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.

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.

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.

Feature,genetic model and distribution of calcareous insulating layers in marine strata of western Pearl River Mouth basin in north of South China Sea

We have systematically investigated the feature, genetic model and distribution of calcareous insulating layers in marine strata of the Ⅰ oil group in member 2 of Zhujiang formation(ZJ2I oil formation), western Pearl River Mouth basin(PRMB) in the north of the South China Sea by using data such as cores, thin sections, X-ray diffraction of whole-rock, and calcite cement carbon and oxygen isotopes. The lithology of the calcareous insulating layers in the study area is mainly composed of the terrigenous clastic bioclastic limestone and a small amount of fine-grained calcareous sandstone. On this basis, two genetic models of calcareous insulating layers are established, including the evaporation seawater genetic model and shallow burial meteoric water genetic model. The calcareous insulating layers of the evaporation seawater genetic model developed in the foreshore subfacies, mainly at the top of the 1-1 strata and 1-3 strata. The calcareous insulating layers of the shallow burial meteoric water genetic model developed in the backshore subfacies, primarily in the 1-2 strata.

The ridgelet transform with non-linear threshold for seismic noise attenuation in marine carbonates

Wavelet transforms have been successfully used in seismic data processing with their ability for local time - frequency analysis. However, identification of directionality is limited because wavelet transform coefficients reveal only three spatial orientations. Whereas the ridgelet transform has a superior capability for direction detection and the ability to process signals with linearly changing characteristics. In this paper, we present the issue of low signal-to-noise ratio （SNR） seismic data processing based on the ridgelet transform. Actual seismic data with low SNR from south China has been processed using ridgelet transforms to improve the SNR and the continuity of seismic events. The results show that the ridgelet transform is better than the wavelet transform for these tasks.

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

基于区域地质图与数字高程模型的地层埋深预测方法及应用

对于页岩气、水溶气等非常规天然气资源早期选区评价,往往因为缺乏地震资料导致难以依赖地震构造解释获得目的层的埋深,故借助其他非地震资料有效预测目的层区域性埋深具有重要意义。区域地质图与数字高程模型(DEM)都是广泛覆盖且容易获取的基础性资料。利用区域地质图蕴含的地层产状、地下构造起伏趋势、地层埋深和地表出露地层年代的关系等信息,再叠合DEM地表高程,建立了一种有效预测目的层构造高度和埋深的新方法。利用四川盆地及周缘地区36幅1∶20万区域地质图和美国航空航天局(NASA)数字高程模型资料,预测了该区下志留统龙马溪组底界埋深,据此编制的龙马溪组底界埋深等值线图为该区页岩气保存条件评价提供了重要参数。该方法不仅可为页岩气早期选区评价提供有效支撑,还可应用于深部高压含水层中水溶气的资源评价、深部咸含水层CO_(2)地质封存的构造优选。

叠合盆地深层海相油气差异富集历史的动态模拟——以塔河油田下古生界含油气系统为例

以塔里木盆地塔河油田下古生界含油气系统为例,针对叠合盆地深层海相油气复杂的差异富集历史,采用成藏动力学模拟方法进行深层油气的生排烃、运聚和调整改造的历史恢复。研究表明:①塔河油田下寒武统烃源岩的热演化史反映出不同构造带的生排烃过程及其强度具有明显不同,是导致深层油气相态差异的主要原因。②走滑断裂和不整合面等构成的复合输导体系控制深层油气早期运移聚集和后期调整,中寒武统台内膏盐岩阻止深层油气的垂向运聚,致使深层油气呈现明显的“断控”特征,其中北东向走滑断裂带和深层油气运移低势区叠加有利于汇聚成藏,且主要沿北东向走滑断裂带呈串珠状分布。③成藏动态模拟揭示“源-断-缝-膏-保”时空配置控制塔河深层油气的差异富集,奥陶系经历多期充注、垂向运聚、侧向调整改造的成藏历史,深层油气一直处于运移聚集和逸散的动态平衡中。④油气残留量统计显示塔河油田深层奥陶系鹰山组和蓬莱坝组仍具有较好的勘探开发潜力,超深层中上寒武统具有一定的油气资源前景。研究为塔里木盆地深层油气的动态定量评价提供了参考依据,也可以为古老克拉通盆地碳酸盐岩相关油气成藏演化的研究提供借鉴。

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.

海积淤泥质软土地层深基坑降水设计与成果分析

以分布深厚海积淤泥质黏土层的深圳地铁5号线前海湾车站基坑为例,通过建立三维有限元数值计算模型,详细分析海积淤泥质软土地层项目降水对基坑性状与周围环境的响应,结果表明:为保证达到降水效果,在海积淤泥质软土地区进行基坑降水时,需要尽量延长降水时间;随着降水深度的增大,使得开挖和降水引起的地表总沉降及不均匀沉降均明显增大,其主要影响范围在50 m左右;地下连续墙等止水措施能降低坑外有效应力的增加和减弱渗流,减弱降水造成坑外土体压缩和固结而产生的沉降。

南海天然气水合物深水浅层水平井下套管钻井液技术

以中国南海某海域的一口深水浅层高造斜率水平井施工项目为例,介绍了深水浅软地层高造斜率水平井的下套管方式与下套管期间的钻井液技术优化方案。该井为首次在深水采用无隔水管的浅层水平井下套管的方式施工。对于深水无隔水管的套管下入,套管在送入钻具接近井口时最容易发生塑性弯曲,井眼质量和钻井液润滑性能是成功下入的关键。工程实践表明,低温双抑制性钻井液体系适用于该井的钻完井作业,其在井眼清洁、井眼稳定、润滑性及防止水合物生成与分解等各方面都有良好表现。对比常规井,深水浅层高造斜率水平井套管的下入应特别注意上层套管内“铁-铁”硬摩擦的减阻措施,实践证明,固体润滑剂比液体润滑剂效果更佳。

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。