页岩裂缝发育主控因素及其对含气性的影响

依据国内外页岩气大量资料和测试数据,对影响页岩裂缝发育的岩性和矿物组成、有机碳含量、岩石力学性质、异常高压等非构造因素和构造因素进行了定性或半定量分析,初步探讨了页岩裂缝发育与含气量之间关系。结果表明:页岩中石英、长石和碳酸盐岩含量高,岩石的泊松比低、杨氏模量高,脆性大,容易在外力作用下形成天然裂缝和诱导裂缝,其发育程度一般与页岩中脆性矿物的含量呈正相关关系。高有机碳含量或异常高压页岩裂缝发育。裂缝发育程度与有机碳含量关系可以划分为4类。页岩裂缝发育程度与总含气量和游离气量呈正相关关系,页岩裂缝越发育,其含气量越大,产气量也越高。裂缝对页岩气藏的形成具有双重作用,一是裂缝可以作为天然气和地层水的有效储集空间和快速运移通道,有利于页岩层系中游离态天然气体积的增加和吸附态天然气的解吸,裂缝密度越大,走向越分散,产气量越高;二是裂缝规模过大,可能导致天然气散失。北美地区页岩裂缝发育带内的页岩气勘探成功率高,产气量高,中国四川盆地下古生界海相富有机质脆性页岩层中天然气有良好显示或高产气井均与裂缝发育密切相关。     

页岩油气富集的主控因素及误辩:以美国、阿根廷和中国典型页岩为例

页岩气富集不均匀,无论对于不同页岩油气藏还是同一页岩油气藏不同地方,产量都是有高有低.有必要系统分析和对比全球不同页岩油气的地质、石油系统与油气富集的关系,总结页岩油气富集的主控因素,从而采取合理的勘探和开发技术.以美国、阿根廷和中国典型页岩为例,基于野外和岩心观察、样品属性测试分析、储层表征、石油系统分析及油气测试,探究了页岩油气富集的主控因素及存在的认识误区.结果表明,富含有机质和脆性矿物的页岩主要分布于远离造山带物源的非深水的沉积和构造背景,富含石英和高伽马页岩并非判断优质储层的矿物和岩石物理标准,优质碳酸盐页岩应以富含碳酸盐和低伽马值为标准.页岩油气藏实际是细粒富含有机质的自生自储或与富含有机质烃源岩相邻的贫有机质细粒沉积储层.天然裂缝对页岩油气富集具有有利和不利的双重作用.因此,页岩油气富集同时受到沉积和构造环境、岩相及矿物组成、天然裂缝的耦合影响,且对不同沉积盆地、不同属性页岩的影响差异明显.      

页岩气富集带地质控制因素及地震预测方法

首先对页岩气富集带的地质控制因素及各家的评价指标进行了探讨,认为页岩气的评价指标可以分为两大类：一类是评价页岩气量的多少,即资源因素,它决定了该区页岩气资源潜力及储量的多少,是页岩气资源评价、有利区块优选的关键指标。主要包括页岩厚度、有机质（TOC）丰度、干酪根类型、成熟度(Ro)、天然气含量及状态（游离、吸附）等。另一类决定了页岩气能否经济地开采出来,以及产量的高低,即所谓的“核心区”或“甜点”区。包括埋藏深度、页岩本身的矿物成分、脆度、孔隙度（裂缝）、渗透率以及原始地应力大小、方向及差异等。这两类指标共同控制了页岩气的富集和最终产量。因此,在页岩气勘探开发过程中,应首先利用地质和地球化学方法对第一类指标进行评价,从中优选出有利区块。在有利区块内,可以利用地震相关技术对第二类指标预测和评价,从中优选出适合钻井和开采的页岩气富集带或“甜点”区。根据对页岩气富集带（甜点）地质控制因素的讨论,可以将页岩气划分为“裂隙” 型页岩气藏及“脆性”型页岩气,两种类型均需位于弱应力各向异性区,以便于压裂过程中得到理想的复杂网状裂缝系统。笔者认为,对于“裂隙”型页岩气藏,几何地震属性分析技术（包括相干体、蚂蚁体、曲率体等）可以很好地刻画断层、隐伏断层及裂缝发育带,对这些成果的解释可以以玫瑰图的方式展示,从而可以揭示该区域的裂缝的主要发育方向及次要方向,进而推断该区的局部主应力方向,为水平井位部署提供依据。而对于“脆性”型页岩气藏,叠前反演技术、叠后反演技术可以揭示低泊松比(υ),纵横波速比等来进行有利目标（甜点）识别。曾经在常规油气勘探中发挥重要作用的地震技术,在页岩气等非常规油气资源勘探开发中,仍然是一种不可或缺的关键技术。     

