Geochemical characteristics of Callovian-Oxfordian carbonates in Samandepe gas field,Amu Darya Basin,Turkmenistan

The Callovian-Oxfordian carbonate reservoirs are the most important hydrocarbon reservoir in the Samandepe gas field,Amu Darya basin,Turkmenistan.Based on the analysis of Fe,Mn and Sr trace elements,and carbon,oxygen and strontium isotopes,the genesis and evolutionary characteristics of the carbonate reservoirs were studied,and the conclusions were follows：1） Sustained transgressive-regressive cycles played an important role during Callovian-Oxfordian.The reservoir of reef-bank facies was well developed in the period of transgression,while the regional dense cap rocks developed in the period of regression;2） The 87 Sr/86 Sr ratio measured from rudist shells yields an age of 157.2 Ma according to the global strontium isotope curve;3） As diagenetic intensity increased,δ 13 C changed little,and δ 18 O showed strong negative deviation but was still limited to the range of Late Jurassic seawater.High Fe and Sr contents,and low Mn content,and the evolutionary trend of δ 13 C and δ 18 O all indicate that diagenesis occurred in a relatively confined environment,where the fluids were relatively reducing and contained hot brine.The stage of diagenesis reached is mesodiagenesis,which is very favorable for preservation of primary pores in carbonates;4） Strong dissolution of reef limestones,burial dolomitization and hydrothermal calcite precipitation were all the results of the interaction between the 87 Sr-rich diagenetic fluid and rocks;5） The analysis results of isotopes,fluid inclusions and vitrinite reflectance show that the diagenetic fluid was compaction-released water that originated from the deep,coal-bearing clastic strata.

Paleoclimate evolution and aridification mechanism of the eastern Tethys during the Callovian–Oxfordian: evidence from geochemical records of the Qiangtang Basin, Tibetan Plateau

Global climate during the Jurassic has been commonly described as a uniform greenhouse climate for a long time.However,the climate scenario of a cool episode during the Callovian-Oxfordian transition following by a warming trend during the Oxfordian(163.53 to157.4 Ma)is documented in many localities of the western Tethys.It is still unclear if a correlatable climate scenario also occurred in the eastern Tethys during the same time interval.In this study,a detailed geochemical analysis on the 1060 m thick successions(the Xiali and Suowa formations)from the Yanshiping section of the Qiangtang Basin,located in the eastern Tethys margin during the Callovian-Oxfordian periods,was performed.To reveal the climate evolution of the basin,carbonate content and soluble salt concentrations(SO_(4)^(2-),Cl^(-))were chosen as climatic indices.The results show that the overall climate patterns during the deposition of the Xiali and Suowa formations can be divided into three stages:relatively humid(164.0 to 160.9 Ma),dry(160.9 to159.6 Ma),semi-dry(159.6 to 156.8 Ma).A similar warming climate scenario also occurred in eastern Tethys during the Callovian-Oxfordian transition(160.9 to159.6 Ma).Besides,we clarify that the Jurassic True polar wander(TPW),the motion of the lithosphere and mantle with respect to Earth’s spin axis,inducing climatic shifts were responsible for the aridification of the Qiangtang Basin during the Callovian-Oxfordian transition with a review of the paleolatitude of the Xiali formation(19.7+2.8/-2.6°N)and the Suowa formation(20.7+4.1/-3.7°N).It is because the TPW rotations shifted the East Asia blocks(the North and South China,Qiangtang,and Qaidam blocks)from the humid zone to the tropical/subtropical arid zone and triggered the remarkable aridification during the Middle-Late Jurassic(ca.165-155 Ma).

How rock samples can be representative of in situ condition:A case study of Callovo-Oxfordian claystones

