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.

Source Rock and Cap Rock Controls on the Upper Ordovician Wufeng Formation–Lower Silurian Longmaxi Formation Shale Gas Accumulation in the Sichuan Basin and its Peripheral Areas

Objective The Upper Ordovician Wufeng Formation-Lower Silurian Longmaxi Formation is one of the priority interval for shale gas exploration in the Sichuan Basin and its peripheral areas, and commercial shale gas has been discovered from this interval in Jiaoshiba, Changning and Weiyuan shale gas fields in Sichuan Province. However, there is no significant discovery in other parts of the basin due to the different quality of black shale and the differences of tectonic evolution. Based on the progress of shale gas geological theory and exploration discoveries, as well as the theory of ＂source rock and cap rock controls on hydrocarbon accumulation＂, of the Upper Ordovician the main controlling factors Wufeng Formation-Lower Silurian Longmaxi Formation shale gas enrichment in the Sichuan Basin and its peripheral areas were analyzed, and the source rock and cap rock controls on the shale gas were also discussed. The results can provide new insights for the next shale gas exploration in this area.

Biostratigraphy and reservoir characteristics of the Ordovician Wufeng Formation-Silurian Longmaxi Formation shale in the Sichuan Basin and its surrounding areas,China

Through graptolite identification in profiles,graptolite zone division,contour map compilation,and analysis of mineral composition,TOC content,lamina distribution features of shale samples,the biostratigraphic and reservoir characteristics of Ordovician Wufeng Formation-Silurian Longmaxi Formation in the Sichuan Basin and its peripheral are sorted out.There are 4 graptolite zones(WF1 to WF4)in Wufeng Formation and 9(LM1 to LM9)in Longmaxi Formation,and the different graptolite zones can be calibrated by lithology and electrical property.The shale layers of these graptolite zones have two depocenters in the southwest and northeast,and differ in mineral composition,TOC,and lamina types.Among them,the graptolite zones of lower WF2 and WF4 are organic matter-poor massive hybrid shale,the upper part of WF1-WF2 and WF3 have horizontal bedding hybrid shale with organic matter,the LM1-LM4 mainly consist of organic-rich siliceous shale with horizontal bedding,and the LM5-LM9 graptolite zones consist of organic-lean hybrid shale with horizontal bedding.The mineral composition,TOC and lamina types of shale depend on the paleo-climate,paleo-water oxidation-reduction conditions,and paleo-sedimentation rate during its deposition.Deposited in oxygen-rich warm water,the lower parts of WF1 and WF2 graptolite zones have massive bedding,low TOC and silicon content.Deposited in cooler and oxygen-rich water,the WF4 has massive bedding,high calcium content and low TOC.Deposited in anoxic water with low rate,the upper part of WF2,WF3,and LM1-LM4 are composed of organic rich siliceous shale with horizontal bedding and high proportion of silt laminae.Deposited in oxygen rich water at a high rate,the graptolite zones LM5-LM9 have low contents of organic matter and siliceous content and high proportions of silt lamina.

Basic characteristics of key interfaces in Upper Ordovician Wufeng Formation – Lower Silurian Longmaxi Formation in Sichuan Basin and its periphery,SW China

Based on anatomy of key areas and data points and analysis of typical features of shell layer in Guanyinqiao Member, basic characteristics of key interfaces, mainly bentonite layers, in the Upper Ordovician Wufeng Formation-Lower Silurian Longmaxi Formation in the Sichuan Basin and its surrounding areas and the relationship between these key interfaces with the deposition of organic-rich shale have been examined systematically. The Wufeng Formation-Longmaxi Formation has four types of marker beds with interface attributes, namely, the characteristic graptolite belt, Guanyinqiao Member shell layer, section with dense bentonite layers, and concretion section, which can be taken as key interfaces for stratigraphic division and correlation of the graptolite shale. The shell layer in Guanyinqiao Member is the most standard key interface in Wufeng Formation-Longmaxi Formation, and can also be regarded as an important indicator for judging the depositional scale of organic-rich shale in key areas. There are 8 dense bentonite sections of two types mainly occurring in 7 graptolite belts in these formations. They have similar interface characteristics with the shell layer in Guanyinqiao Member in thickness and natural gamma response, and belong to tectonic interfaces(i.e., event deposits). They have three kinds of distribution scales: whole region, large part of the region, and local part, and can be the third, fourth and fifth order sequence interfaces, and have a differential control effect on organic-rich shale deposits. The horizon the characteristic graptolite belt occurs first is the isochronous interface, which is not directly related to the deposition of organic-rich shale. Concretions only appear in local areas, and show poor stability in vertical and horizontal directions, and have no obvious relationship with the deposition of the organic-rich shale.

