Shale Gas Formation and Occurrence in China: An Overview of the Current Status and Future Potential

Shale gas is one of the most promising unconventional resources both in China and abroad. It is known as a form of self-contained source-reservoir system with large and continuous dimensions. Through years of considerable exploration efforts, China has identified three large shale gas fields in the Fuling, Changning and Weiyuan areas of the Sichuan Basin, and has announced more than 540 billion m~3 of proven shale gas reserves in marine shale systems. The geological theories for shale gas development have progressed rapidly in China as well. For example, the new depositional patterns have been introduced for deciphering the paleogeography and sedimentary systems of the Wufeng shale and Longmaxi shale in the Sichuan Basin. The shale gas storage mechanism has been widely accepted as differing from conventional natural gas in that it is adsorbed on organic matter or a mineral surface or occurs as free gas trapped in pores and fractures of the shale. Significant advances in the techniques of microstructural characterization have provided new insights on how gas molecules are stored in micro- and nano-scale porous shales. Furthermore, newly-developed concepts and practices in the petroleum industry, such as hydraulic fracturing, microseismic monitoring and multiwell horizontal drilling, have made the production of this unevenly distributed but promising unconventional natural gas a reality. China has 10–36 trillion m~3 of promising shale gas among the world's whole predicted technically recoverable reserves of 206.6 trillion m~3. China is on the way to achieving its goal of an annual yield of 30–50 billion m~3 by launching more trials within shale gas projects.     

河元背地区绳索取心钻进泵压计算模型的建立与应用

泵压是反映金刚石绳索取心钻进时井内作业是否正常的重要参数。为了进一步研究泵压波动变化与实际钻进作业之间的关系,指导钻进工作的快速、安全开展,结合江西相山河元背地区CUSD2井实际泵压波动数据及相关钻进资料,建立了适用于本井的循环系统压力损失计算模型。对比分析模型计算的理论泵压与实际泵压的波动变化趋势,将模型应用于实际钻进,在此基础上预测后续地层的泵压波动区域范围,发现7 MPa的泵压安全值不再适用于后续地层钻进,调整设置泵压安全值为10 MPa,并利用邻井泵压波动数据进一步验证其可靠性。适当调整修正理论模型,使其可应用于河元背以及相山地区绳索取心钻进中,指导该地区钻探工作。     

“松科二井”用硬岩长寿命钻头的设计与应用

为提高“松科二井”在深井硬岩钻进中的寿命与效率,选用了高性能胎体材料、高强度焊接材料,并采用了合理的钻头结构与水路结构设计,研制的φ216/124 mm金刚石取心钻头在“松科二井”取得了良好的效果,本文介绍了适用于深井硬岩的金刚石钻头的设计及应用效果。     

3500m岩心钻探装备在油气井勘查中的示范应用

3500 m岩心钻探装备（YDX—6型钻机）是我国自主研发的深部矿产资源勘查技术装备,采用N级口径钻深可达3500 m,其最大特点是采用长油缸钻进和起下钻。本文主要介绍了该钻机在油气井勘查中生产试验情况,同时对矿区地层、钻孔结构、钻进过程、钻进效果、遇到的主要问题及解决办法等进行了介绍。     

桂北地区罗地1井钻探施工实践

页岩具有较强的水敏性,在页岩气勘查钻进施工中,井内易发生坍塌、剥落造成超径或缩径等井壁失稳现象。罗地1井采用金刚石绳索取心工艺进行钻进,完井井深1501.06 m,岩心采取率、井斜等各项指标均符合地质设计要求。本文主要从罗地1井的钻井设备、井身结构、施工难点等方面进行总结,可为今后页岩气调查井的施工提供参考。     

