Impact of elliptical boreholes on in situ stress estimation from leak-off test data

We developed an inversion technique to determine in situ stresses for elliptical boreholes of arbitrary trajectory. In this approach, borehole geometry, drilling-induced fracture information, and other available leak-off test data were used to construct a mathematical model, which was in turn applied to finding the inverse of an overdetermined system of equations.The method has been demonstrated by a case study in the Appalachian Basin, USA. The calculated horizontal stresses are in reasonable agreement with the reported regional stress study of the area, although there are no field measurement data of the studied well for direct calibration. The results also indicate that 2% of axis difference in the elliptical borehole geometry can cause a 5% difference in minimum horizontal stress calculation and a 10% difference in maximum horizontal stress calculation.

Research progress and application of deep in-situ condition preserved coring and testing

With the depletion of shallow resources,the exploration of deep earth resources has become a global strategy.The study of the different patterns in the physical mechanical properties of rocks at different occurrence depths is the basis for exploring deep into the earth,with the core and premise being the acquisition and testing of deep in-situ core specimens.Based on the original idea of deep in-situ condition preserved coring(ICP-Coring)and testing,combined with theoretical modeling,numerical analysis,test platform development,indoor testing and engineering application,the principles and technologies of deep ICP-Coring are developed.This principle and technology consists of five parts:in-situ pressurepreserved coring(IPP-Coring),in-situ substance-preserved coring(ISP-Coring),in-situ temperaturepreserved coring(ITP-Coring),in-situ light-preserved coring(ILP-Coring),and in-situ moisturepreserved coring(IMP-Coring).The theory and technology of temperature and pressure reconstruction at different occurrence depths and in different environments are proposed,and prototype trial production was completed by following the principle of displacement and tests based on the in-situ reconstructed environment.The notable advances are as follows:(1)Deep in-situ coring system:A pressure-preserved controller with an ultimate bearing capacity greater than 140 MPa,highperformance(temperature-resistant,pressure-resistant,and low thermally conductive)temperaturepreserved materials,an active temperature control system,and high-barrier quality-preserved membrane materials were developed;a deep ICP-Coring capacity calibration platform was independently developed,a deep in-situ coring technology system was developed,and the acquisition of deep in-situ cores was realized.(2)In-situ storage displacement system:Following the dual-circuit hydraulic design idea,a single-drive source push-pull composite grabbing mechanism was designed;the design of the overall structure for the deep in-situ displacement storage system and ultrahigh pressure cabin structure was completed,which could realize docking the coring device and core displacement in the in-situ reconstructed environment.(3)Test analysis system:A noncontact acoustic-electric-magnetic test system was developed under the in-situ reconstructed environment,and the errors between the test results and traditional contact test results were mostly less than 10%;a detachable deep in-situ core true triaxial test system was developed,which could perform loading tests for deep in-situ cores.The relevant technological achievements were successfully applied to the exploration and development of deep resources,such as deep mines,deep-sea natural gas hydrates,and deep oil and gas.The research results provide technical and equipment support for the construction of a theoretical system for deep in-situ rock mechanics,the development of deep earth resources and energy,and the scientific exploration of different layers and occurrence depths(deep and ultradeep)of the Earth.

Borehole stability in naturally fractured reservoirs luring production tests

基于软弱理论的飞机，为在不同压力国家下面在折断的水库预言地上凿穿稳定性的一个模型是 estiblisted，为解决地上凿穿稳定性的方程被开发。要求在不同自然破裂出现下面维持地上凿穿稳定性的最小的 downhole 压力被在 Tazhong (中央 Tarim ) 从一口井使用数据计算区域， Tarim 盆，西方中国。几个结论从不到 10

Rock borehole shear tests in dam foundation of Xiangjiaba hydropower station

Xiangjiaba hydropower station is one of the cascade power stations on the Jinsha River, China. Due to the complicated geological conditions of its dam foundation, evaluating the rock mass quality and determining the mechanical parameters of rock masses are very important issues. To address these issues, several groups of rock borehole shear tests (RBSTs) were conducted on the black mudstone in the dam foundation of Xiangjiaba hydropower station in the second construction phase. Forty three groups of shear strengths of black mudstone samples were obtained from RBSTs, and the shear strength parameters (c and f ) were calculated using the least squares method. In addition, the limitations and merits of RBST employed in the Xiangjiaba hydropower station were discussed. Test results indicate that the shear strength parameters obtained from RBST have a good correlation with the results from sound wave test in borehole. It is believed that RBST has a good adaptability and applicability in geotechnical engineering.