Formation, preservation and connectivity control of organic pores in shale

In view of strong heterogeneity and complex formation and evolution of organic pores,field emission scanning electron microscopy(FESEM),Raman spectrum and fluid injection+CT/SEM imaging technology were used to study the macerals,organic pores and connectivity of organic pores in the lower Paleozoic organic-rich shale samples from Southern China.Combined with the mechanism of hydrocarbon generation and expulsion and pore forming mechanism of organic matter-based activated carbon,the relationships between organic pore development and the organic matter type,hydrocarbon generation process,diagenesis and pore pressure were explored to reveal the controlling factors of the formation,preservation and connectivity of organic pores in shale.(1)The generation of organic pores goes on through the whole hydrocarbon generation process,and is controlled by the type,maturity and decomposition of organic matter;the different hydrocarbon generation components and differential hydrocarbon-generation evolution of kerogen and solid asphalt lead to different pore development characteristics;organic pores mainly develop in solid bitumen and hydrogen-rich kerogen.(2)The preservation of organic pores is controlled by maturity and diagenesis,including the steric hindrance effect of in-situ hydrocarbon retention,rigid mineral framework formed by recrystallization,the coupling mechanism of pore-fluid pressure and shale brittleness-ductility transition.(3)The Ro of 4.0%is the maturity threshold of organic pore extinction,the shale layers with Ro larger than 3.5%have high risk for shale gas exploration,these shale layers have low gas contents,as they were in an open state before uplift,and had high hydrocarbon expulsion efficiency and strong aromatization,thus having the"congenital deficiency"of high maturity and pore densification.(4)The pores in the same organic matter particle have good connectivity;and the effective connectivity between different organic matter pores and inorganic pores and fractures depends on the abundance and distribution of organic matter,and development degree of pores and fractures in the shale;the accumulation,preservation and laminar distribution of different types of organic matter in high abundance is the prerequisite for the development and connection of organic pores,grain margin fractures and bedding fractures in reservoir.

Enlightenment of calcite veins in deep Ordovician Wufeng-Silurian Longmaxi shales fractures to migration and enrichment of shale gas in southern Sichuan Basin, SW China

The relationship between fracture calcite veins and shale gas enrichment in the deep Ordovician Wufeng Formation-Silurian Longmaxi Formation (Wufeng-Longmaxi) shales in southern Sichuan Basin was investigated through core and thin section observations, cathodoluminescence analysis, isotopic geochemistry analysis, fluid inclusion testing, and basin simulation. Tectonic fracture calcite veins mainly in the undulating part of the structure and non-tectonic fracture calcite veins are mainly formed in the gentle part of the structure. The latter, mainly induced by hydrocarbon generation, occurred at the stage of peak oil and gas generation, while the former turned up with the formation of Luzhou paleouplift during the Indosinian. Under the influence of hydrocarbon generation pressurization process, fractures were opened and closed frequently, and oil and gas episodic activities are recorded by veins. The formation pressure coefficient at the maximum paleodepth exceeds 2.0. The formation uplift stage after the Late Yanshanian is the key period for shale gas migration. Shale gas migrates along the bedding to the high part of the structure. The greater the structural fluctuation is, the more intense the shale gas migration activity is, and the loss is more. The gentler the formation is, the weaker the shale gas migration activity is, and the loss is less. The shale gas enrichment in the core of gentle anticlines and gentle synclines is relatively higher.

