Evaluation and re-understanding of the global natural gas hydrate resources

Natural gas hydrate(NGH)has been widely considered as an alternative to conventional oil and gas resources in the future energy resource supply since Trofimuk’s first resource assessment in 1973.At least 29 global estimates have been published from various studies so far,among which 24 estimates are greater than the total conventional gas resources.If drawn in chronological order,the 29 historical resource estimates show a clear downward trend,reflecting the changes in our perception with respect to its resource potential with increasing our knowledge on the NGH with time.A time series of the 29 estimates was used to establish a statistical model for predict the future trend.The model produces an expected resource value of 41.46×1012 m3 at the year of 2050.The statistical trend projected future gas hydrate resource is only about 10%of total natural gas resource in conventional reservoir,consistent with estimates of global technically recoverable resources(TRR)in gas hydrate from Monte Carlo technique based on volumetric and material balance approaches.Considering the technical challenges and high cost in commercial production and the lack of competitive advantages compared with rapid growing unconventional and renewable resources,only those on the very top of the gas hydrate resource pyramid will be added to future energy supply.It is unlikely that the NGH will be the major energy source in the future.

Numerical modelling of structural controls on fluid flow and mineralization

This paper presents the results of a set of numerical models focussing on structural controls on hydrothermal mineralization. We first give an overview of natural phenomena of structurally-controlled ore formation and the background theory and mechanisms for such controls. We then provide the results of a group of simple 2D numerical models validated through comparison with Cu-vein structure observed near the Shilu Copper deposit （Yangchun, Guangdong Province, China） and finally a case study of 3D numerical modelling applied to the Hodgkinson Province in North Queensland （Australia）. Two modelling approaches, discrete deformation modelling and continuum coupled deformation and fluid flow modelling, are involved. The 2D model-derived patterns are remarkably consistent with the Cu-vein structure from the Shilu Copper deposit, and show that both modelling approaches can realistically simulate the mechanical behaviours of shear and dilatant fractures. The continuum coupled deformation and fluid flow model indicates that pattern of the Cu- veins near the Shilu deposit is the result of shear strain localization, development of dilation and fluid focussing into the dilatant fracture segments. The 3D case-study models （with deformation and fluid flow coupling） on the Hodgkinson Province generated a number of potential gold mineralization

A Combination of N2 and CO2 Adsorption to Characterize Nanopore Structure of Organic-Rich Lower Silurian Shale in the Upper Yangtze Platform, South China： Implications for Shale Gas Sorption Capacity

The pores in shales are mainly of nanometer-scale, and their pore size distribution is very important for the preservation and exploitation of shale gas. This study focused on the organic-rich Lower Silurian black shale from four wells in the Upper Yangtze Platform, and their TOC, mineralogical composition and pore characterization were investigated. Low pressure N2 and CO2 adsorption were conducted at 77.35 K and 273.15 K, respectively, and the pore structures were characterized by modified Brunauer-Emmett-Teller （BET）, Dubinin-Radushkevich （DR）, t-plot, Barrett- Joyner-Halenda （BJH） and density functional theory （DFT） methods and then the relationship between pore structure and shale gas sorption capacity was discussed. The results indicate that （1） The Lower Silurian shale has high TOC content of 0.92%~96%, high quartz content of 30.6%-69.5%, and high clays content of 24.1%-51.2%. The total specific surface area varies from 7.56 m^2/g to 25.86 m^2/g. Both the total specific surface area and quartz content are positively associated with the TOC content. （2） Shale samples with higher TOC content have more micropores, which results in more complex nanopore structure. Micropore volumes/surface areas and non-micropore surface areas all increase with the increasing TOC content. （3） A combination of N2 and CO2 adsorption provides the most suitable detection range （~0.3-60 nm） and has high reliability and accuracy for nanopore structure characterization. （4） The TOC content is the key factor to control the gas sorption capacity of the Lower Silurian shale in the Upper Yangtze Platform.