Research on in-situ condition preserved coring and testing systems

As shallow resources are increasingly depleted,the mechanics'theory and testing technology of deep insitu rock has become urgent.Traditional coring technologies obtain rock samples without retaining the in-situ environmental conditions,leading to distortion of the measured parameters.Herein,a coring and testing systems retaining in-situ geological conditions is presented:the coring system that obtains in-situ rock samples,and the transfer and testing system that stores and analyzes the rocks under a reconstructed environment.The ICP-Coring system mainly consists of the pressure controller,active insulated core reactor and insulation layer and sealing film.The ultimate bearing strength of 100 MPa for pressurepreservation,temperature control accuracy of 0.97%for temperature-retained are realized.CH_(4)and CO permeability of the optimized sealing film are as low as 3.85 and 0.33 ppm/min.The average tensile elongation of the film is 152.4%and the light transmittance is reduced to 0%.Additionally,the pressure and steady-state temperature accuracy for reconstructing the in-situ environment of transfer and storage system up to 1%and±0.2 is achieved.The error recorded of the noncontact sensor ring made of lowdensity polymer is less than 6%than that of the contact test.The system can provide technical support for the deep in-situ rock mechanics research,improving deep resource acquisition capabilities and further clarifying deep-earth processes.

Research of in-situ hydraulic test method by using double packer equipment

Double packer equipment for hydraulic test can be used to measure pressure of test zone directly, and it is frequently used to perform many kinds of hydraulic tests and take groundwater sample from borehole. The test method of this equipment mainly includes the test design, implementation, interpretation and synthetic analysis. By adopting the double packer equipment for hydraulic test, the parameter distribution of rock permeability along borehole can be acquired, as well as the connectivity, water conductivity and water bearing capacity of the disclosed structure and the chemical characteristics of the deep groundwater. It is a necessary method for the research and evaluation of the complex hypotonicity terrace site selection under geological conditions. This method is not only suitable for the geological disposal of high level radioactive waste, but also can be used in the site selection of underground facilities such as storage of petroleum and carbon dioxide. Meanwhile, it has a good application prospect in other hydrogeological investigation fields.

Thermal performance analysis of borehole size effect on geothermal heat exchanger

Thermal performance was the most important factor in the development of borehole heat exchanger utilizing geothermal energy.The thermal performance was affected by many different design parameters,such as configuration type and borehole size of geothermal heat exchanger.These eventually determined the operation and cost efficiency of the geothermal heat exchanger system.The main purpose of this work was to assess the thermal performance of geothermal heat exchanger with variation of borehole sizes and numbers of U-tubes inside a borehole.For this,a thermal response test rig was established with line-source theory.The thermal response test was performed with in-line variable input heat source.Effective thermal conductivity and thermal resistance were obtained from the measured data.From the measurement,the effective thermal conductivity is found to have similar values for twopair type(4 U-tubes)and three-pair type(6 U-tubes)borehole heat exchanger systems indicating similar heat transfer ability.Meanwhile,the thermal resistance shows lower value for the three-pair type compared to the two-pair type.Measured data based resistance have lower value compared to computed result from design programs.Overall comparison finds better thermal performance for the three-pair type,however,fluctuating temperature variation indicates complex flow behavior inside the borehole and requires further study on flow characteristics.

An investigation of machine learning techniques to estimate minimum horizontal stress magnitude from borehole breakout

Borehole breakout is a widely utilised phenomenon in horizontal stress orientation determination,and breakout geometrical parameters,such as width and depth,have been used to estimate both horizontal stress magnitudes.However,the accuracy of minimum horizontal stress estimation from borehole breakout remains relatively low in comparison to maximum horizontal stress estimation.This paper aims to compare and improve the minimum horizontal stress estimation via a number of machine learning(ML)regression techniques,including parametric and non-parametric models,which have rarely been explored.ML models were trained based on 79 laboratory data from published literature and validated against 23 field data.A systematic bias was observed in the prediction for the validation dataset whenever the horizontal stress value exceeded the maximum value in the training data.Nevertheless,the pattern was captured,and the removal of systematic bias showed that the artificial neural network is capable of predicting the minimum horizontal stress with an average error rate of 10.16%and a root mean square error of 3.87 MPa when compared to actual values obtained through conventional in-situ measurement techniques.This is a meaningful improvement considering the importance of in-situ stress knowledge for underground operations and the availability of borehole breakout data.