Within the framework of feasibility studies for a reversible, deep geological repository of high-and intermediate-level long-lived radioactive waste(HLW, IL-LLW), the French National Radioactive Waste Management Agency(Andra) is investigating the Callovo-Oxfordian(COx) formation near Bure(northeast part of France) as a potential host rock for the repository. The hydro-mechanical(HM) behaviour is an important issue to design and optimise different components of the disposal such as shaft, ramp, drift,and waste package disposal facilities. Over the past 20 years, a large number of laboratory experiments have been carried out to characterise and understand the HM behaviours of COx claystones. At the beginning, samples came from deep boreholes drilled at the ground surface with oil base mud. From2000 onwards, with the launch of the construction of the Meuse/Haute-Marne Underground Research Laboratory(MHM URL), most samples have been extracted from a large number of air drilled boreholes in the URL. In parallel, various constitutive models have been developed for modelling. The thermohydro-mechanical(THM) behaviours of the COx claystones were investigated under different repository conditions. Core samples are subjected to a complex HM loading path before testing, due to drilling, conditioning and preparation. Various kinds of effects on the characteristics of the claystones are highlighted and discussed, and the procedures for core extraction and packaging as well as a systematic sample preparation protocol are proposed in order to minimise the uncertainties on test results. The representativeness of the test results is also addressed with regard to the in situ rock mass.

Carbon and Oxygen Isotope Stratigraphy of the Oxfordian Carbonate Rocks in Amu Darya Basin

Based on the detailed research on petrologic and geochemical characteristics of deposi- tion and diagenesis of Oxfordian carbonate rocks in Amu Darya Basin, Turkmenistan, carbon and oxygen isotopes were analyzed. The results show that the paleoenvironmental evolution reflected by the samples with well-preserved original carbon isotopes coincides with the carbon-isotope stratigraphic curve and is almost consistent with the global sea-level curve, the Mid-Oxfordian wide transgression, and the positive carbon-isotope excursion event. The Mid-Oxfordian continuing transgression not only laid the foundation for the development of the Oxfordian reef and shoal reservoirs in Amu Darya Basin but also provided an example for the Oxfordian global transgression and the resulting development of reefs and banks and high-speed organic carbon burial events. The response of oxygen isotopes in diagenetic environment showed that micrite limestones and granular limestones underwent weak diagenetic alteration, and the samples largely retained the original seawater features. Dolomitization and the precipitation of hydrothermal calcites filling solution vugs and fractures before hydrocarbon accumulation occurred in a closed diagenetic environment where the main controlling factor is the temperature, and the diagenetic fluids were from the deep hot brine. The chalkification of the lime- stones after hydrocarbon accumulation occurred in the oilfield water systems.

Callovian-Oxfordian hecticoceratins from western India:Their biostratigraphic and palaeobiogeographic implications

The Kutch Basin of western India is famous for its rich assemblages of the Callovian-Oxfordian ammonites.The family Oppelidae Douvillé is the second most diverse ammonite group after perisphinctids during the Middle-Upper Jurassic.Hecticoceratinae is the most diverse subfamily within Oppelidae and has wide palaeobiogeographic(near cosmopolitan) and temporal distributions(Bathonian-Oxfordian).Some species were well timediagnostic and thus help in interprovincial correlation.The taxonomy of the subfamily Hecticoceratinae of Kutch was in a state of flux until recently.It was not revised since Spath’s(1927-1933) great contribution.Many genera and species were morphogenera or morphospecies and they again suffer from excessive subjective splitting.It was therefore badly needed for a comprehensive taxonomic revision of the subfamily with modern aspects of systematics i.e.,sexual dimorphism and population dynamics.A lithostratigraphic framework has already been well documented in the Kutch Basin of western India.A high resolution biostratigraphy incorporating stage-intrastage fossil assemblages have been used in interbasinal correlation based on the Callovian-Oxfordian hecticoceratins.Near cosmopolitan distribution of many hecticoceratin genera were widely used for biostratigraphic zonation as well as an understanding of the palaeobiogeographic pattern.The phylogeny of the subfamily Hecticoceratinae has been used to construct the cladograms depicting area relationships among different provinces during the Callovian-Oxfordian.

Palaeogeography of a shallow carbonate platform:The case of the Middle to Late Oxfordian in the Swiss Jura Mountains

