Tectonic Evolution and Geological Characteristics of Hydrocarbon Reservoirs in Marine Mesozoic-Paleozoic Strata in the South Yellow Sea Basin

The South Yellow Sea Basin is the main body of the lower Yangtze area in which marine Mesozoic–Paleozoic strata are widely distributed.The latest geophysical data were used to overcome the limitation of previous poor-quality deep data.Meanwhile,the geological characteristics of hydrocarbon reservoirs in the marine Mesozoic–Paleozoic strata in the South Yellow Sea Basin were analyzed by comparing the source rocks and the reservoir and utilizing drilling and outcrop data.It is believed that the South Yellow Sea Basin roughly underwent six evolutionary stages:plate spreading,plate convergence,stable platform development,foreland basin development,faulted basin development,and depression basin development.The South Yellow Sea Basin has characteristics of a composite platform-fault depression geological structure,with a half-graben geological structure and with a ‘sandwich structure' in the vertical direction.Four sets of hydrocarbon source rocks developed – the upper Permian Longtan–Dalong formation,the lower Permian Qixia formation,the lower Silurian Gaojiabian formation,and the lower Cambrian Hetang formation/Mufushan formation,giving the South Yellow Sea Basin relatively good hydrocarbon potential.The carbonate is the main reservoir rock type in the South Yellow Sea area,and there are four carbonate reservoir types:porous dolomitic,reef-bank,weathered crust,and fractured.There are reservoir-forming horizons similar to the typical hydrocarbon reservoirs in the Yangtze land area developed in the South Yellow Sea,and there are three sets of complete source-reservoir-cap rock assemblages developed in the marine strata,with very good hydrocarbon potential.

Hydrocarbon Geological Conditions and Exploration Potential of Mesozoic–Paleozoic Marine Strata in the South Yellow Sea Basin

No substantial breakthroughs have been made in hydrocarbon exploration of the South Yellow Sea Basin.It is believed that the Mesozoic-Paleozoic marine sedimentary formation in the South Yellow Sea Basin is similar to that in the Sichuan Basin.Therefore,outcrop,drilling,and seismic data were determined and compared with the research results on petroleum geological conditions in the Yangtze land area,and the hydrocarbon geological conditions were analyzed comprehensively from multiple aspects,such as basin evolution and main source rocks,reservoir characteristics,preservation conditions,and structural traps.The results show that two main stages in the South Yellow Sea Basin(the stable evolution stage of the Mesozoic-Paleozoic marine basin and the Mesozoic-Cenozoic tectonic reformation and basin formation stage)were important for the development and evolution of four sets of main source rocks.Reservoirs dominated by carbonate rocks,three sets of capping beds with good sealing capability,relatively weak magmatic activity,and multiple types of structural traps jointly constituted relatively good hydrocarbon-reservoir-forming conditions.There were four sets of main source-reservoir-cap assemblages and three possible hydrocarbon reservoir types(primary residual-type hydrocarbon reservoir,shallow reformed-type hydrocarbon reservoir,and composite-type hydrocarbon reservoir)developed in the marine strata.It is concluded that the marine strata in the South Yellow Sea Basin have relatively good hydrocarbon potential.The Laoshan Uplift is characterized by stable structure,complete preserved source reservoir cap assemblage,and large structural traps,and thus it is the preferred prospect zone for marine Paleozoic hydrocarbon exploration in this area.

Fluid migration paths in the marine strata of typical structures in the western Hubei-eastern Chongqing area,China

