中国南海天然气水合物开采储层水合物相变与渗流机理:综述与展望

【研究目的】中国地质调查局先后于2017年、2020年在南海北部神狐海域成功实施两轮水合物试采,创造了产气时间最长、产气总量最大、日均产气量最高等多项世界纪录,了解和掌握南海天然气水合物开采储层相变与渗流机理,有助于进一步揭示该类型水合物分解机理、产出规律、增产机制等,可为中国海域水合物资源规模高效开采提供理论基础。【研究方法】基于两轮试采实践,笔者通过深入研究发现,储层结构表征、水合物相变、多相渗流与增渗、产能模拟与调控是制约水合物分解产气效率的重要因素。【研究结果】研究表明,南海水合物相变具有分解温度低,易在储层内形成二次水合物等特点,是由渗流场-应力场-温度场-化学场共同作用的复杂系统;多相渗流作用主要受控于未固结储层的物性特征、水合物相变、开采方式等多元因素影响,具有较强的甲烷吸附性、绝对渗透率易突变、气相流动能力弱等特点;围绕南海水合物长期、稳定、高效开采目标,需要在初始储层改造基础上,通过实施储层二次改造,进一步优化提高储层渗流能力,实现增渗扩产目的。【结论】随着天然气水合物产业化进程不断向前推进,还需要着力解决大规模长时间产气过程中温度压力微观变化及物质能源交换响应机制以及水合物高效分解、二次生成边界条件等难题。创新点：南海水合物相变是由渗流场-应力场-温度场-化学场共同作用的复杂系统;南海泥质粉砂储层具有较强的甲烷吸附性、绝对渗透率易突变、气相流动能力弱等特点,多相渗流机理复杂。     

Hydrate phase transition and seepage mechanism during natural gas hydrates production tests in the South China Sea: A review and prospect

Natural gas hydrates (NGHs) are globally recognized as an important type of strategic alternative energy due to their high combustion efficiency, cleanness, and large amounts of resources. The NGHs reservoirs in the South China Sea (SCS) mainly consist of clayey silts. NGHs reservoirs of this type boast the largest distribution range and the highest percentage of resources among NGHs reservoirs in the world. However, they are more difficult to exploit than sandy reservoirs. The China Geological Survey successfully carried out two NGHs production tests in the Shenhu Area in the northern SCS in 2017 and 2020, setting multiple world records, such as the longest gas production time, the highest total gas production, and the highest average daily gas production, as well as achieving a series of innovative theoretical results. As suggested by the in-depth research on the two production tests, key factors that restrict the gas production efficiency of hydrate dissociation include reservoir structure characterization, hydrate phase transition, multiphase seepage and permeability enhancement, and the simulation and regulation of production capacity, among which the hydrate phase transition and seepage mechanism are crucial. Study results reveal that the hydrate phase transition in the SCS is characterized by low dissociation temperature, is prone to produce secondary hydrates in the reservoirs, and is a complex process under the combined effects of the seepage, stress, temperature, and chemical fields. The multiphase seepage is controlled by multiple factors such as the physical properties of unconsolidated reservoirs, the hydrate phase transition, and exploitation methods and is characterized by strong methane adsorption, abrupt changes in absolute permeability, and the weak flow capacity of gas. To ensure the long-term, stable, and efficient NGHs exploitation in the SCS, it is necessary to further enhance the reservoir seepage capacity and increase gas production through secondary reservoir stimulation based on initial reservoir stimulation. With the constant progress in the NGHs industrialization, great efforts should be made to tackle the difficulties, such as determining the micro-change in temperature and pressure, the response mechanisms of material-energy exchange, the methods for efficient NGHs dissociation, and the boundary conditions for the formation of secondary hydrates in the large-scale, long-term gas production.©2022 China Geology Editorial Office.     

Dominant grains network and behavior of sand–silt mixtures: stress–strain modeling

Stress–strain modeling of sand–silt mixtures is important in the analysis and design of earth structures. In this paper, we develop a stress–strain model that can predict the behavior of sand–silt mixtures with any amount of fines content. This model is based on a micromechanics approach, which involves mean‐field assumptions. For the mixtures with low amount of fines, the mechanical behavior is dominated by sand grains network. On the other hand, for the mixtures with high amount of fines, the mechanical behavior is dominated by silt grains network. Using this concept of dominant grains network, the behavior of mixtures with any amount of fines can be predicted from knowing the behavior of sand and silt, alone. We also modeled the critical state friction angle, critical state void ratio, and elastic stiffness for the mixtures as a function of fines content. The applicability of this developed stress–strain model is shown by comparing the simulated and measured results for two different types of sand–silt mixtures with full range of fines content. Copyright © 2012 John Wiley & Sons, Ltd.     

