Features and origins of massive dolomite of Lower Ordovician Penglaiba Formation in the northwest Tarim Basin:Evidence from petrography and geochemistry

An integrated petrographical and geochemical study of the massive dolomite of the lower Ordovician Penglaiba Formation of the Tarim Basin,outcropping at Yonganba recognized three dolomite types:very finely to finely crystalline nonplanar-a to planar-s dolomite(D1);medium crystalline planar-s to planar-e dolomite(D2);and coarse crystalline nonplanar-a dolomite(D3).All have been affected by burial.D1 and D2 dolomites developed initially before or during shallow burial and later recrystallized,whereas D3 dolomite replaced the initial limestone entirely during burial.All three dolomites have similar geochemical features.The D2 dolomite tends to have more inter-crystalline pores(inherited from primary pores)and higher porosity due to its outstanding compaction resistance during shallow burial;whereas D3 dolomite does not retain appreciable primary pores due to strong cementation and pressure dissolution before dolomitization.This study provides a useful model for understanding the origin and porosity development of burial dolomite,in particular Paleozoic dolomite.

Petrography and origin of the Lower Ordovician microbial carbonates in the Songzi Area of Hubei Province,middle Yangtze region,China

This study is the first systematic assessment of the Lower Ordovician microbial carbonates in Songzi,Hubei Province,China.This paper divides the microbial carbonates into two types according to growth patterns,namely nongranular and granular.The nongranular types include stromatolites,thrombolites,dendrolites,leiolites and laminites;the granular types are mainly oncolites and may include a small amount of microbiogenic oolite.According to their geometric features,the stromatolites can be divided into four types:stratiform,wavy,columnar and domal.Additionally,dipyramidal columnar stromatolites are identified for the first time and represent a new type of columnar stromatolite.The thrombolites are divided into three types:speckled,reticulated and banded.The grazing gastropod Ecculiomphalus and traces of bioturbation are observed in the speckled and reticulated thrombolites.This paper considers these two kinds of thrombolites to represent bioturbated thrombolites.These findings not only fill gaps in the field of domestic Ordovician bioturbated thrombolites but also provide new information for the study of thrombolites.Based on the analysis of the sedimentary characteristics of microbialites,the depositional environments of the various types of microbialites are described,and the distribution patterns of their depositional environments are summarized.The relationship between the development of microbialites and the evolution and radiation of metazoans during the Early to Middle Ordovician is discussed.Consistent with the correspondence between the stepwise and rapid radiation of metazoans and the abrupt reduction in the number of microbialites between the late Early Ordovician and the early Middle Ordovician,fossils of benthonic grazing gastropods(Ecculiomphalus)were found in the stromatolites and thrombolite of the study area.It is believed that the gradual reduction in microbialites was related to the rapid increase in the abundance of metazoans.Grazers not only grazed on the microorganisms that formed stromatolites,resulting in a continuous reduction in the number of stromatolites,but also disrupted the growth state of the stromatolites,resulting in the formation of unique bioturbated thrombolites in the study area.Hydrocarbon potential analysis shows that the microbialites in the Nanjinguan Formation represent better source rocks than those in the other formations.

Characteristics and Dolomitization of Upper Cambrian to Lower Ordovician Dolomite from Outcrop in Keping Uplift, Western Tarim Basin, Northwest China