准噶尔盆地玛湖凹陷二叠系风城组页岩储集层裂缝测井识别与有效性分析*

中国页岩油资源潜力巨大,裂缝的发育程度是影响页岩油产量高低的重要因素。以准噶尔盆地玛湖凹陷风城组页岩储集层为研究对象,通过岩心观察、薄片鉴定、常规及成像测井方法总结归纳了研究区裂缝的发育特征,提出“常规+成像+岩心”的页岩储集层裂缝测井综合识别方法,建立了典型裂缝发育类型的测井综合识别图版。结果表明,玛湖地区天然裂缝在风三段密集发育,风一段次之,风二段中部几乎不发育。裂缝主要在长英质页岩、云质页岩和混合质页岩中发育,以高角度构造裂缝与低角度成岩裂缝为主,开启程度高,少数被碳酸盐矿物充填,走向主要为NW-SE向。基于裂缝参数定量计算结果,结合岩性及矿物组分和地应力等因素分析了储集层裂缝有效性。研究认为,脆性矿物组分含量高、走向平行于现今水平最大主应力的高角度未充填裂缝发育段对储集层有效性存在明显的控制作用,与产液资料较为吻合。此裂缝测井综合评价方法效果显著,可为页岩储集层裂缝识别与有效性评价提供方法支撑。     

准噶尔盆地玛湖凹陷二叠系风城组页岩储集层裂缝测井识别与有效性分析*

中国页岩油资源潜力巨大,裂缝的发育程度是影响页岩油产量高低的重要因素。以准噶尔盆地玛湖凹陷风城组页岩储集层为研究对象,通过岩心观察、薄片鉴定、常规及成像测井方法总结归纳了研究区裂缝的发育特征,提出“常规+成像+岩心”的页岩储集层裂缝测井综合识别方法,建立了典型裂缝发育类型的测井综合识别图版。结果表明,玛湖地区天然裂缝在风三段密集发育,风一段次之,风二段中部几乎不发育。裂缝主要在长英质页岩、云质页岩和混合质页岩中发育,以高角度构造裂缝与低角度成岩裂缝为主,开启程度高,少数被碳酸盐矿物充填,走向主要为NW-SE向。基于裂缝参数定量计算结果,结合岩性及矿物组分和地应力等因素分析了储集层裂缝有效性。研究认为,脆性矿物组分含量高、走向平行于现今水平最大主应力的高角度未充填裂缝发育段对储集层有效性存在明显的控制作用,与产液资料较为吻合。此裂缝测井综合评价方法效果显著,可为页岩储集层裂缝识别与有效性评价提供方法支撑。     

Summary of Numerical Models for Predicting Productivity of Shale Gas Horizontal Wells