宁波港北仑港区深水资源及港口建设

宁波北仑地区海域水文泥沙条件为：深水贴岸、港域受控于落潮流且掩护条件好、近岸水体含沙量高;港口建设中,码头走向应与主流向一致,码头与岸应以透空栈桥相连接。     

金沙江中游云南龙街粉砂层沉积环境演化特征

沿金沙江攀枝花三堆子至武定县白马口段河谷两岸分布一套以灰黑色、灰黄色、灰白色粉砂、粘土质粉砂和粘土为主的湖相地层,尤以云南省元谋县龙街盆地内最为发育,被称为龙街粉砂层。通过龙街YA钻孔和龙街、白泥湾剖面的磁性地层学和光释光年代学的研究,探讨龙街粉砂层的时代与归属。龙街YA钻孔地层厚度101.18m,其中龙街粉砂层厚92.96m,上覆7.5m的红棕色细砂和砂砾石层,下伏厚度大于0.72m的灰绿色含角砾粗砂。综合分析YA钻孔的磁性地层学和光释光年龄,认为获取龙街粉砂层的沉积时代为150~30ka BP,属于晚更新世。通过地层沉积特征变化,反演晚更新世以来湖泊的形成及沉积环境变化,探讨晚更新世以来区域新构造的活动阶段及其对河流演化过程的控制作用。     

MICROFABRIC EVIDENCE FOR PODZOLIC SOIL INVERSION BY SOLIFLUCTION PROCESSES

The inverted stratigraphy of a turf-banked solifluction lobe formed in a podzol in northern Norway is presented. Additional evidence for soil inversion takes the form of an inverted micromorphological profile. Encircling silt cappings, and related microstructures, are described from thin sections. This microstructure is created by grain rotation during the spring thaw of sediment when excess pore water pressures promote viscous flow. Melting ice lenses release silt which is then trapped on all sides of detrital grains. The presence of these microstructures in the near-surface and base of the solifluction lobe, but not at mid-depths, supports the notion of an inverted stratigraphy.     

基于GIS/GPS的淤地坝泥沙淤积速率的评价方法探讨——以内蒙南部砒砂岩区淤地坝为例

淤地坝是黄河中游地区治理水土流失的主要措施之一.本文通过利用高精度测量的全球定位系统(GPS)动态测量技术和MAPGIS的分析功能,结合淤地坝内泥沙颗粒的沉积旋回和沉积物的分析,对内蒙南部砒砂岩分布区内一淤地坝内的泥沙淤积速率进行了定量评价,计算结果表明该淤地坝的年平均泥沙淤积总量是41651.419 t/a,年平均淤积速率是10371 t/a·km2.     

海底淤泥层对海洋工程地震作用环境的影响问题

本提出了海底淤泥的流变性质对海洋工程的地震 作用环境的影响问题,并进行了有关的讨论。     

不良地质环境中基坑边坡加固技术分析及其应用

结合现有边坡加固理论和加固经验,对一紧临道路和8层老楼房且下部有厚度达14 m淤泥软弱土层的基坑边坡进行了复合加固设计。通过对边坡稳定性计算、分析,加固后的边坡满足最小安全系数的要求。按照本设计进行施工后,基坑边坡的变形和周围建筑物的沉降均在安全允许的范围之内,保证了地下室结构部分的顺利施工。所提供的加固技术对同类深基坑支护工程具有重要的参考价值。     

黄河三角洲粉质土硬壳层特征及成因研究

在黄河三角洲选择硬壳层发育的典型研究区,用人工振动模拟波浪荷载,通过孔隙水压力的监测和强度的原位测试研究了1 m范围内粉土硬壳层的重复液化和强度变化规律。结果表明,硬壳层动态响应沿深度存在较大差异,经过重复液化后强度总体是升高的,上层土体强度提高相对显著。采集荷载施加前后的原状样品进行SEM图像定量分析,得到了微结构的变化规律,如不均匀系数变小,粒度分维值升高,孔隙比显著减小,定向性增强等,但各项指标的变化程度不同,沿深度存在着显著的差异,主要变化集中在上部土层。讨论了硬壳层的动态响应特征与微结构调整的对应耦合关系,初步了解了循环荷载作用下粉土硬壳层的特征及成因的微结构控制规律。