Microfacies types and distribution of epicontinental shale: A case study of the Wufeng–Longmaxi shale in southern Sichuan Basin, China

For black shales,laminae and bedding are hard to identify,grain size is difficult to measure,and trace fossils do not exist.Taking the Ordovician Wufeng–Silurian Longmaxi shale in southern Sichuan Basin,China,as an example,the types,characteristics and models of microfacies in epicontinental shale are analyzed by means of full-scale observation of large thin sections,argon-ion polishing field emission-scanning electron microscopy(FE-SEM),and kerogen microscopy.The epicontinental sea develops delta,tidal flat and shelf facies,with black shale found in microfacies such as the underwater distributary channel and interdistributary bay under delta front facies,the calcareous and clayey flats under intertidal flat facies,the calcareous and clayey shelfs under shallow shelf facies,the deep slope,deep plain and deep depression under deep shelf facies,and the overflow under gravity flow facies.Basinward,silty lamina decreases and clayey lamina increases,the grain size changes from coarse silt to fine mud,the silica content increases from about 20%to above 55%,the carbonate and clay minerals content decreases from above 40%to around 10%,and the kerogen type changes from type II2 to type II1 and type I.Provenance and topography dominate the types and distribution of shale microfacies.The underwater distributary channel,interdistributary bay,clayey flat,clayey shelf,and overflow microfacies are developed in areas with sufficient sediment supply.The calcareous flat and calcareous shelf are developed in areas with insufficient sediment supply.The deep shelf shale area is divided into deep slope,deep plain,and deep depression microfacies as a result of three breaks.The formation of epicontinental shale with different microfacies is closely related to the tectonic setting,paleoclimate,and sea level rise.The relatively active tectonic setting increases the supply of terrigenous clasts,forming muddy water fine-grained sediment.The warm and humid paleoclimate is conducive to the enrichment of organic matter.The rapid sea level rise is helpful to the widespread black shale.

泸州地区五峰组——龙马溪组页岩气成藏特征

为寻找四川盆地泸州地区五峰组—龙马溪组页岩气有利区,在开展流体包裹体检测、页岩微观孔隙观测、气泡变孔模拟等研究基础上,查明了泸州地区构造埋藏过程和生烃热演化过程,总结了泸州地区页岩气成藏特征和成藏规律。研究结果表明:泸州地区五峰组—龙马溪组富有机质页岩厚度大,在二叠纪—早三叠世生油,经历了中三叠世和燕山运动期—喜马拉雅运动期2次构造抬升,中三叠世抬升幅度有限,未导致大规模烃散失,燕山运动期—喜马拉雅运动期构造抬升晚于川东南且幅度小,利于页岩气保存;泸州地区五峰组—龙马溪组页岩有机孔发育,是由于中三叠世隆升时间短,强度小,未发生大规模排烃,大量液态烃保留在储集层中,有利于后期有机孔的大量形成,同时在晚三叠世—中白垩世,地层深埋发生液态烃裂解产气,地层广泛超压,有利于有机孔的后期保存;泸州地区三叠纪隆升虽然时间短、强度小,但是从模拟实验结果来看,可以导致原油稠化和气孔形成,对页岩气富集成藏有利。因此,发生在印支运动期的泸州地区的隆升造成原油稠化,有利于页岩气富集成藏;泸州地区地层抬升时间晚,页岩气散失时间短,低角度层理缝发育,而纵向裂缝少,均有利于形成超压页岩气富集区。提出的泸州地区五峰组—龙马溪组页岩富集成藏规律,对于指导其他同类型油气勘探具有借鉴意义。

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。

深层页岩气水平井天然裂缝发育特征及其对精细开发的启示——以川南泸州区块五峰组—龙马溪组为例

天然裂缝发育特征分析是深层页岩气勘探开发评价的重要环节,对储层品质综合评价、压裂差异化设计具有指导意义。以四川盆地南部(以下简称川南)泸州区块五峰组—龙马溪组深层页岩为研究对象,综合利用岩心分析化验、水平井成像测井和地震等资料,从岩心天然裂缝描述、水平井成像测井发育特征、水平井天然裂缝与地震预测裂缝带之间的匹配关系等方面进行了系统研究。结果表明:水平井成像测井可准确识别3种天然裂缝类型,即高导缝、高阻缝和微断层;水平井识别裂缝走向与现今最大水平主应力方向一致,裂缝倾角分布规律与处于相同构造部位的评价井直井段总体相似;地震预测裂缝带控制成像测井岩心尺度天然裂缝发育,中强度曲率体裂缝带、低强度曲率体裂缝带、蚂蚁体裂缝带对岩心尺度天然裂缝的影响距离分别为110、80、30~50 m。泸州区块岩心尺度天然裂缝具“双高”特征(倾角高、方解石充填程度高),揭示的水平井岩心尺度天然裂缝发育特征与直井段、地震预测裂缝带之间的对应匹配关系,可为川南地区海相页岩天然裂缝精细表征、储层分类评价和差异化压裂工艺试验攻关方向提供借鉴。

