基于岩石物理模型的裂缝型储层AVOA反演方法

纵波各向异性裂缝预测方法是目前应用比较广泛、效果较好的一种裂缝预测方法；但传统椭圆拟合方法的准确性受到一系列因素的影响，致使裂缝密度反演结果不准确。本次研究根据Ruger方程精确式推导各向异性介质中储层裂缝密度的计算方法，该方法首先利用入射角、方位角、Thomsen各向异性三参数以及介质弹性参数的函数来计算纵波反射系数，然后根据纵波反射系数计算待测储层中裂缝的切向各向异性系数，最后根据各向异性系数计算待测储层的裂缝密度。利用该方法在四川盆地正坝南地区通过实际纵波AVOA数据反演法向和切向裂隙弱度预测裂缝密度，裂缝参数反演结果与钻井信息吻合；表明该方法能够用于裂缝储层预测，确定研究区裂缝发育情况。     

复杂碳酸盐岩储层裂缝预测方法对比性研究

围绕着复杂碳酸盐岩储层裂缝的预测方法,以普光地区嘉陵江组为例,在统计研究区裂缝发育规律的基础上,分别利用构造曲率法、纵波宽方位各向异性法和有限元法对裂缝进行预测,比较各个方法预测结果和适用条件。对比结果表明:曲率法基于几何学理论,可以定性的分析裂缝发育强度,无法预测裂缝方位,该方法适用于基础资料较少、构造简单、褶皱发育的地区;纵波宽方位各向异性法是地球物理法预测裂缝的首选方法,可以直接反映有效裂缝的方位和密度,但是该方法适用于倾斜裂缝和高角度裂缝发育区,对地震资料质量和处理要求较高;有限元数值模拟法从正演角度再现了裂缝形成过程,计算分析裂缝的发育强度和方位,该方法需要对研究区裂缝形成机理认识充分,预测结果的精度取决于模型的精细程度。      

准噶尔盆地哈山西地区石炭系火成岩裂缝预测

哈山西地区石炭系裂缝空间发育规律复杂,导致裂缝储层难以准确预测。在裂缝地质特征剖析的基础上,运用叠后相干技术对裂缝发育带进行了宏观定性描述,同时基于技术适用性分析,针对研究区复杂高陡裂缝采用叠前AVAz技术对裂缝发育方向、密度等详细特征进行了定量预测。最终通过叠前、叠后结果的相互补充、验证得到了裂缝的综合发育特征。预测结果显示裂缝发育主体区位于哈山1井—哈山2井—哈浅7井一线以南,平面上呈点状或条带状不连续展布,剖面上呈串珠状、近块状分布,井间差别大,且多存在于断裂发育区;裂缝方向以北东向为主。最终预测结果与构造背景相匹配、与实钻情况相吻合,取得了较好的预测效果。     

有限元数值模拟技术在潜山裂缝定量预测中的应用——以珠江口盆地惠州凹陷惠州26构造为例

潜山储层的裂缝发育预测是勘探开发领域一个技术难题。目前多采用地震刻画、地震属性提取、周边钻井资料揭示以及岩芯观察等方法对地下裂缝的分布情况进行预测,但存在不少问题。笔者等通过有限元数值模拟方法对珠江口盆地惠州26构造裂缝发育情况进行预测,并提出预测流程。该方法首先采用断层生长连接分析结合演化史分析建立合适的几何模型和数理模型,通过给定力学参数和边界条件,模拟裂缝主要形成期文昌期、恩平期的古构造应力场,最终通过对张应力和剪应力大小及分布的分析来预测储层构造裂缝的发育程度。模拟结果显示,文昌期裂缝强烈发育区位于F2断层西段和F1断层西段,在惠州26构造处,构造的高部位裂缝发育强度较强,在4井位置裂缝发育较弱,在7井位置发育较好的裂缝。恩平期受应力方向和大小的改变影响,主要的裂缝发育区集中在F2断层下盘惠州26构造高部位。将预测结果与钻井结果进行比较,预测结果和钻探结果较一致,印证了该方法在古潜山裂缝预测中的实用性。有限元数值模拟方法不仅能够恢复构造裂缝形成期构造应力场的分布情况,也可以对储层构造裂缝的分布及发育程度进行预测,为裂缝型潜山油气藏勘探开发提供技术支持。     

