Pore structure and adsorption behavior of shale gas reservoir with influence of maturity: a case study of Lower Silurian Longmaxi formation in China

Knowledge of pore structure and adsorption capacity provides guidance for better studying the origin, hydrocarbon distribution, and productivity of shale gas reservoir. In this study, pore structure characteristics of six shale core plugs with different maturity from the Lower Silurian Longmaxi formation in south China were investigated using the Rock-eval analysis, X-ray diffraction, total organic carbon (TOC) content test, and scanning electron microscope (SEM) observation. To further investigate the influence of maturity, the adsorption behavior of gas shale was experimentally measured, with the maximal pressure being 20 MPa. Rock-eval analysis indicates that Ro is 0.67~1.34%. SEM results show that organic matter (OM) pores are abundant in high-maturity shale sample. The OM pores are mainly irregular to elliptical in shape, the size is 8~100 nm. The TOC content is 0.16~4.21% and shows a positive correlation with the BET surface area. A negative relationship exists between TOC content and average pore diameter, which indicates that abundant nanometer pores are related to the OM. A noticeable characteristic in the pore size distribution curve is that the content of micropores (pore width <?2 nm) increases with the increasing TOC content. Additionally, the thermal maturity results in significant difference in methane adsorption capacity. Maximal adsorption capacity of shale samples is also lineally correlated with TOC content, which increases with maturity. This study provides a quantitative understanding of how maturity affects pore structure and adsorption behavior of shale gas reservoir.     

煤层气与页岩气吸附差异性分析

查明页岩气与煤层气的吸附差异对指导其勘探开发具有重要意义。通过测试不同成熟度和有机质(TOC)的煤与页岩的等温吸附曲线,结果表明:TOC含量是影响页岩吸附的主要因素,成熟度相当的煤与页岩相比,煤的吸附量远远大于页岩,主要是由于成藏特征、物质组成和孔隙结构不同造成的;页岩吸附过程中出现的异常吸附可能有其他的吸附理论支撑。      

柴达木盆地鱼卡凹陷侏罗系泥页岩地球化学特征及储集条件——以柴页1井为例

柴达木盆地北缘鱼卡凹陷发育的侏罗系泥页岩是中国北方陆相页岩气勘探的目的层系之一。为进一步明确鱼卡凹陷侏罗系泥页岩地化-储集条件,系统采集了柴页1井泥页岩岩心样品,开展了总有机碳、热解氢指数、镜质体反射率、孔隙度和渗透率、扫描电镜、矿物组成及等温吸附特征实验分析。结果表明,柴页1井中侏罗统大煤沟组泥页岩有机质类型和成熟度利于有机质孔隙发育,较高的总有机碳含量利于页岩气富集;粘土矿物的存在虽然抑制了泥页岩微孔隙的发育,但对其吸附能力有促进作用。鱼卡凹陷具有良好的页岩气生成和储集条件,是页岩气勘探的有利地区。     

柴北缘盆地YQ-1井中侏罗统石门沟组泥页岩纳米孔隙特征及影响因素

柴达木北缘(柴北缘)盆地侏罗纪是典型的陆相湖沼盆地,是目前具有页岩气潜力的盆地之一。本文运用氮气吸附、有机碳含量、有机质成熟度、全岩X衍射分析等方法,对柴北缘鱼卡地区YQ - 1井中侏罗统石门沟组泥页岩的纳米孔隙特征及控制因素进行研究。结果表明,石门沟组泥页岩纳米孔隙结构复杂,根据吸附回线及孔径分布特征可划分为两类,第一类以一端不透气性孔和开放性平行板状狭缝孔为主,孔径主要集中在3～5 nm范围内,呈单峰状分布;第二类则以一端不透气性孔和开放性倾斜板狭缝孔为主,孔径主要分布在3～5 nm和8～14 nm范围内,呈双峰状分布。孔径小于50 nm的微孔和介孔是比表面积和孔体积的主要贡献者;黏土矿物含量与微孔、介孔、总孔体积呈正相关;在较低的成熟度制约下,泥页岩有机质孔隙基本不发育,有机质丰度较高的石门沟组上段H9泥页岩TOC含量与微孔、介孔、总孔体积呈负相关性,有机质丰度较差的下段H8泥页岩TOC含量与孔体积相关性则不甚明显;孔隙结构及孔径分布受沉积环境水动力条件影响;黏土矿物是石门沟组泥页岩纳米孔隙的主要提供者,是孔隙发育的主控因素,TOC含量与沉积环境也会对泥页岩孔隙发育产生一定影响。     

