Sealing Features of Fluid-Rock System and its Control on Acidic Dissolution in Cretaceous Sandstone Reservoirs,Kuqa Subbasin

The Cretaceous Bashijiqike Formation is the main gas-bearing strata in the northern structural deformation zone of Kuqa subbasin. The acidic dissolution of this formation arose at 5-4Ma, which corresponds to the late burial stage of the Bashijiqike Formation. Variability of interlayer due to rock composition is negligible. Differentiation of acidic dissolution in sandstones was controlled by difference in amount of exogenous acid fluid from underlying strata. For the absence of sedimentary and structural carrier system between the isolated sandstone reservoirs, most fluid-rock systems show relative sealing feature during later burial stage by sealing feature of formation pressure, geochemical characteristics of formation water and content of diagenetic products in sandstones. Variation of sealing effects for different fluid-rock systems is obvious. The pressure coefficient is inversely proportional to acidic dissolved porosity of sandstone reservoirs, indicating that the variation of sealing effects for fluid- rock system mainly controls the differentiation of acidic dissolution.

Formation Conditions and Sedimentary Model of Over-Flooding Lake Deltas within Continental Lake Basins: An Example from the Paleogene in the Jiyang Subbasin, Bohai Bay Basin

A large quantity of drilling core, paleontology, geochemistry and geophysics data revealed several features of the Jiyang subbasin during the deposition of the Ekl-ES4x members： （1） the paleotopography of the gentle slope belt had an extremely low gradient; （2） the paleoclimate frequently alternated between dry and wet periods in a generally arid setting; （3） there was strong weathering around the periphery of the basin; （4） the lake was very shallow; （5） the lake level frequently rose and fell; and （6） the sedimentary environment of the gentle slope belt was an over- flooding lake. All of these factors provided favorable geological conditions for the development of an over-flooding lake delta. The lithologies of the continental over-flooding lake delta deposits are complex and diverse. The compositional maturity is moderate to low, and the grain size distribution curves and sedimentary structures indicate the presence of both gravity and traction currents. The sedimentary microfacies associations consist of a combination of ordered superposition of flood channels, distributary channels and sheet sands. The delta exhibits a weak foreset seismic reflection. The over-flooding lake delta deposits are laterally extensive. The sandstone content is high, and the individual sandstone beds are thin. The flood channel and distributary channel deposits exhibit evidence of bifurcation and lateral migration. The distribution of the sandbodies and the oxidation color of the mudstones provide evidence of cyclic deposition. The paleoclimate was the dominant factor controlling the development of the over-flooding lake delta. Due to the frequently alternating wet and dry paleoclimates, the over-flooding lake delta is characterized by the development of a broad upper plain and a lower delta plain. The upper delta plain is characterized by flood channel deposits, whereas the lower delta plain is represented by distributary channel deposits. The transition zone is characterized by the interaction of flood channels and distributary channels. Due to fault activity, the sandbodies of the over-flooding lake delta were juxtaposed against hydrocarbon source rocks, which was favorable for the development of lithologic reservoirs or structural-lithologic reservoirs. The lower delta plain deposits comprise the most favorable reservoirs.

Three-stage tectonic subsidence and its implications for the evolution of conjugate margins of the southwest subbasin,South China Sea

To reveal the tectonic characteristics of the continental margins in the southwest subbasin(SWB)of the South China Sea,a long high-resolution seismic profile was studied using empty basin subsidence.We find that tectonic subsidence features on both margins are uniformly divided into three stages:(1)slow subsidence from Tg to 18.5 Ma(synrift stage);(2)extremely slow subsidence/uplift from18.5 to 16 Ma(spreading stage);and(3)accelerated subsidence from 16 to 0 Ma(post-spreading stage).This feature differs from the classic tectonic subsidence pattern of rifted basins,which exhibits fast subsidence during synrift stage and slow subsidence during the post-rift stage.The tectonic uplift occurred during the spreading stage and the magnitude increased from the continent to the ocean,which is likely related to mantle flow during seafloor spreading.We propose that lower crustal flow played a significant role in the tectonic evolution of the continental margins of the SWB.The lower crust of the SWB margins was warmer and therefore weaker,and more prone to flow beneath the faulting center,which compensated for the upper crustal thinning caused by brittle faulting during the synrift period and thus reduced the tectonic subsidence rate.During the spreading stage,faulting attenuated rapidly,and a necking zone appeared at the continentocean transition formed by lithospheric extension.With upwelling asthenosphere,small-scale secondary mantle convection occurred under the necking zone,which raised the continental margin isotherms and increased the buoyancy.Simultaneously,secondary mantle convection lifted the overriding crust,thus the overall subsidence rate decreased sharply or even reversed to uplift.After seafloor spreading,the effect of mantle convection faded away,and sediment loading drove the lower crust to flow landward.Thermal relaxation,lower crust flow,and vanish of secondary mantle convection together led to rapid subsidence in this stage.