The western Hubei-eastern Chongqing area is an important prospective zone for oil and gas exploration in the central Yangtze area. Three representative structures, the Xinchang structure, Longjuba gas-bearing structure and the Jiannan gas field, were selected to analyze biomarker parameters in marine strata and to examine various types of natural gas and hydrocarbon sources. Fluid inclusions; carbon, oxygen, and strontium isotopic characteristics; organic geochemical analysis and simulation of hydrocarbon generation and expulsion history of source rocks were used for tracing fluid migration paths in marine strata of the study area. The Carboniferous-Triassic reservoirs in three typical structures all experienced at least two stages of fluid accumulation. All marine strata above the early Permian were shown to have fluids originating in the Permian rocks, which differed from the late stage fluids. The fluids accumulated in the late Permian reservoirs of the Xinchang structure were Cambrian fluids, while those in the late Carboniferous reservoirs were sourced from a combination of Silurian and Cambrian fluids. A long-distance and large-scale cross-formational flow of fluids destroyed the preservation conditions of earlier accumulated hydrocarbons. A short-distance cross-formational accumulation of Silurian fluids was shown in the late Permian reservoirs of the Longjuba structure with favorable hydrocarbon preservation conditions. The fluid accumulation in the Carboniferous reservoirs of the Jiannan structure mainly originated from neighboring Silurian strata with a small amount from the Cambrian strata. As a result, the Jiannan structure was determined to have the best preservation conditions of the three. Comparative analysis of fluid migration paths in the three structures revealed that the zone with a weaker late tectonism and no superimposition and modification of the Upper and Lower Paleozoic fluids or the Upper Paleozoic zone with the fluid charging from the Lower Paleozoic in the western Hubei-easteru Chongqing area are important target areas for future exploration.

Three Episodes of Hydrocarbon Generation and Accumulation of Marine Carbonate Strata in Eastern Sichuan Basin,China

It is concluded that there are three hydrocarbon generation and accumulation processes in northeastern Sichuan on the basis of the characteristics of solid bitumen, gas-light oils-heavy oils, homogenization temperature of fluid inclusions and diagenesis for beach- and reef-facies dolomite gas- bearing reservoirs in the Puguang Gas Field, northeastern Sichuan Basin, southern China. The first hydrocarbon generation and accumulation episode occurred in the Indosinian movement （late Middle Triassic）. The sapropelic source rocks of the O3w （Upper Ordovician Wufeng Formation）-S1l （Lower Silurian Longmaxi Formation） were buried at depths of 2500 m to 3000 m with the paleogeothermal temperature ranging from 70℃ to 95℃, which yielded heavy oil with lower maturity. At the same time, intercrystalline pores, framework pores and corrosion caused by organic acid were formed within the organic reef facies of P2ch （Upper Permian Changxing Formation）. And the first stage of hydrocarbon reservoir occurred, the level of surface porosity of residual solid bitumen {solid bitumen/ （solid bitumen ＋ residual porosity）} was higher than 60%. The second episode occurred during the Middle Yanshanian movement （late Middle Jurassic）. During that period, the mixed organic source rocks were deposited in an intra-platform sag during the Permian and sapropelic source rocks of O3w-S1l experienced a peak stage of crude oil or light oil and gas generation because they were buried at depths of 3500 m to 6800 m with paleogeothermal temperatures of 96-168℃. At that time, the level of surface porosity of residual solid bitumen of the T1f shoal facies reservoirs was between 25% and 35%, and the homogenization temperatures of the first and second stages of fluid inclusions varied from 100℃ to 150℃. The third episode occurred during the Late Yanshanian （Late Cretaceous） to the Himalayan movement. The hydrocarbon reservoirs formed during the T1f and P2ch had the deepest burial of 7700 m to 8700 m and paleogeotemperatures of 177℃ to 220℃. They could be cracked into dry gas （methane）, and the same with the source rocks of the Permian and O3w-S1l because they all reached the pyrolysis stage under such conditions. Consequently, the present natural gas （methane） reservoirs were developed.

Hydrocarbon Accumulation Process in the Marine Strata in Jianghan Plain Area, Middle China