鄂尔多斯盆地东南部上古生界海陆过渡相页岩储集性与含气性

鄂尔多斯盆地上古生界海陆过渡相页岩是重要的页岩气富集层系,但是含气性及其控制因素研究薄弱,制约了对该地区页岩气的勘探和研究。论文通过对鄂尔多斯东南部本溪和山西组大量页岩样品开展有机地球化学、矿物组成、页岩孔隙及分布的研究,评价了海陆过渡相页岩的储集性;通过含气量现场解吸和等温吸附实验,分析了页岩含气特征和影响因素。结论认为研究区海陆过渡相页岩有机质丰度高(TOC含量0.5%~11%),主要发育III型干酪根,有机质成熟度较高(1.0%~3.0% Ro);矿物组成以富黏土页岩为特征,黏土矿物含量可高达60%以上。总孔隙度分布在2%~8%,部分样品微裂缝发育。孔隙类型以平行板状的狭缝型孔隙介孔为主,在岩石孔隙比表面积和孔体积的贡献占90%以上;TOC含量与孔隙比表面积及孔隙总体积具有密切的相关性,有机质孔隙对岩石总孔隙构成具有重要贡献。现场解吸含气量为0.591~4.05 m3/t,兰氏体积从0.05 m3/t到14 m3/t都有分布,页岩实测含气量与气体吸附能力差异大。TOC含量是控制海陆过渡相页岩含气量和含气能力的重要因素,富黏土矿物的吸附作用可使样品含气能力显著增加。     

Reservoir characteristics and methane adsorption capacity of the Upper Triassic continental shale in Western Sichuan Depression,China

The well-developed continental shale sequences in the Western Sichuan Depression are characterised by extremely low porosity and permeability, complex lithologies and strong lateral facies changes. The overall lack of proper characterisation of the shale properties has restricted gas exploration and development in the region. In this study, shales from the fifth member of the Xujiahe Formation of the Upper Triassic (T₃x⁵) are comprehensively characterised in terms of their organic geochemistry, mineral composition, microscopic pore structure and gas content. In addition, the influence of various geological factors on the adsorbed gas content is investigated. We proposed a new model for predicting the adsorption gas content of continental shale. The T₃x⁵ shale sequence is found to be rich in organic matter but with variable mineral compositions, pore types and reservoir physical properties. The porosity and permeability of shales are better than those of siltstones and fine sandstones interbedded with the shale under an overall densification background. Mesopores (2–50 nm) are common in the shale sequence, followed by micropores and then macropores. The gas-adsorption capacity of organic-rich shales increases with increasing TOC and clay-mineral contents, maturity and pressure, but decreases with increasing quartz content, carbonate minerals and temperature. The gas-adsorption capacity can thus be expressed as a function of organic matter, clay-mineral content, temperature and pressure. The calculated results are in good agreement with the experiment results and indicate that adsorption gas in the studied shales accounts for 78.9% of the total gas content.     