The Oxfordian （Late Jurassic） carbonate-dominated ptatform outcropping in the Swiss Jura Mountains offers a good biostratigraphic, sequence-stratigraphic, and cyclostratigraphic framework to reconstruct changes in facies distribution at a time-resolution of 100 ka. It thus allows interpreting the dynamic evolution of this platform in much more detail than conventional palaeogeographic maps permit. As an example, a Middle to Late Oxfordian time slice is presented, spanning an interval of about 1.6 Ma. The study is based on 12 sections logged at cm-scale. The interpreted depositional environments include marginal-marine emerged ;ands, fresh-water lakes, tidal fiats, shallow lagoons, ooid shoals, and coral reefs. Although limestones dominate, marly intervals and dolomites occur sporadically. Major facies shifts are related to m-scale sea-level changes linked to the orbital short eccentricity cycle （100 ka）. The 20-ka precession cycle caused minor facies changes but cannot always be resolved. Synsedimentary tectonics induced additional accommodation changes by creating shallow basins where days accumulated or highs on which shoals or islands formed. Autocyclic processes such as lateral migration of ooid and bioclastic shoals added to the sedimentary record. CEimate changes intervened to control terrestrial run-off and, consequently, siliciclastic and nutrient input. Coral reefs reacted to such input by becoming dominated by microbialites and eventually by being smothered. Concomitant occurrence of siliciclastics anddolomite in certain intervals further suggests that, at times, it was relatively arid in the study area but there was rainfall in more northern latitudes, eroding the Hercynian substrate. These examples from the Swiss Jura demonstrate the highly dynamic and （geologically speaking） rapid evolution of sedimentary systems, in which tectonically controlled basin morphology, orbitally induced climate and sea-level changes, currents, and the ecology of the carbonate-producing organisms interacted to form the observed stratigraphic record. However, the interpretations have to be treated with caution because the km-wide spacing between the studied sections is too large to monitor the smaU-scale facies mosaics as they can be observed on modern platforms and as they certainly also occurred in the past.

中亚阿姆河右岸东部地区侏罗系盐下碳酸盐岩储层特征及预测新方法

以岩心、薄片及测井资料为基础,分析了中亚阿姆河右岸东部地区侏罗系牛津阶储层的岩性、储集空间及物性特征,利用三维地震数据,通过正演地震模拟、波形聚类技术、分频RGB融合技术以及集成学习等方法,对储层分布及厚度进行了半定量预测。研究结果表明:①阿姆河右岸东部地区侏罗系牛津阶储层岩性主要为生屑灰岩、颗粒灰岩及泥晶灰岩,为裂缝-孔洞型储层,储集空间以生物格架孔、粒内孔和裂缝为主,裂缝为后期溶蚀流体提供了通道;储层平均厚度为41.6 m,平均孔隙度为4.65%。②研究区储层多发育于XVhp层,根据其在XVhp层的分布位置可分为顶部型、底部型和两期型,顶部型储层主要分布于研究区中部及东部,底部型储层主要集中于西部,而两期型储层大量发育于西北部;研究区西部和东北部储层发育较好,厚度为45~75 m,多沿断裂发育带分布,东南部储层发育较差,厚度小于30 m,距离断层更远。③利用集成学习方法计算研究区储层厚度时,采用异质集成方法中的Stacking方法进行模型运算,以基于箱线图的离群值剔除方法剔除极端数据,以交叉验证法评估模型的预测性能,得到的储层厚度与11口实钻井储层厚度的变化趋势相符,相关系数为0.74。

土库曼斯坦阿姆河盆地卡洛夫-牛津阶储层特征及控制因素分析

土库曼斯坦东北部的阿姆河盆地,是中亚地区最重要的含油气盆地之一。根据钻井岩芯和分析化验资料,确定阿姆河盆地卡洛夫-牛津阶为碳酸盐台地相沉积,具有特征的前缘缓斜坡沉积模式,可划分为蒸发台地、局限台地、开阔台地、台地边缘、前缘缓斜坡和盆地6个相带。其中台内、台地边缘和前缘缓斜坡为储层发育相带,尤以发育于台地边缘、开阔台地和前缘缓斜坡相带中的礁、滩微相最有利于储层发育。沉积微相和岩性对储层类型及物性有直接控制,特点为高能环境条件下沉积的块状礁灰岩和中-厚层状滩相颗粒灰岩以发育原生孔隙保存良好的孔隙型和裂缝-孔隙型储层为主,而较低能环境条件下沉积的(含)颗粒微晶灰岩、隐藻灰岩和泥-微晶灰岩以发育基质岩物性很差的裂缝型储层为主。通过综合分析,认为储层发育受沉积微相、岩性和成岩作用复合控制,以各相带内的礁、滩微相灰岩为高效勘探开发目标的'甜心'位置。

