砂土地层泥水盾构开挖面孔隙变化特征理论研究

为保证开挖面的稳定,泥水盾构压力舱中的泥浆必须及时在开挖面土体表层形成泥膜,泥浆压力才能有效平衡地层中的水土压力。在考虑泥浆渗滤效应的基础上,建立了砂土地层泥水盾构开挖面泥浆恒压渗透模型,分析了渗透时间、泥浆浓度、泥浆压力和地层初始孔隙率对土体孔隙率及泥浆成膜的影响。结合刀具周期性切削作用,总结了泥浆反复渗透引起的开挖面表层土体孔隙率变化规律。基于刀盘、刀具布置形式和盾构掘进参数,分析了盾构掘进期间开挖面支护机制。结果表明：在无刀具切削作用时,泥浆渗透规律主要受到泥浆和地层特性影响;在刀具周期性切削作用下,在相同的切削深度下,刀具切削周期越短,泥膜在开挖面上越难形成;刀具较小的纵向切入速度有利于开挖面上更快形成泥膜;适当减少刀盘上同一轨迹刀具布置数量,降低盾构掘进速度和刀盘转动速度,有利于盾构掘进期间开挖面上泥膜存在面积的增大,对开挖面稳定起到积极作用。     

基于岩石物理模型的碳酸盐岩储层微观孔隙特征分析方法

碳酸盐岩储层的微观孔隙结构普遍具有类型复杂和纵向变化快的特征。由于地球物理资料尺度的限制,现有的解释手段不能有效刻画这些关键特征。笔者采用临界孔隙度模型作为理论依据,建立了微观孔隙结构与宏观弹性参数响应之间的定量关系;以岩石物理实验数据为约束,提出了一种基于概率统计学的方法估算储层关键参数并识别岩石孔隙类型。在YS1井的应用表明：新方法有效挖掘了声波测井数据中隐含的微观信息,参数预测结果达到较高的精度（平均相对误差小于10%）,可以为优质储层段的划分提供可靠的参考依据。     

Reservoir Porosity Measurement Uncertainty and its Influence on Shale Gas Resource Assessment

Reservoir porosity is a critical parameter for the process of unconventional oil and gas resources assessment. It is difficult to determine the porosity of a gas shale reservoir, and any large deviation will directly reduce the credibility of any shale gas resources evaluation. However, there is no quantitative explanation for the accuracy of porosity measurement. In this paper, measurement uncertainty, an internationally recognized index, was used to evaluate the results of porosity measurement of gas shale plugs, and its impact on the credibility of shale gas resources assessment was determined. The following conclusions are drawn:(1) the measurement uncertainty of porosity of a shale plug is 1.76%–3.12% using current measurement methods, the upper end of which is too large to be acceptable. It is suggested that the measurement uncertainty should be factored into the standard helium gas injection porosity determination experiment, and the uncertainty should be less than 2.00% when using a high-precision pressure gauge;(2) in order to reduce the risk for exploration and decision-making, attention should be paid to the large uncertainty(30% at least) of shale gas resource assessment results, sometimes with corrections being made based on the practical considerations;(3) a pressure gauge with an accuracy of 0.25% of the full scal cannot meet the requirements of porosity measurement, and a high-precision plug cutting method or high-precision bulk volume measurement method such as one using 3 D scanning, is recommended to effectively reduce porosity uncertainty;(4) the method and process for evaluating the measurement uncertainty of gas shale porosity could also be referred for assessment of experimental quality by other laboratories.     