Main technical innovations of Songke Well No.2 Drilling Project

Songke Well No.2, one of the main part of the scientific drilling project in Songliao Basin, which was drilled 7018 m and acquired the part of cores continuously from the Low Cretaceous to the Carboniferous and the Permian from the 2843 m deep, can be considered as the deepest continental drilling project in Asia. Aiming at the features of longer well sections, larger diameters and multiple spud-ins for coring of Songke Well No.2, this project broke through the “coring in small diameter and reaming in large diameter” spud-in drilling-completion procedures which are always used in large-diameter-well coring for continental scientific drilling projects in domestic and overseas and the drilling method of short-single-cylinder roundtrip footage. At the same time, “coring in the same diameter and completing drilling at one single diameter” was achieved at all φ311 mm and φ216 mm coring sections of more than one thousand meters long, high-efficient operation with “drilling long footage with drill tools combined in multi-cylinders” was achieved at deep coring section. Four world drilling records were created which include more than a thousand meters continuous coring at φ311 mm, and the footage per roundtrip footage at φ311 mm, φ216 mm and φ152 mm is all more than 30 m, all of these breakthroughs reduced at least 300 days for this project; moreover, considering the characteristics of formations that the geothermal gradient is high in the drilled sections and the inside-well temperature is over 240°C after drilling completion, a formate-polymer water-based mud system was developed by compounding attapulgite and sodium bentonite and by adding independently developed high-temperature stabilizer, which can provide critical technical support for successful well completion at 7018 m in the super-high-temperature environment It is the first time that the water-based mud is operated at the working temperature higher than 240°C in China; Besides, considering the high-quality requirement on cores imposed by the project, the method “mechanical cored is charge” to discharge core nondestructively on the ground was worked out, and more than 4000 m scatheless cores were discharged out of the drill pipes while maintaining original stratum structures.     

熔融制样-X射线荧光光谱法测定电气石中12种主次量元素

电气石是一类含硼的铝硅酸盐矿物,化学成分复杂、化学稳定性强,不易湿法分解,B_2O_3含量较高,导致其主次量元素的同时测定存在一定困难。本文采用熔融法制样,建立了X射线荧光光谱法测定电气石Na_2O、MgO、Al_2O_3、SiO_2、P_2O_5、K_2O、CaO、TiO_2、V_2O_5、Cr_2O_3、MnO、TFe_2O_3等主次量元素的分析方法。样品与四硼酸锂-偏硼酸锂-氟化锂(质量比为4.5∶1∶0.4)混合熔剂的稀释比例为1∶10,消除了粒度效应和矿物效应;在缺少电气石标准物质的情况下,选择土壤、水系沉积物及多种类型的地质标准物质绘制校准曲线,利用含量与电气石类似的标准物质验证准确度,测定结果的相对标准偏差小于4.2%。采用所建方法测定四种不同类型电气石实际样品,测定值与经典化学法基本吻合。本方法解决了电气石不易湿法分解和硼的干扰问题,测定结果准确可靠,与其他方法相比操作简便,分析周期短。     

Deformation patterns of upper Quaternary strata and their relation to active tectonics,Po Basin,Italy

Despite increased application of subsurface datasets below the limits of seismic resolution, reconstructing near‐surface deformation of shallow key stratigraphic markers beneath modern alluvial and coastal plains through sediment core analysis has received little attention. Highly resolved stratigraphy of Upper Pleistocene to Holocene (Marine Isotope Stage 5e to Marine Isotope Stage 1) alluvial, deltaic and coastal depositional systems across the southern Po Plain, down to 150 m depth, provides an unambiguous documentation on the deformation of previously flat‐lying strata that goes back in time beyond the limits of morphological, historical and palaeoseismic records. Five prominent key horizons, accurately selected on the basis of their sedimentological characteristics and typified for their fossil content, were used as highly effective stratigraphic markers (M1 to M5) that can be tracked for tens of kilometres across the basin. A facies‐controlled approach tied to a robust chronology (102 radiocarbon dates) reveals considerable deformation of laterally extensive nearshore (M1), continental (M2 and M3) and lagoon (M4 and M5) marker beds originally deposited in a horizontal position (M1, M4 and M5). The areas where antiformal geometries are best observed are remarkably coincident with the axes of buried ramp anticlines, across which new seismic images reveal substantially warped stratal geometries of Lower Pleistocene strata. The striking spatial coincidence of fold crests with the epicentres of historic and instrumental seismicity suggests that deformation of marker beds M1 to M5 might reflect, in part at least, syntectonically generated relief and, thus, active tectonism. Precise identification and lateral tracing of chronologically constrained stratigraphic markers in the ¹⁴C time window through combined sedimentological and palaeoecological data may delineate late Quaternary subsurface stratigraphic architecture at an unprecedented level of detail, outlining cryptic stratal geometries at the sub‐seismic scale. This approach is highly reproducible in tectonically active Quaternary depositional systems and can help to assess patterns of active deformation in the subsurface of modern alluvial and coastal plains worldwide.     

