裂缝性储层水平井钻井井壁稳定模型研究

钻井井壁稳定是钻井过程中的复杂性问题。当水平井筒穿过储层天然裂缝时,天然裂缝可能在较小的井底流体压力下发生剪切破坏,造成井壁垮塌。为此,基于弹性力学和岩石力学理论,并考虑岩石孔隙弹性和热弹性效应影响,推导了井壁主应力计算式。视天然裂缝为地层中的结构弱面,基于主应力与天然裂缝法向的空间位置关系,得出了天然裂缝法向与井壁最大主应力夹角计算式,结合弱面结构剪切破坏准则,得到维持井壁稳定的最小井底流压数学求解模型,提出了模型求解和井壁稳定流压获取方法。通过公式推导及计算实例分析可知:天然裂缝倾角和走向、原地应力和水平井方位将影响钻井过程中防止井壁垮塌的最小井底流体压力的设计,也即影响安全钻井液密度的选择。     

天然气水合物降压开采储层稳定性模型分析

储层稳定性是天然气水合物开采所面临的关键问题。本文基于多孔介质流体动力学和弹性力学,建立了天然气水合物降压开采储层稳定性数学模型,包括储层沉降和井壁稳定性分析两个方面,并以墨西哥湾某处水合物藏的基本参数为例,进行了水合物降压开采储层稳定性的模拟计算。结果表明,在水合物降压开采的过程中,孔隙流体压力降低导致了储层的沉降,最大的沉降发生在井壁附近,水合物分解会加剧储层的沉降;降低井孔压力会造成井壁破坏的潜在危险,在井壁附近,周向和垂向应力达到最大处容易发生失稳破坏,地层的水平应力差会增加井壁的不稳定性。     

高中间主应力下地下厂房高边墙围岩补强支护及效果评价

地应力高、岩石强度应力比低和中间主应力偏高是猴子岩水电站地下厂房的主要地质环境特征,且施工期高边墙围岩稳定性问题普遍、突出。结合开挖揭示的高地应力、围岩坚硬较完整和局部节理裂隙较发育等工程地质环境条件,在总结施工期围岩变形破坏特征和分析监测资料的基础上,研究了高中间主应力条件下地下厂房高边墙围岩补强支护措施,并对其效果进行评价。结果表明,补强支护处的边墙围岩变形速率减小,位移得到了收敛,说明支护合理、有效,为类似工程的围岩补强支护和安全控制提供了借鉴。     

Simulating the effect of subsurface stresses and transient pore pressure on wellbore stability in subsea horizontal wells

The most prominent challenge associated with offshore horizontal drilling is wellbore stability. In this paper, simulation of in-situ stresses around the wellbore is conducted to study the effects of transient pore pressure on the stability of horizontal wells. The rock mechanical analysis based on finite element technique lead to investigate a unique behavior found in subsea horizontal wells known as transient pore pressure behavior and near wellbore pressure gradients. The results demonstrate that near wellbore pore pressure gradient is only active in rock formations which possess transient pore pressure behavior; therefore, simulated solutions require adjustment to achieve accurate results.     

准噶尔盆地中部地区地应力分析及其在钻井优化设计中的应用

准噶尔盆地中部地区是胜利油田西部新区的重点勘探区块之一,中生界侏罗系地层为本区主要目的层,储层埋藏深。本区地质情况复杂,井壁稳定及压力异常问题突出,钻井过程中复杂较多,导致钻井周期长,成本高。通过对准噶尔盆地中部地区已钻井资料分析．利用测井资料,建立了本区地应力模型,确定了三个主应力的方向及大小,并对地应力模型进行验证,其中最大水平主应力方向为近南北方向。建立了本区地层三压力剖面,针对不同目的层,形成了两套井身结构推荐方案,根据地应力模型,确定了有利于井壁稳定的钻井方位和有利于压裂改造的钻井方位,进行了水平井轨道方向优选,形成了本区钻井优化设计方案,并进行实钻应用。现场应用表明,新钻井较周围邻井平均机械钻速提高15％,钻井周期缩短10％,钻井复杂明显减少,井身质量大幅提高。     

