Micromechanical modeling for rate‐dependent behavior of salt rock under cyclic loading     

Xianda Shen  Jihui Ding  Chlo Arson  Judith S. Chester  Frederick M. Chester 《国际地质力学数值与分析法杂志》2021,45(1):28-44

The dependence of rock behavior on the deformation rate is still not well understood. In salt rock, the fundamental mechanisms that drive the accumulation of irreversible deformation, the reduction of stiffness, and the development of hysteresis during cyclic loading are usually attributed to intracrystalline plasticity and diffusion. We hypothesize that at low pressure and low temperature, the rate‐dependent behavior of salt rock is governed by water‐assisted diffusion along grain boundaries. Accordingly, a chemo‐mechanical homogenization framework is proposed in which the representative elementary volume (REV) is viewed as a homogeneous polycrystalline matrix that contains sliding grain‐boundary cracks. The slip is related to the mass of salt ions that diffuse along the crack surface. The relationship between fluid inclusion‐scale and REV‐scale stresses and strains is established by using the Mori–Tanaka homogenization scheme. It is noted from the model that a lower strain rate and a larger number of sliding cracks enhance stiffness reduction and hysteresis. Thinner sliding cracks (i.e., thinner brine films) promote stiffness reduction and accelerate stress redistributions. The larger the volume fraction of the crack inclusions, the larger the REV deformation and the larger the hysteresis. Results presented in this study shed light on the mechanical behavior of salt rock that is pertinent to the design of geological storage facilities that undergo cyclic unloading, which could help optimize the energy production cycle with low carbon emissions.  相似文献   

利用扁铲侧胀试验确定粗粒砂土的超固结比     

胡永波 《地质与勘探》2020,56(4):862-869

本文利用扁铲侧胀试验对超固结砂土的土力学参数进行测试,目的是获取砂土的超固结比OCR和静止土压力系数k_0。经过一系列室内试验箱砂土物理模型试验的精确测试,分别得到在加载和卸载阶段的P_0压力值和P_1压力值,并换算成各项扁铲侧胀试验指标。试验结果表明,在扁铲侧胀试验指标中,侧胀水平应力指数K_D更能反映粗颗粒砂土的超固结比,因此,可用相对密实度D_r和侧胀水平应力指数K_D建立超固结比OCR的表达式;由于K_D/k_0和E_D/σ'_m之间有共同的因子,即状态参数ψ,因此可建立两者的关系式来计算静止土压力系数k_0。  相似文献   

全金属螺杆钻具研究现状与关键技术          下载免费PDF全文

刘璐  王瑜  王镇全  路家兴  张凯  刘宝林 《探矿工程》2020,47(4):24-30

螺杆钻具作为一种容积式动力钻具，具有良好的输出硬特性，是当前应用最广泛的井下动力钻具之一。螺杆钻具的耐温性是其研究的热点所在，可扩大其应用范围和延长工作寿命，在深部高温钻探领域，具有良好的发展前景。本文在阐明螺杆钻具的基本原理和特性基础上，调研分析了常规螺杆钻具的发展现状，重点调研分析了美国全金属螺杆钻具的研发现状与国内全金属螺杆钻具的发展，提出了全金属螺杆钻具的关键技术，为国内开展这项前沿钻具技术的研发提供参考。  相似文献   

Porosity in chalk – roles of elastic strain and plastic strain     

Ida Lykke Fabricius 《Sedimentology》2020,67(7):3451-3470

Chalks originate as Cretaceous to Recent pelagic or hemipelagic calcareous ooze, which indurate via burial diagenesis to chalk and limestone. Because they accumulate in pelagic settings with high environmental continuity, chalks may form thick formations and even groups. For this reason, and because chalks have a simple mineralogy (low magnesium calcite, silica and clays), they are ideal for the study of diagenetic processes including the depth-related decrease of porosity. It is the aim of this study to illustrate how the evaluation of in situ elastic strain can help in understanding these processes including the interplay between stress-controlled diagenetic processes and processes furthered by thermal energy. Petrophysical core and well data can be used for analyses of how porosity reduction via pore collapse and pressure dissolution is related to in situ elastic strain. The data in question are: depth, density of overburden, pore pressure, ultrasonic P-wave velocity and dry density/porosity. The analysis reveals that the transition from ooze to chalk is associated with high elastic strain and consequent pressure dissolution at calcite–particle contacts causing contact cementation. The transition from chalk to limestone is also associated with high elastic strain, especially at clay–calcite interphases causing development of stylolites via pressure dissolution, and consequent pore-filling cementation. Following each transformation the elastic strain drops rapidly. The observation of this diagenesis-related pattern in elastic strain of the sedimentary rock is novel and should not only be helpful in understanding the porosity development in sedimentary basins, but also add basic scientific insight.  相似文献   