土库曼斯坦阿姆河右岸卡洛夫—牛津阶裂缝特征及形成期次

土库曼斯坦阿姆河右岸地区侏罗系碳酸盐岩气藏局部储层段物性差、非均质性强,裂缝发育状况成为制约气井产能的关键因素,研究裂缝特征及形成期次具有重要意义。根据该区卡洛夫—牛津阶18口取心井岩心裂缝的观察描述结果,发现该区储层主要发育水平裂缝和低角度斜交裂缝,按裂缝之间的切割、限制、组合关系及产状特征,可识别出成岩裂缝和构造裂缝2种成因类型的裂缝,其中构造裂缝对储层发育具有重要贡献。在认识裂缝特征的基础上,利用次生石英ESR年龄标定、非定向样品声发射实验、裂缝充填物稳定同位素(碳、氧、锶)测定及流体包裹体分析等技术方法,确定构造裂缝具有3个形成期次,分别对应于燕山晚期、喜山早期和喜山中期。研究认为,喜山早期和中期的2期裂缝(或断裂)具有极其重要的通源性质,油气充注成藏始于喜山早期,定位于喜山中期。

土库曼斯坦萨曼杰佩气田卡洛夫-牛津阶碳酸盐岩沉积-成岩系统

以土库曼斯坦阿姆河盆地萨曼杰佩气田主力油、气产层卡洛夫-牛津阶碳酸盐岩为例,根据沉积相、成岩作用方式、成岩演化序列和相对应的地质作用产物特征,综合研究Fe、Mn、Sr微量元素,C、O、Sr稳定同位素,流体包裹体和阴极发光等地球化学特征反映的成岩环境和成岩流体性质。按'水文体制'将卡洛夫-牛津阶划分为不同成岩阶段的海水-淡水、压实卤水和深循环温压水3个成岩系统,认为沉积-成岩系统与储层在时空上具有良好的耦合关系,可归结为:台地边缘生物礁和浅滩相控制了储层的区域分布;早成岩阶段淡水系统溶蚀作用和压实卤水成岩系统的浅埋藏白云岩化作用是形成储层的基础;中成岩阶段的温压水成岩系统埋藏溶蚀作用、中-深埋藏白云石化作用和构造破裂作用扩大了储层规模,提高了储层质量,对优质储层发育贡献最大。

阿姆河盆地卡洛夫-牛津阶碳酸盐岩储层地球化学特征和成岩流体分析

卡洛夫-牛津阶碳酸盐岩为土库曼斯坦阿姆河盆地主力天然气产层,以储层岩石学分析为基础,结合Fe、Sr、Mn微量元素和C、O、Sr同位素及流体包裹体地球化学特征,分析了储层成因和成岩流体性质,得出以下几点认识:(1)由厚壳蛤壳体测定的87Sr/86Sr比值在全球锶同位素地层曲线上可标定的年龄为157.2Ma,储层发育层位属于卡洛夫-牛津阶;(2)卡洛夫-牛津阶为一持续海侵-海退旋回,持续海侵期是礁、滩相储层形成期,而持续海退期为致密盖层发育期;(3)较高的Fe和Sr及较低的Mn含量,以及伴随成岩强度加大δ13C变化不大而δ18O向负值方向偏移的演化趋势,证明成岩作用发生在缺乏大陆淡水影响和以温度为主控因素的还原性封闭系统中;(4)综合同位素地球化学与流体包裹体和镜质体反射率特征,可确定洛夫-牛津阶碳酸盐岩仍处在中成岩阶段;(5)礁、滩相灰岩的溶蚀、埋藏白云化和充填缝、洞的方解石是不同成岩阶段的水-岩反应产物,成岩流体主要来自于深部富Sr的地层热卤水。

阿姆河盆地阿盖雷地区牛津阶碳酸盐岩储层特征

阿姆河盆地阿盖雷地区在Aga-21井和Aga-23井于牛津阶碳酸盐岩钻获高产工业气流,详细研究该区牛津阶碳酸盐岩储层特征,对整个地区的勘探开发具有重要指导意义。在岩心描述的基础上,通过铸体薄片、扫描电镜和储层物性等资料的综合分析,结合测井及地震资料,认为牛津阶碳酸盐岩储层发育和分布受沉积微相和成岩作用共同控制,砂屑滩和生屑滩为储层发育的基础,溶蚀作用为储层形成的关键因素,破裂作用有效地提高了储层品质。同时指出砂屑滩和生屑滩为有利储层发育的沉积微相,是今后主要的勘探开发目标。

