三沙永乐蓝洞成因机制初探*     

高金尉  付腾飞  赵明辉  张汉羽  田丽艳 《热带海洋学报》2022,41(1):171-183

海洋蓝洞保留了原始的水体、沉积物、化石残骸和完整的生物骨骼, 是重要的自然遗产和地质奇观, 具有重要的科学研究价值。三沙永乐蓝洞是目前全球已发现的最深海洋蓝洞, 有着独特的洞体结构和水体化学特征, 但其成因仍是未解之谜。本文结合南海的构造演化, 分析了永乐环礁碳酸盐岩台地的发育历史, 认为永乐环礁的形成以加积和退积为主, 其台地边缘属于陡崖型台地斜坡, 有利于发育断层/裂缝; 永乐环礁之上钻井岩心的氧同位素数据表明, 永乐环礁在14.75~168.60m的深度范围内发生了地下水溶蚀作用, 这与实际观测到的158m深洞体转折处之上发生的洞穴垮塌作用相符。通过综合对比分析认为, 三沙永乐蓝洞的形成是断层/裂缝溶蚀机制与深部洞穴垮塌机制综合作用的结果。地下水(淡水、海水)首先沿着台地边缘发育的断层/裂缝进行溶蚀, 在158m以上通过洞穴垮塌作用形成了近垂直的洞穴, 而在158m以下则沿着断层/裂缝继续向下溶蚀形成了略倾斜的深部洞穴结构, 最终由于海平面的上升淹没而形成了蓝洞。本研究可为未来寻找更多海洋蓝洞提供重要的经验与借鉴。  相似文献   

地震资料中的多尺度断裂与流体响应特征：数值模拟分析          下载免费PDF全文

郭桂红  张智  金抒辛  石双虎  程建武  闫建萍 《地球物理学报》2013,56(6):2002-2011

流体在断裂和岩石骨架间的交换被认为是影响岩石弹性参数各向异性的主要原因,理论研究表明断裂尺度同样对弹性参数的各向异性也有影响.为了说明两者对各向异性影响以实现多尺度断裂裂隙的识别,本文在等效介质模型的基础上,应用数值分析的方法研究速度和衰减(1/Q)随多尺度断裂、频率和流体因子变化规律.结果表明介质弹性参数是频率依赖的,并且参数中存在衰减项,而这种频率依赖性与介质物性参数中的断裂尺度及流体性质存在一定的联系;当断裂定向分布时,参数结果显示为各向异性;不同断裂尺度具有不同的波速频散特性,剪切波分裂程度依赖于频率,断裂尺度起着控制作用,高频时对小尺度的敏感,低频段对大尺度敏感.在地震频段Thomsen参数随着频率的增大而减小,随着断裂尺寸的增大而减小.因此地震数据可能区分断裂和微裂隙引起各向异性,从而可测量断裂尺度.  相似文献   

淄博矿震震源机制探讨     

山长仑  李霞  范培乐  于澄  李亚军 《地震地磁观测与研究》2013,34(3)

依据由分布密集测震台网记录而得到的地震波场介质力学参数分布特征、所在矿区地质构造与采煤概况,对淄博矿震发生成因及机制进行分析,发现矿震以张性破裂为主兼一定剪切破裂,拉张引起的岩体应变量远大于挤压引起的应变量,并具有一定双侧对称性.在震源发生破裂的过程中,震源周围变形的岩体应有一定回弹.  相似文献   

东北地区M≥5.0地震前中等地震集中活动的震兆研究     

曹凤娟  焦明若  王亮  王岩  李彤霞 《地震工程学报》2013,35(2):385-393

定义了描述东北地区中等地震活动增强的3个参量E、T和R,并对东北地区11次M≥5.0地震进行了统计分析.结果显示,东北地区地震活动具有明显的区域性特点:辽宁地区和嫩江断裂以西地区M≥5.0地震前均存在4级地震集中活动的现象,且预期的5级以上地震大部分发生在最近1次4级地震后的半年内;嫩江断裂以东地区5级地震前没有中等地震集中活动的特征.ETR方法在中等地震活跃后判定未来5级地震的震中时具有一定的指示意义.  相似文献   

波浪作用下海上溢油潜浮于水的机理研究进展     

付红蕊  赵兴  玛莎  严志宇 《海洋科学》2019,43(2):91-96

从单油滴角度对波浪作用下漂浮溢油的入水过程(夹带、油滴的形成),演变过程(油滴的变形、破碎和聚并)和上浮过程的研究现状进行综述,介绍了溢油及相关领域的研究手段和实验方法,总结了海上溢油潜浮于水的行为机理及分布规律,并基于实验室和溢油现场的研究成果提出进一步需要探究的问题,为海上溢油污染的应急决策、追踪预测和损害评估等方面提供思路和借鉴。  相似文献   

Simulating damage evolution and fracture propagation in sandstone containing a preexisting 3-D surface flaw under uniaxial compression     

Sanjib Mondal  Louise Olsen-Kettle  Lutz Gross 《国际地质力学数值与分析法杂志》2019,43(7):1448-1466

