Origin of a giant fuzzy reflection zone and its implication for natural gas exploration in the southwestern Qiongdongnan Basin of the South China Sea

The southwestern depression of the Qiongdongnan Basin(QDNB)hosts thick Cenozoic sediments and awaits major hydrocarbon discovery.Multichannel seismic(MCS)profile CFT2011 across the southwestern QDNB reveals a~60-km-wide fuzzy reflection zone(FRZ)within the sediments,but its origin and distribution remain unclear.Here ocean bottom seismometer(OBS)data of Line CFT2011 are processed with focus on the velocity structures by traveltime tomography inversion and analyzed together with the coincident and adjacent MCS profiles.The OBS velocity results show that the giant FRZ features lower velocity with difference up to 1.5 km/s and smaller vertical velocity gradient than the surrounding sedimentary sequences at the same depth,likely resulting from enhanced fluid infilling.The MCS profile exhibits that the giant FRZ is about 3-9-km thick and extends from the Paleogene strata rich in organic matters upward to the lower Pleistocene sediments.Within the shallow overlying sediments,multiple bright spots with reverse polarity are imaged and their reflection amplitudes increase with offset,consistent with the features of gas-charged sediments.They are probably shallow gas reservoirs with gases sourced from the deep FRZ.Therefore,the FRZ is proposed to be a giant gas-charged zone,which probably contains lots of hydrocarbon gases migrated vertically from the deep Paleogene source rocks through the boundary faults of the depressions and the minor fractures generated under overpressure.This FRZ is also imaged on the adjacent MCS profiles MCS-L1 and MCS-L2 with the width of about 40 km and 68 km,respectively.It is roughly estimated to cover an area of~1900 km2 and host a volume of~11400 km3 assuming an average thickness of 6 km,implying huge natural gas potential in the sedimentary depression of the southwestern QDNB of the South China Sea.

Migration of paleo-uplift in southwestern Tarim Basin and its implications for orogenesis and reservoir development, NW China

Based on well horizon calibration,the typical seismic profiles in southwestern Tarim Basin were interpreted systematically,regional geological sections were established,and the regional denudation thickness of each tectonic period was restored.On this basis,the plane morphology maps of ancient structures of the Cambrian pre-salt dolomites in different periods were compiled,and the spatial distribution,development,evolution and migration of paleo-uplift in the late Early Paleozoic were analyzed.In the late Early Paleozoic,there existed a unified regional paleo-uplift widely distributed in southwestern Tarim Basin,which is called the southwestern Tarim plaeo-uplift.The“Tarim SW paleo-uplift”and“Hetian paleo-uplift”proposed in previous literatures are not independent,but the result of the spatio-temporal migration and evolution of the southwestern Tarim paleo-uplift identified in this paper.The southwestern Tarim paleo-uplift emerged at the end of Middle Ordovician,and took its initial shape with increased amplitude in the Late Ordovician.During the Silurian,the southwestern Tarim paleo-uplift rose steadily and expanded rapidly to the east,incorporating Pishan-Hetian and other areas,with the structural high locating in the Pishan-Hetian area.During the Devonian,the southwestern Tarim paleo-uplift began to shrink gradually,to a limited range in the Pishan-Hetian area in the southern part of the basin.During the Carboniferous,the southwestern Tarim paleo-uplift became an underwater uplift,that is,the paleo-uplift gradually died out.The southwestern Tarim paleo-uplift belongs to the forebulge of the southwestern Tarim foreland basin in the late Early Paleozoic,and its formation and evolution are related to the early Paleozoic orogeny of the West Kunlun orogenic belt in the south of the Tarim Basin.The migration of the southwestern Tarim paleo-uplift from the northwestern part of the southwestern Tarim Basin to the Pishan-Hetian area indicates the early Paleozoic orogenic process of the West Kunlun orogenic belt,which started in the western section at the end of Middle Ordovician and extended from west to east in a“scissor”style.The migration and evolution of the southwestern Tarim paleo-uplift controlled the development of unconformities at the end of Middle Ordovician,the end of Late Ordovician,and the end of Middle Devonian,and the spatial distribution of dissolved fracture-cave reservoirs in weathered crust below the unconformities in the southwest of Tarim Basin.The migration of the structural high of the southwestern Tarim paleo-uplift also played an important role in controlling the development of dissolved fracture-cave reservoirs in weathered crust.