阿尔金山前中、下侏罗统页岩气成藏地质条件

柴西阿尔金山前经历了早期断陷、中期拗陷和晚期隆升的多期改造叠合,其中早、侏罗世断陷期发育陆相湖盆泥页岩。地堑半地堑同沉积断裂控制沉积格局,断陷湖盆长轴为北东向,在小梁山凹陷、七个泉断鼻带和铁木里克凸起构造带沉积半深湖深湖相的泥页岩夹薄层砂岩、粉砂岩。泥页岩空间展布受沉积相控制,因此呈北东向带状连续稳定分布,由阿尔金山前七个泉-红沟子-小梁山构造带向盆地内部厚度逐渐减薄,累积厚度超过300 m,有效厚度在50～70 m,是阿尔金山前中、下侏罗统工业性页岩气聚集成藏必备的物质保障。研究证实,阿尔金山前中、下侏罗统泥页岩干酪根显微组分腐泥组、镜质组、惰性组的平均含量分别为60.7％、33.1%和6.2%,依据Tissot和Welte分类标准,有机质干酪根类型以Ⅱ型为主。 对25个野外样品进行岩石热解测试,TOC含量稳定分布在1%～4%,Ro在0.8%～2.5%,泥页岩有机质含量高,处于成熟过成熟阶段,生气条件优越。与北美和四川盆地海相页岩相比,阿尔金山前中、下侏罗统陆相泥页岩的黏土矿物含量相对较高,平均含量为52.51%;含硅质脆性矿物含量相对较低,平均含量为37.42%。泥页岩中发育大量裂缝、微裂缝、粒间孔、粒内孔和有机质孔,有利于页岩气富集和吸附。泥页岩比表面积在9.13～18.14 m2/g,平均值为13.43 m2/g;孔体积在0.026 6～0.088 7 cm3/g,平均值0.065 41cm3/g,平均孔径在25.76～72.48 nm,平均值为47.87 nm。比表面积和孔径呈负相关,孔体积和孔径呈正相关;孔径越小,泥页岩的比表面积越大。TOC和Ro与泥页岩表面积呈正相关,表明随着有机质成熟生烃形成的有机质孔对比表面有重大影响,比表面越大为页岩气吸附提供的吸附位越多,储集性能优越。上覆灰泥岩、泥灰岩和膏盐岩盖层区域广泛分布,早期浅埋-中期深埋、多次排烃-晚期抬升有利于页岩气藏的保存。综合页岩气成藏实际地质参数,优选出小梁山凹陷、七个泉断鼻带、洪水沟断鼻带和铁木里克凸起4个有利区带。     

湘西北下古生界海相页岩储层特征与含气性分析

基于野外地质和钻井资料,结合相关实验测试结果,对湘西北地区下古生界海相页岩储层特征进行了深入研究,并探讨了页岩甲烷含气性及影响因素。结果表明：牛蹄塘组黑色页岩以深水陆棚斜坡相沉积为主,厚度范围为50~250 m;龙马溪组为闭塞海湾沉积,底部黑色页岩发育。两组页岩有机质类型均属于Ⅰ型,有机碳含量平均为3.57%和1.16%,热演化程度较高,平均达2.61%和2.08%。受沉积环境和成岩作用影响,两组页岩均具有高石英、低黏土、少量碳酸盐矿物的组成特征。页岩储集空间可划分为3大类：矿物基质孔、有机质孔、微裂缝。受有机质和黏土矿物等因素影响,页岩内部孔隙结构参数各不同,但主体上孔径小于50 nm的微孔和中孔提供了大部分比表面积和孔体积,为气体存储主要场所。牛蹄塘组页岩甲烷最大吸附量平均为1.98 cm3/g;龙马溪组页岩甲烷最大吸附量较低,为1.16 cm3/g。其中有机质与黏土矿物对页岩甲烷吸附量均有一定的贡献,而过高的成熟度和含水量可导致页岩吸附能力下降。     

Methane adsorption in the low–middle-matured Neoproterozoic Xiamaling marine shale in Zhangjiakou,Hebei