Shale gas production has gradually achieved high and stable output, which makes it possible to make up for the shortage of oil and gas energy as an alternative energy source. Shale reservoir is compact, with well-developed nano-pore, and has the characteristics of adsorption and desorption, diffusion and slippage. At the same time, there are a large number of natural cracks, bedding and foliation. Hydraulic fractures expand irregularly after volume fracturing in horizontal wells. The whole system has multi-field coupling and cross-scale flow effects. Productivity prediction of shale gas is difficult and uncertain, which restricts the efficient development and evaluation of shale reservoirs. In this paper, the development status of productivity numerical models for shale gas horizontal wells is reviewed in consideration of the multi-scale transport characteristics of shale gas. These models include dual media capacity models, multiple media capacity models, and complex seam productivity models. It is considered that the dual medium and multi-media productivity models weaken the large permeable flow area and channel provided by the complex seam network system after shale reservoir lamination, and cannot comprehensively characterize the full-scale coupled transport characteristics of shale gas. The numerical model for productivity prediction of shale gas horizontal wells based on complex fracture network provides a multi-scale flow embedded fracture network system, which solves the problem of systematic flow without losing the ability to accurately characterize each scale flow. It is necessary to obtain the complex fracture network morphological characterization which conforms to reservoir geological characteristics, rock mechanical behavior and fluid-solid coupling mechanism. Fracture network characterization is the key to the productivity prediction of shale gas horizontal wells.     

雪峰隆起西缘湘张地1井牛蹄塘组页岩含气性特征及控制因素

雪峰隆起周缘是四川盆地外围页岩气勘探的重要区域,下寒武统牛蹄塘组为该区主要的页岩气层位,为深入研究页岩含气性特征,以隆起西缘湘张地1井钻井资料为基础,借助现场含气测试数据,对页岩纵向含气性进行精细描述,并以此探讨牛蹄塘组页岩气分布规律与控制因素.湘张地1井牛蹄塘组页岩气整体呈上低下高、局部富集的分布规律,受有机质含量、矿物组分、孔隙与裂缝、物性、滑脱构造等因素共同控制.下部页岩有机质和脆性矿物含量高、裂缝与孔隙较发育,气体吸附的比表面积主要由有机质孔隙提供,脆性矿物有利于孔缝的形成与保存,裂缝与孔隙的发育有效改善了储层物性,为游离气提供大量储集空间,配合存在的滑脱构造带,使下部总含气量较高,且以游离气为主,占比58%~82%,尤其底部滑脱带内吸附气含量极低,孔缝发育程度对总含气量的影响大于有机质含量,同时,孔缝分布的不均也导致气体在局部较为富集;上部页岩孔缝欠发育,有机质与脆性矿物含量均低于下部,整体含气性较差,吸附气占比略大,主要受有机质含量控制,可作为下部含气段直接有效的盖层.此外,下部页岩岩石力学脆性强、成岩作用晚、热演化程度高、抗压强度与主应力差低,具备较强的可压裂性,有利于后期改造.      

页岩储层压裂工艺技术在渝东地区应用

页岩气的工业化开发要求对致密储层进行体积压裂改造,水平井多级分段压裂技术是成功开发页岩气藏的关键技术之一。页岩储层在地应力与致裂压力联合作用下突破页岩基质,沟通天然裂隙等弱结构面,形成高导流能力缝网系统,页岩储层中赋存的游离气和吸附气得以释放,提高了页岩气井的初始产量和最终采收率。根据渝东地区页岩储层工程地质特征,结合渝页A-2HF井、渝页B-2HF井矿场压裂施工数据,探索适用于渝东地区的页岩储层压裂工艺技术,结果表明,采用前置盐酸处理储层保持近井带导流能力,能够保障后续大排量施工压力窗口;低砂比粉砂段塞多级降滤实现“控近扩远”,增加储层改造体积;压力异常层段胶液前置充分造缝,可为后续滑溜水携带支撑剂进入地层创造有利条件。     

