Numerical simulation of mechanical compaction of deepwater shallow sediments     

Jin Sun  Shiguo Wu  Jingen Deng  Hai Lin  Hanyu Zhang  Jiliang Wang  Jinwei Gao 《中国海洋大学学报(英文版)》2018,17(1):53-64

To study the compaction law and overpressure evolution in deepwater shallow sediments, a large-strain compaction model that considers material nonlinearity and moving boundary is formulated. The model considers the dependence of permeability and material properties on void ratio. The modified Cam-Clay model is selected as the constitutive relations of the sediments, and the deactivation/reactivation method is used to capture the moving top surface during the deposition process. A one-dimensional model is used to study the compaction law of the shallow sediments. Results show that the settlement of the shallow sediments is large under their own weight during compaction. The void ratio decreases strictly with burial depth and decreases more quickly near the seafloor than in the deeper layers. The generation of abnormal pressure in the shallow flow sands is closely related to the compaction law of shallow sediments. The two main factors that affect the generation of overpressure in the sands are deposition rate and permeability of overlying clay sediments. Overpressure increases with an increase in deposition rate and a decrease in the permeability of the overlying clay sediment. Moreover, an upper limit for the overpressure exists. A two-dimensional model is used to study the differential compaction of the shallow sediments. The pore pressure will still increase due to the inflow of the pore fluid from the neighboring clay sediment even though the deposition process is interrupted.  相似文献   

A calculation method for the embedded depth of stabilizing piles in reinforced slopes     

Yuping Yan  Shiguo Xiao 《国际地质力学数值与分析法杂志》2020,44(7):1077-1092

Embedded stabilizing piles are a significant optimization measure for traditional piles used to reinforce slopes or landslides. The determination of the embedded depth of the pile top is essential for engineering design. On the basis of the potential overtop-sliding failure mechanism for a piled slope, the corresponding overall slip surface is assumed to consist of the upper part from the original slip surface of the landslide, and the lower part occurs in the local slide mass upslope of the piles. The imbalanced thrust force method is used to determine the thrust force of the upper slide mass, and a variational calculus method within the framework of limit equilibrium for the lower slide mass is provided to calculate its limit resistance. According to the equilibrium relationship between the thrust force and the limit resistance under a design factor of safety of the piled slope, a closed-form solution to the piled-slope stability is specifically derived. It can quantitatively exhibit the influences of some important factors, including the embedded depth on the factor of safety and the corresponding slip surface of the slope. The analysis results of some practical examples show that the factor of safety decreases nonlinearly as the embedded depth increases. The proposed method can be applied in practical engineering.  相似文献   

Pre-drilling prediction techniques on the high-temperature high-pressure hydrocarbon reservoirs offshore Hainan Island,China     

Hanyu Zhang  Huaishan Liu  Shiguo Wu  Jin Sun  Chaoqun Yang  Yangbing Xie  Chuanxu Chen  Jinwei Gao  Jiliang Wang 《中国海洋大学学报(英文版)》2018,17(1):72-82

Decreasing the risks and geohazards associated with drilling engineering in high-temperature high-pressure (HTHP) geologic settings begins with the implementation of pre-drilling prediction techniques (PPTs). To improve the accuracy of geopressure prediction in HTHP hydrocarbon reservoirs offshore Hainan Island, we made a comprehensive summary of current PPTs to identify existing problems and challenges by analyzing the global distribution of HTHP hydrocarbon reservoirs, the research status of PPTs, and the geologic setting and its HTHP formation mechanism. Our research results indicate that the HTHP formation mechanism in the study area is caused by multiple factors, including rapid loading, diapir intrusions, hydrocarbon generation, and the thermal expansion of pore fluids. Due to this multi-factor interaction, a cloud of HTHP hydrocarbon reservoirs has developed in the Ying-Qiong Basin, but only traditional PPTs have been implemented, based on the assumption of conditions that do not conform to the actual geologic environment, e.g., Bellotti’s law and Eaton’s law. In this paper, we focus on these issues, identify some challenges and solutions, and call for further PPT research to address the drawbacks of previous works and meet the challenges associated with the deepwater technology gap. In this way, we hope to contribute to the improved accuracy of geopressure prediction prior to drilling and provide support for future HTHP drilling offshore Hainan Island.  相似文献   