The adsorption capacity of high–over-matured shale has been widely investigated, but the adsorption capacity and the main factors influencing low–middle-matured, type II kerogen-containing, and organic-rich marine shale have been rarely explored. This research conducts organic geochemistry, mineralogical composition, adsorption isotherm tests to reveal the adsorption and main influencing factors of the different geochemistry characteristics, mineralogical compositions, temperature and pressure conditions of the low–middle-matured Neoproterozoic Xiamaling marine shale in Zhangjiakou, Hebei. The investigated shale is in a low–middle maturity stage, contains type II kerogen and is rich in organic matter. The results show that the total organic carbon (TOC) content of the Xiamaling shale is positively correlated with the methane adsorption capacity, which is the most important influencing factor on the adsorptive property of shale. The methane adsorption capacity first decreases to the minimum value as the temperature reaches 360°C equivalent Ro (EqRo = 1.0%), then increases and reaches the maximum value at 620°C (EqRo = 3.28%) and finally decreases again as the temperature rises at the last simulation stage. The mineral components exhibit an insignificant influence on the methane absorbability because of organic-matter coatings. The TOC-normalised methane adsorption capacity is positively correlated with the illite–smectite and clay-mineral contents but shows no significant correlation with brittle minerals, such as quartz. Soluble organic matter and kerogen caused the methane dissolution and adsorbtion, respectively. The strong dissolution property of the soluble organic matter is the most important cause of the larger adsorption capacity of the original shale compared with that of the residual samples. Moreover, the methane adsorption capacity of the Xiamaling shale decreases with increasing temperature, and increases with pressure below the critical pressure but decreases exceeding the critical pressure.     

陆相页岩气储层孔隙发育特征及其主控因素分析:以鄂尔多斯盆地长7段为例

鄂尔多斯盆地延长组是目前最具页岩气潜力的研究层段之一。本文以该盆地东部长7段为研究对象,运用氮气吸附法及氩离子剖光扫描电镜分析对页岩气储层孔隙结构及孔隙类型进行分析和测定,并结合岩石矿物组分、有机质成熟度以及总有机碳（TOC）质量分数,讨论了孔隙结构和影响因素。结果表明,长7段页岩气储层孔隙结构复杂,根据吸附回线形态可分为2类：Ⅰ类回线主要对应孔径为2.6~4.2 nm的狭缝结构或楔形结构的平行板状孔或微裂缝,具体可分为黏土矿物矿片间孔隙、有机质内狭缝状孔隙及基质微裂隙等类型;Ⅱ类回线主要为分布于2.3~3.1、3.5~3.8、4.3~5.2 nm等多个孔径段的开放型圆筒状孔,包括有机质孔和残余粒间孔。中孔和微孔是总孔体积和比表面积的主要贡献者。w（TOC）是延长组页岩总孔体积及比表面积的主要控制因素,与总孔体积及比表面积均呈正相关关系;镜质体反射率及矿物含量对孔隙发育的控制作用不明显,但黏土矿物对微孔孔容贡献较大,其中伊利石质量分数与BET比表面积及孔容有较好的相关性。     

应用高温甲烷吸附实验研究川东北地区五峰组页岩甲烷吸附能力

页岩甲烷吸附能力是决定页岩气井开采方案的重要参数,对评估页岩气藏潜力意义重大。干酪根类型、总有机碳含量、矿物组成、成熟度和孔径等是影响页岩吸附性能的因素,但针对高温高压下过剩吸附现象对页岩甲烷吸附能力影响的研究还需开展进一步的探索。为揭示四川盆地东北地区五峰组页岩甲烷吸附能力,本文通过场发射扫描电镜、低温氮气吸附和高压甲烷吸附实验,研究了高温高压下页岩的甲烷吸附能力,并分析了页岩孔隙结构等对页岩吸附能力的影响。结果表明:①五峰组页岩孔隙结构非均质性强,发育有机孔隙、粒(晶)间孔隙、粒(晶)内孔隙和粒(晶)间溶孔等多种孔隙;②比表面积平均为19.1282m^2/g;孔体积平均为0.0195cm^3/g;孔径平均为5.2226nm;③修正后的饱和吸附气量为2.56m^3/t;④五峰组页岩甲烷吸附性能受控于比表面积、孔体积;有机质含量越大、有机质热演化程度越低,其甲烷吸附性能越强;⑤孔隙结构是影响页岩甲烷吸附能力的重要内因。同时指出低压条件下的实验吸附曲线不适合直接评价页岩甲烷吸附能力。     