渝东南—黔北地区牛蹄塘组页岩微-纳米级孔隙发育特征及主控因素分析

以渝东南-黔北地区牛蹄塘组页岩岩心及野外新鲜露头样品为研究对象,运用低温液氮吸附实验和氩离子抛光扫描电镜观察,划分页岩微纳米级孔隙类型,并对其发育程度和形态结构进行定量表征,结合页岩样品地球化学测试数据,明确页岩微观孔隙发育主控因素,试图建立微纳米级孔隙发育程度与主控因素定性或半定量关系。结果表明：研究区牛蹄塘组页岩微纳米级孔隙分为有机孔、无机孔和微裂缝3大类,包括7个亚类。有机质粒内孔结构特征为球状、细瓶颈状和墨水瓶状,无机孔主要为串珠状、球状和楔状,微裂缝呈四方开口的平行板状、夹板状。有机质粒内孔、矿物粒间孔和微裂缝为主要孔隙类型,且具有较好连通性,可作为页岩气赋存空间和渗流通道。页岩孔隙以中孔为主,其次为宏孔,孔隙直径分布范围主要在1~50 nm。比表面积主要由孔径≤5 nm孔隙所提供,页岩孔隙孔径越小,对比表面积贡献越大,越有利于页岩气吸附聚集,随着孔隙体积的增加,比表面积不断增加。有机碳含量是控制页岩微纳米级孔隙发育和比表面积的最重要内因,特别体现在对微孔和中孔发育的控制上;黏土矿物含量增加能增强页岩吸附能力,但对孔隙体积和比表面积主控作用不明显;脆性矿物含量主要控制宏孔发育,对页岩吸附的贡献可以忽略;热演化程度过低或过高均不利于有机质孔隙的发育,微纳米孔隙体积随着成熟度增加呈现出先增后减的趋势,对于高过成熟页岩,不同干酪根类型的有机质孔隙发育程度和比表面积大小次序为Ⅰ型＞Ⅱ型＞Ⅲ型。     

辽河东部地区页岩气成藏地质条件

页岩气主要是以吸附相和游离相同时赋存于泥岩及其夹层中的天然气。辽河东部地区包括东部凹陷和东部凸起,历经基底和陆块形成阶段、地台发育阶段、裂谷发育阶段和坳陷发育阶段,是一个典型的改造型的叠合盆地。辽东地区发育多套烃源岩,它们各自具有独立性。这些烃源岩不仅为常规油气藏提供物质基础,也是页岩气成藏及勘探的主要对象。综合分析可知,东部地区有3 套页岩具备页岩气成藏条件,生烃条件优越,页岩厚度大,有机质丰度高。泥岩储集性能良好,微孔、微裂缝发育,脆性矿物含量较高,利于后期压裂改造。对储层含气性进行测试可知,古近系中的页岩气以游离态为主,东部凸起则以吸附态为主;因此东部凸起古生界页岩气对构造保存条件要求相对低。东部凹陷古近系热演化程度低,页岩气以游离态为主,且页岩油气共生,保存条件较好。对东部地区进行优选可知： 中生界3井区,东部凹陷青龙台地区、桃园、黄于热地区是页岩气勘探有利区;东部凸起佟3井区、王参1井南部井区是近期页岩气勘探的首选地区。     

China Shale Gas Reservoir Types and Its Controlling Factors

Shale gas is an important unconventional natural gas. This paper classified shale into three types, which are marine, marine-continental transitional and continental facies shales, and summarized strata, distributions and reservoir features of the three kinds of shales. Marine face shale usually occurs in large scale and great thickness, and has widespread distributions; transitional face shale has the characteristics of thin layers, large multiple thickness and frequent interbedding, while the distribution of terrestrial face shale is relative narrow. Different shale reservoirs have similarities in gas compositions, occurrence states, gas origins. But they also differ in thickness, distributions and rock associations, etc., because of different sedimentary environments. Comparing reservoir characteristics of Chinese and American shale, organic matter abundance, maturity and types control the gas generation; mineral compositions and structures, organic matter maturity and types, pore and fracture structures, gas occurrence and migration characteristics, burial depth, and effective thickness control the shale gas accumulation.     