Brittleness index predictions from Lower Barnett Shale well-log data applying an optimized data matching algorithm at various sampling densities

The capability of accurately predicting mineralogical brittleness index(BI)from basic suites of well logs is desir-able as it provides a useful indicator of the fracability of tight formations.Measuring mineralogical components in rocks is expensive and time consuming.However,the basic well log curves are not well correlated with BI so correlation-based,machine-learning methods are not able to derive highly accurate BI predictions using such data.A correlation-free,optimized data-matching algorithm is configured to predict BI on a supervised basis from well log and core data available from two published wells in the Lower Barnett Shale Formation(Texas).This transparent open box(TOB)algorithm matches data records by calculating the sum of squared errors be-tween their variables and selecting the best matches as those with the minimum squared errors.It then applies optimizers to adjust weights applied to individual variable errors to minimize the root mean square error(RMSE)between calculated and predicted(BI).The prediction accuracy achieved by TOB using just five well logs(Gr,pb,Ns,Rs,Dt)to predict BI is dependent on the density of data records sampled.At a sampling density of about one sample per 0.5 ft BI is predicted with RMSE～0.056 and R2～0.790.At a sampling density of about one sample per 0.1 ft BI is predicted with RMSE～0.008 and R2～0.995.Adding a stratigraphic height index as an additional(sixth)input variable method improves BI prediction accuracy to RMSE～0.003 and R2～0.999 for the two wells with only 1 record in 10,000 yielding a BI prediction error of＞±0.1.The model has the potential to be applied in an unsupervised basis to predict BI from basic well log data in surrounding wells lacking mineralogical measure-ments but with similar lithofacies and burial histories.The method could also be extended to predict elastic rock properties in and seismic attributes from wells and seismic data to improve the precision of brittleness index and fracability mapping spatially.     

Discovery and significance of Lizifang metamorphic core complex in Zhuanghe area of southern Liaoning

On the basis of the previous regional geological survey, based on the macroscopic and microscopic structural survey, combined with the comprehensive analysis of the regional magmatic activity and dating data, the authors in this paper revealed that there is another metamorphic core complex structure in Lizifang area of Southern Liaoning, namely Lizifang metamorphic core complex. A typical three-layer structure and five parts exist in the core complex, which are the footwall composed of Neo-archean metamorphic plutonic rocks and mesozoic granite intrusive rocks, the detachment fault zone composed of different levels of tectonic rocks, and the upper plate composed of Precambrian sedimentary cap and Cretaceous extensional basin. Lizifang metamorphic core complex formed in the Early Cretaceous Epoch, and the upper plate moved from NWW to SEE relaive to the footwall, which was similar with Jinzhou metamorphic core complex and Wanfu metamorphic core complex in geometry, kinematics polarity and formation time, indicating the same dynamic background. The determination of the metamorphic core complex may provide a basis for the late Mesozoic lithospheric thinning process and the mechanical and rheological properties of the lithosphere in the east of North China Craton. At the same time, the metamorphic core complex is closely related to the mineralization of gold deposits. So the detachment fault zone of Lizifang metamorphic core complex can serve as the key work area for further gold exploration, which may possess large mineralization potential.