页岩气储层孔隙类型及特征研究:以渝东南下古生界为例

通过薄片分析、扫描电镜及氩离子抛光技术,对渝东南下古生界含气页岩中的孔隙类型及特征进行了分类观察、描述,结合有机碳含量、X衍射、岩石物性、氮气吸附及甲烷等温吸附实验测试,分析了页岩气储层中各类孔隙的储气贡献,探讨这些孔隙对页岩中烃类运移的影响。研究认为,有机质孔隙、颗粒内孔、粒间孔隙及微裂隙是页岩气储层孔隙的4种类型,有机质表面的分散状孔隙多为nm级,石英碎屑可形成粒内或粒间孔隙,黄铁矿颗粒内部小晶体排列分布产生孔隙空间,黏土絮状沉淀形成片粒状结构孔隙,微裂隙普遍发育在页岩基质中,可达mm级。不同类型的孔隙能够为页岩气的赋存提供不同尺度的储集空间,页岩吸附含气量与表征孔隙特征的参数(TOC、BET比表面积、BJH总孔体积)具有显著的正相关关系。微裂隙与粒间孔隙对页岩中烃类的运移最有利。     

宁武盆地山西组过渡相页岩孔隙特征及影响因素

为了研究宁武盆地山西组过渡相页岩的孔隙特征和影响因素,对宁武盆地山西组过渡相页岩进行了系统采样,并针对性地进行了扫描电镜分析、低温氮吸附实验、TOC含量测试、有机质成熟度（R_max）测试、全岩矿物X衍射分析和孔隙度测试,探讨了页岩孔隙类型、孔隙特征及影响因素。结果表明:研究区页岩孔隙类型主要以粒间孔、晶间孔、有机质气孔、有机质原生孔、溶蚀孔及裂缝为主,大小以2~50 nm的介孔为主,孔隙形态包括开放的尖壁形孔、平行壁孔、锥型管状孔、墨水瓶孔等;页岩平均孔隙度为3.64%,平均孔径为7.78 nm,BET比表面积平均为11.70m2/g,总孔体积平均为0.022 2 cm3/g,具有较强的储集性和吸附性;页岩孔隙具有分形特征,分形维数为2.61~2.77,分形维数与微孔体积分数表现出良好的正相关性;页岩孔隙发育受TOC含量、成熟度（R_max）和矿物组成的影响。      