上奥陶统五峰组海底麻坑沉积的首次识别及其地质意义

尽管海底麻坑普遍发育在现代海洋的多种环境,但关于深时、特别是古生代麻坑沉积的研究却极为罕见,研究者对其特征、成因、鉴别标志所知甚少。本次研究在重庆石柱地区柑子坪及歇步头剖面识别了发育在上奥陶统五峰组暗色细粒岩中的海底麻坑沉积,在野外观察、采样的基础上,利用显微薄片及扫描电镜观察了其微观特征,并测试了麻坑与围岩的主量元素和微量元素。研究显示麻坑沉积总体呈楔状或顶平底凹的透镜状,麻坑内岩层紊乱并发育上拱的岩层,被硅质脉分割的角砾普遍发育,麻坑沉积中常见重晶石、沥青及赤铁矿,主量及稀土元素测试结果显示麻坑的形成可能与热液及冷泉无关,推测五峰组自生的低熟油气是麻坑形成的基础。总结认为深时麻坑的识别标志有:地震剖面的负地形形态、碳同位素负偏明显的不规则形态的碳酸盐岩岩体、楔状或透镜状宏观形态、麻坑内杂乱的沉积填充、局部地层的上拱形态及古生物化石显示的沉积间断或时序混乱等。五峰组海底麻坑沉积具岩石学、地层学、古环境及油气地质学意义。

基于构造样式的页岩气富集模式分类-以四川盆地五峰-龙马溪组为例

【研究目的】四川盆地及周缘五峰-龙马溪组页岩经历的构造活动复杂且改造作用强,构造改造程度与页岩气的聚集有着直接的影响,根据构造样式对页岩气富集模式进行划分具有重要意义。【研究方法】本文以构造分区及改造强度变化趋势为主线,整体研究四川盆地及周缘奥陶系上统五峰组-志留系下统龙马溪组页岩层系的构造分区、不同区块构造抬升时间差异,总结不同构造区的页岩气富集模式。【研究结果】通过研究不同地区五峰-龙马溪组页岩目的层系构造改造强度、构造形态、埋藏深度、埋藏抬升时间等的差异性,将四川盆地及周缘下古生界主力海相页岩层系划分为9个一级构造区和20个二级构造区。进一步研究了不同构造区典型井的构造埋藏史及生烃史,结合构造形态、保存条件及产气情况,将四川盆地及周缘划分为9种典型的页岩构造样式及页岩气富集模式:盆内大型斜坡型(威远型)、盆内低陡构造与宽缓向斜型(泸州型)、盆缘向斜型(长宁型)、盆缘复杂构造型(昭通型)、盆缘宽缓断背斜型(焦石坝型)、盆缘斜坡逆断层封堵型(丁山型)、盆外复杂背斜型(巫溪型)、盆外残留向斜型(彭水型)、盆外残留向斜逆断层封堵型(正安型),其页岩气富集及保存条件整体上依次变差。【结论】总结出的9种页岩气富集模式,概况了四川盆地内部到盆地外缘的整体构造演化及页岩气保存富集规律,可以为进一步的页岩气有利区优选提供范围和目标,更好地指导四川盆地及周缘的页岩气勘探。