A Review of the Calculation Formula for the Four-component Borehole Strainmeter and Application to Earthquake Cases

Based on the principle formula for the four-component strainmeters, we can directly obtain the specific plane strain, shear strain and azimuthal angle of the principal strain, and the maximum and minimum principal strains calculated afterwards are the indirect result. The problems of practicality of the sensitivity coefficients A and B of plane strain and shear strain are then discussed. Based on this idea, we analyzed the observation data of several four-component borehole strainmeters near the epicenter of the Yiliang M_S5.7 earthquake in 2012 and the Ludian M_S6.5 earthquake in 2014 in the Zhaotong area, Yunnan Province. The results show that the analysis based on the perspective of plane strain and shear strain has an obviously better effect than that based on the component readings, and can directly peel off the respective abnormality of the plane strain and shear strain. In addition, the correlation coefficient curves between measured data of two plane strains show significant anomalies which often occur several days before and during the earthquake.

Passability test and simulation of sand control string with natural gas hydrates completion in large curvature hole

To meet the requirements of marine natural gas hydrate exploitation,it is necessary to improve the penetration of completion sand control string in the large curvature borehole.In this study,large curvature test wells were selected to carry out the running test of sand control string with pre-packed screen.Meanwhile,the running simulation was performed by using the Landmark software.The results show that the sand control packer and screen can be run smoothly in the wellbore with a dogleg angle of more than 20°/30 m and keep the structure stable.Additionally,the comprehensive friction coefficient is 0.4,under which and the simulation shows that the sand control string for hydrate exploitation can be run smoothly.These findings have important guiding significance for running the completion sand control string in natural gas hydrate exploitation.

Design and feasibility analysis of a new completion monitoring technical scheme for natural gas hydrate production tests

As a prerequisite and a guarantee for safe and efficient natural gas hydrates(NGHs)exploitation,it is imperative to effectively determine the mechanical properties of NGHs reservoirs and clarify the law of the change in the mechanical properties with the dissociation of NGHs during NGHs production tests by depressurization.Based on the development of Japan’s two offshore NGHs production tests in vertical wells,this study innovatively proposed a new subsea communication technology-accurate directional connection using a wet-mate connector.This helps to overcome the technical barrier to the communication between the upper and lower completion of offshore wells.Using this new communication technology,this study explored and designed a mechanical monitoring scheme for lower completion(sand screens).This scheme can be used to monitor the tensile stress and radial compressive stress of sand screens caused by NGHs reservoirs in real time,thus promoting the technical development for the rapid assessment and real-time feedback of the in-situ mechanical response of NGHs reservoirs during offshore NGHs production tests by depressurization.

不同饱和度下膨胀土原位孔内剪切试验及强度响应特征

膨胀土强度随饱和度变化显著,非饱和膨胀土的抗剪强度一直是研究膨胀土工程问题的关键。选取南阳市某高速路沿线边坡膨胀土为研究对象,进行了天然条件下处于不同饱和度状态的膨胀土原位孔内剪切试验,获得了自然条件下膨胀土的抗剪强度随饱和度的变化特征。膨胀土的抗剪强度、黏聚力、内摩擦角随着膨胀土饱和度的增大而逐渐减小。结合现场试验数据和土-水特征曲线,提出了以法向应力、饱和度为变量和以法向应力、基质吸力为变量的两种非饱和膨胀土的抗剪强度计算模型,并结合试验数据对计算模型的适用性进行了验证。与之前常用的非饱和土抗剪强度计算模型相比较,提出的两种计算模型所需的拟合参数少,适用于更宽吸力范围、不同法向应力条件下非饱和膨胀土抗剪强度的计算,且结果更为准确。

In-situ analysis of slip transfer and heterogeneous deformation in tension of Mg-5.4Gd-1.8Y-1.5Zn alloy

Slip transfer is influential in determining damage nucleation of polycrystalline material.The interactions between dislocations and grain boundaries(GBs)was investigated using in-situ tension test in a multi-directionally forged Mg-5.4Gd-1.8Y-1.5Zn(wt%)alloy.It was found that strain accommodation of individual grains by means of slip occurred more easily than slip transfer when several slip systems were operable.The basal-basal slip transfer occurred when the GB misorientation was smaller than 34.2°,whereas basal-pyramidal type took place when the crystallographic misorientation was larger than 48.8°.The product of Luster-Morris m factor and the sum of the Schmid factors of the two correlated slip systems indicated that the threshold for basal-basal slip transfer may exist,however,basal-pyramidal slip transfer shows no such threshold and is more complicated.These results presented here demonstrated that besides the geometrical alignment,the deformation details(such as the number of operable slip systems)and stress state in each individual grain must be considered.