Late Cambrian to Early Ordovician sedimentary rocks in the western Tarim Basin, Northwest China, are composed of shallow-marine platform carbonates. The Keping Uplift is located in the northwest region of this basin. On the basis of petrographic and geochemical features, four matrix replacement dolomites and one type of cement dolomite are identified. Matrix replacement dolomites include （1） micritic dolomites （MD1）; （2） fine-coarse euhedral floating dolomites （MD2）; （3） fine-coarse euhedral dolomites （MD3）; and （4） medium-very coarse anhedral mosaic dolomites （MD4）. Dolomite cement occurs in minor amounts as coarse saddle dolomite cement （CD1） that mostly fills vugs and fractures in the matrix dolomites. These matrix dolomites have δ18O values of ？9.7‰ to ？3.0‰ VPDB （Vienna Pee Dee Belemnite）; δ13C values of ？0.8‰ to 3.5‰ VPDB; 87Sr/86Sr ratios of 0.708516 to 0.709643; Sr concentrations of 50 to 257 ppm; Fe contents of 425 to 16878 ppm; and Mn contents of 28 to 144 ppm. Petrographic and geochemical data suggest that the matrix replacement dolomites were likely formed by normal and evaporative seawater in early stages prior to chemical compaction at shallow burial depths. Compared with matrix dolomites, dolomite cement yields lower δ18O values （？12.9‰ to ？9.1‰ VPDB）; slightly lower δ13C values （？1.6‰-0.6‰ VPDB）; higher 87Sr/86Sr ratios （0.709165-0.709764）; and high homogenization temperature （Th） values （98°C-225°C） and salinities （6 wt%-24 wt% NaCl equivalent）. Limited data from dolomite cement shows a low Sr concentration （58.6 ppm） and high Fe and Mn contents （1233 and 1250 ppm, respectively）. These data imply that the dolomite cement precipitated from higher temperature hydrothermal salinity fluids. These fluids could be related to widespread igneous activities in the Tarim Basin occurring during Permian time when the host dolostones were deeply buried. Faults likely acted as important conduits that channeled dolomitizing fluids from the underlying strata into the basal carbonates, leading to intense dolomitization. Therefore, dolomitization, in the Keping Uplift area is likely related to evaporated seawater via seepage reflux in addition to burial processes and hydrothermal fluids.

A Lower Ordovician Carbonate Contourite Drift on the Margin of the South China Paleocontinent at Jiuxi,Northern Hunan

Carbonate contourite drift at Jiuxi. Taoyuan, northern Hunan, was developed in a deepwater area ofnorthern Hunan on the margin of the Early Ordovician South China palcocontinent. The Lower Ordoviciansequence in the area is more than 350 m thick and contains well-developed contourites that can be groupedinto the following five types: the calcilutitic, the arenitic, the siltitic. the fine ruditic and the bioclastic. Thefirst three often constitute a complete or incomplete contourite succession. The arenitic contourite is nearlyuniformly distributed as interlayers throughout the succession, creating a monotonously rhythmic texture inthe contourite drift. The pattern of spatial distribution of the succession shows that the contourite drift is ahuge ridge-like sedimentary body extending along the trend of paleoslope. Numerous marks of flow direc-tion have pointed to an eastward paleoflow direction along the slope.

Characteristics and genesis of shoal facies reservoir of the Lower Ordovician Tongzi Formation in southeastern Sichuan Basin,China

The Lower Ordovician Tongzi Formation containing abundant shoal sediments is the most promising stratum for the petroleum exploration in the Sichuan Basin.However,the current studies mainly focus on the central part of the Basin,the systematic analysis of the southeastern part with well-developed shoal facies is lacking.This paper aims to clarify the characteristics and genesis of the Tongzi Formation reservoir in Southeastern Sichuan Basin,following an analysis of sedimentary facies within the sequence stratigraphic framework.The research shows that the main types of reservoir rocks are oolitic,intraclastic and bioclastic dolostones.And the reservoir spaces consist mainly of intergranular(dissolved)pores,intercrystalline(dissolved)pores,intragranular dissolved pores and fractures.Among them,intergranular pores account for the highest proportion,which is followed by intragranular dissolved pores.In addition,most throats are necking and flaky which mainly connect intergranular and intercrystalline pores,respectively.The diagenetic sequence shows that penecontemporaneous karst well improved the porosity of the reservoir in the early-stage although the cementation and compaction reduced parts of pores.The reservoir formation is associated with the tectonic-depositional settings,diageneses and terrigenous contamination.Paleohighlands and submerged uplifts,forming in the early Ordovician amalgamation between Yangtze and Cathaysia blocks,accumulated shoal sediments as the material basis for the reservoir formation.Penecontemporaneous karst forming intragranular dissolved pores and the dolomitization aiding grainstones to resist the pressure solution are the key to increasing porosity and preserving pores.The absence of terrigenous contamination prevented intergranular pores from being strongly cemented,which resulted in the reservoir difference between the central and southeastern Sichuan Basin.The study can be used as a reference for the further exploration of Ordovician petroleum in the Sichuan Basin and other regions owning similar geological settings.

