The Influence of Extractable Organic Matter on Pore Development in the Late Triassic Chang 7 Lacustrine Shales, Yanchang Formation, Ordos Basin, China

To investigate the influence of extractable organic matter （EOM） on pore evolution of lacustrine shales, Soxhlet extraction, using dichloromethane, was performed on a series of Chang 7 shale samples （Ordos Basin, China） with vitrinite reflectance of 0.64% to 1.34%. Low-pressure gas adsorption experiments were conducted on the samples before and after extraction. The pore structure parameters were calculated from the gas adsorption data. The results show complex changes to the pore volumes and surface areas after extraction. The pore development of both the initial and extracted samples is strongly controlled by total organic carbon （TOC） content. Micropores developed mainly in organic matter （OM）, while mesopores and macropores predominantly developed in fractions other than OM. The influence of EOM on micropores is stronger than on mesopores and macropores. Organic solvents with a higher boiling point should be used to explore the effect of EOM on pore structure in the future.

Pore Structure Heterogeneity of the Xiamaling Formation Shale Gas Reservoir in the Yanshan Area of China: Evaluation of Geological Controlling Factors

Micro-heterogeneity is an integral parameter of the pore structure of shale gas reservoir and it forms an essential basis for setting and adjusting development parameters.In this study,scanning electron microscopy,high-pressure mercury intrusion and low-temperature nitrogen adsorption experiments were used to qualitatively and quantitatively characterize the pore structure of black shale from the third member of the Xiamaling Formation in the Yanshan area.The pore heterogeneity was studied using fractal theory,and the controlling factors of pore development and heterogeneity were evaluated in combination with geochemical parameters,mineral composition,and geological evolution history.The results show that the pore structure of the reservoir was intricate and complicated.Moreover,various types of micro-nano scale pores such as dissolution pores,intergranular pores,interlayer pores,and micro-cracks are well developed in member 3 of the Xiamaling Formation.The average porosity was found to be 6.30%,and the mean value of the average pore size was 4.78 nm.Micropores and transition pores provided most of the storage space.Pore development was significantly affected by the region and was mainly related to the total organic carbon content,vitrinite reflectance and mineral composition.The fractal dimension,which characterizes the heterogeneity,is 2.66 on average,indicating that the pore structure is highly heterogeneous.Fractal dimension is positively correlated with maturity and clay mineral content,while it is negatively correlated with brittle mineral content and average pore size.These results indicate that pore heterogeneity is closely related to thermal history and material composition.Combined with the geological background of this area,it was found that the pore heterogeneity was mainly controlled by the Jurassic magmatism.The more intense the magma intrusion,the stronger the pore heterogeneity.The pore structure and its heterogeneity characteristics present today are a general reflection of the superimposed geological processes of sedimentary-diagenetic-late transformation.The influence of magmatic intrusion on the reservoir is the main geological factor that should be considered for detailed evaluation of the Xiamaling Formation shale gas reservoir in the Yanshan area.

Nanopore structure comparison between shale oil and shale gas:examples from the Bakken and Longmaxi Formations

In order to analyze and compare the differences in pore structures between shale gas and shale oil formations, a few samples from the Longmaxi and Bakken Formations were collected and studied using X-ray diffraction, LECO TOC measurement, gas adsorption and field-emission scanning electron microscope. The results show that samples from the Bakken Formation have a higher TOC than those from the Longmaxi Formation. The Longmaxi Formation has higher micropore volume and larger micropore surface area and exhibited a smaller average distribution of microsize pores compared to the Bakken Formation. Both formations have similar meso-macropore volume. The Longmaxi Formation has a much larger meso-macropore surface area, which is corresponding to a smaller average meso-macropore size. CO_2 adsorption data processing shows that the pore size of the majority of the micropores in the samples from the Longmaxi Formation is less than 1 nm, while the pore size of the most of the micropores in the samples from the Bakken Formation is larger than 1 nm. Both formations have the same number of pore clusters in the 2–20 nm range, but the Bakken Formation has two additional pore size groups with mean pore size diameters larger than 20 nm. Multifractal analysis of pore size distribution curves that was derived from gas adsorption indicates that the samples from the Longmaxi Formation have more significant micropore heterogeneity and less meso-macropore heterogeneity. Abundant micropores as well as mesomacropores exist in the organic matter in the Longmaxi Formation, while the organic matter of the Bakken Formation hosts mainly micropores.

