气井水力压裂有效缝长评估及影响因素研究

为了准确确定气井压后有效缝长及其影响因素,提高川西须家河气藏水力压裂针对性,对于具备生产历史拟合条件的气井,利用数值模拟软件进行了生产历史拟合获得有效水力裂缝缝长,与采用净压力拟合方法获得的水力裂缝支撑缝长进行对比和拟合,获得了有效缝长和支撑缝长的关系式,计算了川西须家河储层单井压后有效缝长;采用灰色关联分析理论分析了各个参数对有效缝长的影响程度和对压裂设计的启示。结果表明：压后有效缝长与支撑缝长具有较强相关性(Le=00584 Lp1359 3),有效缝长明显比支撑缝长短;施工参数(特别是用液量)是影响须家河储层有效缝长的关键,而储层和隔层间应力差则是影响有效缝长的重要客观因素。该研究方法为水力压裂压后评估和提高压裂设计水平提供了较好的借鉴。     

Testing and evaluation of strength and deformation behaviour of jointed rocks

The objective of the paper is to derive the strength and modulus properties of rockmass as a function of intact rock strength and joint factor. The joint factor reflects the combined effect of joint frequency, joint inclination and joint strength. A study for the strength and deformation characteristics of jointed rock is done by conducting standard laboratory tests on cylindrical specimens of plaster of Paris after introducing artificial joints. The specimens having one to four joints at different inclinations which vary from 0° to 90° were tested at different confining conditions. The test results were examined to understand the effect of joint frequency and joint inclination on the strength and deformation behaviour of rock mass. Empirical correlations were developed for prediction of the uniaxial compressive strength and elastic modulus of jointed rocks. Results are compared with the earlier work on jointed specimens covering a wide variety of rocks. So, knowing the intact rock properties and the joint factor, the jointed rock properties can be estimated. These relations can be used for developing an equivalent continuum model for rock mass for handling boundary value problems. A failure criterion as proposed by Ramamurthy (1993 Ramamurthy, T. 1993. “Strength and modulus response of anisotropic rocks”. In Comprehensive rock engineering, Edited by: Hudson, J.A. Vol. 1, 313–329. Oxford: Pergamon Press.  [Google Scholar]) has been validated from these experimental results.     

高能级强夯在大型石化工程中的应用

大面积的多孔隙、粗颗粒非饱和土地基的加固处理宜采用强夯法。加固深厚地基,特别是大孔隙湿陷性地基、山区大厚度非均匀块石回填地基和抛石填海地基,应该施加高能级强夯进行处理。我国的高能级强夯主要用于石化工程施工中的生产装置和大型储罐地基。结合青岛重交沥青有限公司4座5万m3原油储罐和配套附属设施地基处理工程,对高能级强夯的关键技术、检测方法和综合评价进行了阐述,可供强夯设计施工参考。     

增量位移反分析在水电地下洞室工程中的应用

反分析是确定计算模型参数的有效方法.通常多采用量测所得全量位移进行反演计算.但地下工程中许多量测数据为增量位移,且实际施工过程可以通过建立分步开挖的有限元模型来模拟.据此,结合某水电站地下洞室工程中地下厂房的开挖,建立了模拟动态施工的有限元模型,利用某一开挖步施工前后量测值之差,采用增量位移优化反分析方法对洞室附近初始地应力场及围岩弹性模量进行了反演.计算所得增量位移与实测值符合较好,表明了这种方法的可行性.同时,根据分析结果对该方法进行了评价.     

基于有效固结应力法确定结构性黏性土不排水抗剪强度

由于结构性的存在使得很多天然黏性土的强度和变形特性不同于重塑土和非结构性土。首先回顾了适用于确定重塑土和非结构性土不排水抗剪强度的有效固结应力法,并推导了相应的方程。在此基础上,对于结构性黏性土,采用两段不同斜率（内摩擦角正切）和截距（黏聚力）的直线模拟其抗剪强度包络线,建立了确定其不排水抗剪强度的有效固结应力法方程;当有效应力小于结构屈服应力时,有效固结应力方程中有效应力部分需乘以0.8的修正系数;只要已知剪切前的有效应力,利用相应的有效固结应力法公式,可确定结构性土体的不排水抗剪强度。利用连云港结构性软黏土的等压固结三轴试验数据,验证了有效固结应力法的适用性。分析表明：对于连云港软黏土的不排水抗剪强度,有效固结应力法的计算结果与试验结果吻合较好;对于结构屈服应力,有效固结应力法的预测结果与试验数据点的拟合结果有一定偏差,但并不明显。     

