辽宁省中晚元古代—中生代页岩的化学元素丰度及其演化特征

作者利用全省不同地质时代和不同地质构造单元内的页岩41种元素的分析数据,计算出辽宁省全域内的页岩元素丰度休系。同时探讨了元素从中、晚元古代至中生代的演化规律,指出Ca、Cd、Sb、As、Na、Mn、P、Sr的元素丰度随时间序列的演化不断增长,B、F、K、Rb、W、Mg则显示出降低的趋势。某些元素比值从老至新表现出明显的规律性变化,如Sr/Ba、Ca/Mg值的演化具有阶段性,K/Na、Th/U值的演化具有方向性,Al/Ti值的演化则具有周期性。     

鄂尔多斯盆地南部延长组长7油组页岩层系天然裂缝发育特征及主控因素

利用地表露头、岩心、薄片和测井资料,对鄂尔多斯盆地南部长7油层组陆相页岩层系天然裂缝的成因类型、发育特征和主控因素进行研究。按地质成因,鄂尔多斯盆地南部长7油层组页岩层系的天然裂缝可以分为构造裂缝和成岩裂缝两大类,其中构造裂缝主要包括剪切裂缝和张性裂缝;成岩裂缝主要包括层理缝、页理缝和收缩裂缝。不同岩性中的天然裂缝发育情况明显不同,致密砂岩中以构造裂缝为主,层理缝仅在粉砂岩和局部细砂岩中发育;页岩和凝灰岩中页理缝、层理缝和构造裂缝均比较发育。不同类型的天然裂缝主控因素明显不同,构造裂缝的发育主要受岩性和岩石力学层层厚控制;砂岩中层理缝的发育主要受碳质纹层、粘土矿物转化程度等因素控制;凝灰岩中层理缝的发育主要受刚性玻屑脱玻化作用的控制;页岩中页理缝的发育主要受纹层、TOC含量和黄铁矿含量的控制。     

Taphonomy of large marine vertebrates in the Upper Cretaceous (Cenomanian-Turonian) Tropic Shale of southern Utah

Sediments from the Upper Cretaceous (Cenomanian-Turonian) Tropic Shale were deposited along the western margin of the Western Interior Seaway, in present-day southern Utah. Marine vertebrates from this formation include plesiosaurs, mosasaurs, bony fish, sharks, and turtles. They are concentrated in the lower portion of the Tropic Shale, mostly between Bentonites B and D. Study of the taphonomic condition of these vertebrates has contributed to an understanding of how they were preserved as well as a detailed paleoenvironment for the Tropic Shale. Physical factors played the dominant role in their preservation, with robust and durable skeletal elements, such as teeth and vertebrae, being most common within the shale. Isolated bones and teeth are also relatively common within the formation, while complete and nearly complete skeletons are more rare. Biological factors played a less dominant role, with no evidence of epifaunal or infaunal activity preserved with any of the skeletal remains. In addition, scavenging marks (both bite and gnaw marks) are relatively uncommon, typically only being found on more complete specimens. A signature of post-burial alteration can be recognized as low levels of abrasion, weathering, and compression and high levels of fracturing of vertebrate skeletal material. Slightly higher levels of abrasion and weathering occur to the west, closer to the ancient shoreline, suggesting some pre-burial alteration. The preservation of marine vertebrates in the Tropic Shale suggests a low energy marine environment with some weak bottom currents and low levels of benthic oxygen. The substrate ranged from soft and soupy to firm, with moderate sedimentation rates resulting in relatively rapid burial.     

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.     