The potential of the use of dense fluids for initiating hydraulic stimulation

To improve preferentially the permeability of fractures in the deepest parts of a geothermal reservoir, a dense fluid may be injected during the very first phase of a hydraulic stimulation test. To initiate such a permeability-enhancement process in the 5000 m deep reservoir of the European Enhanced Geothermal System (EGS) project at Soultz-sous-Forêts, France, a concentrated NaCl brine was injected. The effects of this injection were estimated using measured hydraulic and microseismic data. Two tasks associated with hydraulic stimulation have been shown to be important for this purpose: (1) determination of the failure pressures of the various fractures intersecting the open-hole section under stimulation, and (2) calculation of the transient hydraulic pressure profile in the borehole.Using the numerical borehole code HEX-B, the transient pressure profiles during stimulation of wells GPK2 (June 2000) and GPK3 (May 2003) were calculated on the basis of measured wellhead data. A comparison of the temporal history of near-borehole microseismic events during the GPK2 test and downhole pressure development in the open-hole sections of this borehole indicated that use of a dense brine helped stimulate the bottom part of this well. The corresponding analysis for the GPK3 test showed that the failure pressure of the fractures in the bottom part of the wellbore was never exceeded when injecting the dense brine. We can, therefore, assume that the brine had no effect on the fractures in GPK3.     

The vibration characteristics of drillstring with positive displacement motor in compound drilling Part1: Dynamical modelling and monitoring validation

The storage of hydrogen energy is one of the key difficulties in the efficient use of hydrogen. The most important thing for different storage methods is to establish the aisles of the hydrogen to storage space, and efficiently drill a few high-quality well holes. Compound drilling is one of the alternative technologies. However, the bit-rock interaction and the drill string-borehole interaction make the movement of bottom hold assembly more complex and increase the difficulty of well trajectory control. The vibration characteristics of drill string during compound drilling are not clear. The numerical simulation model of drill string with positive displacement motor is established by considering the bit-rock interaction, the rock failure behavior, the drill string-borehole interaction and the drill string structural. The mechanical parameters of shale for the numerical model are measured by wave velocities method. The simulation model is verified by the measuring and motoring data of axial force in the field. The rock element damage failure rate of compound drilling is greater than conventional drilling. The axial force and torque of bit of drill string in compound drilling is greater than that in the conventional drilling. The drill string is in contact with the wellbore in a more complicated way during compound drilling. The research results are benefit for optimal design of borehole quality.     

白鹤滩水电站左岸地下厂房岩壁吊车梁承载特性分析

岩壁吊车梁是地下厂房重要的支撑结构,其安全稳定性尤为关键。基于原型观测结果,分析了受到洞室开挖卸荷作用和吊车荷载作用下岩梁锚杆受力、岩梁与围岩结合面情况和围岩变形情况,对岩壁吊车梁进行承载特性分析和安全稳定评价。结果表明,围岩开挖卸荷引起岩体较大的深部变形和应力调整,岩梁锚杆应力水平较高,在开挖完成后,各监测数据趋于稳定;锚杆应力值、锚索荷载未超过设计强度;岩梁与岩壁最大开合度1.24mm;岩梁荷载试验期间,各观测数据增量均较小。总体上,岩壁吊车梁安全稳定,能够满足生产运行要求。     

Fully Coupled 3-D Conjugate Heat Transfer Algorithm for Borehole Heat Exchanger Performance Prediction

Quantitative three-dimensional prediction of the thermal performance of a vertical borehole heat exchanger (BHE) in a ground-source heat pump installation is sought. As BHE installation exhibits exceptionally disparate characteristic length scales, an alternative formation-fluid-thermal fully coupled algorithm is derived to quickly predict the 3-D temperature distributions. The time scale of the steady prediction is of order minutes. This simulation capability can be readily coupled to long-time (order months) unsteady simulation of an entire wellbore field. Algorithm prediction is validated by comparison with data from an instrumented commercial installation for a unique BHE conduit design, followed by illustrative design optimization or variation assessments.     