Marine strata in the Jianghan Plain area are widely distributed with a total depth of more than 8,000 m from the Upper Sinian to the Middle Triassic. Six reservoir caprock units, named Z-C2, C2-O, S, D--C, P and T1, can be identified with each epoch. The geology, stratigraphy, drilling, oil testing and other basic data as well as the measured inclusion and strontium isotope data in the study area are used in the analysis of the formation and evolution process of marine petroliferous reservoirs in the Jianghan Plain area. This study aims to provide a scientific basis for the further exploration of hydrocarbons in the Jianghan Plain and reduce the risks by analyzing the key factors for hydrocarbon accumulation in the marine strata. Our findings show that in the Lower Palaeozoic hydrocarbon reservoir, oil/gas migration and accumulation chiefly occurred in the early period of the Early Yanshanian, and the hydrocarbon reservoir was destroyed in the middle-late period of the Early Yanshanian. In the Lower Triassic-Carboniferous hydrocarbon reservoir, oil/gas migration and accumulation chiefly occurred in the Early Yanshanian, and the hydrocarbon reservoir suffered destruction from the Late Yanshanian to the Early Himalayanian. The preservation conditions of the marine strata in the Jianghan Plain area have been improved since the Late Himalayanian. However, because all source beds have missed the oil/gas generation fastigium and lost the capacity to generate secondary hydrocarbon, no reaccumulation of hydrocarbons can be detected in the study area＇s marine strata. No industrially exploitable oil/gas reservoir has been discovered in the marine strata of Jianghan Plain area since exploration began in 1958. This study confirms that petroliferous reservoirs in the marine strata have been completely destroyed, and that poor preservation conditions are the primary factor leading to unsuccessful hydrocarbon exploration. It is safely concluded that hydrocarbon exploration in the marine strata of the study area is quite risky.

Progress in Antarctic marine geophysical research by the Chinese Polar Program

Marine geophysical survey by the Chinese National Antarctic Research Expedition （CHINARE） began with the first science expedition in 1984/1985, although only four cruises were performed in the vicinity of the Antarctic Peninsula between then and 1991/1992. After a 20 year hiatus, Antarctic marine geophysical research was relaunched by the Chinese Polar Environmental Comprehensive Investigation and Assessment Programs （known simply as the Chinese Polar Program） in 2011/2012. Integrated geophysical surveys have been carried out annually since, in Prydz Bay and the Ross Sea. During the last 5 years, we have acquired about 5500 km of bathymetric, gravimetric, and magnetic lines; more than 1800 km of seismic reflection lines; and data from several heat flow and Ocean Bottom Seismometer （OBS） stations. This work has deepened understandings of geophysical features and their implications for geological tectonics and glacial history in Antarctica and its surrounding seas. Compiled Antarctic Bouguer and Airy isostatic gravity anomalies show different features of tectonics between the East Antarctic stability and West Antarctic activity. Calculated magnetic anomalies, heat flow anomalies and lithospheric anisotropy offshore of Prydz Bay may imply high heat capacity of mantle shielded by the continental shelf lithosphere, but high heat dissipation of mantle due to the Cretaceous breakup of Gondwana along the continent and ocean transition （COT）, where large sediment ridges would be brought about by the Oligocene ice sheet retreat and would enlarge free-air gravity anomalies. In the western Ross Sea, CHINARE seismic profiles indicate northern termination of the Terror Rift and deposition time of the grounding zone wedge in the northern JOIDES Basin.

The Formation Model for Marine Potash Deposits within China's Small Continental Blocks

Chinese geologists have always been expecting to find out a large scale of potash deposits in marine basins,but only one small-middle scale industrial solid potash deposit had been found at Mengyejing in Langping-Simao basin

深基坑咬合桩力学性状影响因素及敏感性分析

在淤泥填海地层开挖基坑往往会使围护结构产生严重变形,导致基坑失稳或垮塌。本文依托深圳某地铁明挖区间淤泥填海地层基坑工程,利用理正软件模拟深基坑开挖全过程,根据现场实测数据与模拟数据对比验证了模型的正确性,对该基坑咬合桩围护结构力学性状的影响因素进行分析,并基于正交试验分析其敏感性。结果表明:(1)围护结构嵌入深度与围护结构变形及受力性状密切相关;(2)当地面超载15 kPa、坑外水位7 m、围护结构混凝土强度C35及其嵌入深度10 m、土的黏聚力和内摩擦角均为原来的1.2倍时,围护结构变形及受力最小(I1II3III2IV3V3VI3是最佳组合);(3)对基坑围护结构水平位移、弯矩的最大影响因素分别是土的内摩擦角、围护结构嵌入深度。

Geological conditions and reservoir characteristics of various shales in major shalehosted regions of China