Dynamic Field Division of Hydrocarbon Migration,Accumulation and Hydrocarbon Enrichment Rules in Sedimentary Basins

Hydrocarbon distribution rules in the deep and shallow parts of sedimentary basins are considerably different, particularly in the following four aspects. First, the critical porosity for hydrocarbon migration is much lower in the deep parts of basins： at a depth of 7000 m, hydrocarbons can accumulate only in rocks with porosity less than 5%. However, in the shallow parts of basins （i.e., depths of around 1000 m）, hydrocarbon can accumulate in rocks only when porosity is over 20%. Second, hydrocarbon reservoirs tend to exhibit negative pressures after hydrocarbon accumulation at depth, with a pressure coefficient less than 0.7. However, hydrocarbon reservoirs at shallow depths tend to exhibit high pressure after hydrocarbon accumulation. Third, deep reservoirs tend to exhibit characteristics of oil （-gas）-water inversion, indicating that the oil （gas） accumulated under the water. However, the oil （gas） tends to accumulate over water in shallow reservoirs. Fourth, continuous unconventional tight hydrocarbon reservoirs are distributed widely in deep reservoirs, where the buoyancy force is not the primary dynamic force and the caprock is not involved during the process of hydrocarbon accumulation. Conversely, the majority of hydrocarbons in shallow regions accumulate in traps with complex structures. The results of this study indicate that two dynamic boundary conditions are primarily responsible for the above phenomena： a lower limit to the buoyancy force and the lower limit of hydrocarbon accumulation overall, corresponding to about 10%-12% porosity and irreducible water saturation of 100%, respectively. These two dynamic boundary conditions were used to divide sedimentary basins into three different dynamic fields of hydrocarbon accumulation： the free fluid dynamic field, limit fluid dynamic field, and restrain fluid dynamic field. The free fluid dynamic field is located between the surface and the lower limit of the buoyancy force, such that hydrocarbons in this field migrate and accumulate under the influence of, for example, the buoyancy force, pressure, hydrodynamic force, and capillary force. The hydrocarbon reservoirs formed are characterized as ＂four high,＂ indicating that they accumulate in high structures, are sealed in high locations, migrate into areas of high porosity, and are stored in reservoirs at high pressure. The basic features of distribution and accumulation in this case include hydrocarbon migration as a result of the buoyancy force and formation of a reservoir by a caprock. The limit fluid dynamic field is located between the lower limit of the buoyancy force and the lower limit of hydrocarbon accumulation overall; the hydrocarbon migrates and accumulates as a result of, for example, the molecular expansion force and the capillary force. The hydrocarbon reservoirs formed are characterized as ＂four low,＂ indicating that hydrocarbons accumulate in low structures, migrate into areas of low porosity, and accumulate in reservoirs with low pressure, and that oil（-gas）-water inversion occurs at low locations. Continuous hydrocarbon accumulation over a large area is a basic feature of this field. The restrain fluid dynamic field is located under the bottom of hydrocarbon accumulation, such that the entire pore space is filled with water. Hydrocarbons migrate as a result of the molecular diffusion force only. This field lacks many of the basic conditions required for formation of hydrocarbon reservoirs： there is no effective porosity, movable fluid, or hydrocarbon accumulation, and potential for hydrocarbon exploration is low. Many conventional hydrocarbon resources have been discovered and exploited in the free fluid dynamic field of shallow reservoirs, where exploration potential was previously considered to be low. Continuous unconventional tight hydrocarbon resources have been discovered in the limit fluid dynamic field of deep reservoirs; the exploration potential of this setting is thought to be tremendous, indicating that future exploration should be focused primarily in this direction.

Gas diffusion in a cylindrical coal sample – A general solution,approximation and error analyses

The analytical mathematical solutions of gas concentration and fractional gas loss for the diffusion of gas in a cylindrical coal sample were given with detailed mathematical derivations by assuming that the diffusion of gas through the coal matrix is concentration gradient-driven and obeys the Fick’s Second Law of Diffusion.The analytical solutions were approximated in case of small values of time and the error analyses associated with the approximation were also undertaken.The results indicate that the square root relationship of gas release in the early stage of desorption,which is widely used to provide a simple and fast estimation of the lost gas,is the first term of the approximation,and care must be taken in using the square root relationship as a significant error might be introduced with increase in the lost time and decrease in effective diameter of a cylindrical coal sample.