Accumulation conditions and exploration directions of Ordovician lower assemblage natural gas, Ordos Basin, NW China

Based on drilling cores, well logging and seismic data, source rocks and reservoirs are evaluated;and the natural gas genesis is identified through the analysis of natural gas isotopes, components and fluid inclusions, to study the gas accumulation conditions of the gypsum salt rock related strata of the Ordovician lower assemblage in Ordos Basin.(1) The natural gas from Ordovician lower assemblage is high thermal evolution dry gas from marine source rock, characterized by relatively light δ^(13)C value of methane and heavy δ^(13)C value of ethane. The natural gas is identified as gas cracking from crude oil according to component analysis. Thermochemical sulfate reduction(TSR) reaction has happened between the hydrocarbon fluid and sulfate as sulfur crystals are found in the cores, hydrogen sulfide is found in the natural gas, and hydrocarbon and hydrogen sulfide fluid inclusions are widespread in secondary minerals.(2) Around the gypsum-salt lows, argillaceous rocks are extensive in the Ordovician lower assemblage, reaching a cumulative thickness of 20–80 m. The effective source rocks include argillaceous rock rich in organic laminae, algal clump and algal dolomite. Analysis shows that the source rocks have a dominant TOC of 0.1%–0.5%, 0.31% on average and 3.24% at maximum. The source rocks have an average TOC of 0.58% after recovered through organic acid salt method, indicating the source rocks have high hydrocarbon supply potential.(3) In the sedimentary period, the palaeo-uplift controlled the distribution of reservoirs. The inherited secondary palaeo-uplift in Wushenqi–Jingbian east of the central palaeo-uplift and the low uplift formed by thick salt rocks near Shenmu–Zizhou area controlled the distribution of penecontemporaneous grain shoal dolomite reservoirs. The salinization sedimentary environment of gypsum salt rock can promote the development of reservoir. There are three types of dolomite reservoirs, the one with intercrystalline pore, with dissolution pore, and with fracture;intercrystalline and dissolution pores are main reservoir spaces.(4) There are two types of cap rocks, namely tight carbonate rock and gypsum-salt rock, constituting two types of source-reservoir-cap assemblages respectively. The general accumulation model is characterized by marine source rock supplying hydrocarbon, beach facies limy dolomite reservoir, small fractures acting as migration pathways, and structural-lithologic traps as accumulation zones.(5) The third and fourth members of Majiagou Formation are major target layers in the lower assemblage. The Wushengqi–Jingbian secondary paleo-uplift area and Shenmu–Zizhou low uplift are dolomite and limestone transition zone, there develops tight limestone to the east of the uplift zone, which is conducive to the formation of gas reservoir sealed by lithology in the updip. Two risk exploration wells drilled recently have encouraging results, indicating that the two uplift zones are important prospects.