China is home to shales of three facies:Marine shale,continental shale,and marine-continental transitional shale.Different types of shale gas are associated with significantly different formation conditions and major controlling factors.This study compared the geological characteristics of various shales and analyzed the influences of different parameters on the formation and accumulation of shale gas.In general,shales in China’s several regions exhibit high total organic carbon(TOC)contents,which lays a sound material basis for shale gas generation.Marine strata generally show high degrees of thermal evolution.In contrast,continental shales manifest low degrees of thermal evolution,necessitating focusing on areas with relatively high degrees of thermal evolution in the process of shale gas surveys for these shales.The shales of the Wufeng and Silurian formations constitute the most favorable shale gas reservoirs since they exhibit the highest porosity among the three types of shales.These shales are followed by those in the Niutitang and Longtan formations.In contrast,the shales of the Doushantuo,Yanchang,and Qingshankou formations manifest low porosities.Furthermore,the shales of the Wufeng and Longmaxi formations exhibit high brittle mineral contents.Despite a low siliceous mineral content,the shales of the Doushantuo Formation feature a high carbonate mineral content,which can increase the shales’brittleness to some extent.For marine-continental transitional shales,where thin interbeds of tight sandstone with unequal thicknesses are generally found,it is recommended that fracturing combined with drainage of multiple sets of lithologic strata should be employed to enhance their shale gas production.

碳酸盐团簇同位素在海相盆地热史研究中的进展

沉积盆地热史研究对于油气成藏分析至关重要,在油气勘探以及油气资源评价领域有着举足轻重的影响,而海相盆地碳酸盐岩层系由于缺乏有效古温标导致很难对其热史进行恢复。碳酸盐团簇同位素是能够指示碳酸盐岩形成温度的指标,它将温度信息记录在^(13)C—^(18)O配对的化学键中,并通过其丰度变化将温度信息反映出来,即碳酸盐团簇同位素的丰度(Δ_(47))与地层温度演化密切相关。从碳酸盐团簇同位素测温以及热史恢复的基本原理、方法出发,结合近年来其在国内外海相盆地热史恢复的研究实例,综述了碳酸盐团簇同位素古温标的应用情况,并探讨了其存在的问题和未来的发展方向。碳酸盐团簇同位素作为一种新兴的古温标,在碳酸盐岩地层热历史恢复中展现出了巨大的潜力。团簇同位素热史研究实例表明,美国箭峡Bird Spring组经历的最高古温度约为175℃,四川盆地二叠系茅口组最高埋藏温度在213~225℃,塔里木盆地奥陶系受二叠纪岩浆活动影响存在160℃以上的异常高温。团簇同位素由于受热演化模式不成熟,重结晶作用以及沉积埋藏温度变化的影响,使得其在热史恢复方面仍存在不足,并建议精确恢复碳酸盐岩地层热史的下一步发展方向是将碳酸盐团簇同位素和U-Pb定年以及其他古温标相联合。

中国海相超深层油气形成

超深层是指现今或曾经埋藏深度超过6000 m的沉积地层。中国海相超深层时代老,热演化程度高,经历的构造运动多,独特的构造-沉积和生烃环境,决定了海相超深层油气藏形成与分布的复杂性,成烃-成储-成藏规律明显不同于中浅地层,勘探的难度也远远大于国外中新生代克拉通盆地。经过半个多世纪的探索,近年来中国海相超深层油气勘探在中西部盆地取得一系列重大突破,显著提升了超深层领域油气资源的战略地位。与此同时,中国海相超深层油气地质理论也取得重大进展,形成了以重大地质转折期构造活动控制超深层油气地质要素发育、深埋高温环境导致多途径天然气生成、沉积-构造作用控制超深层油气储集空间形成与保持、超深层温压系统控制油气藏相态演化和多期成藏、多层系分布等为核心的理论认识,极大地发展了国外学者基于中新生代海相地层提出的油气生成与成藏模式,拓展了海相油气资源形成和分布的时空界限。