四川盆地下侏罗统陆相页岩气源储特征及耦合评价

四川盆地陆相页岩气勘探前景良好,目前已在川东北地区下侏罗统获得良好页岩气显示和工业气流。与海相页岩相比,陆相页岩具有相变快、岩相组合类型多(夹层发育)、有机质丰度低和源储配置关系复杂等特点。运用“源储耦合”研究思路,利用宏观-微观结合的储层表征技术对下侏罗统自流井组大安寨段页岩的烃源特征、储集特征及其耦合关系开展了分析与评价。结果表明:(1)岩相组合特征。大安寨段为一套以暗色页岩与介壳灰岩不等厚互层为主的浅湖-半深湖沉积,主要发育4种岩相与3种厚度组合,主要包括高碳黏土质页岩夹薄层(<1 m)介壳灰岩、中碳黏土质/含粉砂质页岩夹薄-中层(<3 m)介壳灰岩、低-中碳粉砂质页岩夹中-厚层介壳灰岩及少量粉细砂岩;其中页岩为源岩和主要储层,介壳灰岩为次要储层和隔夹层,致密砂岩物性较差,主要为隔夹层。(2)烃源与储集特征。川东北地区页岩厚度介于30~40 m,TOC含量普遍介于1.0%~2.0%;有机质类型以Ⅱ₂型和Ⅲ型为主;页岩储集空间包括有机孔、无机孔与宏-微观裂缝,页岩中黏土矿物粒缘孔和晶间孔最为发育,有机孔次之,微裂缝发育程度与连通性较好;介壳灰岩夹层以粒间孔、粒内孔、微裂缝为主要储集空间。(3)揭示了大安寨段页岩层系的源储耦合机理。宏观上,TOC含量和孔隙度均随灰质含量的增加而降低,页岩的源储耦合条件优于夹层,以黏土质页岩为最优;微观上,页岩内部存在有机质与有机孔的源储一体耦合、原始有机质与无机孔和微裂缝之间为纳米至微米级距离的迁移耦合,页岩与夹层间为毫米至厘米级距离的迁移耦合,夹层内部则有赖于相邻页岩中有机质与夹层中无机孔和微裂缝的厘米至米级距离的运移耦合。(4)分别针对页岩层和夹层源储耦合特征建立了相应的源储耦合评价参数,对研究区2口典型钻井开展评价并优选了水平井靶窗。     

鄂尔多斯盆地东部太原组页岩气吸附特征及影响因素

鄂尔多斯盆地东部太原组在绥德地区发育一套潜在的烃源岩,总有机碳(Total Organic Carbon,TOC)含量为0.75%~5.71%(平均2.75%); 镜质体反射率(R_o)为1.43%~2.12%(平均1.80%),处在高成熟—过成熟阶段,具有很好的生气潜力。为了探讨鄂尔多斯盆地东部太原组泥页岩的吸附特征,选取了研究区SSD1井10个泥页岩样品进行等温吸附、总有机碳含量、镜质体反射率、X-射线衍射和比表面积等测试分析,在此基础上探讨了盆地东部太原组富有机质泥页岩的吸附能力及其影响因素。结果表明: 研究区SSD1井太原组10个泥页岩样品的兰氏体积为1.11~2.41 m³/t,随着压力的增加,吸附能力迅速增加,当达到一定压力后达到饱和; 泥页岩的吸附能力与总有机碳含量和黏土矿物含量有正相关关系; 页岩比表面积与兰氏体积相关性不明显,推测样品孔隙大小及形态对气体的扩散和吸附有一定的影响。综合评价认为,总有机碳含量、黏土矿物含量是影响太原组泥页岩吸附能力的重要因素,这为盆地东部页岩气勘探提供参考。     

基于氮吸附法的页岩有机孔隙结构表征

页岩的微观孔隙结构对页岩气的赋存至关重要,气体吸附法可以较好对页岩的微观孔隙结构进行表征。通过测量丁页1井不同深度样品的矿物含量、RO值和TOC含量,结果表明丁页1井龙马溪组页岩样品的矿物含量比较稳定,有机质成熟度变化不大,均为过成熟。通过低温氮吸附法计算样品的比表面积和微、介孔容积和孔径分布,结果表明：（1）样品的平均孔径为2.8 ~ 4.9 nm,10 nm以下的孔隙提供了大部分的微、介孔容积。微、介孔容积为0.00136 ~ 0.0108 cm3/g,平均0.004 cm3/g,比表面积为2.54 ~ 13.69 m2/g,平均6.68 m2/g;（2）微、介孔容积、比表面积和TOC三者之间有很强的正相关性。通过计算TOC含量为0时的微、介孔容积和比表面积推算无机孔和有机孔之间的比例和其对比表面积的影响,发现有机孔提供了大部分的微、介孔容积,有机孔还是比表面积的主要贡献因素;（3）样品的吸附曲线符合IPUAC分类中的第IV型吸附曲线,样品的脱附曲线反映样品孔隙形态随TOC含量的增加,由楔形孔（不定型孔）变为连通的墨水瓶型孔（狭缝型孔）或墨水瓶型孔。     