不同构造单元页岩孔隙结构差异及其油气地质意义——以四川盆地泸州地区深层页岩为例

不同构造单元页岩储层品质、含气性差异明显,构造改造作用对页岩气勘探开发具有控制作用,但关于深层页岩气的构造控制作用机理研究较少,相关认识尚不明确,制约了深层页岩气的勘探开发。为此,通过“岩心—薄片—扫描电镜”多尺度观察、全岩矿物X射线衍射分析、核磁共振等技术手段,对比分析了四川盆地南部泸州地区不同构造单元上奥陶统五峰组—下志留统龙马溪组深层页岩孔隙结构和储层特征的差异,探讨了不同构造单元页岩孔隙结构差异与储层品质的耦合关系,明确了页岩气产量差异的内在地质原因,落实了构造改造作用下的页岩气勘探开发有利区。研究结果表明:①向斜区页岩主要以有机质孔隙、非构造裂缝为主,孔径大;背斜区页岩孔隙结构被强烈改造,以矿物粒间孔、构造裂缝为主,矿物粒间孔狭长且定向排列,孔径小。②向斜区构造相对稳定,有机质孔隙、矿物粒间孔以及成岩裂缝保存较好,宏孔占比高,储集性能好,含气量和产量高;背斜区页岩储层发育大量构造裂缝与断层,孔隙和成岩裂缝被压实,孔径减小,储集性能变差,含气量和产量低。③距盆缘剥蚀区越远,构造越稳定的单元,保存条件越好,该类构造单元页岩储层越发育,含气量和产量越高,页岩气勘探开发潜力越大。结论认为,构造运动对于压力系统的影响是形成不同构造单元深层页岩孔隙结构特征差异的重要因素,并控制了页岩储层的含气性与产量;向斜区深层保存条件好,远离剥蚀区,为勘探开发的最有利区,该认识可为深层页岩气勘探开发提供技术支撑。

塔里木盆地古城地区下奥陶统孔隙型白云岩储层成因及演化

塔里木盆地古城地区下奥陶统蓬莱坝组—鹰山组下段的白云岩普遍发育孔隙,表现为针状溶孔及超晶粒孔隙、晶间微孔,一般认为与白云石化作用相关。基于岩心、薄片观察,应用阴极发光、包裹体、稀土元素、碳氧同位素等多种测试资料,对古城地区下奥陶统蓬莱坝组—鹰山组下段白云岩的成因、孔隙类型及成因、孔隙演化模式进行了分析。研究认为:(1)蓬莱坝组—鹰山组下段白云岩成因以准同生期白云石化作用为主,部分叠加深部热液流体改造作用,缝洞充填的白云石为热液成因。(2)超晶粒孔隙在宏观上表现为针状溶孔,发育于原始组构为颗粒的细—中晶白云岩中,以中—粗粒内溶孔、铸模孔、粒间溶孔为主,多发育在单个颗粒滩旋回的中上部,形成于白云石化之前的准同生期大气淡水选择性溶蚀;晶间微孔呈孤立状,连通性差,形成于准同生期白云石化作用。准同生期白云石化虽未直接产生大量孔隙,但提供了抗压实的骨架,并阻碍了后期流体作用沉淀,是孔隙得以保存的关键。(3)古城地区蓬莱坝组—鹰山组下段孔隙型白云岩储层呈多套薄层状,其厚度与规模受多期颗粒滩叠加及其暴露程度的综合影响。

塔里木盆地塔河地区中下奥陶统沉积特征及其演化模式

沉积环境对岩溶型储层的发育起着基础性作用,影响着岩溶体的规模和强度,加强沉积环境研究有助于优质岩溶储层的勘探与预测。为深入认识塔河地区中下奥陶统沉积特征,在野外调查基础上,结合岩石颜色、类型、组合、结构、构造、古生物、地球化学特征等岩石学和岩相学标志,利用岩心、测录井、地震和区域宏观沉积资料,对中下奥陶统沉积环境进行了精细识别和划分。结果显示,研究区岩石类型主要为颗粒灰岩、泥晶灰岩、生物灰岩和过渡岩类;共发育5种沉积环境,蓬莱坝组以局限—半局限台地为主,鹰山组以半局限台地、开阔台地为主,一间房组以开阔台地、台地边缘、淹没台地为主;共发育11种地震相,与各类沉积相带具有较明显的对应关系。总的来说,研究区以台地相为主,时空演化差异明显。纵向上,自蓬莱坝组至一间房组沉积水体逐渐加深,沉积环境由局限逐渐变为开阔;横向上,研究区主体以开阔台地、台地边缘为主,向东、向南至研究区外部逐渐过渡为斜坡、盆地相。综合前人资料,建立了研究区自下奥陶统蓬莱坝组局限台地→半局限台地→中下奥陶统鹰山组开阔台地→中奥陶统一间房组台地边缘→一间房组晚期、吐木休克组淹没台地的演化模式。