海相地层新意法施工隧道掌子面失稳模式及围岩变形规律分析

以深圳地铁12号线2期工程松岗站与既有6号线折返线北侧暗挖通道为研究背景,通过FLAC3D有限元数值模拟和理论分析的方法研究了新意法施工条件下不同海相地层围岩级别、隧道埋置深度、隧道洞径、隧道掌子面预加固强度对隧道掌子面失稳模式及围岩变形规律。当隧道掌子面不进行预加固时,掌子面挤出位移随着隧道埋置深度的增加而增加;围岩等级越大,掌子面挤出位移随隧道埋深的变化越明显;当围岩等级为VI6时,隧道埋深在5 m到45 m,掌子面均发生了失稳现象;当隧道埋深取5 m、洞径取5.8 m时,其他固定参数不变;随着围岩内摩擦角、黏聚力、掌子面预加固深度的增大,隧道掌子面挤出位移逐渐减小。

川西深层、超深层气井排水采气技术初探

川西北部投产的海相深层气井产层中深普遍超过6000 m,具有温度高、压力高、硫化氢含量高、完井管柱复杂和气水关系复杂、水量范围大的特点,目前排水采气工艺举升深度主要在6000 m以内的气井,6000 m以上气井排水采气尚无应用先例。针对深层、超深层气井特征,通过统计对比研究,初步形成了适应该类气井的排水采气措施:一是针对气井排水采气难点及需求、结合技术应用现状,优选出适合该类气井的排水采气主体技术;二是开展气举工艺可行性论证,结论表明气举能够适应川西海相深层气井生产初期的排水需求,但工艺所需最低地层压力较高,后期需进行工艺接替;三是根据阶段生产特征,制定了“初期降井口压力、中后期降井底流压”的阶段排水采气方案;四是提出超深井排水采气攻关方向及后续接替工艺措施,延长工艺有效期。川西深层、超深层气井排水采气技术的研究和探讨对该类气井稳定生产具有现实指导意义。

中国古老超深层海相碳酸盐岩储集层成因研究新进展

中国海相碳酸盐岩具有年代老、埋藏深、后期成岩改造强的特点,随着油气勘探逐渐走向“更老”、“更深”、“更复杂”的深层和超深层,碳酸盐岩储集层成因和分布规律成为影响油气勘探开发效益的关键因素。近年来,在塔里木、四川和鄂尔多斯三大海相盆地多个领域取得了一系列的勘探新突破,古老超深层碳酸盐岩储集层地质理论和相关技术取得显著进展。地质理论进展包括:(1)近地表环境成因孔隙构成超深层碳酸盐岩储集层的基础;(2)浅埋藏阶段的孔隙保持是决定超深层储集层质量的关键;(3)构造活动驱动深部流体运动对储集层质量具有重要改造作用。技术进展包括微量稀土元素面扫、激光U-Pb定年、团簇同位素和非传统稳定同位素等储集层地球化学实验分析技术和高温高压溶蚀模拟技术。勘探的深入和分析技术手段的进步,显著提升了对三大盆地重点领域规模优质储集层发育及分布规律的认识,为下步油田勘探取得重大突破奠定了基础。

川西南-滇东北地区晚二叠世早期海陆过渡相沉积地层特征及岩相古地理探讨

川滇地区的峨眉山玄武岩组底部一般以玄武岩或玄武质角砾岩与下伏的中二叠统灰岩呈不整合接触。为进一步揭示峨眉山玄武岩的初始喷发时限、古地理环境,对川西南-滇东北地区的峨眉山玄武岩及下伏的阳新组开展了详细的路线地质调查、实测剖面和古生物化石观察等地质调查工作,研究了在金河-箐河深断裂以东的四川峨眉山市挖断山、乐山市沙湾、美姑县柳红、普格县西罗等13个地区的陆相峨眉山玄武岩组与阳新组(茅口组)浅海相灰岩之间发现的一套海陆过渡相含煤岩系地层。认为该套地层单元厚度薄,区域上层位相对稳定,与上覆、下伏地层均为平行不整合接触,是中二叠世晚期研究区整体不均衡隆升、残余海盆向陆演化的沉积过程响应,控制了峨眉山玄武岩喷发的最初时限,其岩石组合和古生物化石指示了川西南-滇东北地区在阳新世冷坞期早时处于滨海→湖泊→沼泽相演化的古地理特征,应建单独的地层单位进行研究。