Geological Factors Controlling the Accumulation and High Yield of Marine-Facies Shale Gas: Case Study of the Wufeng-Longmaxi Formation in the Dingshan Area of Southeast Sichuan,China

The main geological factors controlling the accumulation and yield of marine-facies shale gas reservoirs are the focus of the current shale gas exploration and development research. In this study, the Wufeng-Longmaxi Formation in the Dingshan area of southeast Sichuan was investigated. Shale cores underwent laboratory testing, which included the evaluation of total organic carbon(TOC), vitrinite reflectance(Ro), whole-rock X-ray diffraction(XRD), pore permeability,and imaging through field emission scanning electron microscopy(FE-SEM). Based on the results of natural gamma ray spectrum logging, conventional logging, imaging logging, and seismic coherence properties, the exploration and development potential of shale gas in the Dingshan area have been discussed comprehensively. The results showed that(1)layer No. 4(WF2-LM4) of the Wufeng-Longmaxi Formation has a Th/U ratio 2 and a Th/K ratio of 3.5–12. Graptolites and pyrite are relatively abundant in the shale core, indicating sub-high-energy and low-energy marine-facies anoxic reducing environments.(2) The organic matter is mainly I-type kerogen with a small amount of II1-type kerogen. There is a good correlation among TOC, Ro, gas content, and brittle minerals; the fracturing property(brittleness) is 57.3%. Organic and inorganic pores are moderately developed. A higher pressure coefficient is correlated with the increase in porosity and the decrease in permeability.(3) The DY1 well of the shale gas reservoir was affected by natural defects and important latestage double destructive effects, and it is poorly preserved. The DY2 well is located far from the Qiyueshan Fault. Large faults are absent, and upward fractures in the Longmaxi Formation are poorly developed. The well is affected by low tectonic deformation intensity, and it is well preserved.(4) The Dingshan area is located at the junction of the two sedimentary centers of Jiaoshiba and Changning. The thickness of the high-quality shale interval(WF2-LM4) is relatively small, which may be an important reason for the unstable production of shale gas thus far. Based on the systematic analysis of the geological factors controlling high-yield shale gas enrichment in the Dingshan area, and the comparative analysis with the surrounding typical exploration areas, the geological understanding of marine shale gas enrichment in southern China has been improved. Therefore, this study can provide a useful reference for shale gas exploration and further development.     

康滇古陆东缘磷块岩型铀矿找矿前景分析

摘要：“康滇古陆东缘”北起四川峨眉,南至云南玉溪,面积近30000km2。在大地构造上属杨子陆块西南缘康滇地块东侧。20世纪50年代至20世纪末,在该地轴震旦系上统与寒武下统层位中发现了磷块岩型铀矿（化）点7个,放射性异常（点）带100多个。这类矿化是川滇地区轴资源重要找矿信息,根据该区内磷块岩型铀矿化的成矿地质条件、矿化特征和控矿因素,分析认为磷块岩型铀矿化找矿前景良好,四川会东大黑山地区和云南昆明鸣矣河地区,是下一步铀矿勘查的首选靶区。     

页岩气在中国发展应循序渐进

页岩气储集层通常为低孔、低渗透率,开采寿命长,生产周期长,采收率变化较大,且低于常规天然气采收率,先进的开采技术使页岩气成为未来能源的希望。从理论研究、资源量评估、技术标准、钻完井压裂技术、国家政策、环境保护、天然气价格等方面分析当前中国开发页岩气的现状,得出目前中国还不适合大规模开采页岩气,其理论价值远大于工业价值。     

川东南丁山地区龙马溪组页岩裂缝特征及对含气性的影响

川东南丁山地区是近年来四川盆地页岩气勘探开发的热点区域,裂缝的发育对页岩含气性及保存条件有重要的影响。综合运用野外露头、岩心、测井资料,结合岩石脆性矿物含量、岩石力学参数等数据,深入分析龙马溪组页岩裂缝发育特征和控制因素,并探讨了裂缝发育对含气性的影响。结果表明,丁山地区龙马溪组页岩裂缝主要以构造成因的剪切缝为主,裂缝优势方位共6组,主要包括4组平面剪切缝和2组剖面剪切缝,其发育主要受2个方向、3个阶段的构造应力场影响而成;裂缝延伸稳定,平均密度小,宽度小,充填程度高,主要被方解石和黄铁矿等充填。裂缝受控因素主要包括古构造应力场、构造部位、脆性矿物组分、岩石力学性质等;断层对裂缝发育具有明显的控制作用,其中断层两盘均存在裂缝发育程度急剧下降的临界范围,临界范围内裂缝发育程度高,超过此临界范围,裂缝发育程度变差且变化趋于平缓;不同期次的裂缝中,形成时间晚、规模过大、充填程度不高、与现今地应力方向一致或呈低角度相交的裂缝易造成页岩气的散失,对提高页岩含气性不利;龙马溪组岩石脆性矿物含量高,脆性指数属中等偏上程度,有利于构造缝发育且可压性较好。随着距齐岳山断裂距离的适当增加,龙马溪组页岩埋藏深度适中,地层压力增大,抗压强度增强高,脆性指数适中,构造保存条件变好,有利于不同方位的裂缝发育和页岩含气量的增加,位于该区域的DY2井与DY4井均位于该有利区域,含气性良好。研究结果对下一步深化页岩气勘探开发具有重要指导作用。     