Carbon Geochemistry of Gas Hydrate-associated Sediments in the Southwestern Taiwan Basin

Marine gas hydrates, one of the largest methane reservoirs on Earth, may greatly affect the deep sea sedimentary environment and biogeochemistry; however, the carbon geochemistry in gas hydrate-bearing sediments is poorly understood. In this study, we investigated the carbon variables in sediment core 973-3 from the southwestern Taiwan Basin in the South China Sea to understand the effect of environmental factors and archaeal communities on carbon geochemistry. The carbon profiles suggest the methanogenesis with the incerase of dissolved inorganic carbon （DIC） and high total organic carbon （TOC） （mean = 0.46%） originated from terrigenous organic matter （mean j13CToc value of -23.6%0） driven by the abundant methanogen ＇Methanosaeta and Methanomicrobiales＇. The active anaerobic oxidation of methane is characterized by the increase of DIC and inorganic carbon （IC）, and the depleted δ13CIC, coupled with the increase of TOC and the decrease of δ13Croc values owing to the methanotroph ＇Methanosarcinales/ANME＇ in 430-840 cm. Environmental factors and archaeal communities in core 973-3 are significantly correlated to carbon variables owing to methane production and oxidation. Our results indicate that the carbon geochemical characteristics are obviously responding to the formation and decomposition of gas hydrates. Furthermore, pH, Eh and grain size, and Methanosaeta greatly affect the carbon geochemistry in gas hydrate-associated sediments.

Characteristics of Uranium Mineralization in Red Clastic Formations in the Southwestern Margin of the Ordos Basin

In the southwestern margin of the Ordos Basin,uranium mineralization is primarily hosted by predominantly oxidative red clastic formations in the Lower Cretaceous.The main target layers for uranium exploration are the Madongshan and Liwaxia formations of the Liupanshan Group,followed by the Jingchuan Formation of the Zhidan Group.The host rocks(medium-fine feldspar quartz sandstone),which are bleached to a light grayish white color,contain a minor organic matter component and pyrite.Uranium mineralization changes from surficial infiltration or phreatic oxidation in the upper part to interlayer oxidation in the lower part.Uranium ore bodies are mostly lenticular or tabular in shape,locally shaped like crescent rolls.Individual ore bodies are typically small and shallow.Uranium predominantly manifests as pitchblende and coffinite.Coffinite is usually short and columnar or granular in habit,whereas pitchblende occurs as an irregular colloidal covering on the surface or in fissures of ferric oxide,silicate,clay or carbonate.Secondary uranium minerals are torbernite,uranophane,and uranopilite.Minerals associated with uranium are mainly pyrite,chalcopyrite and,to a minor extent,arsenopyrite and fluorite.The associated elements are Mo,V,Se,Co,Ni,and Mn,the host sandstone being high in Cu and Ba.Overall,the red clastic formations in the southwestern margin of the Ordos Basin are characterized by’five multiples but one low’which means multiple target layers,multiple stages of mineralization,multiple ore body shapes,multiple kinds of uranium minerals,multiple associated elements,but low organic matter.This implies an overall complex uranium metallogenic environment and mineralization process.It is recommended that future uranium exploration should take into consideration regional metallogenic conditions and mineralization features,with target layers in the wide-smooth synclinal slope being focused on.Most uranium deposits are small to medium in size,and the main type of uranium mineralization can vary by target layer.

Distribution of Nanhua-Sinian rifts and proto-type basin evolution in southwestern Tarim Basin, NW China

Based on seismic data,outcrop evidence,logging data and regional aeromagnetic data,the distribution of Nanhua–Sinian rifts in the southwestern Tarim Basin was analyzed,and on the basis of restoration of lithofacies paleogeography in different periods of Neoproterozoic–Cambrian,the evolution model of the proto-type rift basin was discussed.The Neoproterozoic Rodinia supercontinent split event formed the trigeminal rift system at the edge and inside of the craton in the southwestern Tarim Basin located in the Kunlun piedmont and Maigaiti slope.The rift in Kunlun piedmont zone was distributed along the E-W direction and was the oceanic rift in the trigeminal rift system.Two decadent rifts in N-E strike developed in the Luonan and Yubei areas of Maigaiti slope,and the interior of the rifts were characterized by a composite graben-horst structure composed of multiple grabens and horsts.The Neoproterozoic–Cambrian proto-type basin evolution in the southwestern Tarim Basin can be divided into three stages:rift in the Nanhua,embryonic passive continental margin in the Sinian,and stable passive continental margin in the Cambrian.Despite the regional tectonic movements in the end of Nanhua and Sinian,the tectonic framework of the southwestern Tarim Basin had not changed significantly,the sedimentary center of Nanhua rift basin showed the characteristics of succession in the Sinian–Early Cambrian.The Nanhua rift in Kunlun piedmont evolved into a craton marginal depression during the Sinian–Early Paleozoic,while the Luonan decadent rift in the midsection of Maigaiti slope evolved into a sag inside platform in Early Cambrian,constituting the paleogeographic framework of"two paleouplifts and one sag"with the paleouplifts in east and west sides of the slope.The later evolution of the Luonan decadent rift in the midsection of the Maigaiti slope formed two sets of reservoir-forming assemblages,the Sinian and the Lower Cambrian ones,which are important exploration targets in future.