阿姆河盆地卡洛夫-牛津阶碳酸盐岩阴极发光性及其研究意义

以岩石学特征分析为基础,阴极发光为手段,结合Fe-Mn-Sr微量元素和O同位素地球化学特征,综合研究了土库曼斯坦阿姆河盆地卡洛夫-牛津阶各类碳酸盐岩的成岩作用特征,认为:(1)泥-微晶灰岩具备较弱的阴极发光性,与很低的Mn和较高的Fe含量有关,保存了原始海水信息;(2)各类生物碎屑发光性不尽相同,以腕足、厚壳蛤和有孔虫化石发光性最弱、对原始海水的信息保存最好;(3)原生孔隙发育的颗粒灰岩和生物礁灰岩中的胶结物阴极发光性显示出明显的多世代现象,分别保存了海水成岩环境、近地表-浅埋藏地层封存水成岩环境和中-深埋藏深循环温压水成岩环境的成岩流体信息;(4)白云质灰岩中的微-粉晶白云石发光性最弱,结合其偏负的δ18O和较高的Fe与Mn含量,表明白云石化机制与埋藏成岩作用密切相关;(5)按裂缝充填物的阴极发光性差异,可识别出3个与声发射试验结果相吻合的破裂期次。

阿姆河盆地奥贾尔雷地区牛津阶碳酸盐岩储层特征

以岩心观察和薄片鉴定为基础,综合利用测井、地震和物性分析等资料,探讨了阿姆河盆地奥贾尔雷地区牛津阶碳酸盐岩储层特征。奥贾尔雷牛津阶属于台地相沉积,可划分为台地前缘缓斜坡沉积亚相和生屑滩、鲕粒滩等若干微相;牛津阶储集岩类主要为颗粒灰岩,储集空间主要为粒间溶孔和粒内溶孔;压实作用、压溶作用和胶结作用是破坏储层储集性能的主要因素,而溶蚀和破裂作用是提高和改善储层储集性能的重要因素,生屑滩和鲕粒滩为最有利储层发育的沉积微相,是主要的勘探开发目标。

土库曼斯坦萨曼杰佩气田卡洛夫阶—牛津阶碳酸盐岩储层特征

土库曼斯坦萨曼杰佩气田卡洛夫阶—牛津阶碳酸盐岩沉积相类型丰富,发育有台地前缘缓斜坡、台地边缘生物礁和浅滩、开阔台地和局限台地5个相带,储层岩性主要为台地边缘生物礁和浅滩相的礁灰岩、生物屑灰岩和鲕粒灰岩等,具有厚度大和大多为优质储层的特点。以岩芯观察描述和薄片鉴定为基础,综合利用地质、钻井、地震等资料,深入探讨了萨曼杰佩气田卡洛夫阶—牛津阶碳酸盐岩沉积相特征和储层类型,划分出孔洞缝型、孔隙型、裂缝-孔隙型和裂缝性储层类型,确定孔洞缝复合型储集层主要发育于高能环境下形成的台地边缘生物礁相带;孔隙型和裂缝-孔隙型储层主要发育在相对高能的台地边缘浅滩相带,在开阔台地台内浅滩中也有一定规模的发育;裂缝型储层主要分布在泻湖和潮下等低能相带。在此基础上建立了不同储层类型的测井相响应模式。研究了岩性、沉积相以及成岩作用对储集层发育的控制作用,认为高能的礁、滩相带最有利储层发育,而强烈的压实和胶结作用是破坏储层储集性能的主要因素。

土库曼斯坦阿姆河盆地卡洛夫-牛津阶层序-古地理特征及演化

通过沉积相和层序地层分析,确定土库曼斯坦阿姆河盆地中-上侏罗统卡洛夫-牛津阶主要为一套碳酸盐岩台地沉积体系,可划分出SQ1~SQ3三个三级层序,其经历了从缓斜坡台地→镶边缓斜坡台地→缓斜坡台地的沉积演化过程,主力储层、产层发育于SQ1和SQ2层序,此三个层序又可进一步划分为TST和HST两个体系域。以体系域为编图单元,编制了SQ1、SQ2和SQ3层序各体系域的岩相古地理图,并探讨了有利储集相带的展布规律,认为SQ1-HST、SQ2-TST和SQ2-HST三个体系域中叠置发育的台缘礁滩为最有利储层发育的相带,应成为今后的勘探重点。