特殊测井在准南地区乌鲁木齐一带芦草沟组页岩油气层评价中运用

以地表地质调查成果为基础,以钻探、地质综合录井、核磁共振测井、电成像测井、正交多极子阵列声波等测井方法为手段,以岩石学特征、储层物性、储集空间类型和储集性能研究为重点,开展准南冲段带东段乌鲁木齐一带二叠系芦草沟组页岩油气评价。研究结果表明:该区带芦草沟组页岩含油气7层,其中优质含油层2层(64和66层);页岩储层矿物成分以高脆性矿物为主,物性特征表现为天然高导裂缝发育和低孔特低渗;油气藏表现为具中等含油饱和度的典型裂缝型油气藏特征。页岩储层各向异性较强,总体最大水平主应力为NWW向。     

基于逾渗模型的泥页岩导电机理模拟

泥页岩储层储集空间以纳米/微米级的微孔隙和微裂缝为主,结构复杂,加之干酪根和黏土矿物含量较高,并含有一定量的黄铁矿等导电矿物,造成储层导电机理异于常规储层,岩电实验I-S_w曲线呈现非线性特征,阿尔奇公式等传统评价模型适用性较差.针对上述问题,根据实际岩心实验资料,结合随机算法建立三维逾渗模型并通过数值模拟和超松弛迭代法进行求解,分析泥页岩储层非阿尔奇性产生原因以及泥页岩储层电性的影响因素及规律.模拟结果显示,岩石孔隙拓扑结构和形状尺寸、矿物组成以及地层水电阻率等因素均对泥页岩储层电阻率产生不同程度的影响,通过改变上述因素的设定值,可以建立储层电阻率与各因素的单相关关系,并据此建立修正模型,实现储层含水饱和度的计算.该模型在四川某页岩气产区取得了较好的效果,具有良好的应用前景,为利用逾渗模型模拟方法解决油田勘探开发中的复杂问题提供了新思路.     

相邻两井对大地震的不同水力响应模型研究——页岩影响分析

大地震引起了左家庄和宝坻(相距～50km)两井中截然不同的同震水位响应.我们用水位的气压和潮汐响应来分析解释此现象.结果表明,宝坻井的观测含水层中存在页岩,且此井受裂隙影响很大,储水效应较差.页岩的复杂裂隙或者各向异性可能会导致此井观测含水层处于半封闭状态,从而导致垂直向排水的发生.通过多方计算分析后,我们将这两口井划分为两种模型—1.水平流动模型;2.水平流动+垂直流动的混合流动模型.由于裂隙影响,宝坻井的观测含水层介质与外界的水力沟通性在震前就较强(震前渗透率就比较大),所以宝坻井观测含水层与外界的孔隙压差异较小,导致同震渗透率上升较小甚至没有变化,这些因素是导致该井同震水位变化幅度总是非常微小的原因.     

Mesozoic–Cenozoic stress field magnitude in Sichuan Basin,China and its adjacent areas and the implication on shale gas reservoir: Determination by acoustic emission in rocks

The Sichuan Basin is one of the vital basins in China, boasting abundant hydrocarbon reservoirs. To clarify the intensity of the tectonic stress field of different tectonic episodes since the Mesozoic and to identify the regional dynamic background of different tectonic movements in the Sichuan Basin and its adjacent areas, the characteristics of the acoustic emission in rocks in different strata of these areas were researched in this paper. Meanwhile, the tectonic stress magnitude in these areas since the Mesozoic was restored. The laws state that the tectonic stress varied with depth was revealed, followed by the discussion of the influence of structural stress intensity on structural patterns in different tectonic episodes. These were conducted based on the paleostress measurement by acoustic emission method and the inversion principle of the stress fields in ancient periods and the present, as well as previous research achievements. The results of this paper demonstrate that the third episode of Yanshanian Movement (Yanshanian III) had the maximum activity intensity and tremendously influenced the structural pattern in the study area. The maximum horizontal principal stress of Yanshanian III varied with depth as follows: 0.0168 x + 37.001 (MPa), R² = 0.8891. The regional structural fractures were mainly formed in Yanshanian III in Xujiahe Formation, west Sichuan Basin, of which the maximum paleoprincipal stress ranging from 85.1 MPa to 120.1 MPa. In addition, the law stating the present maximum horizontal principal stress varies with depth was determined to be 0.0159 x+10.221 (MPa), R²=0.7868 in Wuling Mountain area. Meanwhile, it was determined to be 0.0221 x+9.4733 (MPa), R²=0.9121 in the western part of Xuefeng Mountain area and 0.0174 x+10.247 (MPa), R²=0.8064 in the whole study area. These research results will not only provide data for the simulation of stress field, the evaluation of deformation degree, and the prediction of structural fractures, but also offer absolute geological scientific bases for the elevation of favorable shale gas preservation.     