Tuff beds in Kurnool subbasin,southern India and implications for felsic volcanism in Proterozoic intracratonic basins

A first report on tuff beds from the Owk Shale in the Proterozoic Kurnool sub-basin in southern India is presented. The rhyolitic to rhodacitic tufts, overlying shelfal limestones formed at depths below storm wave base, have rheomorphie features indicative of viscoplastic flow, and geochem- ical signatures of rhyolitic to rhyodacitic unwelded to welded tufts, similar to those described from other Proterozoic intracratonic basins like Vindhyan and Chhattisgarh basins in India. Fragmentary nature of altered glass with perlitic cracks and local admixture with intrabasinal sediments suggest phreatomag- matic reactions. The widespread and repeated occurrences of felsic tufts in these basins, possibly derived from low degree melting of continental crust, suggest intermittent tectonothermal instability which likely influenced basinal topography and cyclic development of the carbonate platforms.

Identification and geochemical significance of unusual C24 tetracyclic terpanes in Shahejie Formation source rocks in the Bozhong subbasin,Bohai Bay Basin

C_(24)tetracyclic terpanes are common compounds in source rocks and crude oils,and C_(24)17,21-secohopane is the most common and widely used source-related indicator.In this study,three unusual C_(24)tetracyclic terpanes were detected on the m/z 191 chromatogram of saturated hydrocarbons in the Shahejie Formation source rocks in the Bozhong subbasin.Based on the mass spectra characteristics,diagnostic ion fragments,retention time and comparisons with published literature,three unusual C_(24)tetracyclic terpanes were identified as 10β(H)-des-A-oleanane,10β(H)-des-A-lupane and C_(24)des-Ahopane.To the best of our knowledge,this is the first study to detect and publicly report these three compounds in source rock samples from the Shahejie Formation of the Bozhong subbasin,Bohai Bay Basin.The results indicated that 10β(H)-des-A-oleanane and 10β(H)-des-A-lupane likely originated from terre strial angiosperms,while C_(24)des-A-hopane likely originated fro m prokaryotic o rganisms.Te rrestrial angiosperms provide the material basis for the generation of compounds A and B,and the distribution and concentration of these two compounds are affected by thermal maturity.In the low maturity stage(0.5%<R_(0)<0.7%),compounds A and B are relatively enriched in the source rocks.

珠江口盆地珠三坳陷文昌组有机质碳同位素异常成因

部分中国近海湖盆和大西洋裂谷盆地发现了腐泥型有机质碳同位素偏重的现象,并伴随异常高总有机碳含量和生烃潜力。本文依据泥岩有机碳测试、孢粉分析、主微量元素、泥岩和原油碳同位素及饱和烃色质色谱资料,并结合现代湖泊盘星藻发育特征,从有机质来源、古环境条件和有机质保存改造三个方面探讨了珠江口盆地珠三坳陷古近系文昌组碳同位素正偏移的成因机制。珠三坳陷文昌组碳同位素异常与气候、古生产力、古水深和藻类勃发等古环境因素有关。然而,从三级层序尺度看,古水深可能是一个不可忽视的重要因素:指示水深的Rb/K比值随深度加深而增加,与碳同位素和TOC含量变化趋势一致。同时现代湖泊研究也证实了盘星藻分布于不同水深范围,因此“深水型盘星藻”的繁盛很可能是珠三坳陷文昌组二段烃源岩碳同位素偏重的根本原因。