The Mine Geostress Testing Methods and Design

The?mine geostress measurement is the indispensable key to safe and efficient production of the mine. Currently, stress relief method, hydraulic fracturing method and acoustic emission method are widely used in mine geostress test fields. As deficiencies of the above several methods, the author designed a detailed borehole acoustic program for the tectonic fault conditions of a mine in Huainan, and got geostress parameter values according to the combination of site measured velocity values and laboratory tests.

基于孔内多属性测试的地下岩土体工程地质信息评价研究

针对钻探取芯的传统勘察方法探测地下岩土体结构特征信息存在精度低、信息不全面等问题,利用钻孔多属性测试技术,通过分析光学成像和声波波速等钻孔孔内多属性测试数据与地层结构特征信息之间的关系,可获取孔内声波波速和孔内摄像等数据,并得到地下岩土体的工程地质信息。基于钻孔多属性测试技术,研究了地下岩土体精细化分层、结构面定量描述的技术方法,阐述了岩体质量分级、岩土体动弹性力学参数和场地土类型的分析过程,并引入了孔壁岩体质量指标(WRQD)评价岩体完整性,总结归纳了基于钻孔孔内多属性测试的地下岩土体工程地质信息综合分析方法。通过工程应用验证了该方法的合理性、准确性,可为地下岩土体工程地质信息分析提供了一种多手段综合勘探的思路和方法。

岩体原位点触探测试的约束刚度差异性表征及影响分析

为了分析不同约束刚度差异性对岩体点触探特性的影响,通过理论分析和数值分析修正给出以应变状态为标准的约束刚度差异性表征方法,并通过室内试验研究不同约束刚度对岩体点触探测试的影响。研究结果表明:在不同孔径和试样尺寸条件下,点触探压头下方拉伸应变不同,表明各条件下岩体结构的约束刚度存在差异性,原位钻孔条件下触探岩体的约束刚度最大,原位半空间条件下的其次,有限试样条件下触探岩体的约束刚度最小。若有限试样尺寸越大,则触探岩体的约束刚度越大;若原位钻孔孔径越小,则触探岩体的约束刚度越大。不同约束刚度对岩石点触探特性有重要影响。对于不同的约束刚度条件,试样初次破裂之前,其荷载-位移曲线斜率基本保持一致,随着约束刚度提高,试样的初次破裂位移与荷载逐渐提高;初次破裂后,点触探加载刚度弱化逐渐减小,最终试样破坏荷载逐渐增加。基于试验得到的初次破裂荷载比与本文给出的约束刚度比有较好的一致性,因此,通过横向拉伸应变条件定义的约束刚度比能够对刚度影响下的点触探指标进行合理表征。

大采长工作面中部煤层预抽瓦斯以孔代巷技术应用

为解决治理大采长工作面回采区域瓦斯需要施工多条岩石抽采巷和大量穿层钻孔,采用大采长工作面中部煤层预抽瓦斯以孔代巷技术,利用自主研制的轻型定向钻机在己15-17-12110工作面开展了现场工业性试验,分析了定向穿层钻孔覆盖工作面中部的范围及瓦斯抽采效果。结果表明:大采长工作面中部煤层预抽瓦斯以孔代巷技术可以为大采长工作面减少岩石抽采巷和穿层钻孔工程量,节约施工成本;在中抽巷和机抽巷各施工79个定向钻孔,钻孔总工程量13 806 m,其中定向钻孔岩孔8 022.5 m,水力冲孔煤孔5 783.5 m,累计冲煤量2 965.7 t,平均冲煤量0.51 t/m;定向穿层钻孔卸压抽采后,可有效提升瓦斯抽采浓度;工作面回采期间的瓦斯浓度在0.6%以下,保证了工作面安全回采。

