Genesis of Fibrous Calcite in the Chang 7 Member of the Yanchang Formation, Ordos Basin, China

To explore the genesis of the laminated calcite veins developed in the black shale of Chang 73 submember of the Ordos Basin, the petrology, microstructure and geochemistry of calcite veins are studied using thin sections, fluid inclusions, trace elements and isotopic geochemistry. The source, the time of formation, the mechanism of formation, and the dynamic background of the veins are discussed. The veins are mostly made up of calcite, mixed with lenticular or spindle-shape solid wall rock inclusions. Three structures are identified in the calcite minerals: fibrous, rhombic cleavage, and wedge-like structure. Trace elements and isotopes of carbon and oxygen confirm that the calcite veins were formed from a high density hydrothermal fluid. It is assumed that calcite veins formed prior to wall rock consolidation during the formation of the Qinling Orogenic Belt in the Middle and Late Triassic. The results show that the sedimentary sources of Chang 73 submember were influenced by hydrothermal materials besides terrigenous detritus. The fibrous calcite is different from the fibrous calcite reported in the morphology and mechanism of formation. In this way, the research complements and improves the morphology and the mechanism of formation of fibrous calcite.     

鄂尔多斯高原地区明清时期气象灾害特征研究

气象灾害的发生往往具有一定的气候变化背景,对历史时期的气象灾害的研究是研究当时气候变化的一种途径。通过对鄂尔多斯高原地区文献资料的搜集整理,运用统计分析和小波变换,分析了该地区明清时期干旱、风沙、霜雪、冰雹、洪水等气象灾害的频次和周期特征,探讨了当时的气候特征。结果表明,鄂尔多斯高原地区明清时期旱灾发生频次最高;各类气象灾害都有随时间而增多的趋向。15世纪后期至16世纪初期、17世纪中期至18世纪中期、20世纪初期是各种气象灾害的多发阶段。各类灾害短周期一般为3～9年,中周期一般为17～21年,长周期一般为28～42年。鄂尔多斯高原地区明清时期的气候分为两个阶段:1368—1659年为暖湿期,1660—1911年为冷干期,以冷干为主,并经历了以下次一级的气候波动:暖湿→暖干→暖湿→冷干→冷湿→冷干。在气象灾害群发期,伴随着环境的恶化。     

鄂尔多斯盆地樊学油区长8砂岩裂缝平面展布及控制因素

裂缝发育程度及其平面展布是影响低孔特低渗储层有效、高效注水开发的关键。鄂尔多斯盆地樊学油区长8油藏及周边油藏投产油井存在砂岩裂缝发育区含水上升快、裂缝侧向油井水驱开发效率低等问题。本文基于岩心、声电成像测井资料标定常规测井资料,选取特征参数构建裂缝识别综合指数,实现樊学油区长8储层中砂岩裂缝的识别。依据识别结果绘制砂岩裂缝平面展布图,进而结合区域构造应力场及沉积特征分析裂缝发育的控制因素及其对生产开发的影响。研究表明,基底断裂中生代以来的重新活动控制了樊学油区裂缝的形成与展布,裂缝优势展布方位为北北西向和北东东向,砂岩裂缝的发育程度受区域构造应力场、砂体厚度以及岩层组合等因素影响。裂缝发育区油井具有初产高、产量递减快的特点,因此,在实际生产开发中,需要选择合适的注采井网,尽量采用大井距、小排距的方式提高驱油效率。上述认识为油藏开发部署提供一定的参考。     

鄂尔多斯盆地北部砂岩铀矿床粘土矿物与氧化带成因关系研究

对鄂尔多斯盆地北部铀成矿带产铀层位中侏罗统直罗组砂岩进行系统采样和分析,以探讨砂岩中粘土矿物特征与氧化带成因之间的关系。采用X?射线粉晶衍射、电子探针分析等现代分析手段,测定粘土矿物相对含量、微观形貌特征。结果表明:研究区古层间氧化的演变序列为砂体原始灰色→古氧化作用(红色或黄色)→碳酸盐化(残留了部分红色)→后期还原作用(绿色),对应的岩石蚀变期次为早期氧化酸性蚀变→氧化期后弱碱性蚀变→晚期还原弱碱性蚀变;早期氧化砂岩在还原性气体作用下,Fe³⁺还原转化为Fe²⁺,高岭石在有Fe2+存在的条件下会向绿泥石转化,这一反应在碎屑颗粒表面,形成许多极细小的针叶状绿泥石,从而使古层间氧化亚带呈现特征的绿色。     

Experimental investigation of thermal maturation on shale reservoir properties from hydrous pyrolysis of Chang 7 shale,Ordos Basin

Thermal maturity has a significant impact on hydrocarbon generation and the storage capacity within shales, but explicit and quantitative characterization of that impact on continental shales is scarce. To better understand how thermal maturation affects the organic and inorganic changes of the continental shale reservoirs, hydrous pyrolysis was performed to simulate the maturation process. TOC, Rock-Eval and adsorption isotherms tests were used to obtain various geochemical parameters of the shale solid residues. The results indicate that with pyrolysis temperature increasing from ambient temperature to 550 °C, the vitrinite reflectance increases from 0.5% to 2.5% Ro and the TOC (total organic carbon) loss weight reaches 25%. Regarding porosity, the fraction of micro-to meso-pores in the shale increases with an increase in the pyrolysis temperature, whereas the macro-pores do not change significantly. The total amount of gas adsorption does not necessarily increase as the TOC is consumed, but the gas adsorption capacity per unit of TOC increases with increasing thermal maturity. Our finding provides theoretical modelling for identifying shale gas development prospective zones according to thermal maturity mapping and for predicting quantitatively the geochemical and inorganic changes that occur with thermal evolution.     