圆形深基坑排桩框架支护结构算法   总被引：2，自引：0，他引：2  

张家国  肖世国 《冰川冻土》2016,38(4):915-921

圆形深基坑工程在我国西南地区渐有出现,在其中的以砂卵石地层为主的地区深基坑支护结构型式多为排桩结合多道圈梁构成的排桩框架结构,但实践中一直没有合适的结构计算方法.针对工程实际的迫切需要,基于结构力学分析方法,提出了确定圆形深基坑排桩框架结构内力和变形的理论计算方法,即按多跨连续梁和弹性地基梁模型分段分析围护桩内力与变形,并考虑桩梁变形协调分析圈梁内力及变形,推导出了围护桩和圈梁的内力及变形理论计算公式.开展了模型试验研究,结果表明,桩顶侧向位移理论值与试验值分布规律整体上具有相似性,说明了理论计算方法具有一定的合理性.最后,给出了一具体实际工程的排桩和圈梁的内力及位移分析结果.  相似文献   

Accuracy of the staggered-grid finite-difference method of the acoustic wave equation for marine seismic reflection modeling     

钱进  吴时国  崔若飞 《中国海洋湖沼学报》2013,31(1):169-177

Seismic wave modeling is a cornerstone of geophysical data acquisition, processing, and interpretation, for which finite-difference methods are often applied. In this paper, we extend the velocity-pressure formulation of the acoustic wave equation to marine seismic modeling using the staggered-grid finite-difference method. The scheme is developed using a fourth-order spatial and a second-order temporal operator. Then, we define a stability coefficient (SC) and calculate its maximum value under the stability condition. Based on the dispersion relationship, we conduct a detailed dispersion analysis for submarine sediments in terms of the phase and group velocity over a range of angles, stability coefficients, and orders. We also compare the numerical solution with the exact solution for a P-wave line source in a homogeneous submarine model. Additionally, the numerical results determined by a Marmousi2 model with a rugged seafloor indicate that this method is sufficient for modeling complex submarine structures.  相似文献   

Focused fluid flow in the Baiyun Sag, northern South China Sea: implications for the source of gas in hydrate reservoirs   总被引：1，自引：0，他引：1  

陈端新  吴时国  董冬冬  米立军  付少英  施和生 《中国海洋湖沼学报》2013,31(1):178-189

The origin and migration of natural gas and the accumulation of gas hydrates within the Pearl River Mouth Basin of the northern South China Sea are poorly understood. Based on high-resolution 2D/3D seismic data, three environments of focused fluid flow: gas chimneys, mud diapirs and active faults have been identified. Widespread gas chimneys that act as important conduits for fluid flow are located below bottom simulating reflections and above basal uplifts. The occurrence and evolution of gas chimneys can be divided into a violent eruptive stage and a quiet seepage stage. For most gas chimneys, the strong eruptions are deduced to have happened during the Dongsha Movement in the latest Miocene, which are observed below Pliocene strata and few active faults develop above the top of the Miocene. The formation pressures of the Baiyun Sag currently are considered to be normal, based on these terms: 1) Borehole pressure tests with pressure coefficients of 1.043–1.047; 2) The distribution of gas chimneys is limited to strata older than the Pliocene; 3) Disseminated methane hydrates, rather than fractured hydrates, are found in the hydrate samples; 4) The gas hydrate is mainly charged with biogenic gas rather than thermogenic gas based on the chemical tests from gas hydrates cores. However, periods of quiet focused fluid flow also enable the establishment of good conduits for the migration of abundant biogenic gas and lesser volumes of thermogenic gas. A geological model governing fluid flow has been proposed to interpret the release of overpressure, the migration of fluids and the formation of gas hydrates, in an integrated manner. This model suggests that gas chimneys positioned above basal uplifts were caused by the Dongsha Movement at about 5.5 Ma. Biogenic gas occupies the strata above the base of the middle Miocene and migrates slowly into the gas chimney columns. Some of the biogenic gas and small volumes of thermogenic gas eventually contribute to the formation of the gas hydrates.  相似文献   

南极普里兹湾全新世的冰海沉积          下载免费PDF全文

吴时国  罗又郎  王有强  陆钧  郑范  孙绍先 《极地研究》1998,10(1):50-57

ＮＰ９３－２柱样采自南极普里兹湾陆架区域,具有明显的冰海沉积作用特征,受冰川和海洋共同作用。粒度参数、矿物组成、微体古生物和地球化学等资料揭示了该区１２９３７ａ以来的沉积作用特征和沉积环境与气候变动的信息。大约在１０ｋａ,气候波动突然明显回暖,冰筏源碎屑物质增加,晚期还有一个短暂气候波动。  相似文献   