Relationship between Formation of Zhongyebei Basin and Spreading of Southwest Subbasin, South China Sea

The Zhongyebei （中业北） basin （ZYBB） is an NE-striking, narrow and small sedimentary basin superimposing the southern 1/2 segment of the proposed spreading axes of the SW subbasin of the South China Sea （SCS）. More than 4 500 m strata were identified in the Zhongyebei basin, including the Paleogene lower structure layer and the Neogene upper structure layer. The SW subbasin of the South China Sea has been regarded as an oceanic basin opened by seafloor spreading, as evidenced by the flat and deep （〉 4 000 m mostly） seafloor with linear magnetic anomalies, and by the shallow Moho depth of 〈 12 km as estimated from gravity modeling. The classic model of seafloor spreading predicts that sediments on the oceanic crust are younger and thinner towards the spreading axes. But in the southwestern segment of the SW subbasin, contradictions appear. Firstly, the thick sedimentation in the ZYBB is along the proposed spreading axes. Secondly, the sediments are thinner （500-1 500 m） and younger away from the proposed spreading axes. Thirdly, geological elements of the two sides of spreading axes develop asymmetrically in the southwestern SW subbasin. Two models, the early opening model and the limited modeling model, are suggested for resolving this paradox. The former suggests that the opening of the SW subbasin was in Late Eocene and earlier than the oldest sediment in the ZYBB. The latter proposes that the opening of the SW subbasin was limited to its northeastern portion, and did not extend to the southwest portion. The ZYBB is a rift basin survived from the spreading but subjected to severe syn-spreading magmatic disturbance. The SW subbasin and the ZYBB of the SCS provide a unique opportunity for studying the structural evolution and dynamic mechanism at the tip of a propagating seafloor spreading. Both models have unresolved questions, and further studies are needed.

Complex petroleum accumulating process and accumulation series in the buried-hill trend in the rift basin:An example of Xinglongtai structure trend,Liaohe subbasin

The buried-hill trend is a typical style of the petroliferous structure in the faulted basin of eastern China. The Xinglongtai structure trend in the Liaohe subbasin,Bohai Bay Basin is a buried faulted-hill trend resulting from the periodic faulting of the Tai’an-Dawa faults. The structure was cut by various faults,which are interlinked and constitute the conduits for petroleum migration. Petroleum accumulated in the Tertiary sandstones and pre-Tertiary basement of metamorphosed rocks through the migration pathways of the fault system. Petroleum in the structure was derived from different hydrocarbon kitchens to form a hybrid field complex. Petroleum charged the structure from different directions and accumulated in various reservoirs through different pathways in different times. The accumulations in the buried hill trend of Xingongtai are composed of two types of traps in the two stratigraphic systems: traps in the Tertiary sandstones were formed by the fault blocks and by the pinchout of the sandstone,and traps in the pre-Tertiary basement of metamorphosed rocks were formed by fissures in the inner part of the buried hills and by the unconformity near the surface of the buried hills.

The propagation of seafloor spreading in the southwestern subbasin,South China Sea

On the basis of the summary of basic characteristics of propagation, the dynamic model of the tectonic evolution in the South-western Subbasin (SWSB), South China Sea (SCS), has been established through high resolution multi-beam swatch bathymetry and multi-channel seismic profiles, combined with magnetic anomaly analysis. Spreading propagates from NE to SW and shows a transition from steady seafloor spreading, to initial seafloor spreading, and to continental rifting in the southwest end. The spreading in SWSB (SCS) is tectonic dominated, with a series of phenomena of inhomogeneous tectonics and sedimentation.

