetic facies of the Fengcheng Formation tight reservoir in the alkaline lake sedimentary environment, the southern margin of Mahu Sag, Junggar Basin, China","authors":"Zongbin Zhang ,&nbsp;Jun Qin ,&nbsp;Zhongchen Ba ,&nbsp;Wenbiao Huang ,&nbsp;Mengyun Han ,&nbsp;Yuhui Gao ,&nbsp;Dong Wu","doi":"10.1016/j.jnggs.2025.01.003","DOIUrl":"10.1016/j.jnggs.2025.01.003","url":null,"abstract":"<div><div>With the aim of exploring the diagenetic characteristics, influence mechanisms, and distribution of dominant diagenetic facies in the Fengcheng Formation, at the southern margin of Mahu Sag in the Junggar Basin, this paper quantitatively characterized the reservoir transformation intensity of compaction, cementation, and dissolution on the basis of the analysis of petrological characteristics, pore types, diagenesis, and diagenetic environment evolution, and established a diagenetic facies division scheme. Based on single-well core interval evaluations, the diagenetic facies distribution was described, and the mechanisms influencing their distribution were explained. The results show that the reservoir space in the Fengcheng Formation is characterized by a dual medium of “matrix-pores dominated and micro-fractures supplemented”, with intra- and intergranular dissolved pores being predominant types in matrix pores. The Fengcheng Formation underwent an evolution through an alkaline sedimentary environment and an alkali-acid-alkaline diagenetic sequence. During the alkaline sedimentary and early alkaline diagenetic stages, significant intergranular pore loss occurred due to cementation, while volcanic material hydrolysis and plagioclase albitization facilitated the formation of solution pores. The reaming in the acidic diagenetic environment in the middle stage caused additional dissolution pore become the main reservoir space, and mitigating the densification to some extent. In the late alkaline diagenetic environment, the concentration of alkaline mineral ions increased, leading to precipitation in the remaining intergranular pores, solution pores, and other reservoir spaces, and the reservoir densification degree is further improved. In the study area, the cementation and dissolution of fan delta plain and front junction were weak, resulting in more compact phases developed, with an average porosity of about 4.9%. Moving from the inner front of the fan delta to the junction of the outer front, dissolution became more dominant than cementation, leading to development of cementation-dissolution phases, with an average porosity of about 6.6%. The dissolution phases near the central and southern faults prevailed, with an average porosity of 9%. The outer front of the fan delta is mostly associated with solution-cementation facies, resulting in an average porosity of the reservoir of about 3.1%. In general, alkaline diagenesis in the alkaline lake sedimentary setting has a dual effect on reservoir reconstruction. The cementation-dissolution and dissolution phases, under the control of acid/alkaline dissolution process, are favorable sites for tight oil accumulation in this area, and are also the key factors for the high productivity in this area.</div></div>","PeriodicalId":100808,"journal":{"name":"Journal of Natural Gas Geoscience","volume":"10 1","pages":"Pages 41-57"},"PeriodicalIF":0.0,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143529719","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Geological characteristics of biogenic gas formation and direction of favorable zones in the Quaternary mudstone of the Qaidam Basin, China","authors":"Jixian Tian ,&nbsp;Zeyu Shao ,&nbsp;Jian Li ,&nbsp;Dekang Song ,&nbsp;Zhou Fei ,&nbsp;Ya'nan Li ,&nbsp;Wei Sha ,&nbsp;Hao Zhang ,&nbsp;Lili Hou ,&nbsp;Xiaoqiu Zhang ,&nbsp;Haining Zhang ,&nbsp;Yixuan Yang","doi":"10.1016/j.jnggs.2025.01.002","DOIUrl":"10.1016/j.jnggs.2025.01.002","url":null,"abstract":"<div><div>Quaternary biogas is the main natural gas resource in the Qaidam Basin, where sandstone reservoirs have traditionally been the primary producers. However, reserve growth in these reservoirs has become increasingly difficult in recent years. Mudstone gas, representing a new exploration field, has a low exploration level, and its formation, reservoir characteristics, and potential remain unknown. In this study, we utilize core data from the mudstone sections of two newly drilled wells in the study area as the object, and carry out a comprehensive study of the formation and reservoir characteristics of mudstone biogas through systematic experimental analysis, on the basis of which, favourable exploration areas for mudstone biogas are identified. The results of the study show that: (1) The Quaternary mudstone is mainly composed of dark grey mudstone in shallow and semi-deep lake, and influenced by the anoxic environment of brackish water and semi-brine water, exhibiting blocky, striped, and laminar structures. The mudstone layers frequently feature interbeds of sand and carbonate rocks. in which the mudstone is mainly concentrated in the Ⅲ, Ⅵ, and Ⅷ layer groups, characterized by large thickness and good continuity. (2) The low abundance of organic matter in the Quaternary mudstone, but a substantial proportion of organic matter suitable for microbial modification, and the large amount of different types of organic matter, such as hydrocarbons and algae, improve the biogas gas production capacity of the Quaternary system. (3) The Quaternary mudstone exhibits various pore types, including primary intergranular pores, dissolution pores, cracks, and a small number of organic pores. It is characterized by high porosity and permeability, although the pore radii of macropores, mesopores, and micropores are relatively small. (4) On-site analysis shows that mudstone layers are generally gas-bearing, with free gas being the main gas. Gas accumulation is prominent in brittle mineral developmental zones and tectonic high points within gas-bearing sections. (5) The loose Quaternary mudstone, with its high porosity and permeability, is controlled by various factors such as water content, overburden pressure, and mudstone thickness, and has the ability of self-containment and self-sealing properties. It is concluded that the Quaternary mudstone gas reservoir follows a formation model characterized by “integrated source and storage, brittle mineral content-controlled accumulation, mudstone thickness and pore sealing, and tectonic direction control”. Favorable areas for mudstone gas accumulation include the three major fields and the northern slope of the study area.</div></div>","PeriodicalId":100808,"journal":{"name":"Journal of Natural Gas Geoscience","volume":"10 1","pages":"Pages 13-25"},"PeriodicalIF":0.0,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143529717","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}