有限元数值模拟技术在潜山裂缝定量预测中的应用——以珠江口盆地惠州洼陷惠州26构造为例

潜山储层的裂缝发育预测是勘探开发领域一个技术难题。目前多采用地震刻画、地震属性提取、周边钻井资料揭示以及岩芯观察等方法对地下裂缝的分布情况进行预测,但存在不少问题。笔者等通过有限元数值模拟方法对珠江口盆地惠州26构造裂缝发育情况进行预测,并提出预测流程。该方法首先采用断层生长连接分析结合演化史建立合适的几何模型和数理模型,通过给定力学参数和边界条件,模拟裂缝主要形成期文昌期、恩平期的古构造应力场,最终通过对张应力和剪应力大小及分布的分析来预测储层构造裂缝的发育程度。模拟结果显示,文昌期裂缝强烈发育区位于F2断层西段和F1断层西段,在惠州26构造处,构造的高部位裂缝发育强度较强,在4井位置裂缝发育较弱,在7井位置发育较好的裂缝。恩平期受应力方向和大小的改变影响,主要的裂缝发育区集中在F2断层下盘惠州26构造高部位。将预测结果与钻井结果进行比较,预测结果和钻探结果较一致,印证了该方法在古潜山裂缝预测中的实用性。有限元数值模拟方法不仅能够恢复构造裂缝形成期构造应力场的分布情况,也可以对储层构造裂缝的分布及发育程度进行预测,为裂缝型潜山油气藏勘探开发提供技术支持。     

基于构造应变分析的裂缝预测方法及其应用

地层应变是构造裂缝产生的直接因素,根据构造应变大小可以预测构造裂缝发育的位置和强度,对研究区的主要裂缝发育区进行划分。文章以松辽盆地徐家围子断陷徐中地区营城组四段（简称营四段）为研究对象,在建立研究区精细的三维构造模型基础上,利用“构造恢复”方法实现研究区古构造恢复,通过开展有限应变值计算来预测构造裂缝的平面分布。研究表明:研究区营四段主要包括3个造缝期,即营城组末期、泉头组—青山口组时期、嫩江组时期,其中,营城组末期与泉头组—青山口组时期的构造变形较为强烈,是裂缝的主要形成时期。根据应变大小与试气产量的关系,将研究区划分为3类裂缝发育区,Ⅰ类裂缝发育区已钻井验证,表明利用构造应变对裂缝的预测结果可靠,Ⅱ类裂缝发育区可作为深层天然气的下一步挖潜的重要方向,Ⅲ类裂缝发育区产能较低,裂缝对储层的改造作用有限。      

塔里木盆地克深2区块储层裂缝数值模拟研究

储层裂缝定量预测是塔里木盆地克拉苏构造带克深2区块后期开发工作的重要保障。在对单井裂缝特征进行描述以及通过构造解析和反演拟合确定古今地应力的基础上,建立了研究区的力学模型,并结合地应力与裂缝参数之间的定量关系,对克深2区块巴什基奇克组的储层裂缝进行了数值模拟。结果显示,断层带是裂缝各项参数的高值区,背斜顶部具有裂缝线密度低而裂缝开度、裂缝孔隙度和裂缝渗透率高的特征,背斜翼部则与之相反。分析其原因认为,断层带附近裂缝密度大,沟通了单砂体,背斜高部位相对翼部裂缝密度低,但裂缝整体开度大,充填程度弱,有效性高。数值模拟结果与单井岩心裂缝、成像裂缝解释结果匹配较好,预测开发井裂缝渗透率符合率约75%,为塔里木盆地克拉苏构造带克深区块的天然气勘探与开发提供了一定依据。     