Passive seismic experiment and ScS wave splitting in the southwestern subbasin of South China Sea

The seismic experiment of 3D array of OBS in the southwestern sub-basin of the South China Sea(SCS) is briefly introduced in this paper.The data analysis of broadband OBS shows that totally 93 earthquakes with magnitude of Ms 6.0-6.9 and 10 earthquakes with magnitude above Ms 7.0 were recorded in high quality during this experiment,especially the catastrophic earthquake Ms 9.0 occurred in the east sea area of Japan on March 11,2011.The anisotropy parameters inversion of ScS wave of four events above Ms 7.0 indicates that the fast direction of shear wave is N58°E parallel to the ceased spreading ridge of the southwestern sub-basin of SCS(the slow direction is S35°E perpendicular to the spreading ridge),which means the spreading ridge is under compressing stress at present and the cessation of seafloor spreading is related to such stress field as well.

渤中凹陷断拗转换期湖扩—湖退型层序及其对规模湖底扇发育展布的控制

湖、海层序充填存在巨大差异,因此亟待建立具有湖底扇预测功能的层序模式,以便解决渤中凹陷深层东营组规模湖底扇成因类型与时空展布的勘探难题。文中利用地震和钻/测井资料在渤中凹陷深层东营组共识别出5个不整合面和4个最大洪泛面,并据此将其划分为4个沉积层序,每个沉积层序均发育早期湖扩(退积—加积式准层序组)和晚期湖退(进积式准层序组)2个体系域,构成湖扩—湖退型层序模式。规模水道型湖底扇主要形成于湖扩体系域,紧邻层序界面发育,出现在盆外远源大型水系和坡折前方缓坡背景下,是湖平面上升条件下充沛物源供给、活跃重力流和坡折地貌的综合响应,发育补给水道和末端朵叶2个亚相,其中末端朵叶发育朵叶核部、朵叶核缘和朵叶边缘3个微相。若规模水道型湖底扇与其他成藏条件相匹配,则能够形成大型岩性圈闭群,这是渤中凹陷深层最有利的大型岩性勘探目标。规模滑塌型湖底扇主要形成于湖退体系域,出现在盆外远源大型水系和坡折前方陡坡背景下或边界大断层下降盘,是湖平面下降条件下物源供给贫乏、重力流罕见和坡折地貌的综合响应,发育相对富泥的块体流沉积和相对富砂的砂质碎屑流沉积2个亚相。若是在汇聚背景和有利输导条件下发育的规模滑塌型湖底扇,也可形成大型湖底扇岩性圈闭群,这是渤中凹陷深层较有利的大型岩性勘探目标。

加拿大东部斯科舍盆地塞布尔次盆下白垩统深水重力流沉积研究

针对加拿大东部斯科舍盆地重力流沉积演化研究不足的问题,综合岩心、测井、地震及磁异常等资料,明确斯科舍盆地塞布尔次盆下白垩统重力流沉积单元,揭示其沉积演化并探讨发育控制因素。研究结果表明:斯科舍盆地塞布尔次盆下白垩统密西沙加组和洛根峡谷组发育规模性重力流沉积,可以识别出块体搬运、重力流水道、天然堤及朵叶体等沉积单元;密西沙加组沉积初期(距今147Ma)研究区西部发育小型重力流沉积,沉积末期(距今130 Ma)研究区中部发育大型坡底扇;洛根峡谷组沉积初期(距今113Ma)研究区普遍发育小型重力流沉积,沉积末期(距今101Ma)研究区东南部发育大型坡底扇。陆架边缘三角洲进积及陆坡窄、陡,分别为重力流发育提供了物质基础和动力条件。

南海西南次海盆V型尖端地壳岩石圈最终裂解的特征及过程

为了明确南海西南次海盆V型尖端地壳岩石圈发生最终裂解的特征及其演化过程,通过精细的构造解释、断层活动性定量分析、不同构造演化阶段盆地原型分析、沉降速率分析、沉降史模拟等方法综合分析表明,南海西南次海盆V型尖端临界破裂区为远端带和洋陆转换带构成的地壳岩石圈强烈伸展区,依据地壳岩石圈几何形态,该区域可进一步划分为箱型域和楔型域。楔型域内盆地原型可划分为断陷盆地(Tb-SD)、拆离盆地(SD-PD)和拗陷盆地(PD-Bi);箱型域在古新世-渐新世(Tb-SD)盆地原型为断陷盆地,之后该区域进入被动沉降期。新生代以来,南海西南次海盆V型尖端在构造演化过程中,盆地沉降中心由陆向洋方向逐渐迁移,岩浆作用在断拗转换幕发育最强烈,致使岩石圈地壳最终发生裂解。区域资料对比分析表明,南海西南次海盆V型尖端在不同构造带内,盆地构造-地层格架具有差异性,且南海西南次海盆V型尖端经历“双拆离作用”后地壳发生破裂,岩浆侵入,形成原洋洋壳。该认识对南海西南部深水盆地内油气勘探具有重大指示意义。