Basin Fluid Mineralization during Multistage Evolution of the Lanping Sedimentary Basin,Southwestern China

The Lanping sedimentary basin has experienced a five-stage evolution since the late Paleozoic： ocean-continent transformation （late Paleozoic to early mid-Triassic）; intracontinental rift basin （late mid-Triassic to early Jurassic）; down-warped basin （middle to late Jurassic）; foreland basin （Cretaceous）; and strike-slip basin （Cenozoic）. Three major genetic types of Ag-Cu polymetallic ore deposits, including the reworked hydrothermal sedimentary, sedimentary-hydrothermally reworked and hydrothermal vein types, are considered to be the products of basin fluid activity at specific sedimentary-tectonic evolutionary stages. Tectonic differences of the different evolutionary stages resulted in considerable discrepancy in the mechanisms of formation-transportation, migration direction and emplacement processes of the basin fluids, thus causing differences in mineralization styles as well as in genetic types of ore deposit.

中国西南地区CCUS区域中心建设路径与政策建议

西南地区正在加快推动成渝地区双城经济圈和国家天然气(页岩气)千亿立方米产能基地等国家战略实施,面临能源消费量增长硬需求和碳减排硬约束之间的矛盾,推动CCUS产业发展是解决该问题的必由之路,而建设CCUS区域中心是CCUS产业规模化、集群化发展的必然趋势,其中四川盆地是西南地区打造CCUS区域中心的最佳选择。为了加快建设中国西南地区CCUS区域中心,系统梳理了国外的经验做法,分析了其优势和挑战,结合我国西南地区的CO_(2)排放及分布情况、封存地质条件、源汇匹配关系,针对性提出了建设路径和政策建议。研究结果表明:①打造中国西南地区CCUS区域中心具有企业减碳和增产的需求巨大、高耗能行业企业碳源丰富且较为集中、地质封存潜力大且分布集中、源汇匹配情况较好、地方政府积极支持等5大优势;②当前面临的主要问题是缺乏顶层设计和统一规划、缺乏全产业链协同技术攻关的共享平台、缺乏碳减排的激励和约束政策体系等;③下一步应聚焦CCUS-EGR、CCS、DACCS等3条路径,分启动、扩展、规模化发展3个阶段打造西南地区CCUS区域中心,形成两个千万吨级产业集群和3个百万吨级产业集群,并比选技术路径和商业化路径。结论认为,要重点从完善顶层设计,出台统一的战略规划;强化科技攻关体系建设,加快形成技术成熟、经济可行的CCUS全链条技术;强化政策支持、推动国际合作等3个方面入手,加快推动中国西南地区CCUS区域中心建设。

GEOLOGICAL AND GEOCHEMICAL FEATURES AND GENESIS BY FLUID CONVECTION FOR PERMIAN Cu-BEARING Cu-Ag TYPE DEPOSITS AT THE SOUTHWESTERN EDGE OF THE SICHUAN BASIN

Kupferschiefer type Cu-Ag deposits occur in the Upper Permian Xuanwei Formation in the Leshan-Muchuan region at the southwestern edge of the Sichuan Basin. Evidences from geology, major element, REE and thermolurninescence analyses suggest that these Kupferschiefer type CuAg deposits were formed during diagenesis and the ore-forming fluids were derived frorn the underlying basalt. Fluid dynamic analyses show that the ore-forming fluids migrated in a unicellular convection, fluids migrated through the basalt, leaching Cu and Ag frorn basalt and forming orebearing solutions, up the western basement highs, moved laterally along the Xuanwei Formation toward the basin centers, presumably to sink back down into the basalt, completing a convection cycle which was about 15 km long, 300 m high and subhorizontal. Further analysis and calculation suggest that there are good geological, tectonic and fluid-dynamic conditions to form middle-scale Cu and giant Ag Kupferschiefer type deposits, but superlarge deposits are unlikely to be formed in this region.