偏/同心不耦合非装药段孔壁压力分布规律研究

孔壁压力是分析爆炸载荷在隧道掘进过程中对围岩损伤破坏的重要参数,针对隧道周边孔理论装药结构为同心不耦合装药,而实际装药结构为偏心不耦合装药的问题,采用模型试验方法,研究偏心与同心不耦合装药结构爆炸非装药段的孔壁压力。结果表明:偏心装药非装药段测距在0.2 m内的同截面,上孔壁峰值压力大于下孔壁;超过0.2 m时,炮孔同截面孔壁峰值压力近似相等。测距在0.2 m内时,偏心装药非装药段上孔壁峰值压力较同心装药大,偏心装药下孔壁峰值压力较同心装药小;测距大于0.2 m时,同心装药非装药段孔壁峰值压力均大于偏心装药。偏心装药非装药段上孔壁峰值压力随测距衰减最快,下孔壁次之,同心装药孔壁峰值压力衰减最慢。研究结果可为合理设计装药结构提供参考。

Study on Shear Strength Characteristics of Columnar Jointed Basalt Based on in-situ Direct Shear Test at Baihetan Hydropower Station

Columnar jointed basalt(CJB) widely distributes in the dam site of the Baihetan Hydropower Station.The columnar joint structure and fracture development of CJB have significant influence on the mechanical properties of rock mass,and the mechanical properties of CJB are of great significance to the Baihetan Hydropower Project.Therefore,in-situ direct shear tests were carried out on ten test adit at different locations in the dam site area to study the shear behavior of CJB.In this study,21 sets of in-situ direct shear tests were conducted for rock types of type Ⅱ_(2),type Ⅲ_(1)and type Ⅲ_(2),with horizontal and vertical shear planes and two different specimen sizes of CJB.Shear strength parameters of CJB were obtained by linear fitting of in-situ direct shear test results based on the Mohr-Coulomb strength criterion.The results indicate that the shear strength parameters of CJB with horizontal shear plane increase as the increase of rock type grade.The shear strength parameters of CJB show obvious anisotropy and the friction coefficient of the horizontal shear plane is greater than the vertical shear plane.The friction coefficient in the horizontal direction of the shear plane is 1.27 times that in the vertical direction of the shear plane.With the increase of rock type grade,the difference of friction coefficient becomes larger.However,the cohesion changes little whether the shear plane is horizontal or vertical.In addition,the size effect of CJB in this area is significant.The shear strength parameters of large size(100 cm × 100 cm) specimens are lower than those of regular size(50 cm × 50 cm) specimens.The reduction of cohesion is greater than that of the friction coefficient.For rock type Ⅲ_(2),the cohesion of large-size specimens is 0.637 of the regular-size specimens.The reduction percentage of the friction coefficient for type Ⅲ_(2)is 1.66 times that of type Ⅲ_(1).The reduction percentage of the cohesion for type Ⅲ_(2)is 1.27 times that of type Ⅲ_(1).The size effect decreases with the increase of rock type grade.The research results of this study can provide an important basis for the selection of rock mechanics parameters in the dam site area of Baihetan Hydropower Station and the stability analysis of the dam foundation and rocky slopes.

新型电控式钻孔剪切仪的研制及测试验证

针对传统钻孔剪切仪剪切速率难以控制、测试误差大、试验参数取值依靠经验等缺点,研制了新型电控式钻孔剪切仪,并阐述了新仪器的结构、测试原理及方法。为测试新仪器的稳定性,将新仪器应用于滑坡场地,与传统剪切仪测试结果进行对比。结果表明:首级法向应力可等于或稍大于初始法向应力σ_(0);法向应力增量Δσ与临塑应力σ_(f)与初始法向应力σ_(0)之间存在(σ_(0)–σ_(f))/Δσ=4.0~4.5的关系,可指导Δσ取值;当法向位移与时间关系曲线趋于水平、法向位移速率趋于0时,固结稳定,据此可确定土体固结时间;根据剪应力与剪切位移关系曲线,可直观地判断土体所受应力状态,指导剪切力施加;新仪器与传统剪切仪相比,测试的抗剪强度指标可靠,而后者所测黏聚力值c很小,甚至为负值。4.5m深度处剪切板压入土体和剪切过程的数值模拟表明:法向应力介于法向位移曲线的线性变形阶段时,土体可有效固结。剪切破坏时,剪切板附近土体产生明显错动,形成条状塑性破坏带,并逐渐形成上下贯通的塑性破坏带。