SWAT模型在大尺度流域径流模拟影响因素分析——以巴拉那河上游流域为例

为了探讨SWAT模型在大尺度流域水文分析模拟的效果,以巴西巴拉那河上游流域为研究区,利用构建的流域大尺度SWAT模型,定量分析美国国家环境预报中心再分析数据(CFSR)降水再分析数据质量、子流域划分数量及模型参数对径流模拟结果的影响。结果表明,CFSR再分析数据对流域降水的空间分布估计偏差较大,导致径流模拟误差较大,模型参数经1次迭代后,确定系数(R^(2))值均小于0.2。随着子流域划分数量的增加,实测站点降水数据可以更准确地估计子流域面雨量,进而提高径流模拟拟合度。在子流域划分数量分别为66、781和4111的情况下,比较模型参数经过1次迭代后的径流模拟效果发现,子流域个数为781个时,R^(2)值相对于两种情况有明显提高。在涉及SWAT模型径流模拟的20个参数中,土壤蒸发补偿系数(ESCO)和SCS径流曲线数(CN2)是最敏感的两个参数。由分析可知,SWAT模型可以在大尺度流域径流模拟中应用,研究结果可以为大尺度流域水文模型的构建与应用提供参考。

地层记录中的古气候信息及其与烃源岩发育的相关性——以渤海黄河口凹陷古近系为例

近年来的研究表明,凹陷中优质烃源岩的形成决定于有利的古气候和古湖盆环境,并受控于断陷期快速沉降的构造背景。着重论述了古气候条件对烃源岩发育的控制作用。根据渤海海域黄河口凹陷典型钻井样品中的孢粉、藻类等古生物资料,并结合岩相特征,对该地区古近纪各时期的古气候、古环境特征进行了恢复,本区古近纪共存在4个气候湿热、古湖盆水体发育的时期。另外通过与烃源岩发育特征的对比,发现各湿热的古气候时期均与优质烃源岩的发育情况有很好的对应关系,说明温暖、湿润的古气候条件对烃源岩的发育具有重要的控制作用。最后对气候影响烃源岩形成和保存的机理进行了分析。

构造应变与砂岩成岩的构造非均质性——以塔里木盆地库车坳陷研究为例

孔隙性砂岩在应变过程中首先发生应变局域化并形成肉眼不易识别的变形条带(deforrnation band),这与低孔隙性的碳酸盐岩的应变效应迥然不同。实例分析说明,天山南缘库车坳陷后期构造变形强烈,自白垩纪以来构造应变具有南北分带、东西分异的显著特征。结合盆地构造格架以及砂岩物性分布特征,本文提出了该区六类砂岩储层改造的构造样式,并描述了其中砂岩的构造非均质性。其中深层卷入型(3类)主要发育于盆地西部,而浅层卷入型发育于盆地东部,其分布受基底构造、盐煤等滑脱层、近南北向的调节断裂、盆山边界接触方式的控制。除变形条带外,研究发现本区最大埋深大于6500～7000m的白垩系致密砂岩的应变属性亲近灰岩,其由于后期抬升或深层次构造应变将容易导致裂隙的发育,这一点在有效储层预测中值得重视。