基于主应力迹线分层的挡墙被动土压力分析方法     

张慧姐  曹文贵  刘涛 《岩土力学》2020,41(9):3022-3030

为了探讨墙背倾斜与粗糙程度对挡墙被动土压力的影响，首先，结合被动状态下受挡墙墙背和滑动面摩擦影响的滑动土楔内主应力传递特点，采用圆弧形主应力迹线描述滑动土楔中最大主应力传递规律，并提出了最大主应力迹线几何参数的确定方法；然后，采用沿最大主应力迹线的分层方法将挡墙后滑动土楔划分为若干圆弧形曲线薄层单元，并通过该薄层单元受力分析，依据其静力平衡条件建立了挡墙被动土压力分析新方法。该方法不仅可反映墙土摩擦和墙背倾斜程度对被动土压力的影响，而且有效避免了目前土压力分析方法研究中普遍采用的直线薄层单元难以准确考虑复杂的单元实际受力情况的问题，从理论上确保了新提出的挡墙被动土压力分析方法更具合理性；最后，通过试验、现有同类方法及所提方法分析曲线的对比，表明了新方法的合理性与优越性。就墙背倾斜与粗糙程度对挡墙被动土压力分布及合力作用点高度的影响规律也进行了探讨。  相似文献   

A solution to estimate the total and effective stresses in backfilled stopes with an impervious base during the filling operation of cohesionless backfill     

Jian Zheng  Li Li  Yu-Chao Li 《国际地质力学数值与分析法杂志》2020,44(11):1570-1586

Mining backfill is commonly used in underground mines. A critical concern of this practice is to evaluate the pressures and total stresses in backfilled stopes to ensure a safe and economic design of barricades, constructed to retain the backfill. When a slurried backfill is placed in a mine stope, excess pore water pressure (PWP) can instantaneously generate and progressively dissipate. The dissipation of the excess PWP and consolidation lead to the development of effective stresses, which in turn lead to an arching effect in the backfilled stope. Until now, arching effect has been largely considered for stress estimation in dry or submerged backfill. The former corresponds to the final state at the end process of the drainage and consolidation of the backfill with a pervious while the latter with an impervious barricade. However, previous studies have shown that the most critical moment for the stability of barricades is during the stope filling. Therefore, the design of barricades requires a proper estimation of the pressure and total stresses during the filling operation. This in turn needs joint consideration of the arching effect and consolidation of the backfill. In this paper, a new solution is developed to evaluate the pressures and stresses in backfilled stopes during the filling operation of cohesionless backfill by considering the self-weight consolidation and arching effect. The proposed solution is validated by numerical modeling with Plaxis2D. It can thus be used to evaluate the pressures and stresses in backfilled stopes during the stope filling with an impervious barricade.  相似文献   

Radial Permeability Measurements for Shale Using Variable Pressure Gradients     

FAN Kunkun  SUN Renyuan  Derek ELSWORTH  DONG Mingzhe  LI Yajun  YIN Congbin  LI Yanchao  CHEN Zhongwei  WANG Chunguang 《《地质学报》英文版》2020,94(2):269-279

Shale gas is becoming an important component of the global energy supply, with permeability a critical controlling factor for long-term gas production. Obvious deviation may exist between helium permeability determined using small pressure gradient(SPG) methods and methane permeability obtained under actual field production with variable pressure gradients(VPG). In order to more accurately evaluate the matrix permeability of shale, a VPG method using real gas(rather than He) is established to render permeability measurements that are more representative of reservoir conditions and hence response. Dynamic methane production experiments were performed to measure permeability using the annular space in the shale cores. For each production stage, boundary pressure is maintained at a constant and the gas production with time is measured on the basis of volume change history in the measuring pump. A mathematical model explicitly accommodating gas desorption uses pseudo-pressure and pseudo-time to accommodate the effects of variations in pressuredependent PVT parameters. Analytical and semi-analytical solutions to the model are obtained and discussed. These provide a convenient approach to estimate radial permeability in the core by nonlinear fitting to match the semi-analytical solution with the recorded gas production data. Results indicate that the radial permeability of the shale determined using methane is in the range of 1×10-6– 1×10-5 mD and decreases with a decrease in average pore pressure. This is contrary to the observed change in permeability estimated using helium. Bedding geometry has a significant influence on shale permeability with permeability in parallel bedding orientation larger than that in perpendicular bedding orientation. The superiority of the VPG method is confirmed by comparing permeability test results obtained from both VPG and SPG methods. Although several assumptions are used, the results obtained from the VPG method with reservoir gas are much closer to reality and may be directly used for actual gas production evaluation and prediction, through accommodating realistic pressure dependent impacts.  相似文献   