A general solution and approximation for the diffusion of gas in a spherical coal sample

The square root relationship of gas release in the early stage of desorption is widely used to provide a simple and fast estimation of the lost gas in coal mines. However, questions arise as to how the relationship was theoretically derived, what are the assumptions and applicable conditions and how large the error will be. In this paper, the analytical solutions of gas concentration and fractional gas loss for the diffusion of gas in a spherical coal sample were given with detailed mathematical derivations based on the diffusion equation. The analytical solutions were approximated in case of small values of time and the error analyses associated with the approximation were also undertaken. The results indicate that the square root relationship of gas release is the first term of the approximation, and care must be taken in using the square root relationship as a significant error might be introduced with increase in the lost time and decrease in effective diameter of a spherical coal sample.

Inertisation options for BG method and optimisation using CFD modelling

Spontaneous combustion(sponcom) is one of the issues of concern with the blasting gallery(BG) method of coal mining and has the potential to cause fires, and impact on production and safety, greenhouse gas(GHG) emissions and huge costs involved in controlling the aftermath situations. Some of the research attempts made to prevent and control coal mine fires and spontaneous combustion in thick seams worked with bord and pillar mining methods are presented in this paper. In the study, computational fluid dynamics(CFD) modelling techniques were used to simulate and assess the effects of various mining methods, layouts, designs, and different operational and ventilation parameters on the flow of goaf gases in BG panels. A wide range of parametric studies were conducted to develop proactive strategies to control and prevent ingress of oxygen into the goaf area preventing spontaneous combustion and mine fires.

Modelling fracture propagation and failure in a rock pillar under mechanical and thermal loadings

The Aspoe Pillar Stability Experiment （APSE） was conducted to study the rock mass response in a heated rock pillar between two large boreholes. This paper summarizes the back calculations of the APSE using a two-dimensional （2D） fracture propagation code FRACOD. To be able to model all the loading phases of the APSE, including the thermal loading, the code was improved in several ways. A sequential excavation function was developed to model promptly the stepwise changing loading geometry. Prior to the mod- elling, short-term compressive strength test models were set up aiming to reproduce the stress-strain behaviour observed for the Aspoe diorite in laboratory. These models simulate both the axial and lateral strains of radial-controlled laboratory tests, The volumetric strain was calculated from the simulations and compared with the laboratory results, The pillar models include vertical and horizontal 2D models from where the stress in the pillar wall was investigated, The vertical model assesses the stability of the experimental rock volume and suggests the resultant stress below the tunnel floor in the pillar area. The horizontal model considers cross-sections of the pillar between the two large boreholes. The horizon- tal model is used to simulate the evolution of the stress in the rock mass during the excavation of the boreholes and during and the heating phase to give an estimation of the spalling strength. The modelling results suggest that the excavation-induced stresses will cause slight fracturing in the pillar walls, if the strength of the APSE pillar is set to about 123 MPa. Fracture propagation driven by thermal loading leads to minor spalling. The thermal evolution, elastic behaviour and brittle failure observed in the experiment are well reflected by the models.

渝东南两套富有机质页岩的孔隙结构特征--来自FIB-SEM的新启示

使用聚焦离子束扫描电镜（FIB-SEM）对渝东南地区下寒武统牛蹄塘组和上奥陶统五峰组—下志留统龙马溪组2套富有机质页岩的孔隙结构进行了系统观察,并对页岩纳米级有机质孔隙进行了三维重构和孔隙结构参数定量分析。研究发现,五峰组—龙马溪组页岩内层间微裂隙、矿物粒内孔、矿物粒间孔和有机质孔隙均较为发育。其中,有机质孔隙呈蜂窝状均匀发育,孔隙半径集中在3-100 nm,孔隙连通性较好,FIB-SEM三维重构计算有机质孔隙度在9.13%-18.42%之间,岩石总孔隙度中有机质孔隙度的贡献受控于TOC含量;牛蹄塘组页岩内溶蚀孔和粒间孔较为发育,有机质孔隙发育不均匀,孔隙呈扁平状或针孔状,孔隙半径集中在3-25 nm,孔隙连通性较差,有机质孔隙度在1.59%以下,有机质孔隙度对岩石总孔隙度的贡献与TOC含量关系较小,页岩的总孔隙度主要来自于矿物基质孔。FIB-SEM揭示了2套页岩有机质孔隙结构存在较大差异。