Preexisting flaws and rock heterogeneity have important ramifications on the process of rock fracturing and on rock stability in many applications. Therefore, there is great interest in numerical modelling of rock fracture and the underlying mechanisms. We simulated damage evolution and fracture propagation in sandstone specimens containing a preexisting 3-D surface flaw under uniaxial compression. We applied the linear elastic damage model based on the unified strength theory following the rock failure process analysis code. However, in contrast to the rock failure process analysis code, we used the finite element method with tetrahedron elements on unstructured meshes. It provided higher geometrical flexibility and allowed for a more accurate representation of the disk-shaped flaw with various flaw depths, angles, and lengths through locally adapted meshes. The rock heterogeneity was modelled by sampling the initial local Young's modulus from a Weibull distribution over a cubic grid. The values were then interpolated to the computational finite element method mesh. This method introduced an additional length scale for the rock heterogeneity represented by the cell size in the sampling grid. The generation of three typical surface cracking patterns, called wing cracks, anti-wing cracks, and far-field cracks, were identified in the simulation results. These depend on the geometry of the preexisting surface flaw. The simulated fracture propagation, coalescence types, and failure modes for the specimens with preexisting surface flaw show good agreement with recent experimental studies.  相似文献   

Interface and embedded joint methods for modeling dynamic fracture opening by explosive products          下载免费PDF全文

Oleg Y. Vorobiev  Randolph Settgast  Joseph P. Morris 《国际地质力学数值与分析法杂志》2018,42(13):1531-1553

Two computational approaches are proposed in the paper to model dynamic fracture opening by explosive products. The first method assumes that the fractures may be modeled using flow elements embedded along the mesh lines. This method models crack opening in a straightforward way by splitting the nodes of the computational grid. It can account for crack branching; however, the crack directions are constrained by existing mesh faces, which may lead to mesh dependence. Also, the stress in flow elements is calculated explicitly separate from the surrounding solid elements that can impose additional limits on the time step stability condition for explicit integration. The second approach uses embedded flow elements to model the cracks. Typical thickness of the cracks is much smaller than the element size. Therefore, gas pressure in the cracks is assumed to be in stress equilibrium with the element stress. To achieve this, the crack thickness and the state of the gas is updated simultaneously with the state of the solid element which contains the crack. Therefore, the time step is controlled by the explicit solver applied for the solid and does not depend on the thickness of the crack. The main disadvantage of the second approach is due to the complexity of modeling multiple intersecting cracks, which go through the same element. We discuss the areas of possible applications of these 2 methods and the ways to improve and enhance them for future practical applications.  相似文献   

Explicit versus implicit front advancing schemes for the simulation of hydraulic fracture growth     

Haseeb Zia  Brice Lecampion 《国际地质力学数值与分析法杂志》2019,43(6):1300-1315

The proper computation of the time evolution of the fracture front is the main challenge of three-dimensional (3D) hydraulic fracture growth simulation. We discuss explicit and implicit variants of a hydraulic fracture propagation scheme based on a level set representation of the fracture. Such a scheme couples a finite discretization of the governing equations and the near-tip hydraulic fracture asymptotes. We benchmark the accuracy, robustness, and stability of these different front advancing schemes on a number of test cases. Our results indicate a large computational gain of the explicit scheme at the expense of a slightly less accurate solution (few percent less accuracy over few time steps) when crossing heterogeneities. The predictor corrector scheme combines at least an approximately 25% computational gain while retaining the stability and accuracy of the fully implicit version of the scheme in all cases.  相似文献   

The effect of stress boundary conditions on fluid-driven fracture propagation in porous media using a phase-field modeling approach     

Sogo Shiozawa  Sanghyun Lee  Mary F. Wheeler 《国际地质力学数值与分析法杂志》2019,43(6):1316-1340

A phase-field approach for fluid-driven fracture propagation in porous media with varying constant compatible stress boundary conditions is discussed and implemented. Since crack opening displacement, fracture path, and stress values near the fracture are highly dependent on the given boundary conditions, it is crucial to take into account the impact of in situ stresses on fracturing propagation for realistic applications. We illustrate several numerical examples that include the effects of different boundary conditions on the fracture propagation. In addition, an example using realistic boundary conditions from a reservoir simulator is included to show the capabilities of our computational framework.  相似文献   

Discrete fracture model for simulating waterflooding processes under fracturing conditions          下载免费PDF全文

Emil Gallyamov  Timur Garipov  Denis Voskov  Paul Van den Hoek 《国际地质力学数值与分析法杂志》2018,42(13):1445-1470

In our study, we develop a model for simulating fracturing processes in a poroelastic medium. The proposed approach combines the discrete fracture model enriched with contact plane mechanics. The model captures mechanical interactions of fractures and a deformable medium, fluid, and heat transfer in fractures and in a porous medium. Both effects of poroelasticity and thermoelasticity are accounted in our model. Mass and heat conservation equations are approximated by the finite volume method, and mechanical equilibrium equations are discretized by means of the Galerkin finite element approach. Two‐dimensional grid facets between 3‐dimensional finite elements are considered as possible fracture surfaces. Most of these facets are inactive from the beginning and are activated throughout the simulation. A fracture propagation criterion, based on Irwin's approach, is verified on each nonlinear iteration. When the criterion is satisfied, additional contact elements are added into finite element and discrete fracture model formulations respectively. The proposed approach allows modeling of existing natural and artificially created fractures within one framework. The model is tested on single‐ and multiple‐phase fluid flow examples for both isothermal and thermal conditions and verified against existing semianalytical solutions. The applicability of the approach is demonstrated on an example of practical interests where a sector model of an oil reservoir is simulated with different injection and production regimes.  相似文献