Controlling Factors of Organic Nanopore Development: A Case Study on Marine Shale in the Middle and Upper Yangtze Region, South China

The Upper Ordovician Wufeng-Lower Silurian Longmaxi and the Lower Cambrian Qiongzhusi shales are the major targets for shale gas exploration and development in China.Although the two organic-rich shales share similar distribution ranges and thicknesses,they exhibit substantially different exploration and development results.This work analyzed the nanopore structures of the shale reservoirs in this region.Pore development of 51 shale samples collected from various formations and locations was compared using the petromineralogical,geochemical,structural geological and reservoir geological methods.The results indicate that the reservoir space in these shales is dominated by organic pores and the total pore volume of micropores,mesopores,macropores in different tectonic areas and formations show different trends with the increase of TOC.It is suggested that organic pores of shale can be well preserved in areas with simple structure and suitable preservation conditions,and the shale with smaller maximum ancient burial depth and later hydrocarbongeneration-end-time is also more conducive to pore preservation.Organic pore evolution models are established,and they are as follows:①Organic matter pore development stage,②Early stage of organic matter pore destruction,and③late stage of organic matter pore destruction.The areas conducive to pore development are favorable for shale gas development.Research results can effectively guide the optimization and evaluation of favorable areas of shale gas.

A New Discovery on the Deformation Behavior of Shale Gas Reservoirs Affecting Pore Morphology in the Juhugeng Coal Mining Area of Qinghai Province, Northwest China

Objective The Juhugeng mining area in Qinghai Province of northwest China has attracted wide attention among geologists for it hosts typical coal measure gases.The shale gas reservoirs were reformed by intensive structural movements during geological periods,

Graptolite-Derived Organic Matter and Pore Characteristics in the Wufeng-Longmaxi Black Shale of the Sichuan Basin and its Periphery

A key target of shale gas exploration and production in China is the organic-rich black shale of the Wufeng Formation-Longmaxi Formation in the Sichuan Basin and its periphery.The set of black shale contains abundant graptolites,which are mainly preserved as flattened rhabdosomes with carbonized periderms,is an important organic component of the shale.However,few previous studies had focused on the organic matter(OM)which is derived from graptolite and its pore structure.In particular,the contributions of graptolites to gas generation,storage,and flow have not yet been examined.In this study,focused ion beam-scanning electron microscope(FIB-SEM)was used to investigate the characteristics of the graptolite-derived OM and the micro-nanopores of graptolite periderms.The results suggested that the proportion of OM in the graptolite was between 19.7%and 30.2%,and between 8.9%and 14.4%in the surrounding rock.The total organic carbon(TOC)content of the graptolite was found to be higher than that of the surrounding rock,which indicated that the graptolite played a significant role in the dispersed organic matter.Four types of pores were developed in the graptolite periderm,including organic gas pores,pyrite moulage pores,authigenic quartz moldic pores,and microfractures.These well-developed micro-nano pores and fractures had formed an interconnected system within the graptolites which provided storage spaces for shale gas.The stacked layers and large accumulation of graptolites resulted in lamellation fractures openning easily,and provided effective pathways for the gas flow.A few nanoscale gas pores were observed in the graptolite-derived OM,with surface porosity lie in 1.5%–2.4%,and pore diameters of 5–20 nm.The sapropel detritus was determined to be rich in nanometer-sized pores with surface porosity of 3.1%–6.2%,and pore diameters of 20–80 nm.Due to the small amount of hydrocarbon generation of the graptolite,supporting the overlying pressure was difficult,which caused the pores to become compacted or collapsed.