库车克拉2气田多期油气充注的古流体证据

对库车前陆盆地克拉2气田储集层进行流体包裹体分析、荧光光谱分析、场发射扫描电镜观察、岩心显微CT扫描及油气地球化学分析,从古流体证据的角度综合研究克拉2气田多阶段油气充注过程。克拉2气田经历了中新世早中期(N1)原油充注、上新世库车组沉积期(N2)高成熟油气充注与破坏、第四系(Q1以来)高—过成熟煤成气充注的3期成藏过程。储集层中广泛分布的残余干沥青、较发育的气液两相烃包裹体、纳米孔中的残余油、现今气层和水层中较高的颗粒(抽提物)荧光指数、储集层岩石较大的热解值等均是早期原油充注的证据;残余干沥青、含沥青的3相烃包裹体、凝析油轻质正构烷烃大量损失、石蜡质和芳烃等重组分含量相对较高、金刚烷含量异常高等均是早期原油遭受气洗发生脱沥青作用的有力证据。

核磁共振与高压压汞实验联合表征致密油储层微观孔喉分布特征

通过设计算法程序,利用压汞实验得到的致密储层孔喉分布数据,校正优化了核磁共振实验T2弛豫时间与孔喉半径的换算系数,提高了核磁共振表征孔喉分布的精度,建立了表征致密储层微观孔隙分布特征的核磁实验方法。该方法应用于松辽盆地南部白垩系致密油样品孔喉分布表征,不同含油饱和度样品孔喉分布数据表明,含油饱和度小于10%的样品孔喉集中在10-300 nm;含油饱和度介于10%~40%的样品孔喉集中在20-1 000 nm;含油饱和度大于40%的样品孔喉集中在20-3 000 nm。致密储层中不同级别微纳米级孔隙系统的发育控制了致密油含油性。

致密油流动孔隙度下限——高压压汞技术在松辽盆地南部白垩系泉四段的应用

以松辽盆地南部让字井斜坡区白垩系泉头组四段致密层密闭取心井30块样品为研究对象,根据高压压汞实验和氦气测定孔隙度,以及含油饱和度数据分析,确定其致密油流动孔隙度下限及流动孔隙度控制因素。将油藏条件毛管压力与压汞实验得到的毛管压力进行换算,可计算不同油藏注入压力条件下的流动孔隙度,通过求取含油样品流动孔隙度最小值与不含油样品流动孔隙度最大值,确定研究区含油样品的流动孔隙度下限为3.2%,对应油藏条件下注入压力为0.35 MPa,高于此注入压力致密油可发生有效流动与聚集。致密层流动孔隙度与孔喉比呈负相关,储集层孔喉连通性变差时,需要更高注入压力流动孔隙度才能达到3.2%;流动孔隙度达到3.2%所需注入压力与储集层质量系数呈较好负相关性,随着储集层质量系数增加,流动孔隙度达到3.2%需要的注入压力有降低趋势。基于致密油流动孔隙度下限和油藏条件下注入压力,建立了致密油有效聚集判别图版。

致密油充注过程中储层润湿性变化对含油性影响--以川中侏罗系致密油为例

以四川盆地川中侏罗系致密油储层岩心样品为例,开展了致密油微观充注物理模拟实验。实验模型采用砂岩薄片模型(尺寸为2.5 cm×2.5 cm,厚度约0.6 mm),将实验用油注入模型引槽中,压力由小到大逐步增加至每个模型出口端只出油不出水为止,观测渗流特征并计算含油饱和度。实验结果显示,充注前样品束缚水饱和度与充注后含油饱和度总和大于100%,基于核磁共振法对储层束缚水等流体饱和度与储层润湿性的分析,提出了充注前后储层润湿性的改变(水润湿转变为油润湿)使得最终含油饱和度高于被驱替的动水饱和度。致密油运聚过程中储层润湿性改变抵消了致密油储层高束缚水饱和度对致密油含油性的抑制作用,利于致密油运聚,是致密油成藏含油饱和度提高的重要原因。