塔里木盆地西南部寒武系充填层序及沉积样式演化

针对塔里木盆地西南部寒武系存在的古隆起陆棚相分歧,利用锆石U-Pb(铀-铅同位素测年)年龄、井-震联合开展了寒武系层序充填与沉积演化的研究。研究表明:在巴楚隆起,寒武系直接覆盖在克拉通结晶基底之上,寒武系沉积充填与前寒武系结构呈“镜像”关系。受前寒武系地形、构造运动和海平面升降控制,塔里木盆地西南部寒武系发育4个Ⅱ级层序,分别为寒武系层序1(玉尔吐斯组—肖尔布拉克组)、寒武系层序2(吾松格尔组—沙依里克组)、寒武系层序3(阿瓦塔格组)、寒武系层序4(下丘里塔格群),共包含7个沉积相、10个沉积亚相。塔里木盆地西南部寒武系层序1—寒武系层序3早、中寒武世巴楚隆起—麦盖提斜坡—塔西南坳陷沉积相为台地—缓坡—斜坡—深水陆棚相沉积,表现为向海凝缩减薄的沉积特征并发育寒武系烃源岩;寒武系层序4晚寒武世塔里木盆地西南部主体演化为局限台地,塔里木盆地西台东盆沉积格局正式形成。

塔西南山前地区柯克亚周缘叶探1井油气勘探重大突破及意义

塔西南山前西昆仑冲断带柯东构造带叶探1井在二叠系普斯格组获得重大突破,标志着塔西南山前地区发现一个重要的勘探接替层系。结合区域地质资料,根据野外露头、钻井、地震等综合研究,对柯克亚周缘二叠系普斯格组的成藏条件进行再认识。研究认为,研究区内二叠系普斯格组发育陆相湖泊—三角洲沉积体系,上段发育半深湖—深湖相烃源岩,面积1.0×10^(4)km^(2),厚度最大达到800m,集中段有机质丰度为0.92%~1.16%,以菌藻类生源为主,有机质类型主要为Ⅱ型,有机质丰度高;普斯格组下段发育三角洲前缘、滨浅湖沙坝优质砂岩储层,砂体厚度为42.5~63m,砂地比为27%~47%,是一套分布较广的区域性储层,与普斯格组上段泥岩组成优质储盖组合;柯克亚周缘发育印支期、喜马拉雅期两期构造变形,古生界叠瓦冲断、强烈逆掩叠置,圈闭成排成带,喜马拉雅期进一步挤压抬升改造,局部复杂化,形成的叠瓦冲断带为勘探有利区。根据普斯格组天然气干燥系数分析,折算Ro为1.31%~1.42%,与下盘烃源岩成熟度相当,表明油气来自下盘逆掩叠置烃源岩,经历早油晚气的成藏过程,成藏具有“逆掩叠置下盘供烃、下生上储、断裂输导”的特点。综合分析认为该地区二叠系普斯格组圈闭成排成带分布,已发现圈闭9个,面积301km^(2),天然气资源量约为2930×10^(8)m^(3),凝析油资源量约为2×10^(8)t,具有较好的勘探前景。

塔里木盆地西南部晚白垩世——早古新世沉积环境演化:来自皮山PBX1井的地化证据

【研究目的】白垩纪与古近纪之交发生过地质历史上重大的灾变和异常事件,致使K/Pg界线成为全球最重要的地质界线之一。通过对塔里木盆地晚白垩世—早古新世沉积环境的研究,有助于重建特提斯北部盆地群塔里木盆地的古环境。【研究方法】本文通过塔里木盆地西南部PBX1井岩心的地球化学元素敏感指标研究K/Pg上下环境的变化。【研究结果】晚白垩世晚期古气候属于干热型,早古新世呈现短暂温湿型。古盐度由晚白垩世正常海洋环境向早古新世半咸水、海陆过渡盐湖环境转换,K/Pg界线位置处,古盐度达到最低值。氧化-还原环境由晚白垩世富氧→贫氧的弱氧化-弱还原环境经历了K/Pg事件之后短暂向早古新世富氧环境转化,而后整体上由贫氧的弱氧化-弱还原环境向极贫氧的还原环境演化。【结论】PBX1井地球化学元素敏感指标揭示了中生代—新生代之交灾变异常事件在塔里木盆地响应特征,也是特提斯洋北部盆地群晚白垩世—早古新世沉积环境演化的有效证据。