柴达木地块北缘南北沟岩体地球化学特征及成矿前景

南北沟岩体位于柴达木地块北缘,出露面积4.5km2。岩石主要类型有淡色辉长岩、辉长岩、暗色辉长岩,各岩石类型之间多为过渡关系,局部呈侵入接触。主量元素化学组成属拉斑玄武岩系列。岩石相对富集大离子亲石元素,亏损高场强元素,明显亏损Nb、Ta。岩体原生岩浆属于高镁拉斑玄武岩(MgO质量分数为11.1%),在岩浆演化过程中遭受了一定程度中—上地壳物质的同化混染作用。岩体形成于古岛弧环境,是早古生代柴达木地块向祁连地块俯冲过程的产物。从岩浆分异程度、原生岩浆性质、同化混染等方面综合评价认为,南北沟岩体具有较好的铜镍硫化物矿床成矿潜力。     

Paleomagnetism of the middle Cretaceous Iritono granite in the Abukuma region, northeast Japan

We have studied the paleomagnetism of the middle Cretaceous Iritono granite of the Abukuma massif in northeast Japan together with ⁴⁰Ar–³⁹Ar dating. Paleomagnetic samples were collected from ten sites of the Iritono granite (102 Ma ⁴⁰Ar–³⁹Ar age) and two sites of its associated gabbroic dikes. The samples were carefully subjected to alternating field and thermal demagnetizations and to rock magnetic analyses. Most of natural remanent magnetizations show mixtures of two components: (1) H component, high coercivity (B_c > 50–90 mT) or high blocking temperature (T_b > 350–560 °C) component and (2) L component, relatively low B_c or low T_b component. H component was obtained from all the 12 sites to give a mean direction of shallow inclination and northwesterly declination (I = 29.9°, D = 311.0°, α₉₅ = 2.7°, N = 12). This direction is different from the geocentric axial dipole field at the present latitude (I = 56.5°) and the typical direction of the Cenozoic remagnetization in northeast Japan. Since rock magnetic properties indicate that the H component of the Iritono granite is carried mainly by magnetite inclusions in plagioclase, this component probably retains a primary one. Thus the shallow inclination indicates that the Abukuma massif was located at a low latitude (16.1 ± 1.6°N) about 100 Ma and then drifted northward by about 20° in latitude. The northwesterly deflection is attributed mostly to the counterclockwise rotation of northeast Japan due to Miocene opening of the Japan Sea. According to this model, the low-pressure and high-temperature (low-P/high-T) metamorphism of the Abukuma massif, which has been well known as a typical location, would have not occurred in the present location. On the other hand, the L component is carried mainly by pyrrhotite and its mean direction shows a moderate inclination and a northwesterly declination (I = 42.8°, D = 311.5°, α₉₅ = 3.3°, N = 9). Since this direction is intermediate between the H component and early Cenozoic remagnetization in northeast Japan, some thermal event would have occurred at lower temperature than pyrrhotite Curie point ( 320 °C) during the middle Cretaceous to early Cenozoic time to have resulted in partial remagnetization.     

特低渗透砂岩储层可动流体变化特征与差异性成因——以鄂尔多斯盆地延长组为例

特低渗透砂岩储层微观孔隙结构复杂,流体赋存状态不同于常规储层,利用核磁共振技术对鄂尔多斯盆地延长组3个层位样品的可动流体变化特征与差异性成因进行了分析。结果表明,样品T2谱分布主要表现出4种形态、T2截止值中等—偏高、可动流体参数变化幅度较大;沉积和成岩作用差异导致微观特征参数不同,造成各层位可动流体参数复杂变化;渗透率较小时,可动流体参数变化幅度大,当渗透率增大到一定程度后,可动流体参数数据点收敛,变化幅度减小;储层物性、孔隙(尤其是次生孔隙)发育连通程度、微裂缝的发育程度、粘土矿物的存在形式及其对孔隙的充填程度等微观孔隙结构特征变化是可动流体参数差异性产生的主要原因。可动流体参数本身就是储层诸多微观特征参数的综合反映,应在储层评价中予以考虑。     

重新认识鄂尔多斯南部早奥陶世马家沟期碳酸盐台地沉积模式

地层、沉积岩组合及古地貌特征显示,鄂尔多斯盆地南部地区早奥陶世马家沟期为3个沉积单元区,即:北东部区为白云岩-蒸发盐组合;南部区为白云岩-少量蒸发盐组合;西部区以石灰岩为主。相应地北东部区以发育台内盆地-盆缘坪为主;南部区发育洼地-台坪-台地边缘-海槽;西部区则发育台地边缘-海槽。野外剖面与钻井岩心观测以及区域资料研究表明,鄂尔多斯盆地南部边缘大致在洛南瓦窑沟—西安—宝鸡一带。马家沟期研究区沉积模式总体上为:横向上"西槽、南洼、东坪、北盆",纵向上"咸-淡交替";灰岩-白云岩-蒸发岩横向上呈带状展布,纵向上则为不等厚交替沉积。     

鄂尔多斯盆地延长组湖盆中部长6厚层砂体成因分析

笔者对鄂尔多斯盆地湖盆中部地区延长组长6物源分析、沉积相类型、坡折带控砂、砂体分布规律等进行了研究。东北、西南两大物源提供了充足的物质基础,发育三角洲牵引流作用的沉积砂岩和重力搬运的浊积砂岩,主要为叠置水下分流河道、河口砂坝-水下分流河道和滑塌浊积岩等不同类型的砂体组合,形成了垂直湖岸线和平行湖岸线展布的巨型厚砂岩分布带。