Characterization of a Lacustrine Shale Reservoir and the Evolution of its Nanopores: A Case Study of the Upper Cretaceous Qingshankou Formation in the Songliao Basin,Northeastern China

The Songliao Basin is one of the most important petroliferous basins in northern China. With a recent gradual decline in conventional oil production in the basin, the exploration and development of unconventional resources are becoming increasingly urgent. The Qingshankou Formation consists of typical Upper Cretaceous continental strata, and represents a promising and practical replacement resource for shale oil in the Songliao Basin. Previous studies have shown that low-mature to mature Qingshankou shale mainly preserves type Ⅰ and type Ⅱ1 organic matter, with relatively high total organic carbon(TOC) content. It is estimated that there is a great potential to explore for shale oil resources in the Qingshankou Formation in this basin. However, not enough systematic research has been conducted on pore characteristics and their main controlling factors in this lacustrine shale reservoir. In this study, 19 Qingshankou shales from two wells drilled in the study area were tested and analyzed for mineral composition, pore distribution and feature evolution using Xray diffraction(XRD), scanning electron microscopy(SEM), low-pressure nitrogen gas adsorption(N2-GA), and thermal simulation experiments. The XRD results show that clay, quartz, and feldspar are the dominant mineral constituents of Qingshankou shale. The clay minerals are mostly illite/smectite mixed layers with a mean content of 83.5%, followed by illite, chlorite, and kaolinite. There are abundant deposits of clay-rich shale in the Qingshankou Formation in the study area, within which many mineral and organic matter pores were observed using SEM. Mineral pores contribute the most to shale porosity;specifically, clay mineral pores and carbonate pores comprise most of the mineral pores in the shale. Among the three types of organic matter pores, type B is more dominant the other two. Pores with diameters greater than 10 nm supply the main pore volume;most are half-open slits and wedge-shaped pores. The total pore volume had no obvious linear relationship with TOC content, but had some degree of positive correlation with the content of quartz + feldspar and clay minerals respectively. However, it was negatively correlated with carbonate mineral content. The specific surface area of the pores is negatively related to TOC content, average pore diameter, and carbonate mineral content. Moreover, it had a somewhat positive correlation with clay mineral content and no clear linear relationship with the content of quartz + feldspar. With increases in maturity, there was also an increase in the number of carbonate mineral dissolution pores and organic matter pores, average pore diameter, and pore volume, whereas there was a decrease in specific surface area of the pores. Generally, the Qingshankou shale is at a low-mature to mature stage with a TOC content of more than 1.0%, and could be as thick as 250 m in the study area. Pores with diameters of more than 10 nm are well-developed in the shale. This research illustrates that there are favorable conditions for shale oil occurrence and enrichment in the Qingshankou shale in the study area.     

Geological and geochemical characteristics of the Middle–Lower Jurassic shales in the Kuqa Depression,Tarim Basin: an evaluation of shale gas resources