利用测井资料识别层序地层单元技术与方法进展及趋势

测井曲线包含丰富的地质信息,测井曲线的形态、幅度可以反映出岩性和沉积旋回韵律等地层特征。在综述国内外研究成果的基础上,认为基于测井资料进行层序地层单元划分的方法可以分为定性和定量识别两种,其中,定性方法有自然电位和自然电位镜像法、声波时差与电阻率曲线重叠法、声波时差法、自然电位和视电阻率组合法以及累计地层倾角测井法等;定量识别方法有时频分析技术、INPEFA技术、多尺度小波分析技术、经验模态分解法、测井曲线分形分析和测井多尺度数据融合方法等。人工神经网络、人工智能技术和多尺度数据融合方法将是测井识别层序地层单元研究的趋势。结合INPEFA定量识别方法对西湖凹陷钻井层序地层单元定量识别进行实例分析,效果良好。

松辽盆地南部白垩系致密油微观赋存特征

建立环境扫描电镜观察与X射线能谱定量测定烃类碳含量相结合的实验方法,表征松辽盆地南部白垩系泉头组四段致密油微观赋存特征。对致密油7口典型井17块样品168个测点的观察与分析表明,致密油主要具有2种赋存形态：油珠与油膜,以油膜为主;具有3类微观赋存空间：粒间孔、粒内孔和微裂缝,以粒间孔为主。油膜平面尺寸主要为（1~5μm）×（1~5μm）,形状不规则,以浸染粘连状形态赋存于粒间孔或微裂缝中,含碳质量百分比主要集中在40%~90%;油珠平面尺寸主要为（0.2~1.0μm）×（0.2~1.0μm）,赋存空间相对较小,含碳质量百分比主要集中在15%~30%。储集层类型与孔喉分布控制致密油赋存状态：由Ⅰ类到Ⅲ类储集层,原油含碳质量百分比及赋存油膜厚度呈逐渐减小趋势,储集层中值孔喉半径与储集层质量系数控制含碳质量百分比与油膜厚度。

陆相湖盆层序构型及其岩性预测意义：以珠江口盆地惠州凹陷为例

地层岩相组合有规律地分布于层序的不同体系域。为了有效地进行储层发育、烃源岩分布的预测,文中提出层序构型的明确概念、类型、识别标志及其意义。层序构型是指三级层序内不同体系域地层单元时间-空间组成配置关系,其类型可分为L型、T型、TH型、H型(E-H型和L-H型)4种,其中,L型层序主要为富砂层序,储层相对发育;T型层序为富泥层序,烃源岩最为发育;TH型层序为富泥层序,烃源岩相对发育;E-H型层序为富泥层序,烃源岩发育程度次于TH型层序;L-H型层序主要为富砂层序,储层相对发育。珠江口盆地富烃的惠州凹陷文昌组层序构型实例分析表明,惠州凹陷南缘主要为T型层序,烃源岩相对发育,北缘主要为H型层序,储层相对发育。