塔里木盆地中新生代海侵和海相地层研究的新进展

中新生代海侵是塔里木盆地地质发展史上的重要事件之一。通过对新近发现的古生物化石和海相地层资料研究,本文提出了早白垩世、晚白垩世、古近纪的海侵范围的新认识。同时,依据露头和钻井资料提出了中新世海水分布的新范围。这些新成果对厘定塔里木盆地中新生代地层时代、建立整个盆地中新生代地层格架和油气远景分析具有重要意义。

天津地区第四纪年代地层剖面研究

通过钻孔岩心光释光测年与古地磁测试,对天津地区黄骅坳陷和沧县隆起两个构造单元的年代地层进行了研究,对区内第四纪分层界线重新进行了划分,建立了本区第四纪年代地层剖面。黄骅坳陷和沧县隆起两个构造单元的沉积发展历史具有一定相似性,同时还存在较大的差异。主要表现在:第四纪以来,黄骅坳陷和沧县隆起均有海侵发生,沉积一些海相地层,但是其发育程度不同,反映两个构造单元有着差异较大的海侵历史;二者在第四纪年代地层序列上存在较大差异,形成的相应沉积物的类型和厚度明显不同,为两个不同的第四纪沉积单元;天津地区原来第四系内部的分层界线为:Qh埋深20m,Q3p为70～80m,Qp2为180～210m,Qp1为400m。研究表明,天津地区的第四系在黄骅坳陷和沧县隆起上明显不同:黄骅坳陷中的全新统、更新统上段及中段底界深度约分别为19,45,103m,第四系底界深度>200m;沧县隆起上的全新统、更新统上段及中段底界深度分别为13,30,56m,而第四系底界埋深为162m左右,远远浅于原来第四系分层的界线。

拉张槽对四川盆地海相油气分布的控制作用

四川盆地现今为挤压性的沉积盆地,地表所见构造也均为压性构造;但四川盆地沉积盖层在形成、演化过程中发生了拉张运动(地裂运动)并形成了张性构造(拉张槽等)。现今盆地内已发现的主要拉张槽有开江-梁平海槽(拉张槽)和绵阳-长宁拉张槽。开江-梁平海槽(拉张槽)是四川盆地内深埋地下的二叠纪-三叠纪之间的一个北西-南东向展布的深水碳酸盐岩沉积区,是在峨眉地裂运动理论启示下因生物礁油气藏勘探而发现的。绵阳-长宁拉张槽是四川盆地内发育于早寒武世的一个南北向的下寒武统巨厚碎屑岩沉积(降)区,是在兴凯地裂运动理论指导下通过构造-沉积综合研究而发现的。2个拉张槽的发现和特征研究均经历了漫长过程。拉张槽的形成演化不仅控制了优质泥质烃源岩和优质碳酸盐岩储集岩的发育,而且为优质泥质烃源岩-优质碳酸盐岩储集岩组合的形成和油气成藏效应及规模的提高创造了条件,致使环拉张槽周缘地区是克拉通盆地内油气分布最丰富的地区。

中国南方海相地层油气保存条件综合评价技术体系探讨

中国南方海相地层的油气藏分别在加里东、印支和燕山期经历了多期多阶段的演变过程,被构造活动改造的强度大。油气保存条件破坏严重,且缺乏有效的评价方法。本文试图通过研究地下流体的化学-动力学行为规律,从动态和演化的角度分析剥蚀作用、断裂-破碎作用、大气水下渗作用等对油气藏破坏的程度、方式,综合评价油气的成藏、保存条件,探索针对南方海相地层油气保存条件评价的技术体系。

下扬子地区古生界页岩气地质条件与勘探前景

通过对下扬子地区海相古生界暗色泥页岩发育的构造背景、沉积环境、空间展布、地球化学参数等的分析,认为下扬子地区海相古生界暗色泥页岩具备了页岩气富集的基本条件,提出了2套重点目的层,即下寒武统荷塘组和上二叠统龙潭组,并针对这2套泥页岩发育的层位分别提出了有利勘探区。同时认为,后期改造相对较弱的地区应该是页岩气勘探开发的主战场。