Nanoscale pore morphology and distribution of lacustrine shale reservoirs:Examples from the Upper Triassic Yanchang Formation,Ordos Basin

Pore structure plays an important role in the gas storage and flow capacity of shale gas reservoirs. Fieldemission environmental scanning electron microscopy（FE-SEM） in combination with low-pressure carbon dioxide gas adsorption（CO2GA）,nitrogen gas adsorption（N2GA）,and high-pressure mercury intrusion（HPMI） were used to study the nanostructure pore morphology and pore-size distributions（PSDs） of lacustrine shale from the Upper Triassic Yanchang Formation,Ordos Basin. Results show that the pores in the shale reservoirs are generally nanoscale and can be classified into four types： organic,interparticle,intraparticle,and microfracture. The interparticle pores between clay particles and organic-matter pores develop most often,l with pore sizes that vary from several to more than 100 nm. Mercury porosimetry analysis shows total porosities ranging between 1.93 and 7.68%,with a mean value of 5.27%. The BET surface areas as determined by N2 adsorption in the nine samples range from 10 to 20 m2/g and the CO2 equivalent surface areas（2 nm）vary from 18 to 71 m2/g. Together,the HPMI,N2 GA,and CO2 GA curves indicate that the pore volumes are mainly due to pores 100 nm in size. In contrast,however,most of the specific surface areas are provided by the micropores. The total organic carbon（TOC） and clay minerals are the primary controls of the structures of nanoscale pores（especially micropores and mesopores）. Micropores are predominantly determined by the content of the TOC,and mesopores are possibly related to the content of clay minerals,particularly the illite-montmorillonite mixed-layer content.

Classification of microscopic pore-throats and the grading evaluation on shale oil reservoirs

On the basis of the characterization of microscopic pore-throats in shale oil reservoirs by high-pressure mercury intrusion technique, a grading evaluation standard of shale oil reservoirs and a lower limit for reservoir formation were established. Simultaneously, a new method for the classification of shale oil flow units based on logging data was established. A new classification scheme for shale oil reservoirs was proposed according to the inflection points and fractal features of mercury injection curves: microscopic pore-throats(less than 25 nm), small pore-throats(25-100 nm), medium pore-throats(100-1 000 nm) and big pore-throats(greater than 1 000 nm). Correspondingly, the shale reservoirs are divided into four classes, I, II, III and IV according to the number of microscopic pores they contain, and the average pore-throat radii corresponding to the dividing points are 150 nm, 70 nm and 10 nm respectively. By using the correlation between permeability and pore-throat radius, the permeability thresholds for the reservoir classification are determined at 1.00× 10^(-3) μm^2, 0.40×10^(-3) μm^2 and 0.05×10^(-3) μm^2 respectively. By using the exponential relationship between porosity and permeability of the same hydrodynamic flow unit, a new method was set up to evaluate the reservoir flow belt index and to identify shale oil flow units with logging data. The application in the Dongying sag shows that the standard proposed is suitable for grading evaluation of shale oil reservoirs.

Pore Structure Characteristics of Taiyuan Formation Shale in Qinshui Basin

Qinshui Basin is located in the southeast of Shanxi Province, China. Taking the shale of Taiyuan Formation in Qinshui Basin as the research object, the study analyzed the pore size of the shale of Taiyuan formation in detail from micropore to macropore by the methods of mercury injection, liquid nitrogen analysis and combination of liquid nitrogen and mercury injection. The results show that: 1) the visible pores and macropores are poorly developed and distributed unevenly in the shale of Taiyuan formation, and the micropores are well developed in the shale, and there are more open pores in the pore diameter range, and the pore connectivity is good;2) the liquid nitrogen experiment shows that the pores of Taiyuan Shale are relatively developed between 15 nm and 20 nm, and the formation of hysteresis loop may be caused by some narrow slit pores with similar layered structure;3) the comprehensive analysis of liquid nitrogen and mercury injection experiments shows that the shale of the Taiyuan formation mainly develops micropores, the Mesopores is not developed, the pore volume at 10 - 100 nm is more developed than other parts, and the specific surface is mainly contributed by micropores, which can improve the efficiency of shale gas resolution;at the same time, it provides a channel for Shale gas migration, which is beneficial to the development of shale gas.