镇泾油田低渗透油藏岩石渗透率应力敏感性研究

对镇泾油田低渗透油藏岩石进行了渗透率应力敏感性实验研究,并对其进行了应力敏感性评价。实验是在一定围压下,通过降低和增加内压的方式完成的,共进行了2个围压下的变内压实验。实验结果和应力敏感性评价结果表明,镇泾油田低渗透油藏不存在渗透率强应力敏感性,在原始地层压力条件下,衰竭式开发对地层的渗透率几乎没有影响,注水开发对地层的渗透率会有一定程度的改善。同时,通过对有效应力定律方程的研究,得出渗透率有效应力系数为常数且值很小,这从机理上解释了镇泾油田低渗透油藏岩石的渗透率对应力不敏感的原因。     

堆载预压过程中的地基稳定性计算方法

在分期堆载预压过程中,需要对每一级堆载以及对下一级堆载高度下进行地基稳定性计算,并根据计算结果确定加堆高度和时间。计算时,根据不同堆载高度下的比奥固结理论有限单元法计算结果,用考虑地基强度增长总应力法和考虑超孔隙水压力的有效应力法分别进行地基稳定性计算,以保证地基在每一次加载时的稳定性。结合具体的工程实例,得到了一个很有用的结论：考虑地基土强度增长的总应力法和考虑超孔隙水压力的有效应力法进行地基稳定性计算所得的安全系数趋于相等。     

Generating soil thickness maps by means of geomorphological-empirical approach and random forest algorithm in Wanzhou County,Three Gorges Reservoir

Soil thickness, intended as depth to bedrock, is a key input parameter for many environmental models. Nevertheless, it is often difficult to obtain a reliable spatially exhaustive soil thickness map in wide-area applications, and existing prediction models have been extensively applied only to test sites with shallow soil depths. This study addresses this limitation by showing the results of an application to a section of Wanzhou County (Three Gorges Reservoir Area, China), where soil thickness varies from 0 to ～40 m. Two different approaches were used to derive soil thickness maps: a modified version of the geomorphologically indexed soil thickness (GIST) model, purposely customized to better account for the peculiar setting of the test site, and a regression performed with a machine learning algorithm, i.e., the random forest, combined with the geomorphological parameters of GIST (GIST-RF). Additionally, the errors of the two models were quantified, and validation with geophysical data was carried out. The results showed that the GIST model could not fully contend with the high spatial variability of soil thickness in the study area: the mean absolute error was 10.68 m with the root-mean-square error (RMSE) of 12.61 m, and the frequency distribution residuals showed a tendency toward underestimation. In contrast, GIST-RF returned a better performance with the mean absolute error of 3.52 m and RMSE of 4.56 m. The derived soil thickness map could be considered a critical fundamental input parameter for further analyses.     

准噶尔盆地断拗转换期剥蚀厚度及其分布规律

准噶尔盆地为我国重要的陆上含油气盆地, 对其进行地层剥蚀厚度恢复能够有效地研究盆地演化历史以及油气资源评价.通过分析声波时差法的方法原理及其适用条件, 认为此方法适用于恢复准噶尔盆地断拗转换期剥蚀地层的厚度.实际计算结果表明: 断拗转换期上、中二叠统之间为主不整合, 剥蚀厚度大; 三叠系与二叠系之间形成次级不整合, 盆地剥蚀厚度相对较大, 区域位于西部盆缘地带, 自北西向南东剥蚀量逐步降低, 至盆地中心剥蚀量最低.各构造单元中, 凸起相比于凹陷所遭受的剥蚀程度较大, 反映古地貌呈现盆地西北缘高、腹部低的地形特征, 同时反映准噶尔盆地断拗转换期二叠纪晚期至三叠纪早期改造具西强东弱、边缘强内部弱的特点.     

土工格室补强路基整治路基病害的试验研究

土工格室广泛运用于道路或铁路路基的补强和病害整治,针对不同几何尺寸土工格室的整治效果不同,采用焊距为340、400、680 mm和高度为0.10、0.15、0.20 m组合的9种不同规格土工格室进行整治铁路基床下沉病害的现场试验,并与换砂法试验进行了对比,分析不同整治法的轨下动应力衰减规律。结果表明,格室每增高0.01 m,动应力衰减增加约0.6%～1%;焊距每增加100 mm,动应力衰减降低约5%;相比较于换砂法,土工格室法轨下动应力衰减快、分布均,路基强度高,表明换填厚度的大小与整治方法密切相关。在试验的基础上提出了换填厚度设计容许应力法,综合考虑了路基应力水平、格室与砂垫层动应力衰减性能以及路基基床土的容许承载力,为换填厚度设计提供了理论设计方法。