深埋软岩隧道开挖及支护变形特征研究

针对滇中引水工程中磨盘山隧道的深埋软岩段,利用ANSYS建立三维数值模型,通过FLAC~(3D)进行计算,研究了深埋软岩隧道开挖及支护后围岩的变形和破坏特征。结果表明,围岩强度和隧道埋深是影响隧道变形破坏的重要因素。隧道开挖后,应力重分布,隧道前段围岩强度较小,变形总位移、塑性区范围大于后段,在拱腰两侧对称形成两个应力集中区。隧道支护后,有效限制了隧道变形的继续发展,各部位总位移值减小,塑性区范围也得到抑制,拱腰两侧应力集中区向洞壁靠拢,应力分布也变得均匀。     

含交叉裂隙类岩石试样物理力学特性试验及其RFPA模拟

为探究含交叉裂隙试样在单轴应力下的物理力学特性,制备了与岩石力学性质相似的类岩石材料,利用预制树脂片法模拟了不同倾角交叉裂隙的情况,对其进行了单轴压缩试验,同时利用RFPA软件对不同工况进行了数值模拟。结果表明,含交叉裂隙类岩石试样在单轴应力下主要有单一裂隙扩展模式、主裂纹扩展贯通模式、次生裂纹扩展贯通模式三种破坏模式;单一裂隙扩展模式与主裂纹扩展模式下,次生裂隙尖端产生剪破坏,主裂纹尖端产生拉破坏,而次生裂纹扩展模式下主裂纹尖端产生剪破坏,次生裂纹尖端产生拉破坏,最终产生的翼裂纹与反翼裂纹属于拉剪破坏;单轴应力下的含交叉裂隙试样应力-应变曲线经历弹性变形阶段、非线性变形阶段、残余变形阶段三个阶段;主裂纹倾角对含交叉裂隙试样的峰值强度起到控制性作用,而次生裂隙仅在主裂纹倾角为0°时对试样的峰值强度有较大影响。     

环空注氮气稠油热采井筒中的干度变化

蒸汽干度是影响注汽开采稠油工艺的主要参数,本文运用传热学、热力学及流体力学等学科知识,提出一种蒸汽干度的计算方法。首先分析了注汽井筒的传热过程,并在考虑压力变化的前提下建立了数学模型,计算得出井筒热损失量,最后确定井筒中任意处的蒸汽干度。以海底蒸汽井为例,分析井中干度随深度的变化情况,为热采注汽系统的现场工艺设计提供参考。     

基于卸围压试验的砂岩卸荷本构模型及其应用

鉴于岩体本构模型受岩样应力路径、加卸载状态等因素的影响,为研究卸荷条件下砂岩的本构模型,采用RMT-150C岩石力学试验系统对宜昌砂岩岩样进行了升轴压峰前卸围压、轴压和围压等量减小两种应力路径下的卸围压试验。结果表明,卸荷应力路径不同时,卸荷变形阶段的应力—应变曲线形态有很大差异,但岩样变形模量随围压降低而劣化的规律一致;岩样卸荷破坏强度特征可用Hoek-Brown准则拟合。由此推导出增量形式的卸荷弹脆塑型本构模型,并以算例分析验证了该模型的正确性。     

国内泡沫钻井流体应用与研究进展

综述泡沫钻井流体在国内的现场应用及室内研究,总结泡沫钻井流体的优点和不足.泡沫钻井流体具有密度低、滤失量小、携岩能力强和机械钻速高等特点,对于衰竭、水敏性地层有着广泛的应用前景,已成为油气田开发过程中钻井流体的一个重要发展方向.指出泡沫钻井流体在井壁稳定方面具有独特优势,为稳定井壁提供了新的技术手段；同时,也存在泡沫体系稳定性差、现场消泡困难以及井壁稳定评价方法欠缺等问题.以工程应用和室内研究为两条主线,介绍泡沫钻井流体在我国的应用进程和研究进展.最后指出,加强对泡沫钻井流体的认知和研究,进一步开发和优选发泡剂、稳泡剂,提高体系稳定性；增加消泡技术研究,促进泡沫钻井流体的可循环利用；研究抑制剂、井壁稳定剂,建立专用的室内井壁稳定评价方法和统一的标准,促进泡沫钻井流体在国内的进一步推广应用.     