Model construction of micro-pores in shale: A case study of Silurian Longmaxi Formation shale in Dianqianbei area, SW China

Based on scanning electron microscopy and nitrogen adsorption experiment at low temperature, the pore types and structures of the Longmaxi Formation shale in the Dianqianbei area, SW China were analyzed, and a molecular model was built. According to mathematical statistics, the validation of the model was solved by converting it into a mathematical formula. It is found by SEM that the pores in clay mineral layers and organic pores occupy most of the pores in shale; the nitrogen adsorption experiment at low temperature reveals that groove pores formed by flaky particles and micro-pores are the main types of pores, and the results of the two are in good agreement. A molecular model was established by illite and graphene molecular structures. Moreover, based on the fractal theory and the Frenkel-Halsey-Hill formula, a modified Frenkel-Halsey-Hill formula was proposed. The reliability of the molecular model was verified to some extent by obtaining parameters such as the fractal dimension, replacement rate and fractal coefficients of correction, and mathematical calculation. This study provides the theoretical basis for quantitative study of shale reservoirs.

Full-Sized Pore Structure and Fractal Characteristics of Marine-Continental Transitional Shale: A Case Study in Qinshui Basin, North China

Based on 10 shale samples collected from 4 wells in Qinshui Basin,we investigate the full-sized pore structure and fractal characteristics of Marine-Continental transitional shale by performing organic geochemistry,mineralogical composition,Nitrogen gas adsorption(N2 adsorption)and Nuclear Magnetic Resonance(NMR)measurements and fractal analysis.Results show that the TOC content of the shale samples is relatively high,with an average value of 2.44wt%,and the thermal evolution is during the mature-over mature stage.The NMR T2 spectrum can be used to characterize the fullsized pore structure characteristics of shale.By combining N2 adsorption pore structure parameters and NMR T2 spectrums,the surface relaxivity of samples are calculated to be between 1.7877 um/s and 5.2272 um/s.On this basis,the T2 spectrums are converted to full-sized pore volume and surface area distribution curves.The statistics show that the pore volume is mainly provided by mesopore,followed by micropore,and the average percentages are 65.04%and 30.83%respectively;the surface area is mainly provided by micropore,followed by mesopore,and the average percentages are 60.8004%and 39.137%respectively;macropore contributes little to pore volume and surface area.The pore structure characteristics of shale have no relationship with TOC,but strong relationships with clay minerals content.NMR fractal dimensions Dmicro and Dmeso have strong positive relationships with the N2 adsorption fractal dimensions D1 and D2 respectively,indicating that Dmicro can be used to characterize the fractal characteristics of pore surface,and Dmeso can be used to characterize the fractal characteristics of pore structure.The shale surface relaxivity is controlled by multiple factors.The increasing of clay mineral content,pore surface area,pore surface fractal dimension and the decreasing of average pore size,will all lead to the decreasing of shale surface relaxivity.

Mineralogy and Thermal Analysis of Natural Pozzolana Opal Shale with Nano-pores

Thermodynamic stability, microvoid distribution and phases transformation of natural pozzolana opal shale（POS） were studied systematically in this work. XRD analysis showed that opal-CT, including microcrystal cristobalite and tridymite, is a major component of POS. DTA and FT-IR indicated that there were many hydroxyl groups and acid sites on the surface of amorphous SiO2 materials. FE-SEM analysis exhibited amorphous SiO2 particles（opal-A） covering over stacking sequences microcrystal cristobalite and tridymite. Meanwhile, MIP analysis demonstrated that porosity and pore size distribution of POS remained uniform below 600 ℃. Because stable porous microstructure is a key factor in improving photocatalyst activity, POS is suited to preparing highly active supported.