评价页岩压裂形成缝网能力的新方法

页岩储层的“体积压裂”,使美国页岩气产业取得巨大成功,有效评价压裂裂缝网络形成的难易程度,是压裂开采的首要目标,目前国内外尚未发现有效的评价方法,为此开发了一种新的测试方法。针对10种岩芯,测试岩石力学参数,并对比分析常用的3种页岩脆性评价方法。采用压后裂隙结构面迹长分布的分维值和面密度对裂缝进行定量表征,并对压后崩落碎块进行对比分析。通过实验认为,杨氏模量和泊松比判别法与塑性系数判别法用于评价岩石脆性,精确度更高;脆性岩石通常表现为高杨氏模量或（和）低泊松比的特征,与单轴抗压强度、抗张强度和压入硬度没有对应关系;压裂裂缝的分布具有统计意义上的分形特征,分维可用于定量评价压后裂缝网络复杂度;硬度越高,压后裂缝密度越小;脆性越强,压后裂缝密度越大。新方法是岩石脆性、硬度和天然裂缝系统（和沉积层理）特征的综合体现,用于评价页岩压后形成缝网的能力,不仅直观可靠,而且简单有效,有利于现场推广应用,对于今后页岩气或致密砂岩气开发的理论研究和现场应用具有一定的指导意义。     

Fracture development in Paleozoic shale of Chongqing area (South China). Part one: Fracture characteristics and comparative analysis of main controlling factors

Natural macro- and micro-fractures in the Longmaxi shale (Lower Silurian) from Yuye-1 well and the Niutitang shale (Lower Cambrian) from Yuke-1 well are characterized. Regional geological structural evolution and shale geochemistry (including TOC and mineral composition, etc.) are analyzed. The controlling factors of natural fractures in Palaeozoic shale in the southeast of Chongqing have been confirmed, which have been analyzed qualitatively or semi-quantitatively. The results show that fractures are abundant, in both the Longmaxi Shale and Niutitang shale, due to the multiphase strong tectonic movement in the southeast of Chongqing. Therefore, tectonic factors are the principal factors that control fracture development in the Paleozoic shale of this region, followed by the mineral composition of the shale. Vertically, the mineral composition of shale in Yuke-1 well has a high dispersion degree and a strong heterogeneity (the dispersion coefficients of quartz and dolomite were 0.48 and 1, respectively), therefore, the development and distribution of fractures are controlled by quartz and dolomite content in the Niutitang shale, moreover, the quartz content shows positive correlation with the fractures quantity, and fractures are most abundant where dolomite content up to 64.7%. While the mineral composition of shale in Yuye-1 well has a low dispersion degree and a strong homogeneity in a vertical position (the dispersion coefficients of quartz and plagioclase were 0.15 and 0.26, respectively), which shows unconspicuous control effect for fractures, therefore, the development and distribution of fractures are mainly controlled by the TOC content, moreover, the TOC content shows positive correlation with the fractures quantity. Fractures are sealed by calcite, quartz and pyrite. Although sealed fractures do not contribute to the permeability of the reservoir, they are important planes of weakness that tend to be reactivated by hydraulically induced fractures. SEM images show that intergranular pore is connected by microfractures, thereby, the validity of porosity has been improved. The mixed network of microfractures and micropore provide enhanced permeability or storage capacity for the reservoir.     