The calculation and analysis of glass-to-metal sealing stress in solar absorber tube

The failure or degradation of solar absorber tubes is the single largest cost factor for current parabolic trough solar power plant. The main failure reason is that there are residual stresses in the glass-to-metal joint which are generated during the cooling process of sealing. According to the thin shell theory and thermal stress theory, this paper presents the analytic solution for the glass-to-metal sealing residual stress. It also analyses how the thickness of glass tube, thickness of metal ring, and thermal expansion coefficient affect the residual stress distribution. In order to verify the calculation results, the photoelastic technique is used to measure the residual stress and the tensile test is used to obtain the point of the most dangerous stress and the tensile strength for the sealed specimens. It can be concluded that the maximum tensile stress happens at some distance near the sealing interface on the outer surface of glass tube. The seal strength increases when the thickness of the glass tube is increased. The analytic solution is proved feasible to analyze the residual stress of glass-to-metal seals in solar absorber tubes.     

带预制裂隙岩石单轴压缩破裂特征颗粒流模拟

为研究带预制裂隙岩样的单轴压缩破裂特征,采用颗粒流法对带两条预制裂隙深埋大理岩样在单轴压缩条件下的变形破裂进行数值模拟研究。结果表明,单轴压缩岩样模型主要产生拉裂纹,剪裂纹在峰值应力之后产生;岩样裂纹在预制裂隙端部启裂,之后朝向主应力方向;裂纹近似平行,岩石破裂为板状,预制裂隙岩样破坏后承载力降低很快,预制裂隙影响岩样在残余强度时裂纹扩展的情况,完整岩样在残余强度时裂纹数目稳定,预制裂隙岩样在残余强度时裂纹缓慢增加,预制裂隙减小了岩样的弹性模型,减弱了岩样的启裂应力及岩样抵抗变形破坏的能力。     

The drillstring dynamic time domains harmonic response and acceleration characteristics of compound drilling for the high-quality slim borehole

The harmonic response and acceleration characteristic of drillstring is established to improve borehole quality for the hydrogen underground storage (HUS). The harmonic response laws of drillstring is discussed. Harmonic response analysis includes non-failure case and failure case. Absorber control measure is simulated to lower vibration amplitude of drillstring. The drill string collides violently with the wellbore reduces the wellbore quality and increases the unreliability of the HUS. Lateral harmonic response has the greatest damage to well wall. Torsional harmonic response causes less damage than lateral vibration. High WOB (weight on bit) and high RPM (rotary per minute) are not conducive to the quality of HUS. In course of designing drilling parameter, it is required to avoid or reduce drillstring resonance under low-order inherent frequency as much as possible. The research result is of much significance to improve wellbore quality of hydrogen underground storage.     

Establishment and evaluation of strength criterion for clayey silt hydrate-bearing sediments

Appropriate strength criterion is the prerequisite for wellbore stability analysis. In this paper, the Modified Mohr-Coulomb criterion that considering the effects of hydrate is established based on the experimental results of the artificial clayey silt samples with hydrate. Meanwhile, the new criterion was evaluated by comparing the differences in the safe lower limit of drilling mud density calculated by both the traditional and modified Mohr-Coulomb criteria. The result demonstrates that the mud density window calculated by the new criterion is narrower, which reveals the applicability of the modified Mohr-Coulomb criterion in the analysis of wellbore stability in hydrate formation.     

冻结融解作用对岩石边坡稳定的影响

主要通过岩石室内试验,分析子了冻结融解作用对岩石物理力学性质的影响以及岩石裂缝发展的规律,同时结合边坡的破坏事例调查成果,结论认为表层崩塌的破坏模式是岩石边坡长期冻结融解作用的主要表现形式。     

锚杆参数对边坡稳定性影响的数值分析及锚杆受力研究

岩土工程中采用锚杆支护是维护边坡稳定的重要手段之一,以某边坡工程为背景,通过有限差分软件FLAC3D分析了锚杆长度、倾角及注浆粘结力的变化对边坡稳定性和锚杆剪应力的影响,发现锚固边坡存在最优锚固角和锚固长度,在其他因素不变的情况下,锚固倾角为20°左右时边坡的安全系数最大;注浆粘结力的改变并不影响锚杆中性点的位置。同时,研究了荷载沿锚杆的分布规律,说明全长粘结式锚杆对边坡滑动面有缝缀作用,且改善了坡体的结构性,从而提高了边坡的整体稳定性。