Improved prediction of shear wave velocity for clastic sedimentary rocks using hybrid model with core data

Accurate measurement of acoustic velocities of sedimentary rocks is essential for prediction of rock elastic constants and well failure analysis during drilling operations.Direct measurement by advanced logging tools such as dipole sonic imager is not always possible.For older wells,such data are not available in most cases.Therefore,it is an alternate way to develop a reliable correlation to estimate the shear wave velocity from existing log and/or core data.The objective of this research is to investigate the nature of dependency of different reservoir parameters on the shear wave velocity(VS) of clastic sedimentary rocks,and to identify the parameter/variable which shows the highest level of dependency.In the study,data-driven connectionist models are developed using machine learning approach of least square support vector machine(LSSVM).The coupled simulated annealing(CSA) approach is utilized to optimize the tuning and kernel parameters in the model development.The performance of the simulation-based model is evaluated using statistical parameters.It is found that the most dependency predictor variable is the compressional wave velocity,followed by the rock porosity,bulk density and shale volume in turn.A new correlation is developed to estimate VS,which captures the most influential parameters of sedimentary rocks.The new correlation is verified and compared with existing models using measured data of sandstone,and it exhibits a minimal error and high correlation coefficient(R^(2)-0.96).The hybridized LSSVM-CSA connectionist model development strategy can be applied for further analysis to predict rock mechanical properties.Additionally,the improved correlation of VS can be adopted to estimate rock elastic constants and conduct wellbore failure analysis for safe drilling and field development decisions,reducing the exploration costs.

Correlations between ultrasonic pulse wave velocities and rock properties of quartz-mica schist

Physico-mechanical properties are critically important parameters for rocks. This study aims to examine some of the rock properties of quartz-mica schist（QMS） rocks in a cost-effective manner by establishing correlations between non-destructive and destructive tests. Using simple regression analysis, good correlations were obtained between the pulse wave velocities and the properties of QMS rocks. The results were further improved by using multiple regression analysis as compared to those obtained by the simple linear regression analysis. The results were also compared to the ones obtained by other empirical equations available. The general equations encompassing all types of rocks did not give reliable results of rock properties and showed large relative errors, ranging from 23% to 1146%. It is suggested that empirical correlations must be investigated separately for different types of rocks. The general empirical equations should not be used for the design and planning purposes before they are verified at least on one rock sample from the project site, as they may contain large unacceptable errors.

天然气水合物岩石物理实验研究进展

天然气水合物是我国地质调查和资源勘查的重要矿体之一,勘探开发面临着诸多难题,如地震响应特征、力学和电学性质等需要开展深入研究。天然气水合物的赋存需要特定的温度和压力范围,环境温度和压力的变化可能会造成天然气水合物的分解,这在海洋环境和地质灾害等研究领域造成了诸多问题。天然气水合物地层的物性和岩石物理变化特征较复杂,在实验室开展天然气水合物测试分析是了解其岩石物理性质、获取岩石物理参数的一种有效手段。回顾了凝水成冰法、四氢呋喃(THF)溶液法、过量水法、过量气法、温度法、冰粉混合法等实验室生成水合物的方法,总结了温度、气体压力、粒径、矿物成分、含水率、表面活性剂、含盐量、地层骨架等水合物生成实验的影响因素,介绍了水合物岩石物理实验研究中声学、力学、电学等方面的研究进展,展望了天然气水合物岩石物理实验未来的研究方向。

灰岩在三轴变围压循环压缩中的变形特征研究

岩石在周期荷载作用下的力学性能是影响岩体工程长期稳定性的重要因素之一,需研究循环荷载作用下岩石的特性及演化规律。首先采用声波纵、横波波速测量方法,对岩样进行筛选。设计灰岩在施加不同围压和恒定循环上限应力作用下,三轴变围压循环加卸载下岩石变形特征测试方案。三轴变围压循环试验在GCTS-1000型岩石力学测试系统上进行,通过对试验结果的分析表明:(1)灰岩在变、恒围压加、卸载循环中,形成一封闭的塑性滞回环。在轴向变形上滞回环面积逐次缩小;而变围压循环在径向变形上滞回环面积逐次增大,而恒围压循环在径向变形上滞回环面积几乎相等。(2)在三轴变围压循环压缩试验中,围压增加和循环上限应力不变,残余变形量随着循环次数的增加而呈现出一个递减的趋势,轴向应变和径向应变的发展趋势是相反的。(3)在整个循环加卸载过程中,各个加卸载阶段变形模量值不同,卸载阶段变形模量高于加载阶段变形模量。(4)变围压循环加、卸载阶段变形模量的值大于恒围压循环加、卸载阶段下变形模量的值。通过试验,揭示灰岩在三轴变围压循环下,加载和卸载2种力学状态时变形特性的差异。同时分析变围压循环和恒围压循环状态下岩石弹性参数的差异性。

基于岩石物理诊断的横波速度估算方法

横波速度是进行叠前地震反演和叠前地震属性分析的必要资料,但目前绝大多数钻井都缺少横波测井资料。本文通过常数胶结模型分析了岩石速度的影响因素,岩石固体部分的黏土成分、孔隙度、胶结分数、沉淀模型以及配位数等参数都会影响计算结果,流体部分的饱和度、气油比以及流体混合方式也会影响计算结果。结合Gassmann方程和常数胶结模型,本文将固结分数作为反演过程中的可调因子,利用岩石的纵波速度反演得到岩石的胶结分数值,进而进行横波速度预测。通过对实际测井数据的处理,证明该方法能准确有效地预测出横波速度。

基于格子玻尔兹曼方法的致密砂岩驱替模拟

基于数字岩心建模方法和格子玻尔兹曼方法,开展致密砂岩水驱模拟研究,分析致密砂岩水驱微观过程和机制。首先利用大庆油田龙虎泡地区高台子组致密砂岩CT扫描数据,建立三维数字岩心模型;然后利用Shan-Chen格子玻尔兹曼方法,建立油水两相驱替数值模型;之后对比分析不同注入速度和注入压力条件下驱替效率、换油率与驱替参数的关系,并给出致密砂岩三维微观孔隙尺度的驱替过程。结果表明:相同累积注入量条件下,提高水驱注入速度和驱替压差可以提高最终驱替效率;水驱注入速度和驱替压差存在驱替效率拐点;恒速水驱的平均最终驱替效率为49.6%,恒压水驱的平均最终驱替效率为47.3%。

SHPB测试中岩石试件应力均匀性分析研究

对花岗岩、千枚岩、磁铁石英岩三种岩石进行SHPB应力均匀性试验测试,研究表明:试件内达到应力均匀时间介于弹塑性状态假设条件下试件内达到应力均匀时间之间,且试件内达到应力均匀时间与二者的平均值具有一定的相关性。试验中子弹的冲击速度在一定范围内,能够使三种岩石满足应力均匀性的要求,且在断裂应变达到1%之前均有较长的恒应变率时间段。

双向匀速摆动光学平台的运动规划与虚拟仿真

根据设计要求先对输出摇杆进行了运动规划以得到理想的角速度曲线,利用运动学反求法得到输入曲柄的运动规律;再在ADAMS中对该机构进行了虚拟样机仿真,驱动曲柄按照得到的伺服输入运动规律转动,得到了摇杆的实际输出角速度曲线;经误差分析,结果表明,所设计的曲柄摇杆机构满足光学平台的双向匀速摆动输出要求。