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.

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.

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.

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.

Effects of astronomical orbital cycle and volcanic activity on organic carbon accumulation during Late Ordovician–Early Silurian in the Upper Yangtze area, South China

Based on field outcrop data,the effects of cyclic change of astronomical orbit and volcanic activity on organic carbon accumulation during the Late Ordovician-Early Silurian in the Upper Yangtze area were studied using cyclostratigraphic and geochemical methods.d13 C and chemical index of alteration(CIA)were used to filter the astronomical orbit parameters recorded in sediments.It is found that the climate change driven by orbital cycle controls the fluctuations of sea level at different scales,obliquity forcing climate changes drive thermohaline circulation(THC)of the ocean,and THC-induced bottom currents transport nutrient-laden water from high latitude regions to the surface water of low-latitude area.Hence,THC is the main dynamic mechanism of organic-carbon supply.The marine productivity indexes of Ba/Al and Ni/Al indicate that volcanic activities had limited effect on marine productivity but had great influences on organic carbon preservation efficiency in late Hirnantian(E4).Paleo-ocean redox environmental indicators Th/U,V/Cr and V/(V+Ni)show that there is a significant correlation between volcanism and oxygen content in Paleo-ocean,so it is inferred that volcanisms controlled the organic carbon preservation efficiency by regulating oxygen content in Paleo-ocean,and the difference in volcanism intensity in different areas is an important factor for the differential preservation efficiency of organic carbon.The organic carbon input driven by orbital cycle and the preservation efficiency affected by volcanisms worked together to control the enrichment of organic carbon in the Middle–Upper Yangtze region.

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。

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)。

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。

Rock physics model for velocity–pressure relations and its application to shale pore pressure estimation

Acoustic wave velocity has been commonly utilized to predict subsurface geopressure using empirical relations.Acoustic wave velocity is, however, affected by many factors. To estimate pore pressure accurately, we here propose to use elastic rock physics models to understand and analyze quantitatively the various contributions from these different factors affecting wave velocity. We report a closed-form relationship between the frame flexibility factor(γ) in a rock physics model and differential pressure, which presents the major control of pressure on elastic properties such as bulk modulus and compressional wave velocity. For a gas-bearing shale with abundant micro-cracks and fractures, its bulk modulus is much lower at abnormally high pore pressure(high γ values) where thin cracks and flat pores are open than that at normal hydrostatic pressure(low γ values) where pores are more rounded on average. The developed relations between bulk modulus and differential pressure have been successfully applied to the Upper Ordovician Wufeng and Lower Silurian Longmaxi formations in the Dingshan area of the Sichuan Basin to map the three-dimensional spatial distribution of pore pressure in the shale, integrating core, log and seismic data. The estimated results agree well with field measurements. Pressure coefficient is positively correlated to gas content. The relations and methods reported here could be useful for hydrocarbon exploration, production, and drilling safety in both unconventional and conventional fields.

四川盆地五峰组—龙马溪组页岩气勘探进展、挑战与前景

四川盆地黑色页岩层系多、页岩气资源丰富,是迄今为止中国主要的页岩气勘探开发盆地。为了给今后四川盆地乃至整个中国南方地区页岩气勘探开发提供指导和参考,以该盆地上奥陶统五峰组—下志留统龙马溪组页岩气勘探开发实践为对象,总结了其发展阶段与进展,明确了页岩气富集成藏的有利条件,梳理了制约页岩气发展的理论与技术挑战,进而探讨了未来的勘探开发前景。研究结果表明:(1)深水陆棚相形成高富含有机质页岩且连续段厚度大、品质好,复背(向)斜宽缓区构造相对稳定是该盆地五峰组—龙马溪组页岩气持续聚集的有利条件,保存条件是页岩气富集的关键因素,页理(纹理)、微裂缝发育是页岩气高产的重要因素,超压是页岩气高产的重要条件;(2)制约该盆地五峰组—龙马溪组页岩气工业化发展的技术瓶颈,主要包括富有机质页岩沉积相与沉积模式,页岩储层成岩过程与评价体系,页岩气形成与聚集机理,页岩气层地球物理识别与预测,资源动用率低、不确定性大,3500 m以深页岩气勘探开发技术尚未突破。结论认为,四川盆地五峰组—龙马溪组仍是今后相当长一段时间内中国页岩气勘探开发的重点层系。