不同孔隙结构碳酸盐岩的岩石物理响应特征及储层预测新方法——以鄂尔多斯盆地奥陶系马家沟组四段为例

近年来,在鄂尔多斯盆地中东部地区下奥陶统马家沟组四段(以下简称马四段)的台内丘滩体钻遇了优质白云岩储层,但该套储层厚度薄、与围岩弹性参数差异较小,利用常规方法很难准确识别和预测。为了提高白云岩储层的预测精度,基于铸体薄片与岩心CT扫描,详细分析了马四段碳酸盐岩的特征,通过岩石物理弹性测试,结合物性测试及试采资料建立了马四段岩石弹性参数与孔隙结构的关系,提出了研究区一种变基质多孔微分等效介质模型的预测孔隙结构和储层的新方法,并进行了矿场验证。研究结果表明:(1)马四段碳酸盐岩发育孔隙型和裂缝型2类储层,其中孔隙型储层可细分为以晶间孔为主和以晶间溶孔+晶间孔为主2类;(2)晶间孔为白云岩化作用形成,孔隙纵横比较大,晶间溶孔由晶间孔经过溶蚀作用改造形成,孔隙纵横比变小;(3)裂缝主要为构造缝和溶蚀缝,孔隙纵横比最小;(4)沉积和成岩作用对碳酸盐岩的孔隙结构影响大,孔隙结构的差异会引起岩石弹性参数的较大变化,利用该差异可以有效预测白云岩优质储层。结论认为,该方法首先通过变基质骨架建模准确划分岩石的基质类型,然后利用多重孔微分等效介质模型预测岩石的孔隙结构类型,并定量计算不同孔隙类型孔隙的体积占比,为提高白云岩储层的预测精度奠定了技术基础,有助于碳酸盐岩优质储层的精确预测的深入研究。

Hydrocarbon generation and storage mechanisms of deepwater shelf shales of Ordovician Wufeng Formation–Silurian Longmaxi Formation in Sichuan Basin, China

As the hydrocarbon generation and storage mechanisms of high quality shales of Upper Ordovician Wufeng Formation– Lower Silurian Longmaxi Formation remain unclear, based on geological conditions and experimental modelling of shale gas formation, the shale gas generation and accumulation mechanisms as well as their coupling relationships of deep-water shelf shales in Wufeng–Longmaxi Formation of Sichuan Basin were analyzed from petrology, mineralogy, and geochemistry. The high quality shales of Wufeng–Longmaxi Formation in Sichuan Basin are characterized by high thermal evolution, high hydrocarbon generation intensity, good material base, and good roof and floor conditions;the high quality deep-water shelf shale not only has high biogenic silicon content and organic carbon content, but also high porosity coupling. It is concluded that:(1) The shales had good preservation conditions and high retainment of crude oil in the early times, and the shale gas was mainly from cracking of crude oil.(2) The biogenic silicon(opal A) turned into crystal quartz in early times of burial diagenesis, lots of micro-size intergranular pores were produced in the same time;moreover, the biogenic silicon frame had high resistance to compaction, thus it provided the conditions not only for oil charge in the early stage, but also for formation and preservation of nanometer cellular-like pores, and was the key factor enabling the preservation of organic pores.(3) The high quality shale of Wufeng–Longmaxi Formation had high brittleness, strong homogeneity, siliceous intergranular micro-pores and nanometer organic pores, which were conducive to the formation of complicated fissure network connecting the siliceous intergranular nano-pores, and thus high and stable production of shale gas.