川西南地区中二叠统茅口组一段沉积微相特征及有机质富集模式

为了研究四川盆地中二叠统茅口组一段(茅一段)沉积微相和有机质富集规律,开展了岩石学、沉积微相分析。将川西南乐山沙湾剖面茅一段划分为生物碎屑含灰泥岩(MF1)、生物碎屑泥灰岩(MF2)、生物碎屑含泥灰岩(MF3)、灰泥灰岩(MF4)、生物碎屑粒泥灰岩(MF5)、钙藻粒泥灰岩(MF6)、生物碎屑泥粒灰岩(MF7)和钙藻泥粒灰岩(MF8)共8个沉积微相。结合沉积古环境及地球化学分析认为:①茅一段早、中期,主要发育MF2沉积微相,其次为MF7和MF8沉积微相。该期整体为海侵、缺氧环境,发育上升洋流,初级生产力较高。中、晚期主要发育MF6、MF7和MF8沉积微相,为相对海退环境,含氧量略有上升,上升洋流强度减弱,初级生产力下降。末期以MF2沉积微相为主,含氧量略有上升,初级生产力增强。②茅一段的有机质富集主要受海洋初级生产力与缺氧环境的调控,同时受上升洋流的间接影响。较高的初级生产力与较低的含氧量有利于有机质富集与保存。上升洋流可带来深层营养成分,从而增强海洋初级生产力。③MF2与MF7沉积微相在区域上稳定分布,且具有较高初级生产力和较低含氧量沉积环境,是茅一段有机质富集的有利沉积微相。

塔里木盆地塔西南山前带地震技术攻关进展及发展方向

塔里木盆地西南坳陷复杂山地山前带处于西昆仑造山带与天山造山带的交汇处,强烈挤压作用造成地下构造高陡破碎,与复杂多变的近地表地震地质条件共同造成地震原始数据信噪比极低,构造成像困难,是国内少有的超高难度探区。受地震资料品质影响,该区油气勘探长期未取得实质性突破。近年来持续开展了地震勘探攻关,采集方面加强近地表调查及激发接收参数优选,优化观测系统设计,开展线束地震及高密度宽方位三维地震采集技术攻关;处理方面探索多重联合约束初至层析反演、黄土区“黑三角”带强能量噪声压制、真地表速度建模和深度偏移成像等技术。经过技术攻关,地震资料品质不断得到提高,发现和落实了一批钻探目标,首次在侏罗系砂岩和石炭—二叠系碳酸盐岩取得两项重大突破,打开了塔西南山前带油气勘探新局面。

川西南部地区下二叠统栖霞阶层序地层特征及岩相古地理

【目的】西接康滇古陆的四川盆地西南部下二叠统栖霞阶近年来展示出良好的勘探潜力,然而针对该地区地层充填规律及古地理格局的观点还并不统一,严重制约了下一步盆内精细的油气勘探和井位部署。【方法】以四川盆地西南部下二叠统栖霞阶梁山组和栖霞组为研究对象,综合利用野外剖面、钻井岩心和测录井等资料,在岩石类型与沉积相分析的基础上,运用海相碳酸盐岩层序地层学原理与方法,对栖霞阶层序界面进行识别。并采用单因素分析多因素综合作图法,以三级层序为编图单位,结合优势相原则,分别绘制研究区栖霞阶SQ0+SQ1和SQ2层序岩相古地理图。【结果】在栖霞阶中识别出4个三级层序界面,从下到上分别为梁山组底界面(I型)、栖一段内部界面(II型)、栖一段\栖二段界面(II型)和栖霞组\茅口组界面(I型),并将其划分为3个三级层序,每个层序均由海侵域和高位域组成。通过层序地层格架的对比分析,认为栖霞阶下部的SQ0层序大致对应于传统划分的梁山组+栖一段下部地层,仅发育于研究区内的栖霞阶地层沉积前古地貌低地,并且具有向古地貌高地超覆的层序充填特征,中部的SQ1层序和上部的SQ2层序则遍布全区。川西南栖霞阶层序岩相古地理格局总体上表现为西接康滇古陆的海相碳酸盐岩台地,古地貌和沉积相带分异比较明显,自西向东依次为:康滇古陆及其东缘的潮坪、台内洼地、台内丘滩体,以及开阔—半局限海台地,而且沿台内坡折带发育的台内丘滩体往往具有环洼规模分布的趋势。【结论】通过剖析台内坡折带对碳酸盐岩成储的影响,指出SQ2层序(栖二段)是研究区栖霞阶最有利于台内丘滩体这一潜力储集相带发育的层位,环台洼坡折带发育的丘滩体相带附近是有利的勘探区。从层序地层学角度重新认识栖霞阶充填模式及岩相古地理特征,为川西南部下二叠统栖霞阶的下一步储层预测及勘探开发提供全新的理论支撑。