高邮凹陷古近系阜宁组一段沉积特征对储层成岩作用及物性的影响

本次通过对高邮凹陷阜宁组一段38口井的岩芯描述和400余块样品的普通薄片、铸体薄片和扫描电镜的镜下观察以及物性分析和含油性分析等,对储层的岩性、粒度、杂基含量、层理结构、生物扰动构造等因素与储层的成岩现象、物性特征和含油性的关系进行了详细研究,总结了沉积微相对成岩作用、储层物性的影响和与储层含油气性的关系。储层的岩石成分对储层的成岩作用及物性有重要影响,岩屑较软,易被压实和溶解,浅埋藏时,孔隙度和渗透率随着岩屑含量的增大而增大;当埋藏较深时,孔隙度和渗透率随岩屑含量增加而快速下降。储层的粒度对储层的成岩作用及物性也有重要影响,一般随着粒度的增大,孔隙度、渗透率都相应增大。储层的层理类型对成岩作用及物性也有重要影响,块状层理、交错层理或平行层理砂岩的分选性好,杂基含量较低,属于颗粒支撑结构,从而有利于原生孔隙的保存,为后期地下酸性流体对储层的溶蚀改造提供了渗流条件;波状交错层理等砂岩除不具备这一条件外,砂层内部弯曲的纹层给地下流体的流动增加了困难,不利于次生孔隙的发育和油气的进入。沉积微相对储层物性的控制,主要表现在其对原始物性的控制,分选好、原始物性好的储层在埋藏成岩演化过程中,由于对地层流体的流动的阻力小,其储集空间可以由于致密胶结作用完全消失,也可以得到溶蚀改善和保存;但泥质含量高的储层,其原始物性不好,对地层流体的流动阻力大,尤其是油气难于进入,储层主要遭受破坏,而难以得到改善和保存。

利津洼陷沙四上亚段滩坝沉积特征及控制因素分析

通过岩心观察、测井和地震资料分析,运用沉积学、层序地层学理论,将利津洼陷沙四上亚段分为1个层序3个体系域(LST、TST、HST),并细分为7个准层序组。研究了滩坝砂岩的沉积特征和在准层序组内的平面展布,以准层序组1、2滨浅湖滩坝最发育,准层序组3、4风暴滩坝最发育,准层序组6、7砂质滩坝发育差但发育碳酸盐滩坝。对滩坝控制因素进行了探讨,首次提出了"气(气候)-源(物源)-盆(盆地)"系统控滩坝的分析思路,是对传统"源控论"的完善与补充,可更合理解释滩坝的成因和分布,增加预测性。

辽河坳陷西部凹陷油气成藏体系及天然气分布

辽河坳陷西部凹陷是中国东部油气资源丰度最高的地质单元之一,目前已产出大量原油,但天然气勘探研究相对薄弱。为此,根据地质条件及其变化关系分析,并侧重油气分布地质规律认识,将该坳陷西部凹陷划分为各自特征明显的4个油气成藏体系,分别是北部陡坡带、西部斜坡带、中部断背斜带和南部陡坡带成藏体系。各成藏体系的形成演化及含油气地质特点与西部凹陷的沉降—沉积中心由北向南、由西向东的迁移特点密切相关,有机质的生烃能力、油气的富集程度以及天然气的聚集丰度均受制于这一地质过程。作为多因素地质作用的结果,油气分布具有顺层、近源、受层系控制的成藏及分布模式,天然气分布主要出现在各成藏体系中靠近洼陷中心的地方,环绕鸳鸯沟、清水、盘山等南部洼陷,形成了天然气分布的环圈状特点,沉降—沉积中心的迁移和成藏体系的展布控制了该区天然气的空间分布。

南海北部渐新世末沉积环境及物源突变事件

南海北部沉积物成分在渐新世末(23.8Ma)发生剧烈改变,出现地球化学成分上的突变,并在深海沉积中发生沉积间断及滑塌堆积。这些沉积事件在时间上与南海扩张轴由东西方向转为北东—南西方向发生跳跃的时间十分吻合,是渐新世以来南海构造演化史上最为重大的构造事件。经过这次构造事件,白云凹陷由渐新世晚期的浅水陆架环境转为中新世以后的深水陆坡环境,南海北部地区沉积物源由渐新世近源为主转变为中新世远源为主的供给特点;并使南海北部地区自中新世以来总体呈现海侵的特征。这次沉积环境与物源突变事件对南海北部地区油气藏的形成影响深远。