四川盆地涪陵南地区奥陶系五峰组—志留系龙马溪组页岩古构造应力场及裂缝特征

通过岩石力学实验、声发射实验和地震资料综合解释,利用有限元数值模拟方法,对涪陵南地区奥陶系五峰组—志留系龙马溪组海相页岩古构造应力场进行了数值模拟,并结合岩心实测结果,预测了构造裂缝的发育特征。研究结果表明:①涪陵南地区裂缝主要形成期(燕山晚期)构造应力和裂缝的分布受断层、岩石力学性质和构造应力的影响,断层广泛发育的区域容易出现应力集中,并引起较大的应力梯度。②利用库伦-莫尔破裂准则预测了研究区构造裂缝的发育,同时引入剪切破裂指数R定量表征裂缝发育的强度,其值越大反映裂缝发育程度越高。窄陡断背斜和断层附近裂缝发育,以高角度剪切裂缝为主,而在宽缓向斜部位裂缝发育程度最弱,研究区五峰组—龙马溪组底部硅质页岩应力集中,裂缝最发育。③涪陵南地区海相页岩气保存有利区主要为3个区带:远离大断层的凤来向斜内部,主要构造变形期未遭受大的破坏作用,其位于应力低值区,具有良好的保存条件,为Ⅰ类有利区;白马向斜内部小断层发育,应力值位于中等水平,保存条件中等,为Ⅱ类较有利区;石门—金坪断背斜遭受到强烈改造作用,容易产生大规模剪切裂缝,破坏了保存条件,为Ⅲ类不利区。

川南地区五峰组—龙马溪组沉积环境演化及其对页岩发育的控制

基于岩心观察、薄片观察、电镜观察、XRF元素扫描以及全岩X-衍射、ICP-MS元素分析、总有机碳含量测试等手段,对川南地区五峰组—龙马溪组页岩岩相类型及其沉积环境演化进行分析,并探讨沉积环境高频演化对岩相的控制作用。将川南地区五峰组—龙马溪组页岩划分为富有机质层状生物硅质页岩、富有机质纹层状(长英质-钙质)粉砂页岩、富有机质(钙质)粉砂页岩、富有机质纹层状钙质页岩、中有机质纹层状(长英质-钙质)粉砂页岩、中有机质块状黏土质页岩6种岩相类型。在岩相识别基础上借助特征元素比值Sr/Ba、U/Th、V/Cr、V/Ni、Ni/Co、Sr/Cu及Mo、Cu、Sr含量变化进行古沉积环境恢复,划分出7个演化阶段。结果表明:五峰组沉积早期气候温暖潮湿、水体较为氧化、盐度较低;五峰组沉积中期水体还原性增强、古生产力提高;五峰组晚期气候干冷,水体较为氧化,经历了赫南特冰期;龙马溪组自下而上古气候经历了暖湿—相对干热—暖湿—相对干热的演化,同时古水体也经历了还原—相对氧化—还原—相对氧化的演化。沉积环境高频演化对页岩岩相发育以及有机质富集具有明显的控制作用,不同岩相有机质含量与海洋古生产力和水体还原性均呈现良好的正相关性,其中在古生产力较高、水体还原性较强的阶段沉积的富有机质层状生物硅质页岩和富有机质纹层状(长英质-钙质)粉砂页岩有机质最为富集,且石英含量最高,是页岩气勘探开发的优势岩相。

论海相页岩气富集机理——以四川盆地五峰组—龙马溪组为例

深入探究页岩气富集机理是保障勘探开发高效推进的基础。本研究通过对四川盆地五峰组—龙马溪组页岩气勘探开发实践的系统分析,梳理总结前人研究成果,从生成机理、运移机理、赋存机理和保存机理四个方面对海相页岩气富集机理进行了深入分析,并讨论了深层和常压页岩气的勘探开发潜力。结果表明:在生成机理方面,埋藏史和热演化史控制了页岩生排烃史、生排烃量和现今含气量;页岩气运移机理涉及运移动力、运移相态、运移方式和运移通道四方面内容,页岩气运移主要是烃源岩内的初次运移,同时讨论了初次运移的影响因素;在赋存机理方面,甲烷—页岩间表现出单/多分子层吸附和微孔充填等多种赋存机制,组分润湿性和孔隙有效性是决定甲烷吸附赋存和解吸运移的关键;在保存机理方面,盖层和物性自封闭是主要的保存机理,构造运动引起的裂缝—流体活动是页岩气保存条件遭到破坏的主要原因,流体活动时间和期次研究是页岩气保存条件和含气量定量评价的重要内容。页岩气富集机理的系统分析和创新认识为页岩气勘探开发评价提供了重要依据,建议加强页岩气演化历史全过程的动态评价。结合深层和常压页岩气勘探实践,分析了深层和常压页岩气的成因机制及主要特征,指出了下一步攻关内容及勘探方向。