塔西南石炭系卡拉沙依组烃源岩评价与优选

塔西南地区石炭系油气显示丰富,为明确塔西南石炭系卡拉沙依组烃源岩生烃潜力,通过干酪根镜鉴、有机碳测试及盆地模拟等技术方法,对卡拉沙依组烃源岩进行研究评价,结果显示:卡拉沙依组烃源岩主要为Ⅲ型干酪根,TOC(总有机碳)含量介于0.2%~2.8%,平均值为1.0%,Ro(镜质体反射率)均超过0.7%。但烃源岩热演化过程存在差异,巴楚地区石炭系烃源岩仅在海西晚期一次生烃,麦盖提斜坡石炭系烃源岩存在海西晚期和喜山期两期生烃,结合烃源岩厚度、TOC、成熟度和生排烃史等多种因素,认为麦盖提斜坡区卡拉沙依组烃源岩均已成熟并持续生烃,西部山前带烃源岩品质及生烃强度最优。

远源致密砂岩气成藏主控因素及成藏概率定量评价——以四川盆地西南部中侏罗统沙溪庙组气藏为例

四川盆地西南部(以下简称川西南部地区)中侏罗统沙溪庙组致密砂岩气藏属于远源次生气藏,不同构造天然气富集差异性大,成藏主控因素不清。为此,基于远源致密砂岩气成藏条件分析,对比了川西南部地区沙溪庙组7个含气构造的成藏差异性,明确了成藏主控因素,在综合考虑控制致密砂岩气成藏差异性的各类地质因素的基础上,建立了远源致密砂岩气成藏概率的定量评价方法,并预测了天府气田简阳区块沙溪庙组天然气储量丰度。研究结果表明:(1)川西南部地区沙溪庙组主要发育构造—岩性气藏,天然气均源自下伏上三叠统须家河组煤系烃源岩,不同含气构造在天然气组分、储层特征、输导保存条件等方面存在明显差异;(2)烃源岩排烃能力奠定了物质基础,断—盖配置决定了天然气富集层系,断—储耦合控制着天然气聚集效率,储层品质决定了天然气富集规模;(3)烃源岩排烃能力指数、源—储距离指数、储层物性指数、储层厚度指数、断—盖耦合类型指数及断—储配置类型指数可作为评价致密砂岩气成藏概率指标,提出的远源致密砂岩气成藏概率指数(HAI)可用于该地区远源致密砂岩气地质储量预测。结论认为,HAI与储量丰度具有很好的正相关关系,并预测了天府气田简阳区块的HAI值为0.53,沙溪庙组气藏的储量丰度为1.32×10^(8)m^(3)/km^(2),提出的天然气成藏定量评价方法准确度较高,为川西南部地区沙溪庙组天然气勘探开发指明了方向。

松辽盆地西南部姚家组下段局部排泄源特征及与铀矿化关系分析

松辽盆地西南部上白垩统姚家组下段含水层是重要的铀矿化区域。为了深入了解该地区的铀成矿机制,文章采用水文地质分析、放射性元素含量测定、水化学特征分析等手段,结合区域构造和含水层结构研究,对姚家组下段局部排泄源及其与铀矿化的关系进行了深入研究。研究揭示了姚家组下段具备完整的补给-径流-排泄体系;补给区大面积发育潜水氧化带,径流区发育层间氧化带;更重要的是,确定了局部排泄源为隐伏排泄源,并发现含矿含水层地下水向上部第四系含水层排泄过程中,在局部排泄源区域引起了一系列水文地质特征的变化。局部排泄源的空间存在对铀矿化形成具有控制作用,这为松辽盆地西南部铀矿的进一步勘探提供了重要的理论依据。