川东地区侏罗系大安寨段页岩储层特征及发育控制因素

为探究陆相页岩储层特征及页岩储集空间发育的控制因素,文中以四川盆地东部大安寨段页岩为例,基于页岩岩心的分析化验资料,对页岩储层孔隙发育控制因素进行了研究,明确了优势岩相及甜点储层特征。研究结果表明:1)川东地区大安寨段页岩岩相类型包括硅质页岩、混合质页岩以及黏土质页岩,其中黏土质页岩总有机碳质量分数最高,其次为混合质页岩。2)页岩孔隙类型以片状黏土矿物晶间孔与有机质孔为主,裂缝以页理缝为主。3)页岩储集空间的发育主要受矿物组分、成岩作用以及构造因素的共同控制。4)基于页岩生烃潜力与储集能力,认为混合质页岩为大安寨段的优势页岩岩相。大安寨段页岩甜点储层段主要分布于大二亚段a小层,主要为混合质页岩与介壳灰岩的薄夹层。

注热化学流体吞吐解除岩石储层反凝析伤害评价

为长期有效解除凝析气藏反凝析带来的储层伤害,提出了一种注热化学流体吞吐解除凝析油堵塞孔喉的新方法。针对致密砂岩、碳酸盐岩和页岩3类岩石,开展了注热化学流体吞吐岩心驱油实验,评价了热化学流体解除凝析油堵塞的可行性,并基于核磁共振技术分析了吞吐前后3类岩石微观孔隙结构的变化特征,明确了热化学流体解除反凝析伤害机理。实验结果表明,热化学流体(NH_(4)Cl和NaNO_(2))在乙酸溶液催化下能够迅速释放大量气体和蒸汽,提高岩心压力和温度,降低原油黏度,使凝析油由液态转变为气态,减小渗流阻力。致密砂岩、碳酸盐岩和页岩岩心注热化学流体吞吐累积凝析油采出程度分别为65.7%,73.9%和46.3%。其中,致密砂岩和碳酸盐岩岩心仅需2轮吞吐即可有效清除55.5%和67.6%的凝析油堵塞。而页岩岩心需要延长焖井时间及增加吞吐次数方能提高凝析油的采出程度。热化学流体吞吐后,致密砂岩、碳酸盐岩和页岩岩心平均孔径分别由0.37,1.04和0.0021μm增大至0.84,2.04和0.0058μm。热化学流体吞吐效果是注CH_(4)吞吐和注甲醇吞吐效果的1.85和1.32倍。