方解石双晶古温标基本原理及其利用--以川南上奥陶统五峰组-下志留统龙马溪组为例

我国西部盆地深层—超深层古老碳酸盐岩层系由于缺少传统古温标/地质热温度计,其盆地热史演化与古地温场特征备受争议。笔者等介绍方解石机械双晶形成演化机制及其与变形温度相关性,以川南地区上奥陶统五峰组—下志留统龙马溪组脉体方解石为例,结合流体地球化学和埋深热史过程恢复,表明方解石机械双晶能有效揭示五峰组—龙马溪组热史特征。方解石机械双晶具有双晶位错形成、双晶增厚和合并生长增厚的3个演化过程,导致方解石不同双晶结构(薄片、板状、锥状弧形等)分别形成于低于170℃、170~200℃和大于200℃环境,且伴随温度增大具有双晶密度减小、宽度增大的趋势特征。川南威远地区五峰组—龙马溪组发育典型板状方解石双晶,双晶宽度为1~4μm、密度30~50条/mm;长宁五峰组—龙马溪组方解石双晶宽度较大(约为3μm)、密度较低(15~20条/mm)。包裹体均一温度和埋深热史综合表明,长宁地区包裹体均一温度峰值为120~140℃、160~180℃和200~220℃,其埋藏热史明显大于威远地区,它们共同揭示长宁地区五峰组—龙马溪组相对威远地区具有较高的机械双晶形成环境温度。因而,方解石机械双晶形态几何学能够作为典型的古温标应用于我国西部古老深层碳酸盐岩层系热史研究。

渝东地区五峰组—龙马溪组沉积环境及有机质主控因素分析——以接龙剖面为例

【目的】研究渝东地区五峰组—龙马溪组黑色页岩的沉积环境及有机质主控因素。【方法】选取重庆市武隆区接龙剖面开展系统研究,通过实测观察、连续采样及相关地球化学分析,获得了剖面总有机碳(TOC)、主量元素、微量元素垂向变化特征。在此基础上,横向对比QQ1井,探讨研究区五峰组—龙马溪组古环境演化并进行TOC富集因素分析。【结果】Al、Zr、Ti陆源输入指标在五峰组沉积时期供给变化比较大,进入观音桥组沉积时期有所下降,在龙马溪组底部快速提升。V/Cr、V/(V+Ni)氧化还原指标显示,五峰组为缺氧环境、观音桥组为弱氧环境、龙马溪组为还原环境。页岩古生产力指标P/Al值和Ba(xs)含量指示了五峰组—龙马溪组均具有相对高的生产力。其中,龙马溪组最高,五峰组次之。根据TOC与陆源输入指标Al、Zr和古生产力指标P/Al、Ba(xs)及氧化还原指标V/Cr、V(/V+Ni)进行相关性分析,并对比QQ1井,发现渝东地区五峰组—龙马溪组页岩的TOC主控因素为水体的氧化还原性。并且这种氧化还原性受控于水体深度,具体表现为位于沉降中心深水陆棚区的接龙剖面还原性明显高于位于沉降周缘浅水陆棚区的QQ1井,导致接龙剖面TOC明显高于QQ1井。【结论】虽然五峰组—龙马溪组富有机质层段均形成于缺氧环境,但是两组页岩形成的沉积环境却不同。五峰组页岩沉积于流通性极差的强滞留水体环境,而龙马溪组则主要为静海相的缺氧环境。