某工程蚀变岩孔隙特征及其软弱程度研究

孔隙作为岩体的初始损伤,对岩体的强度及变形特性的影响尤为明显,而孔隙发育是研究区内一类力学性质较软弱岩石的显著特征。对蚀变岩孔隙特征的研究是了解蚀变岩的软弱程度及孔隙度对其软弱程度的影响的有效方法。针对此蚀变岩进行岩矿及铸体薄片分析得出蚀变岩孔隙有原生、浅表生及构造3种成因,其中以原生为主。从饱水蚀变岩的常规单轴压缩试验应力-应变全过程曲线上求取蚀变岩的饱和单轴抗压强度及割线模量,再与相应试样的孔隙度进行相关性分析,结果显示出蚀变岩的饱和单轴抗压强度及割线模量均随孔隙度的增加而减小,且呈幂函数关系。由于蚀变岩的饱和单轴抗压强度(R c)及割线模量(E s)作为软硬岩评判标准具有一致性,且两者与孔隙度(n)存在较好的相关性,以此将3者共同作为蚀变岩软弱程度的划分标准,并得出软硬岩分界处n为12%、R c为30 M Pa、E s为5 GPa。     

双相介质分界面上弹性波的反射与透射

本文基于Biot理论,推导出Zoeppritz形式的双相介质分界面上弹性波的反射与透射公式,对单相Zoeppritz公式与双相反射系数公式进行了比较,对双相介质含油、水、气不同流体时的反射规律以及孔隙度、渗透率、饱和度等储层参数对纵波反射的影响进行了研究.数值模拟分析表明,双相与单相反射公式的主要差异在于双相介质反射公式中考虑了液相、固液耦合相弹性模量的影响;油砂、水砂、气砂岩的慢P波反射差异明显;快P波反射对孔隙度的变化敏感,饱和度次之,对渗透率和频率的变化不敏感.     

高孔隙多金属硫化物海水围压下切削模拟

考虑海底多金属硫化物(SMS)高孔隙率、受围压等特点,首先采用蒙特卡罗法,结合APDL语言建立了具有一定孔隙率的SMS矿体几何模型,然后基于LS-DYNA仿真平台建立了高海水围压条件下单截齿切削破碎具有一定孔隙率SMS矿体的仿真模型,并进行了相应的数值模拟。研究结果表明:在高海水围压条件下,多金属硫化物的切削难度明显增强,高围压作用使切屑更难从矿体基岩剥离,截齿受到的三向阻力明显增大;随着多金属硫化物矿体的孔隙率增大,截齿破碎矿体受到的切削阻力会减小。     

Numerical prediction of the effective wake profiles of a high-speed underwater vehicle with contra-rotating propellers

A numerical method is proposed to predict the effective wake profiles of high speed underwater vehicles propelled by contra-rotating propellers (CRPs), in which the hydrodynamic effects of the CRPs are simulated by distributed body forces. First, Reynolds-averaged Navier-Stokes (RANS) simulations are conducted for identical body-force distributions in open-water and self-propulsion conditions. The effective wake profiles at the CRP disks are then obtained by subtracting the velocities induced by the body forces in the open water from those induced by the body forces in the self-propulsion condition. The effective wake profiles were then predicted for a generic underwater vehicle with an established CRP design. Next, the hydrodynamic performance of the CRPs in the effective wake was computed using an in-house vortex-lattice code. The potential-flow results agree well with those provided by the RANS simulation under the self-propulsion condition, indicating that the proposed method can predict the effective wake profiles for CRPs with reasonable accuracy. The influences of different wake components on the blade forces were investigated, determining that for CRPs, and especially for the aft propeller, the circumferential wake cannot be neglected in the design.     

Spatial distribution of micrometre‐scale porosity and permeability across the damage zone of a reverse‐reactivated normal fault in a tight sandstone: Insights from the Otway Basin,SE Australia