四川盆地五峰组—龙马溪组深水陆棚相页岩生储机理探讨

针对上奥陶统五峰组—下志留统龙马溪组优质页岩生储机理不清的问题,以四川盆地五峰组—龙马溪组深水陆棚相优质页岩为研究对象,结合页岩气形成地质条件和实验分析模拟,从岩石学、矿物学、地球化学等多方面对页岩成烃、成储机制及内在耦合关系等进行分析。结果表明,四川盆地五峰组—龙马溪组优质页岩热演化程度高、生烃强度大、物质基础好,具有良好的顶底板条件;深水陆棚相优质页岩不仅具有高生物成因硅、高有机碳含量,而且具有相对高孔隙度耦合特征。研究认为:①四川盆地五峰组—龙马溪组高演化深水陆棚相优质页岩保存条件好,早期原油滞留效率高,其气源主要来自原油滞留裂解气。②深水陆棚相生物成因的硅质(蛋白石A),在埋藏成岩早期转化成高硬度晶态石英,伴生形成大量微米级粒间孔,而生物成因的硅质格架抗压性强,为优质页岩储集层早期原油充注及纳米级蜂窝状有机孔的发育和保持提供了空间和保护,是有机孔得以保存的关键因素。③五峰组—龙马溪组优质页岩脆性好,均质性强,微米级硅质粒间孔与纳米级有机孔共生,是压裂形成复杂缝网、硅质粒间纳米级有机孔实现高效连通的关键,有利于页岩气高产、稳产。

中国页岩气勘探开发理论认识与实践

基于四川盆地上奥陶统五峰组—下志留统龙马溪组富有机质页岩分布规律、优质页岩表观特征、页岩储集层微观特征、保存条件与页岩气富集、可压裂性等方面的分析,对中国页岩气勘探开发理论认识进行总结,并对未来中国页岩气勘探开发提出针对性建议。四川盆地五峰组—龙马溪组页岩气重要的地质认识可总结为以下几个方面:沉积环境和沉积过程控制了富有机质页岩分布;"甜点段"优质页岩具备高有机碳含量、高脆性、高孔隙度、高含气性的特征;有机质孔隙是页岩气富集的重要储集空间;保存条件是复杂构造区页岩气地质评价的关键因素;页岩气属"人工气藏",可压裂性评价是获得高产的核心;纳米级储集空间与赋存状态决定了页岩气具有特殊的渗流特征。对中国页岩气产业的发展建议:(1)加大基础研究,实现页岩气地质理论体系的新突破;(2)强化勘探实践,形成多层系全方位新发现;(3)研究开发生产规律,建立页岩气开发新模式;(4)创新思维,攻关新技术;(5)探索管理创新,形成页岩气发展新机制。

川南地区五峰组—龙马溪组页岩层序地层及其对储层的控制

随着四川盆地勘探程度的深入,页岩气藏已经成为勘探重点,有必要系统地开展页岩层序地层研究。在岩石地层、生物地层、年代地层研究的基础上,运用露头-钻井-地震、全球海平面变化曲线、地球化学、古生物等资料,在川南地区五峰组—龙马溪组页岩地层中识别出4个三级层序界面,划分了3个三级层序:SQ1相当于五峰组,沉积速率低(1.18~2.19 m/Ma);SQ2相当于龙马溪组下段及上段底部,沉积速率较低(约为15 m/Ma);SQ3相当于龙马溪组上段中上部,沉积速率较高(216.25~340 m/Ma)。建立了该区的层序地层格架。分析了层序对储层的控制作用,主要体现在黑色页岩层序SQ1—SQ2中相对海平面升降与页岩脆性指数呈负相关、与TOC及孔隙度呈正相关,渗透率高值多位于脆性段,渗透率低值多位于塑性段。灰色页岩层序SQ3以塑性段为主,孔、渗均低于SQ1、SQ2凝缩段,其相对海平面与有机质没有明显的相关性。相对海平面变化影响了优质页岩储层发育,SQ1、SQ2海侵期—海退早期为优质页岩储层发育期。综合本次研究成果,明确了层序地层对优质页岩储层的控制作用,对于在层序格架内预测优质页岩储层段具有指导意义。