黔西北地区龙马溪组页岩有机质和脆性矿物的控缝机制

页岩"甜点"层段中有机质和脆性矿物对裂缝的发育具有极为重要的控制作用，揭示并把握裂缝萌生、发育和演化的机理与规律，对于压裂目标层段的优选以及页岩气增产和稳产具有极为重要的工程实践价值。以黔西北地区龙马溪组页岩为例，通过地化测试、岩石力学实验以及扫描电镜，深入剖析和揭示了"甜点"层段中与有机质和脆性矿物相关的控缝机制，并结合数值模拟实验展现了"甜点"层段中裂缝的形成和演化的完整过程。研究结果表明，有机质和脆性矿物的同步富集为裂缝的发育和演化提供了重要的物质基础，其中裂缝趋向于沿着有机质形成的结构面传播，有机质的孔隙结构对裂缝具有较为明显的诱导机制。在外力作用下，内在积累的能量转化为脆性矿物的变形和变位，脆性矿物含量越高者裂缝发育能力越强，裂缝发育程度越高。数值模拟实验呈现了一种由于有机孔隙和脆性矿物所导致的应力集中从而诱发裂缝萌生和演化的整个过程。该研究成果可为深化认识裂缝的成因机理以及压裂施工过程中相关压裂参数的调整提供一定的借鉴与参考。     

页岩沉积环境对其油气潜力的影响:以中国和北美对比研究为例

页岩油气是当前全球油气勘探和研究的热点,但其潜力评价一直是难点。该文以中国和北美的四套典型页岩为例,包括北美湖相Green River组、内陆海相Niobrara组、中国环境来评价相龙马溪组和济阳坳陷湖相页岩,发现页岩沉积环境与其油气潜力具有密切关系,因此可通过分析发现这四套页岩的沉积环境都具有页岩沉积环境评价其页岩油气潜力。通过微量元素、生物标志化合物、扫描电镜、X-CT和X射线衍射等方法,发现这四套页岩都具有一定的还原性和较高的生产力,且具有差异性。内陆海相Niobrara组页岩具有弱还原的沉积环境,在四套页岩中有机碳含量较低,呈块状沉积构造,裂缝与微裂缝较少,储集空间相对有限。焦石坝海相龙马溪组页岩为还原的沉积环境,岩石以富含有机质的硅质岩为主,可观察到大量的大孔隙与少量的微裂缝。Green River页岩和济阳坳陷页岩形成于陆相咸化的强还原沉积环境,有机碳含量高,页岩以纹层状结构为主,岩石组成脆性矿物含量高,含有大量的裂缝。可见,具有强还原沉积环境的页岩通常具有较好的勘探前景。     

鄂尔多斯盆地延长组页岩裂缝特征与地应力研究

鄂尔多斯盆地延长组是我国近些年陆相页岩气的重点勘探区之一。本文从页岩的露头观测、岩石学特征、成像测井分析、地应力特征及可压裂性等方面,研究了鄂尔多斯盆地延长组泥页岩层段的裂缝发育特征,以及地应力对人工压裂诱导缝的影响。基于岩石学分析,延长组长7和长9段的泥页岩脆性矿物平均含量较高,分别为57.2%和44%。根据泥页岩露头观测和成像测井分析,长7段泥页岩发育有北东东向为主的垂直裂缝组,同时可见北北东向和南北向的垂直裂缝组。此外,压裂诱导缝的优势方位和成像测井分析结果表明,现今最大水平主应力方向为70°左右（即北东东向）。裂缝开启性分析表明,北东东向至近东西向裂缝组与现今最大水平地应力方向一致,开启性较好;而北北东裂缝组与现今最大水平地应力交角相对较大,开启性相对较差。因为现今地应力的水平应力比值（σH/σh = 1.54）相对较小,在后期人工压裂中延长组泥页岩中的诱导裂缝更倾向形成复杂的裂缝网格系统,这样会使裂缝与储层之间获得最大的接触,从而更有利于提高产能。