四川盆地须家河组致密砂岩气自生伊利石年龄分布与成藏时代

利用自生伊利石K-Ar、Ar-Ar测年技术对四川盆地须家河组致密砂岩气藏的成藏年代进行测定与研究,并对其演化规律进行深入探讨。须家河组砂岩储层自生伊利石普遍发育,主要为片丝状、短丝状、丝状,具有明显的自生成因特征并且纵、横向分布稳定。须家河组砂岩储层自生伊利石年龄数据明显分为2组,具有2期成藏特征。早期成藏为晚侏罗世—早白垩世(97~145 Ma),广泛分布于川西、川中广大地区,是主要成藏期;晚期成藏为晚白垩世(78~83 Ma),仅见于川西南端平落坝、白马庙气田须家河组二段。主要成藏期也即早期成藏,主力储层须家河组二段、须家河组四段、须家河组六段基本一致,并明显具有连续成藏特征:纵向上,自下而上依次变晚,须家河组二段略早(平均133 Ma)、须家河组四段略晚(平均127 Ma),须家河组六段主要分布在广安气田,与须家河组四段相比也基本具有下早上晚的成藏特征(须家河组四段平均139 Ma,须家河组六段平均134 Ma);平面上,川西须家河组二段由北向南依次变晚,中坝、新场、大邑气田的自生伊利石平均年龄分别为136 Ma、134 Ma和133 Ma(川西南端的平落坝、白马庙气田属于晚期成藏),川中须家河组二段、须家河组四段由东向西依次变晚,东部的广安、合川、荷包场气田略早,中西部的磨溪、充西—莲池、金华、八角场气田略晚。自生伊利石年龄分布特征表明,烃源岩埋深,即生、排烃时间,是须家河组砂岩气藏成藏早晚的最主要控制因素,埋深大、生、排烃早,则年龄大、成藏早,反之则年龄小、成藏晚。岩性对成藏具有一定的控制作用,但分布局限。构造抬升作用主要表现在成藏后期的调整阶段,年龄由东向西变小,即成藏由东向西变晚,与现今埋深即东高西低的构造特征不一致现象,是由成藏后期的构造差异抬升作用所致。

基于层序地层模拟的湖岸线迁移对层序定量识别的指示：以鄂尔多斯盆地山2段为例

湖岸线是水陆沉积的分界线,为探讨其迁移规律与层序间的关系,利用SEDPAK二维层序模拟软件,以鄂尔多斯盆地山2段作为地质原型,对湖岸线迁移进行了定量模拟,进而提出了其可以有效指示层序及内部体系域识别的新认识。对湖岸线迁移规律在水平方向与垂直方向重新进行了划分、定义。在水平方向上,向物源区方向的迁移定义为"正向",对应于湖侵过程;向盆地方向的迁移定义为"负向",对应于湖退过程。"负向"迁移在垂向上可细分为向上方迁移的"同向"迁移和向下方迁移的"反向"迁移,"同向"迁移为正常湖退过程,"反向"迁移为强制湖退过程。湖岸线由"正向"转变为"负向"的分界面为最大洪泛面;反之,为最大湖退面;在"负向"迁移中,由"同向"转变为"反向"的分界面为强制湖退底面;反之,为相对应的整合面。

注入系统压缩性和粘性流体流动对水压致裂破碎压力影响的模拟

基于水压致裂数据估计岩体的最大应力主要取决于对破裂的确定和二次破裂压力。这种估计的误差可归结于注入系统压缩性,耦合粘性流体在水压裂隙中的流动和裂隙通过井孔周围变化的应力场的增长。这些机制的作用还没有很好的定量化。本文中的两个数值模型为评估非理想条件下与破裂压力分析有关的误差提供了一个基本工具。这两个数值模型是注入系统的压缩性和各向异性的岩石应力场中粘性流体在从井孔扩展的水压裂隙中的流动。为了保证足够的精确性,结果对于相关的无量纲参数值采用基于模型的标准,当这些标准在现场条件下满足不了时,模型可以进一步应用获得一级校正,来解释压缩性、粘度和近井孔的影响。

Developing selective mining capability for longwall shearers using thermal infrared-based seam tracking

Longwall mining continues to remain the most efficient method for underground coal recovery. A key aspect in achieving safe and productive longwall mining is to ensure that the shearer is always correctly positioned within the coal seam. At present, this machine positioning task is the role of longwall personnel who must simultaneously monitor the longwall coal face and the shearer's cutting drum position to infer the geological trends of the coal seam. This is a labour intensive task which has negative impacts on the consistency and quality of coal production. As a solution to this problem, this paper presents a sensing method to automatically track geological coal seam features on the longwall face, known as marker bands, using thermal infrared imaging. These non-visible marker bands are geological features that link strongly to the horizontal trends present in layered coal seams. Tracking these line-like features allows the generation of a vertical datum that can be used to maintain the shearer in a position for optimal coal extraction. Details on the theory of thermal infrared imaging are given, as well as practical aspects associated with machine-based implementation underground. The feature detection and tracking tasks are given with real measurements to demonstrate the efficacy of the approach. The outcome is important as it represents a new selective mining capability to help address a long-standing limitation in longwall mining operations.