Knowledge of the permeability structure of fault‐bearing reservoir rocks is fundamental for developing robust hydrocarbon exploration and fluid monitoring strategies. Studies often describe the permeability structure of low porosity host rocks that have experienced simple tectonic histories, while investigations of the influence of faults with multiple‐slip histories on the permeability structure of porous clastic rocks are limited. We present results from an integrated petrophysical, microstructural, and mineralogical investigation of the Eumeralla Formation (a tight volcanogenic sandstone) within the hanging wall of the Castle Cove Fault which strikes 30 km NE–SW in the Otway Basin, southeast Australia. This late Jurassic to Cenozoic‐age basin has experienced multiple phases of extension and compression. Core plugs and thin sections oriented relative to the fault plane were sampled from the hanging wall at distances of up to 225 m from the Castle Cove Fault plane. As the fault plane is approached, connected porosities increase by ca. 10% (17% at 225 m to 24% at 0.5 m) and permeabilities increase by two orders of magnitude (from 0.04 mD at 225 m to 1.26 mD at 0.5 m). Backscattered Scanning Electron Microscope analysis shows that microstructural changes due to faulting have enhanced the micrometre‐scale permeability structure of the Eumeralla Formation. These microstructural changes have been attributed to the formation of microfractures and destruction of original pore‐lining chlorite morphology as a result of fault deformation. Complex deformation, that is, formation of macrofractures, variably oriented microfractures, and a hanging wall anticline, associated with normal faulting and subsequent reverse faulting, has significantly influenced the off‐fault fluid flow properties of the protolith. However, despite enhancement of the host rock permeability structure, the Eumeralla Formation at Castle Cove is still considered a tight sandstone. Our study shows that high‐resolution integrated analyses of the host rock are critical for describing the micrometre‐scale permeability structure of reservoir rocks with high porosities, low permeabilities, and abundant clays that have experienced complex deformation.     

农业资源高效利用评价几个基本问题的探讨

围绕当前农业资源高效利用评价工作中需要先行搞清的一些理论和方法问题进行了议论。讨论了农业资源高效利用的评价标准,在概括农业资源高效利用评价目的,内容和基本方法的基础上,提出加快我国农业资源高效利用评价研究工作纵深化发展的具体建议。     

几种水陆交错带植物对湖滨带底质的稳固作用

为了研究几种常见水陆交错带植物对底质稳固性的影响,选取太湖贡湖湾水陆交错带内的双穗雀稗(Paspalum distichum)、李氏禾(Leersia hexandra)、香菇草(Hydrocotyle vulgaris)、黄花水龙(Ludwigia peploides)和黄菖蒲(Iris pseudacorus)5种水生/湿生植物植物,并利用长江下游常见沙壤土和湖滨带新生底质两种土壤,开展了5种植物对底质稳固作用的室内研究.结果表明底质孔隙度减少、细小粒径(50μm)增加有利于底质稳固,改善上覆水指标,减少扰动给上覆水所带来的悬浮颗粒物.直径≤1 mm的须根量、须根长度和须根面积与底质孔隙度和粒径分布增益值之间存在线性回归关系,双穗雀稗、李氏禾、香菇草的根系参数与增益值之间存在斜率为0.006~1.727的线性正相关关系;黄花水龙、黄菖蒲植物根系参数与增益值之间则存在斜率为-0.091~-0.011的线性负相关关系.黄菖蒲与黄花水龙的根长密度分别为11.495和9.475 cm/cm~3,根表面积密度分别为0.368和0.294 cm~2/cm~3,根重密度分别为1.844和0.944 mg/cm~3,两种植物对底质孔隙度的增益值分别为15%和9%,对底质粒径分布的增益值分别为92%和47%;双穗雀稗、李氏禾、香菇草的根长密度分别为1.057、7.368和0.651 cm/cm~3,根表面积密度分别为0.033、0.228和0.022 cm~2/cm~3,根重密度分别为0.678、2.537和0.160 mg/cm~3,3种植物根系参数对底质孔隙度的增益值分别为6%、36%和1%,3种植物根系参数对底质粒径分布的增益值分别为16%、17%和-13%.5种植物通过根系提高底质的稳定性,减少底质在水力扰动下悬浮物质以及营养盐的释放,从效能上表现为李氏禾双穗雀稗黄菖蒲黄花水龙香菇草.