基于地震属性的致密碳酸盐岩储层裂缝分布的人工智能预测方法

裂缝是致密碳酸盐岩储层的重要渗流通道,影响油藏开发效果.由于裂缝的地球物理响应弱且复杂,使得裂缝预测困难.在深度挖掘地震属性中裂缝特征信息的基础上,建立了基于人工智能的裂缝分布预测方法 .该方法通过支持向量机算法优选裂缝敏感属性,利用梯度提升决策树(GBDT)算法深度挖掘单井裂缝发育情况与地震属性之间的非线性关系,梯度提升决策树算法对于异常值有较强的鲁棒性,可以较好地解决裂缝地震响应弱且复杂的问题.该方法在中东扎格罗斯盆地某油田古近系渐新统-新近系中新统Asmari组主力产油层位的致密碳酸盐岩储层中进行了实例应用,优选出方差、曲率、倾角偏差、倾角、方位角5种裂缝敏感地震属性,利用梯度提升决策树集成不同地震属性中的裂缝特征,建立裂缝分布预测模型,对研究区碳酸盐岩储层裂缝分布进行了预测.与常用裂缝预测方法的对比实验表明,本方法的裂缝预测结果与单井裂缝解释更为符合.预测结果表明,研究区北部裂缝更为发育,构造高部位附近裂缝更为发育,与生产动态认识相符合.     

济阳坳陷四扣洼陷泥质岩裂缝储层预测研究

通过对济阳坳陷四扣洼陷及郭局子地区泥质岩储层的裂缝类型、识别特征进行的研究，认为影响本区裂缝发育程度的因素是区域构造应力及构造部位、岩性、岩相、岩层厚度、埋深及地层压力。并在此基础上建立了地质模型、力学模型和数学模型，运用三维有限元方法对四扣洼陷构造裂缝储层的分布进行了预测。通过预测，提出了研究区裂缝发育在平面上具有不均匀性、连片性差、与断层关系密切的特点，进一步指出了罗42－罗48井区等8个区带为裂缝发育的地区。这项研究不仅对研究区泥岩油气勘探，而且对济阳坳陷及类似地区的泥岩油气勘探有重要指导和启示意义。     

四川盆地J地区志留系龙马溪组页岩裂缝地震预测与评价

利用三维地震资料进行相干体分析﹑应力场分析﹑P波各向异性分析,对四川盆地J地区龙马溪组优质页岩层段不同规模裂缝的优势发育带进行预测,对比分析表明,对于大型裂缝的预测,相干体分析相对较好;对于中小型裂缝的检测,采用P波各向异性技术的效果相对较好。龙马溪组页岩段底部在构造主体部位上主要发育中小型裂缝,是优质页岩储层的主要分布层段。JY1井区两口水平井的测试结果证实,对龙马溪组优质页岩段开展三维地震裂缝预测是可行的,预测结果可有效地指导该区的页岩气勘探。     

Study of desiccation crack initiation and development at ground surface

Cracks are common in clayey or expansive soils and provide preferential pathways for water infiltration into soils. A field study was conducted to investigate the mechanisms of initiation and development of desiccation cracks on two soils. Based on results of the field study and measurements of soil-water retention curves and soil shrinkage properties in the laboratory, the conditions of crack initiation and the development of crack geometric parameters (i.e., crack porosity, crack aperture, and crack density) with water content or drying time were quantified. The results show that desiccation cracks developed in three stages: initial stage, primary stage, and steady state stage. In the initial stage, few cracks developed with gradually decreasing water content. When the water content reached a critical value for crack initiation, cracks developed quickly and this was the start of the primary stage. The critical suction at crack initiation was calculated using a stress criterion, which is in the range of 5.3–21.3 times the preconsolidation pressure of the soil. As the water content approached the shrinkage limit of the soil, cracks developed slowly and approached a steady state. The cracks were found to be repeatable during three drying–wetting cycles.     

Geometric parameters and REV of a crack network in soil

Cracks are common in natural and engineered soils and provide preferential pathways for water infiltration into the soil. Statistical properties of crack geometries are important inputs for analyzing preferential flows in discrete random crack networks. This paper reports the outcome of a field study conducted on a compacted, cracked soil ground at a steady moisture condition. The objectives of the field study were to investigate the crack patterns and probability distributions of the geometric parameters of cracks and to determine the representative elementary volume (REV) of the crack network. The desiccation cracks at the survey site formed an inter-connected columnar structure. The traces of the cracks on the soil surface formed a primary structure consisting of inter-connected crack polygons and a secondary structure comprising of isolated cracks. The locations and orientations of the desiccation cracks followed a uniform distribution, differing from the distribution of fracture sets often observed in fractured rocks. The lengths and apertures of the cracks followed a lognormal distribution as expected. The REV size for the cracked soil was found to be approximately five times the mean crack length, above which the variation in crack porosity in relation to domain size was negligible.     