四川盆地南缘上奥陶统五峰组—下志留统龙马溪组页岩矿物组成与脆性特征

通过X射线全岩衍射、光学薄片鉴定及扫描电镜等技术手段,对四川盆地南缘上奥陶统五峰组-下志留统龙马溪组页岩野外露头及新钻井岩心样品进行测试分析.结果表明,五峰组-龙马溪组页岩矿物组分以石英和粘土矿物为主,其次为方解石和白云石,还有少量的钾长石、斜长石和黄铁矿.其中石英以陆源碎屑来源为主,部分为生物成因;伊利石与绿泥石组合是粘土矿物的特征组合类型;方解石和白云石多以亮晶胶结物和裂缝填充物的形式存在.以矿物组分为依据,将五峰组-龙马溪组页岩划分为富石英页岩、富粘土页岩及富碳酸盐页岩3类端元岩相,每类岩相在矿物组成、结构、构造及沉积背景等方面均表现出不同特征.经计算该页岩脆性指数为0.36-0.74,平均为0.51,表明该套页岩具备良好的脆性与可压裂性,有利于页岩气的开采.其中,底部页岩石英含量高,脆性指数大且富含有机质,有利于页岩气富集与储层压裂改造,是研究区页岩气勘探开发的重点层位.

天文轨道周期及火山活动对中上扬子区晚奥陶世-早志留世有机碳聚集的影响

基于野外露头资料,通过旋回地层学、地球化学等分析方法,运用有机碳同位素组成及化学风化指标数据序列,滤波输出记录在沉积物中的天文轨道参数,探讨天文轨道周期变化及火山活动对中上扬子区晚奥陶世—早志留世有机碳聚集的影响。研究表明,天文轨道周期驱动下的气候变化控制不同级次海平面波动,斜率周期调制的气候变化驱动海洋温盐循环,将位于高纬度区营养物质向中低纬度区转移,温盐循环是低纬度扬子区海洋生产力的主要动力。赫南特晚期海洋生产力指标Ba/Al及Ni/Al值显示,火山活动对海洋生产力贡献有限,对有机碳保存效率有显著影响;古海洋氧化还原环境指标Th/U、V/Cr及V/(V+Ni)值显示,火山活动与古海洋含氧量有显著关系,火山活动通过调节大洋含氧量来控制有机碳的保存效率,不同地区火山活动强度的差异是有机碳差异保存的重要因素。天文轨道周期驱动的有机碳输入动力及火山活动影响有机碳保存效率,二者耦合控制中上扬子区有机碳聚集。图10参74。

黔西北上奥陶统五峰组—下志留统龙马溪组页岩气聚集条件分析

根据野外露头地质调查、最新钻井及样品测试等基础资料,以富有机质页岩形成的地质背景及展布特征——页岩气聚集条件—勘探有利区预测为主线,对黔西北地区上奥陶统五峰组—下志留统龙马溪组页岩气成藏条件进行分析,并采用综合信息叠合法对黔西北地区有利区进行预测。研究发现,页岩气发育的富有机质页岩段主要位于五峰组和龙马溪组底部,具有分布面积广、厚度大、有机质含量高、有机质类型好等特点,且具有充足的储集空间和运移通道。现场解吸实验表明,该套富有机质页岩具有良好的含气性能。总体分析,该区域与北美典型页岩气盆地具有良好的地质对比性,具有良好的页岩气聚集条件,是页岩气勘探研究以及后期页岩气开发的重要领域。