页岩基质孔隙油微观赋存及可动性定量表征——以东营凹陷沙河街组为例

页岩基质孔隙油微观赋存特征及可动性是制约陆相页岩油高效开采的关键要素。本文针对页岩基质孔隙内不同相态油的含量、比例、分布及可动性开展定量化表征研究,从理论上提出了页岩油吸附量、游离量、可动量评价模型以及吸附油占比评价模型(即吸附比例方程),建立了基于饱和—离心—核磁共振联合实验的孔隙油微观赋存及可动性评价方法。上述模型与方法在渤海湾盆地济阳坳陷东营凹陷沙河街组页岩油储层中进行了应用,揭示了实验条件(20℃、常压)下页岩基质孔隙中轻质油(正十二烷)微观赋存与可动性特征。结果显示:(1)富有机质页岩吸附油、游离油含量普遍大于含有机质页岩,吸/游比主体介于1~2,不同类型页岩中吸附油、游离油赋存空间具有差异性。(2)富有机质页岩吸附油平均密度(0.8331 g/cm^(3))略大于含有机质页岩(0.8067 g/cm^(3)),富有机质页岩吸附油平均厚度(1.7475 nm)约为含有机质页岩(0.5734 nm)的3倍,富有机质页岩具有更强的油—岩相互作用。(3)游离油赋存孔隙直径下限(d_(min))数值上等于吸附油平均厚度与孔隙形状因子的乘积,富有机质页岩d_(min)介于3.5~10.5 nm,开始主要富集游离油的孔隙直径约为100 nm;含有机质页岩d_(min)介于1.1~3.4 nm,开始主要富集游离油的孔隙直径约为30 nm。(4)富有机质页岩孔隙油可动性相对更好,其可动性指数(平均6.24 mg·g^(-1)·MPa^(-1))高于含有机质页岩(平均5.20 mg·g^(-1)·MPa^(-1)),孔隙油吸/游比约为1.5时具有较好可动性。(5)以油—岩相互作用为纽带,构建了页岩含油性、储集性及页岩油可动性之间的耦合关系,并数学描述了它们之间的内在联系,为寻找优质页岩油储层奠定了理论基础。

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。

元坝地区千佛崖组二段页岩层序与储层特征分析

川东北元坝地区千佛崖组二段半深湖相页岩具有良好的页岩油气勘探前景。通过层序划分,对页岩岩相发育特征进行研究,对不同页岩岩相控制下的储层特征进行分析,明确准层序格架下不同页岩岩相的成因及对储层发育的影响。研究结果表明:千佛崖组二段可划分为7个准层序,根据准层序内的沉积特征,可将准层序划分为湖侵旋回为主型、湖退旋回为主型和均衡型3种不同的沉积模式。千佛崖组二段页岩发育有纹层状页岩相、层状页岩相和块状页岩相三种主要岩相类型,纹层状页岩相整体孔隙更发育,连通性更好,储集物性更好;层状页岩相整体孔隙发育程度和储集物性较纹层状页岩相次之;块状页岩相孔隙发育情况不佳,连通性一般,物性较差。页岩储层受岩相影响呈现出不同的特征,页岩岩相的纵向演化明显受准层序的控制,不同准层序类型的页岩岩相发育特征存在明显差异。整体来看,优质储层在最大洪泛面附近更为发育,优质页岩储层主要发育在湖侵旋回为主型准层序的中上部,有机质富集、孔隙发育且连通性好,是下一步勘探的有利目标;湖退旋回为主型准层序的中下部发育次优储层。

陆相页岩岩相非均质性及储层孔隙发育特征:以四川盆地自流井组东岳庙段页岩为例

继四川盆地复兴地区涪页10井取得勘探突破后,侏罗系自流井组东岳庙段页岩油气表现出良好的勘探潜力。东岳庙段页岩发育独特的介壳灰岩夹层、黏土矿物含量高(质量分数最高可达60%),储层孔隙类型多样,纵向上具有很强的非均质性。以兴页X井为例,结合测录井资料、岩心观察、氩离子抛光扫描电镜等技术手段,重点剖析了东岳庙段陆相页岩岩相特征及其孔隙发育特征。建立了“夹层+矿物三端元”的陆相页岩岩相划分原则,将东岳庙段陆相页岩纵向上划分为6种岩相,即:介屑纹夹层型黏土页岩相;介屑纹夹层型混合页岩相;介屑灰岩相;粉砂介屑互层型混合页岩相;粉砂介屑互层型黏土页岩相;介壳韵律型混合页岩相。通过氩离子抛光扫描电镜观察发现,该套陆相页岩具有特殊的有机黏土复合体孔,其中介屑纹夹层型黏土页岩相有机孔类型最为发育,而介屑灰岩相有机孔不发育,主要发育粒内溶孔。压汞-氮气吸附联测结果显示6种岩相页岩的孔径分布无明显差异性。综合分析认为,有机质和黏土矿物在成岩演化过程中的相互作用是东岳庙段陆相页岩孔隙发育的主要因素。