A theory of loosening earth pressure above a shallow tunnel in unsaturated ground     

Xu Fang  Mamoru Kikumoto  Ying Cui 《国际地质力学数值与分析法杂志》2020,44(10):1495-1508

A theory is proposed to evaluate the loosening earth pressure (vertical earth pressure after excavation) acting on a shallow tunnel in unsaturated ground with an arbitrary groundwater level. The theory is developed based on the limit equilibrium theory, combining soil–water characteristic curves, Mohr–Coulomb failure criteria, and effective stress for unsaturated soils. The proposed theory is applied to predict the vertical distribution of loosening earth pressure in unsaturated ground, which shows a significant difference from that in saturated ground. In unsaturated ground, suction contributes to the increase in effective loosening earth pressure and shear resistance. The remarkable effects of groundwater depth, soil type, and scale of overburden height and trapdoor width on loosening earth pressure are also revealed. Based on the soil–water characteristic curve, the degree of saturation decreases, which causes wet density to decrease and the total and effective loosening earth pressures to have contrary tendencies. Moreover, effective loosening earth pressures vary with soil type as the degree of saturation varies. The total loosening earth pressures are, however, very similar regardless of soil type, because wet density and shear resistance have similar tendencies. The proposed theory provides a valid model for loosening earth pressure in unsaturated ground that will be useful for shallow tunnel excavations.  相似文献   

流量对水力压裂破裂压力和增压率的影响研究     

邵长跃  潘鹏志  赵德才  姚天波  苗书婷  郁培阳 《岩土力学》2020,41(7):2411-2421

水力压裂现场原位测试试验的破裂压力是计算构造地应力的重要参数。为了探究流量对水力压裂破裂压力和增压率的影响，设计4种不同恒定流量情况的低渗透硬脆灰岩室内大型水力压裂试验，结合声发射监测技术分析不同流量下水力裂缝破裂压力、破坏模式和缝网复杂程度的规律以及流量与增压率的内在关系。试验结果表明：流量越大，破裂压力越高，缝网复杂程度越低；典型压力?时间曲线分为缓慢增压段、急速增压段、稳定增压段和突然下降段；稳定增压段增压率保持不变，压力随时间线性增长，其增压率的大小和流量存在明显的线性关系；基于流量与稳定增压段增压率的线性关系，考虑流量因素的Ito理论可以很好地定量解释流量对破裂压力的影响，试验结果与理论预测吻合度较高。  相似文献   

小口径涡轮钻具减速器非对称齿轮弯曲强度分析          下载免费PDF全文

张翔  周琴  张蔚  张凯 《探矿工程》2020,47(4):80-86

小口径涡轮钻具减速器是小井眼深井钻探钻具的重要部件，具有体积小、承载大的特点。采用非对称齿轮代替传统齿轮是提高减速器承载能力的有效手段。非对称齿轮两侧的齿根圆角半径和压力角是区别于对称齿轮的关键参数，通过改变齿轮的齿形结构进而影响了齿轮的齿根弯曲强度。为了进一步研究齿根圆角半径和工作侧压力角对齿根弯曲应力的影响规律，以φ127 mm涡轮钻具减速器中太阳轮为研究对象，建立非对称齿轮的受力模型，基于平截面法得到非对称齿轮齿根弯曲应力的理论计算公式，并通过有限元法对对称齿轮和非对称齿轮进行对比分析，仿真结果表明：增大齿根圆角半径能增大齿轮齿根过渡曲线的曲率半径，从而改善齿根处的应力集中；工作侧压力角的增大能有效降低齿根弯曲应力，但压力角超过一定值时，齿根弯曲应力逐渐趋于稳定。理论分析和仿真结果基本吻合，研究结果可以为优化减速器非对称齿轮的主要参数提供依据和参考。  相似文献