西沙海域中新世碳酸盐台地的时空分布及其油气成藏模式   总被引：1，自引：0，他引：1  

杨振  张光学  张莉  吴时国  祝幼华  强昆生  鄢伟 《地质学报》2017,91(6):1360-1373

本文基于南海北部西沙海域地震数据及钻井资料,结合碳酸盐台地的边缘特征及其地震反射特征,首次建立了研究区中新世碳酸盐台地边界的三个识别标志:岩性突变界面、断层界面和潮汐水道。在对地震数据系统的解释和钻井资料分析基础之上,厘定了该区生物礁及碳酸盐台地的时空分布,总结其分布规律,西沙海域中新世碳酸盐台地可以分为六期,进一步划分三个演化阶段,分别为中中新世早期的繁盛阶段、中中新世晚期的衰退阶段、晚中新世以来的淹没阶段,各阶段碳酸盐台地的沉积相带发育完整,其中生物礁主要分布台地的西-西南缘。统计结果显示,生物礁及碳酸盐台地全面发育时期的面积达到了80000km~2,后期随着台地的衰退而规模有所减小。西沙海域中新世碳酸盐岩分布广泛、规模巨大,而且在发育过程中经历了多期暴露而遭受淋滤,进一步增大了其孔隙度,具备形成优质储层的前提。结合区域油气地质条件分析与探讨,建立生物礁及碳酸盐台地的成藏模式,提出西沙海域碳酸盐台地具有典型"下生上储上盖"的成藏过程,指出西沙海域邻近华光凹陷和中建南盆地北部的碳酸盐台地是油气勘探的两大有利区带。  相似文献   

Major factors influencing boron adsorption in sediments—a case study of modern sediments in Qinghai Lake     

Changyong Wang  Shiguo Lin  Yaqiong Wei  Yi Zhou  Hailiang Chang  Jiang Liu 《Environmental Earth Sciences》2017,76(4):181

Because the boron (B) concentration in water has an apparent positive correlation with salinity, the B content adsorbed in sediments is often regarded as an important indicator to reconstruct the water salinity in a sedimentary environment. The premise of the quantitative reconstruction of paleosalinity is that the B uptake in sediments is proportional to the B concentration in water; however, the study showed that there is no direct relationship. The B absorption in sediments can be affected by both the content of the clay minerals and the total organic carbon content. The data from testing modern sediments and water samples in the Qinghai Lake show that a higher content in clay minerals is beneficial for B adsorption. Furthermore, the organic carbon from halophiles has a strong effect on the enrichment of B. Therefore, the organic carbon content in sediments should be considered when the paleosalinity of water is reconstructed using its B content. It is also thought that the Adams and Couch formulas are not suitable for reconstructing the salinity of water with a high organic carbon content in sediments because they consider only the effect of clay minerals on the adsorbed B without the contribution of organic carbon.  相似文献   

南海西北次海盆构造演化的沉积响应     

钱星  张莉  吴时国  易海  林珍  杨振 《大地构造与成矿学》2017,41(2)

通过对南海西北次海盆新获得的地震资料进行综合解释和层序地层分析,揭示了海盆中的沉积对构造演化阶段的响应。始新世-早渐新世陆缘裂陷期,盆地以对称裂谷形式,发育地堑裂谷层序,沉积以近物源为特征,相变大,发育了冲积扇-扇三角洲-湖相沉积,沉积体系的配置受同沉积断裂控制明显,快速沉降和充分的物源供给决定了沉积体系的构成特征。晚渐新世海底扩张期,岩石圈破裂,陆缘进一步拉开并开始海底扩张,出现海相沉积,来自陆坡的陆架边缘三角洲越过陆坡进入海盆,在海盆内沉积了一套向海盆中部逐渐减薄的楔状地层,并伴有大量的火山碎屑沉积物。早-中新世以来热沉降期,随着构造沉降增大,相对海平面总体不断上升,进入深水盆地,形成陆架陆坡体系,大量的碎屑物质以重力流、深水底流等深水作用方式进入海盆;沉降晚期陆架-陆坡物源供应减弱,琼东南中央峡谷成为其主要的物质供应来源通道,在此期间二次海平面下降、回升的综合作用下,海盆内发育了多期以下切水道为特征的低水位域沉积体系。  相似文献