构造作用对常规-非常规油气连续聚积耦合成藏控制机制——以川东南平桥地区为例

为探索川东南平桥地区构造作用对常规和非常规气藏成藏过程的动态控制作用及差异,基于地震、地质和包裹体等资料,根据断层相关褶皱理论,系统剖析了该区构造特征及演化过程、常规气藏和非常规气藏动态成藏过程及构造对两者影响的差异性,建立了典型常规—非常规油气连续聚集耦合成藏模式。平桥地区位于川东南SE-NW前展式递进变形带中,受多套滑脱层和江南—雪峰造山带联合控制,发育断展构造和背冲构造。平桥背斜构造形成于燕山期。中燕山期,受江南—雪峰构造体系前展式扩展影响,研究区发生NE向强烈断褶作用。晚燕山期—喜马拉雅期川中隆起阻挡和青藏高原隆升使平桥背斜不断抬升;寒武系筇竹寺组和奥陶系五峰组—志留系龙马溪组烃源岩在早燕山期及以前主要经历了长期的埋藏生烃,中燕山期构造变形扩展至研究区,常规气藏储层(洗象池群)、盖层、油气圈闭及运移均受到影响,气藏保存条件较差。非常规气层被改造成为背斜构造,页岩气向背斜核部聚集,整体保存条件较好。晚燕山期—喜马拉雅期,地层隆升泄压,两类气藏保存条件继续变差。因此,构造作用对常规气藏和非常规气藏成藏控制差异体现在控制方式和改造时间上:中燕山期侧向供烃是常规气藏成藏的关键;晚白垩世构造活动改造和晚燕山期—喜马拉雅期构造抬升影响了页岩气的保存。

低电阻率页岩气储层饱和度方程研究及应用——以川南长宁地区五峰组—龙马溪组为例

页岩气含水(含气)饱和度是游离气量评价至关重要的参数,由于高成熟有机质石墨化、黄铁矿、黏土矿物及地层水等多种导电因素的影响,川南长宁、泸州、渝西等多个区块页岩气勘探开发进程中相继一些页岩气井出现测井超低电阻率现象(R_(t)<5Ωm),造成基于传统电法的饱和度计算方法(Archie公式、Simandoux方程等)不具适用性.因此,为了明确不同导电因素对低电阻率页岩气储层的影响规律,进而建立合理的饱和度评价模型实现提高低电阻率页岩气储层饱和度计算的精度,以川南长宁地区五峰组—龙马溪组低电阻率页岩气储层为例,首先,利用X衍射、地化、激光拉曼、镜下薄片、饱和度测试及测井等资料,在确立低电阻率页岩气储层岩石体积物理模型的基础上,依据并联导电模型,推导了考虑石墨化有机质、黄铁矿等多因素的改进饱和度电性响应方程;其次,通过电阻率响应数值模拟,结合实际井黏土矿物含量、黄铁矿含量、有机质石墨化程度、地层水饱和度及矿化度资料,明确了长宁区块五峰组—龙马溪组页岩高演化有机质石墨化、高含水饱和度是形成超低电阻率页岩气储层的最核心因素;最后,依据建立的饱和度响应方程,利用最优化迭代方法计算了低电阻率页岩气储层的含水饱和度,计算结果与保压取心饱和度测试数据的相关系数达到了0.90以上,有效解决了低电阻率页岩气储层饱和度精确计算难度大的问题,为降低低电阻率页岩气勘探开发风险提供了依据.

四川盆地东缘白马地区常压页岩气开发地质评价

涪陵气田是我国第一个实现商业开发的页岩气田,近几年年产气量稳定在70亿m^(3)以上,开发效果良好。随着开发需求不断增大,开发对象由焦石坝等高压页岩气藏逐步转向了白马常压页岩气藏。2021年白马地区提交探明储量1048.83亿m^(3),地质资源基础得到夯实,而开发地质评价与目标优选是实现储量有效动用第一环。以分析化验、测井解释、地震预测、压裂试气资料为基础,开展白马地区常压页岩气开发有利层段与有利目标评价研究。研究结果表明,白马地区奥陶系五峰组-志留系龙马溪组发育深水陆棚相富有机质页岩,其中深水陆棚硅质页岩是开发最有利层段。明确了地层压力系数、孔隙度、天然裂缝、应力性质是常压页岩气开发地质评价的关键参数。以此为基础,建立了白马常压页岩气藏开发选区地质参数体系,优选白马向斜南部为开发建产第一目标,实现了规模效益建产,对常压页岩气开发具有重要借鉴意义。