鄂尔多斯盆地东部下奥陶统马家沟组盐下含气系统特征与勘探潜力

奥陶系下统马家沟组是鄂尔多斯盆地下古生界重要产气层位,目前已在马家沟组盐上风化壳领域获得了近万亿立方米的天然气地质储量,且盐上组合研究成果丰富,认识较为统一。但是,马家沟组盐下组合含气系统研究不足和认识分歧较大,已严重制约了该区盐下天然气的勘探。为此,从天然气地球化学特征出发,利用地质、地球物理和地球化学手段,对盐下含气系统进行了系统研究;结合盐下天然气来源、烃源岩规模和储层特征以及圈闭成藏要素评价,明确了马家沟组盐下天然气成藏的有利条件和富集区带。研究结果表明:(1)马家沟组盐下天然气的甲烷、乙烷碳同位素偏轻,具有典型油型气特征,其烃源岩可能为马家沟组高频层序相关的薄层海相烃源岩,岩性主要为暗色泥质白云岩和微生物白云岩,具备规模供烃能力;(2)盐下发育多套丘滩和丘坪粉晶白云岩储层,沿台内低隆规模分布,源储盖组合反映盐下具备自生自储成藏条件,疏导断层、侧向封堵是成藏关键要素;(3)榆林—横山和神木—米脂地区是盐下天然气有利富集区带。结论认为,马家沟组盐下含气系统和天然气富集区带新认识的提出有效地支撑了米探1井的天然气勘探突破,对鄂尔多斯盆地深层天然气深化勘探具有重要指导意义。

塔河油田主体区下奥陶统小尺度缝洞体形成机制与分布预测

塔河油田奥陶系碳酸盐岩储层的开发方向已逐渐从地震反射的“串珠型”缝洞储层转移到“非串珠”型的小缝洞储层,确定小尺度缝洞的形成机制和发育规律是提高此类储量动用率的关键。本次研究对塔河油田主体区岩心和薄片开展了缝洞描述,确定了小尺度缝洞的裂缝成因类型、缝洞参数和充填性质等特征。研究区裂缝划分为构造裂缝和非构造成因裂缝,呈高角度或垂直产状,构造裂缝充填程度弱于风化裂缝;孔洞的充填程度相对较高,但仍存在残留的孔隙空间。基于古岩溶地貌、局部残丘构造幅度的刻画、断裂特征分析和构造应力场模拟,确定了小尺度缝洞体的形成机制。小尺度缝洞的形成受古岩溶地貌、局部残丘构造幅度、断裂和构造应力场综合控制。地貌相对高部位利于岩溶的发生,主体东区地貌整体较主体西区高,缝洞相对西区更发育。残丘构造幅度也影响了岩溶储层的分布差异,残丘缓翼构造坡度相对较缓,利于水岩充分反应,更利于岩溶储层形成。主大断裂控制大尺度溶洞的形成,同时大溶洞和断裂又控制着小尺度缝洞的发育,深部小尺度缝洞受断裂控制的发育深度可达T_7~4界面以下200 m深度。构造应力场影响着构造裂缝的分布,构造裂缝的形成又为孔洞的形成提供了溶蚀通道,间接控制着小尺度缝洞体的分布。在小尺度缝洞形成机制分析的基础上,建立了基于非线性神经网络深度学习算法的小尺度缝洞预测方法,确定了小尺度缝洞平面分布,预测结果与单井缝洞发育情况和初期产液能力相匹配。研究成果为油田整体动用小尺度缝洞储量奠定了技术基础。

塔里木盆地顺北地区中下奥陶统流体改造与油气充注耦合关系

为明确顺北地区中下奥陶统流体改造与油气充注耦合关系,通过对方解石充填物进行阴极发光、流体包裹体显微镜下观察和油包裹体及其伴生盐水包裹体均一温度测试分析,结合方解石微区原位U-Pb同位素定年开展顺北地区中下奥陶统流体改造期次及序列、油气充注期次和时期及流体改造与油气充注耦合关系研究。结果表明:一间房组和鹰山组上段均经历多期流体改造,形成了具有不同阴极发光特征的多期方解石充填物,两者区别在于鹰山组地层未经历大气水改造;油包裹体荧光显示呈现蓝绿色-蓝白色,指示原油成熟度较高,且一间房组与油包裹体共生的盐水包裹体均一温度分布范围为84~98℃,平均均一温度为92.49℃和113~130℃,平均均一温度为119.91℃、鹰山组上段均一温度分布范围91.2~104℃,平均均一温度为96.1℃和112.7~128.1℃,平均均一温度为119.97℃,表明存在加里东晚期和海西晚期-印支期两期油气充注,主成藏期为海西晚期-印支期。烃类包裹体宿主矿物方解石微区原位U-Pb测试表明,其主要形成于加里东中晚期[(466.8±8)~(470.6±4.5)Ma],揭示油气充注发生在加里东晚期混源流体改造形成的具备红色-橙红色阴极发光特征方解石之后。