中扬子地区五峰组—龙马溪组页岩气成藏关键地质因素

中国南方中扬子地区上奥陶统五峰组—下志留统龙马溪组具有较好的页岩气勘探前景,但目前对于该区复杂的地质条件及页岩气勘探开发潜力的认识尚不够全面,制约了其勘探成效。为了揭示该区五峰组—龙马溪组页岩气富集的主控因素,以单井储层综合评价为基础,结合钻井、测井、岩心、露头及分析测试数据,对五峰组—龙马溪组黑色页岩的沉积环境、储层发育特征及保存条件等页岩气关键富集条件进行研究,并与四川盆地焦石坝和长宁等页岩气主产区块进行对比。研究结果表明:①该区富有机质页岩段形成于五峰组—龙一3亚段沉积期,为深水陆棚沉积,厚度介于15~39 m,由南至北逐渐增厚;②优质页岩段储层岩石相类型以硅质页岩相为主,孔隙度介于1.60%~7.44%,储集空间以有机孔为主、连通性较好,总有机碳含量高,有机质类型为腐泥型—偏腐泥混合型,热演化程度高,含气性较好,可压裂性好;③当阳复向斜内地层保存较好、产状平缓、断裂发育少、顶底板厚度大且分布稳定,页岩气保存条件较好;④较之于长宁、焦石坝等区块,中扬子地区具有埋藏深、两向应力差较大和地层压力系数较低的特点。结论认为,该区五峰组—龙马溪组具有较好的页岩气富集条件,具备进一步开展勘探工作的潜力;但其高应力差、大埋深和相对较低的压力系数也给后期的页岩气经济开发和规模上产带来了挑战。

页岩气藏超压演化过程:来自四川盆地南部五峰组-龙马溪组裂缝流体包裹体的证据

四川盆地南部(以下简称川南地区)上奥陶统五峰组—下志留统龙马溪组页岩气藏普遍存在着超压现象,部分井页岩地层压力系数远高于1.50,目前对于该区页岩气藏压力演化的过程认识尚不清楚。为了揭示该区五峰组—龙马溪组页岩气藏超压的形成机制与演化过程,以川南地区泸州、威远两地典型井页岩裂缝复合脉体样品为研究对象,通过薄片分析、阴极发光扫描电镜观察,明确裂缝复合脉体胶结物的充填期次,开展不同期次裂缝脉体矿物中包裹体测温和激光拉曼分析,结合埋藏史—地热史研究成果,揭示了不同期次裂缝的开启时间,进而探讨了其与页岩气藏超压演化过程的关系。研究结果表明:①研究区典型井页岩裂缝中主要存在着两期脉体充填,第一期脉体主要分布在裂缝壁,矿物颗粒较小,脉体中流体包裹体均一温度与主生气期温度相符,表明第一期裂缝开启过程与生烃增压作用有关,第二期裂缝脉体主要分布在裂缝中部,矿物颗粒较大,脉体中流体包裹体温度范围较广,与抬升过程地层温度相符,指示第二期裂缝开启过程与构造抬升泄压有关;②研究区页岩最大埋深前甲烷包裹体捕获压力介于103.06~139.82 MPa、压力系数介于2.05~2.50,储层抬升过程中甲烷包裹体捕获压力介于101.32~127.73 MPa、压力系数介于1.89~2.18;③页岩气藏超压来自液态烃裂解生气增压作用,抬升阶段是持续泄压的过程。结论认为,川南地区五峰组—龙马溪组页岩气藏具有良好的保存条件,现今仍能保持较高的压力系数。

四川盆地及周缘上奥陶统五峰组-下志留统龙马溪组关键界面基本特征

以典型剖面详测和重点资料点解剖为基础,结合观音桥段介壳层典型特征分析,以特定斑脱岩层为重点,系统研究四川盆地及周缘上奥陶统五峰组—下志留统龙马溪组内部关键界面基本特征及其与富有机质页岩沉积关系。研究区五峰组—龙马溪组发育特征笔石带、观音桥段介壳层、斑脱岩密集段、结核体等4种具有界面属性的标志层,可成为笔石页岩内地层划分与对比的关键界面:观音桥段介壳层是五峰组—龙马溪组内部最标准的关键界面,也可作为判断重点地区富有机质页岩沉积规模的重要标志;发育两种类型8个斑脱岩密集段,主要赋存于7个笔石带,与观音桥段介壳层在厚度、自然伽马响应等方面具有相似的界面特征,属构造界面(即事件性沉积),并具有全域、大区域和局部3种分布规模,可相应成为三级、四—五级层序界面,对富有机质页岩沉积具有差异控制作用;特征笔石带的首现层位即为等时界面,与富有机质页岩沉积并无直接关系;结核体仅在局部区域产出,且在纵向和横向分布的稳定性较差,与富有机质页岩沉积关系并不明显。