川西南地区侏罗系沙溪庙组致密砂岩成藏特征及主控因素

综合利用地质构造、有机地球化学及储层物性、岩性等资料,从烃源岩、储层物性、有效盖层和输导体系等4个方面分析了川西南地区侏罗系沙溪庙组致密砂岩气的成藏条件及主控因素,并对气藏有利区进行了预测。研究结果表明:①川西南地区侏罗系沙溪庙组致密气具备良好的成藏条件,三叠系须家河组五段煤系烃源岩有机质以Ⅲ型干酪根为主,平均TOC为3.31%,Ro为0.70%~1.75%,为沙溪庙组煤型气的规模聚集奠定了良好的物质基础;上覆遂宁组泥岩厚度大,泥地比大于0.8,突破压力高,是良好的封盖层;区内广泛发育的气源断裂为油气运移提供了良好的输导通道。②研究区致密砂岩气的成藏规模受控于源储距离和储层物性,气藏地质储量与储层物性呈正相关,与源储距离呈抛物线关系;致密气的富集层位受控于源-储-盖配置类型,当源储分离、有区域盖层遮挡时,致密气富集于区域盖层下伏储集层,当源储分离、断穿区域盖层时,优势储层多层系富集;烃源岩生烃潜力与输导通道控制了天然气充注方式,区内整体充注程度高,烃源岩侧向运移排烃的成藏条件要好于垂向运移排烃。③研究区地质储量与成藏指数呈线性正相关,相关系数大于0.8;成藏指数大于0.4、泥地比大于0.5、断层封闭性良好的区域为气藏有利分布区,沙溪庙组一段致密气主要分布在名山—邛崃—新津一带、天府含气区;沙溪庙组二段致密气主要围绕浦江、眉山、成都等地分布。

四川盆地西南部多期叠加变形构造解析:以自流井背斜为例

四川盆地西南部地区由于受到周缘造山带构造隆升及变形扩展作用的影响,构造变形样式复杂,演化期次缺乏准确的时间约束。为了进一步探究该地区的构造演化过程,本次研究选取构造变形幅度相对较小的自流井背斜为研究对象,基于高品质地震反射资料,依据断层相关褶皱理论,精细解析其构造几何样式和运动学特征。研究结果表明,区内构造变形分层特征明显,深部以寒武系膏盐层为滑脱层,发育断层传播褶皱和滑脱褶皱,中部逆冲褶皱变形主要限制在志留系泥页岩顶界不整合面和下三叠统膏盐岩滑脱层之间,而浅部主要在上三叠统及以上地层发育宽缓褶皱和局部小位移断层。其中,深部寒武系滑脱层对区域构造样式控制起到关键作用。识别出的生长地层及构造平衡恢复结果揭示,自流井背斜带主要经历了加里东期、印支期,以及燕山期—喜马拉雅期3期主要挤压构造变形。而上三叠统中发育的北西向断裂指示后期在不同方向构造应力场下发生了叠加变形,可能是受到青藏高原东缘往东向四川盆地扩展作用的影响。

Analysis of the Suitability of Surface Water for Irrigation Purposes: The Southwestern and Coastal River Systems in Ghana

Surface water basins all over the world are very crucial in irrigation industries. Irrigation schemes are particularly crucial in the agricultural economies due largely to the fact that global climate change has led to drastic changes in rainfall patterns. As a result, rain-fed agriculture alone is no more sustainable and irrigation schemes are being encouraged as poverty reduction/eradication strategies in the developing countries. This study was conducted to assess the overall controls on surface water resources in the coastal and south-western river basins in Ghana, and determine the suitability of these surface waters for irrigation activities. Multivariate statistical methods were applied to data on the physico-chemical parameters from the coastal and southwestern river basins. This study finds that the quality of surface water from these basins is controlled principally by leachate of chemicals from solid and mine wastes, the chemistry of rainfall, weathering of underlying silicate mineral-rich rocks and sediments, agricultural and domestic wastes. All the parameters are within the acceptable national concentration ranges for most domestic and industrial purposes. Sodium adsorption ratio (SAR) was used to assess the quality of water from the two basins for irrigation activities. The SAR values for all the months and years sampled are lower than 4 and the electrical conductivity values are equally low due to generally low ionic concentrations. When plotted on the Wilcox diagram, the data for all the months for the two years of the study, plot within the “excellent to good” category, suggesting that water from the area is of acceptable quality for irrigation activities.