土库曼斯坦阿姆河盆地卡洛夫—牛津阶沉积相特征

以岩心描述、薄片和古生物鉴定为依据,结合测井相和地震相特征和区域构造-沉积背景,对土库曼斯坦阿姆河盆地卡洛夫—牛津阶沉积相特征进行研究,确定该地层单元属于碳酸盐台地沉积体系,识别出蒸发台地、局限台地、开阔台地、台地边缘礁滩、前缘缓斜坡、盆地等6种沉积相类型。以连井沉积相剖面对比、沉积相平面分布特征和纵向演化分析为基础,进一步揭示出该盆地卡洛夫—牛津阶经历了台地前缘缓斜坡、台地边缘礁滩、开阔台地、局限台地、蒸发台地等交替发育构成多期次海进—海退旋回演化和"开放性宽缓型镶边缓斜坡台地"沉积模式。

土库曼斯坦萨曼杰佩气田储层成岩作用与孔隙演化

以露头剖面测量、岩心观察和室内薄片鉴定为依据,探讨了土库曼斯坦萨曼杰佩气田碳酸盐岩储层成岩作用与孔隙演化规律,其中对储层起破坏作用的为胶结、压实-压溶、硅化、硬石膏化及天青石化和次生矿物的充填等,而对储层贡献最大的建设性成岩作用主要为白云岩化、重结晶、溶蚀和破裂等,形成了以生物体腔孔、粒间溶孔、粒内溶孔、铸模孔、晶间溶孔和溶裂缝等多种原生与次生孔隙组合的储层基本特征。通过再造成岩序列和恢复孔隙演化历史,可知该气田分别经历了以原生孔隙为主→剩余原生孔隙为主→剩余原生孔隙为主叠加次生孔隙→次生孔隙为主叠加原生孔隙的组合阶段。

恰什古伊地区碳氧同位素地层学分析

土库曼斯坦恰什古伊地区有效储集层为卡洛夫—牛津阶碳酸盐岩,该段GR变化小,旋回分析困难,导致有利储层预测难。利用该区Cha–21井所取岩芯中采集的41个样品测定的碳氧同位素,结合区域沉积演化分析资料,探讨了卡洛夫—牛津阶储层段沉积时的海平面变化。结果表明,氧同位素的原始信息已被成岩作用破坏,而碳同位素基本保持了原始特征,因此碳同位素可用于同位素地层研究和古环境分析;据此计算出盐度指数变化范围为128.25～136.63,明显大于海水和淡水的分界标准,反映成岩流体具有较高盐度海源水性质;由δ13C的变化所确定的研究区的海平面变化曲线与卡洛夫—牛津阶全球海平面变化曲线吻合,印证了该区储层地质年代定为卡洛夫—牛津期是准确的;依据海平面变化曲线,将卡洛夫—牛津阶主力储层段分为3个沉积旋回5个演化阶段。该成果填补了该区碳氧同位素地层研究的空白,对深化盆地沉积演化规律的认识及预测储层有利区块具有重要意义。

阿姆河盆地恰什古伊地区卡洛夫—牛津阶储层特征

恰什古伊气田是中亚管线的核心供气气田之一,受早期恰什古伊地区钻井成功率低及取心收获率低的影响,其储层特征不明确,这给该区的勘探评价与开发工作造成了较大困难。利用目的层段的系统岩心资料,开展了岩心观察、铸体薄片鉴定、岩心物性和孔隙结构分析等实验,在结合前人研究成果的基础上,对该气田主要层段的储层特征进行了研究。结果表明:恰什古伊地区储层的储集性能主要表现为中—低孔、低渗,储层孔喉组合以中、小孔-小喉组合为主。通过综合评价,将区块内储层分为3级,并研究了各级储层特征,同时发现区块的岩石类型、沉积微相和成岩作用对储层发育影响显著。该研究可为恰什古伊气田的进一步评价提供坚实的基础,同时也为气田周边的滚动勘探与开发提供借鉴。