川东南五峰组-龙马溪组深层、超深层页岩储层特征及其页岩气勘探意义

四川盆地东南地区上奥陶统五峰组—下志留统龙马溪组中深层领域页岩气勘探及页岩储层特征与主控因素的研究已经取得了丰硕成果,而作为当前页岩气勘探重点的深层、超深层领域,由于受钻井等因素的制约,对于其储层发育特征及与中深层页岩储层的差异等研究还不够深入。为了明确五峰组—龙马溪组深层、超深层页岩储层特征,为勘探部署提供依据,选取川东南地区4口埋深在2000~6000 m的典型页岩气钻井,系统开展了深层、超深层页岩储层发育特征及差异对比研究,探讨了储层孔隙发育的成因。研究表明:(1)埋深在6000 m以内,五峰组—龙马溪组页岩储层依然能够发育高孔有效储层,且随埋深的增大孔隙度无明显变化,但是有机质孔的形态、孔隙结构及连通性存在一定差异,即随着埋深的增大,有机质孔孔径相对变小,孔隙连通性变差;(2)明确了生物成因的硅质是孔隙发育的基础,流体超压是储层孔隙保持的关键,在两者联合作用下,深层、超深层页岩高孔隙优质储层得以发育和保持;(3)基于储层发育的研究,将页岩气勘探拓深至6000 m,明确了下一步页岩气勘探方向。初步评价四川盆地及周缘五峰组—龙马溪组深层、超深层页岩气(埋深为4000~5000 m)资源量超2×10^(12)m^(3)。

塔里木盆地跃进地区奥陶系储层成因机理

通过对岩芯、薄片的观察,结合扫描电镜、阴极发光、碳氧同位素、锶同位素和稀土元素的分析化验资料,探讨了塔里木盆地跃进地区中下奥陶统缝洞型储层的成因机理。沿裂缝断续分布的溶蚀孔洞、围岩和裂缝中的萤石交代产物表明存在热液溶蚀和交代作用,而基质晶间孔中的短柱状和柱状石英晶体、溶蚀孔洞方解石的低^(87 )Sr/^(86 )Sr比值(0.708407)、硅质结核的Eu正异常均表明存在岩浆期后的深部热液流体的溶蚀、交代和胶结作用。跃进地区中下奥陶统发育多期活动的走滑断裂带,由于基质低孔低渗,二叠纪晚期的岩浆期后热液流体主要沿断裂带进入中下奥陶统地层中进行溶蚀改造,随后的胶结作用对围岩中的孔隙网络造成严重的破坏,进一步增强了研究区内储层的非均质性。走滑断裂带控制着跃进地区中下奥陶统规模缝洞型储层的形成与分布,热液溶蚀作用进一步改善了缝洞型储层内部的渗流能力。

广域电磁法在豫西地区济源凹陷古生界油气勘探中的应用

豫西地区济源凹陷由山地和丘陵组成,地形条件复杂,地震资料品质较差,盆地内断裂形态结构、深部古生界展布特征等不清楚,制约着济源凹陷的油气勘探和资源潜力评价。本文利用广域电磁法在豫西地区济源凹陷进行方法应用研究,采用“地球物理资料综合处理解释一体化系统”进行数据处理与反演,获得了地下真实的电性特征,建立了目标层与视电阻率的电性关系,刻画了研究区目标层的构造特征。本研究查明了济源凹陷西部斜坡的断裂结构特征,新识别出12条断裂;揭示石炭-二叠系厚度分布范围在200~1800 m,最大埋深2200 m;奥陶系顶界面埋深分布在300~2450 m,呈“条带状”展布,得到了地质调查井岩心编录的证实。