Middle–Lower Jurassic terrigenous shales constitute a set of significant hydrocarbon source rocks in the Kuqa Depression of the Tarim Basin. Until recently, however, most investigations regarding this set of hydrocarbon source rocks have mainly focused on conventional oil and gas reservoirs, and little research has been conducted on the formation conditions of shale gases. This research, which is based on core samples from nine wells in the Kuqa Depression, investigated the geological, geochemical, mineralogical and porosity characteristics of the shales, analysed the geological and geochemical conditions for the formation of shale gases, and evaluated the shale gas resource potential. The results show that the distribution of the Middle–Lower Jurassic shales is broad, with thicknesses reaching up to 300–500 km. The total organic carbon (TOC) content is relatively high, ranging from 0.2 to 13.5 wt% with a mean of 2.7 wt%. The remaining hydrocarbon generative potential is between 0.1 and 22.34 mg/g, with a large range of variation and a mean value of 3.98 mg/g. It is dominated by type III kerogen with the presence of minor type II₁ kerogen. The vitrinite reflectance values range from 0.517 to 1.572%, indicating the shales are in a mature or highly mature stage. The shales are mainly composed of quartz (19–76%), clay (18–68%) and plagioclase (1–10%) with mean contents of 50.36 wt%, 41.42 wt%, and 3.37 wt%, respectively. The pore spaces are completely dominated by primary porosity, secondary porosity and microfractures. The porosity is less than 10% and is mainly between 0.5 and 4%, and the permeability is generally less than 0.1 mD. These results classify the shale as a low-porosity and ultra-low-permeability reservoir. The porosity has no obvious correlation with the brittle or clay mineral contents, but it is significantly positively correlated with the TOC content. The maximum adsorbed gas content is between 0.82 and 8.52 m³/t with a mean of 3.37 m³/t. In general, the shale gas adsorption content increases with increasing the TOC content, especially when the TOC content is greater than 1.0%. The volumetric method, used to calculate the geological resources of the Middle–Lower Jurassic shales in the Kuqa Depression, shows that the geological resources of the Middle and Lower Jurassic shales reach 667.681 and 988.115 × 10⁹ m³, respectively with good conditions for the formation of shale gas and good prospects for shale gas exploration.     

桂中坳陷环江凹陷上古生界海相页岩储层孔隙结构和分形特征研究

通过有机地化分析、全岩X衍射矿物分析、甲烷等温吸附及低压氮气吸附实验,本文对桂中坳陷环江凹陷上古生界页岩样品的孔隙结构及分形特征进行了研究.结果表明:研究区页岩总有机碳含量(TOC)平均为2.40%,热成熟度(Ro)平均为2.65%,处于过成熟演化阶段.页岩主要的矿物组成为石英和黏土.页岩的比表面积平均为5.86 m2/g,孔容平均为0.014 9 mL/g,平均孔径为11.2 nm.页岩中发育大量的中孔,主要呈两端开口的圆筒形孔或四边开放的平行板状孔.页岩中TOC含量和石英含量越多,微-中孔越发育、比表面积和孔容越大,而平均孔径则变小.通过Frenkel-Halsey-Hill (FHH)模型和氮气吸附实验数据计算得到孔隙表面分形维数D1(平均为2.428 4)和孔隙结构分形维数D2(平均为2.622 2),对应的相对压力(P/P0)分别是0~ 0.45和0.45 ~ 0.99.分形维数D1、D2随着比表面积、孔容的增加而增加,而平均孔径随着前者的增加而减小.分形维数D1、D2、TOC含量、石英含量和甲烷吸附量之间呈现较好的正相关性,但随着黏土矿物含量的增多而减小.分形维数D1与Langmuir压力存在弱负相关性,分形维数D2随Langmuir压力增大有变大的趋势.桂中坳陷西北部页岩分形维数越大,孔隙结构越复杂,其对天然气的吸附和存储能力越强.     

辽西金羊盆地下侏罗统北票组页岩气地球化学特征及其成因

金岭寺-羊山盆地(金羊盆地)是中国北方侏罗系发育最完备的地区之一,盆地内充填的下侏罗统北票组为一套湖相泥岩,具有良好的油气潜力。在金羊盆地章吉营子凹陷西缘布置实施的4口地质调查井中,有3口井见油气显示。通过对SZK2及SZK3钻井岩心进行现场解析,北票组泥页岩在浅层测试到可观的页岩气含量,且随着深度的变化,总含气量及甲烷含量有所增加。另外,其总含气量与有机碳含量呈良好的正相关关系,是影响页岩含气量的关键因素。对比金羊盆地北票组泥页岩吸附气C同位素特征,其气体成因主要存在生物成因气和煤型气2种类型,表明下侏罗统北票组页岩气具有混合多成因的特征。通过X衍射分析综合评价,金羊盆地下侏罗统北票组泥页岩压裂条件好、天然气吸附能力强,具备一定的页岩气勘探前景,是有利的页岩气勘探开发新层系。