Jurassic source rocks in the Vienna Basin (Austria): Assessment of conventional and unconventional petroleum potential

The Upper Jurassic marlstones (Mikulov Fm.) and marly limestones (Falkenstein Fm.) are the main source rocks for conventional hydrocarbons in the Vienna Basin in Austria. In addition, the Mikulov Formation has been considered a potential shale gas play. In this paper, organic geochemical, petrographical and mineralogical data from both formations in borehole Staatz 1 are used to determine the source potential and its vertical variability. Additional samples from other boreholes are used to evaluate lateral trends. Deltaic sediments (Lower Quarzarenite Member) and prodelta shales (Lower Shale Member) of the Middle Jurassic Gresten Formation have been discussed as secondary sources for hydrocarbons in the Vienna Basin area and are therefore included in the present study.The Falkenstein and Mikulov formations in Staatz 1 contain up to 2.5 wt%TOC. The organic matter is dominated by algal material. Nevertheless, HI values are relative low (<400 mgHC/gTOC), a result of organic matter degradation in a dysoxic environment. Both formations hold a fair to good petroleum potential. Because of its great thickness (∼1500 m), the source potential index of the Upper Jurrasic interval is high (7.5 tHC/m²). Within the oil window, the Falkenstein and Mikulov formations will produce paraffinic-naphtenic-aromatic low wax oil with low sulfur content. Whereas vertical variations are minor, limited data from the deep overmature samples suggest that original TOC contents may have increased basinwards. Based on TOC contents (typically <2.0 wt%) and the very deep position of the maturity cut-off values for shale oil/gas production (∼4000 and 5000 m, respectively), the potential for economic recovery of unconventional petroleum is limited. The Lower Quarzarenite Member of the Middle Jurassic Gresten Formation hosts a moderate oil potential, while the Lower Shale Member is are poor source rock.     

Controls of hydrocarbon generation on the development of expulsion fractures in organic-rich shale: Based on the Paleogene Shahejie Formation in the Jiyang Depression,Bohai Bay Basin,East China

The development of expulsion fractures in organic-rich shale is closely related to hydrocarbon generation and expulsion from kerogen. Organic-rich shales from the upper part of the fourth member and the lower part of the third member of the Paleogene Shahejie Formation in the Jiyang Depression, Bohai Bay Basin, East China, are used as an example. Based on thin sections, SEM and thermal simulation experiments, the characteristics of hydrocarbon generation and the conditions supporting the development of expulsion fractures were explored. The key factors influencing these fractures include the presence of kerogens, their distribution along laminae and around particle boundaries, their exposure to heat and the build-up in pressure due to confinement by low permeability. The development of excess pore fluid pressures and intrinsic low rock fracture strength are the main influencing factors. Pressurization by rapid generation of hydrocarbon provides impetus for fracture initiation and cause bitumen to migrate quickly. The shale laminae results in distinctly lower fracture strength laminae-parallel than laminae-normal and this directs the formation of new fractures in the direction of weakness. When pore fluid pressure increases, maximum and minimum principal effective stresses decrease by different proportions with a larger reduction in the maximum principal effective stress. This increases the deviatoric stress and reduces the mean stress, thus driving the rock towards failure. Moreover, the tabular shape of the kerogen aids the generation of hydrocarbon and the initiation of expulsion fractures from the tip and edge. The resulting fractures extend along the laminae when the tensile strength is lower in the vertical direction than in the horizontal direction. Particle contact boundaries are weak and allow fractures to expand around particles and to curve as the stress/strength regime changes. When pore fluid pressure fields at different fracture tips overlap, fractures will propagate and interconnect, forming a network. This paper could provide us more detailed understanding of the forming processes of expulsion fractures and better comprehension about hydrocarbon expulsion (primary migration) in source rocks.