四川盆地大安区块五峰组—龙马溪组深层页岩地质特征与勘探有利区

近年来,四川盆地渝西地区大安区块上奥陶统五峰组—下志留统龙一1亚段连续获得多口高产工业气井,展示了该区块页岩气良好的勘探开发前景。但由于该区块页岩埋藏深,勘探程度低,深层优质页岩段沉积微相类型、储层特征及其空间展布规律不清,页岩气有利区优选依据不充分,制约了该区页岩气的深化勘探与开发。为此,通过岩心观察、扫描电镜、地球化学与物性测试、含气量测定和核磁共振等实验手段分析,结合钻测井资料,研究了大安区块五峰组—龙一1亚段各小层地质特征及储层展布规律,建立了深层页岩气有利区评价标准,优选了深层页岩气勘探有利区。研究结果表明:①高碳硅质页岩微相和高碳含黏土硅质页岩微相是最优质页岩气储层发育的沉积微相,主要发育于五峰组—龙一13小层。②龙一11—龙一14小层孔隙度平均超过4%,储集性好;五峰组—龙一13小层超大孔和裂缝较发育,所占比例分别为66%和25%。③五峰组—龙一13小层脆性矿物平均含量为55%,可压性好;含气量平均值不低于4.0 m^(3)/t,含气条件较好;龙一11—龙一13小层各层平均总有机碳含量超过3.0%,生烃条件好;地层压力系数普遍大于1.90。结论认为:①五峰组—龙一13小层页岩储层品质最优;②Ⅰ类、Ⅱ类和Ⅲ类页岩气有利区资源量分别为3775.78×10^(8) m^(3)、2970.05×10^(8) m^(3)、599.83×10^(8) m^(3);③该区深层页岩气勘探潜力大,是四川盆地重要的天然气产能接替区,其中临江向斜为下一步页岩气勘探的最有利区。

速度-压力岩石物理模型及其在页岩孔隙压力预测中的应用

针对现有基于声波速度的经验公式进行地层压力预测时影响因素复杂的问题,应用弹性岩石物理模型来定量分析研究速度-压力关系的各种控制因素,提出孔构参数(γ)与压差之间的解析关系,并揭示压力对岩石体积模量和纵波速度等弹性性质的主控作用,进而准确预测孔隙压力。含气页岩中微裂缝及断裂发育时,异常高压下(高γ值)细小裂缝及扁平孔隙张开,岩石体积模量远低于其在静水压力下(低γ值)平均孔隙结构偏圆时的状态。结合岩心、测井及地震数据,利用此岩石物理压力关系刻画四川盆地丁山地区上奥陶统五峰组—下志留统龙马溪组页岩的孔隙压力三维空间分布变化,压力系数与含气量呈正相关,该预测结果与现场实测数据吻合较好。岩石物理压力关系的分析和方法的提出对非常规和常规油气田的勘探、生产和钻井安全都具有重要借鉴价值。

塔里木盆地和田河气田下奥陶统白云岩成因

塔里木盆地和田河气田是最近探明的大型碳酸盐岩气田 ,下奥陶统主要发育两类白云岩。下部为层状白云岩 ,以细晶为主 ,阴极发光呈紫红色和蓝紫色 ,有序度为 0 .5 7～ 0 .6 8,Sr、Na含量低 ,碳氧同位素偏负 ,成岩深度约15 0 0m ;上部斑状灰质白云岩与层状白云岩相比 ,晶形较粗、以中晶为主 ,有序度较高、为 0 .85～ 0 .90 ,Sr偏高、Na偏低 ,碳氧同位素更偏负 ,成岩深度约 2 0 0 0m。通过对上述特征综合研究 ,认为层状白云岩形成于早期浅埋藏海水—淡水混合环境 ,提出斑状灰质白云岩形成于晚期深埋藏压实流—淡水混合环境 ,总结了两种成因机理 ,建立了相关的白云石化模式。