三星堆城墙干缩裂缝开裂与扩展机理

针对土遗址干缩裂缝病害,以三星堆月亮湾城墙剖面为依托,探讨干缩裂缝的开裂条件、扩展特征以及失稳扩展条件。研究结果有助于揭示土遗址开裂规律,对遗址保护的工程实践具有指导意义。针对月亮湾城墙土体进行室内干燥试验,通过电子天平记录试样失水过程,采用图像分析技术得到裂缝的开裂与扩展过程,利用数字图像相关技术得到开裂过程的位移场与应变场。结果表明:试样表面缺陷降低了开裂所需的拉应力,缺陷与边界的距离越小,引发开裂的缺陷临界尺寸就越小,因此裂缝更易在试样边界附近缺陷处产生;根据断裂力学理论,考虑含水率对土体性质的影响,裂缝失稳扩展需满足应力强度因子对含水率的增加率大于断裂韧性;理论推导出裂缝失稳扩展临界长度的计算方法,该方法初步得到了实测数据验证;随着含水率从45.6%降低到29.1%,失稳扩展临界长度与试样宽度比值从0.109减小到0.024,含水率越低裂缝越易进入失稳扩展阶段,开裂处一个微小的缺陷就可能引发裂缝的快速扩展;对土遗址表面进行保护时,应着重修补分布在土层边界区域的大尺寸缺陷;定期监测土遗址临空面,一旦发现开裂,应及时对裂缝及其附近缺陷进行修复,以防止裂缝失稳扩展。     

沿海地区复杂地层抗拔桩在深基坑中的试桩实例

通过沿海地区复杂地层中抗拔桩试桩实例,介绍了抗拔试验桩试验参数与方法以及深基坑中的抗拔桩施工技术：填石夹填土层成孔技术、桩端岩心取样技术与桩基清孔技术。试验表明,抗拔试验参数较为可靠且能满足结构设计的抗拔要求,为抗拔桩在深基坑中的应用研究提供了数据支撑。     

Modeling the 3D crack network and anisotropic permeability of saturated cracked soil

Cracks on a natural soil surface provide preferential pathways for water infiltration and contaminant solute transport. Before the mechanical property and permeability of cracked soil can be studied, a crack network model must first be established. Based on statistical analysis of crack geometry from field observations, a new method of representing a 3D crack network was developed. A horizontal plane of a crack network was derived using the Voronoi diagram. Each vertical crack was idealized as an inverted triangular prism. The 3D permeability tensor was determined by modeling the water flow through the crack network. A computer program was developed to generate a 3D crack network automatically and compute the permeability tensor of cracked soil at different depths. The model was verified by comparing the measured permeability and computed permeability of cracked soil. The results showed that the computed permeability was consistent with the measured permeability.     

融沉系数在季冻区高速公路路基冻害研究中的应用

在季节冻土地区, 防治路基冻害问题, 强调较多的往往是室内冻胀指标, 而对融沉指标考虑的较少. 根据2000-2002年对吉林省几条高速公路所做的路基冻害钻探调查和现场观测获得的资料, 对融沉系数与含水量和干容重的关系进行了统计分析, 举例说明了春季冻害调查和融沉系数资料在估计现场融沉和冻胀大小、分析路基冻害原因、评价筑路材料的抗冻性能等方面的应用.     

Deformation and crack development of a nailed loose fill slope subjected to water infiltration

The paper presents the characteristics of progressive movement and crack development observed in a loose fill slope reinforced by soil nails subjected to water infiltration. The purpose-built test slope was constructed by end-tipping completely decomposed granite on moderately gentle sloping ground with minimal compaction, and two rows of soil nails were installed after completion of the slope. Based on the field monitoring data obtained from a comprehensive instrumentation system, this field test has identified the initiation and development mechanism of deformation, including crack propagation in the test slope. The test results on the temporal and spatial variation of wetting-induced movement, water content distribution, and suction change as well as the formation and propagation of surficial cracks are presented. The causative mechanisms of wetting-induced deformations and their implications on the stability of nailed fill slopes are also presented and discussed.     

Influencing factors of geometrical structure of surface shrinkage cracks in clayey soils

In order to investigate the effects of temperature, thickness of soil layer, wetting and drying cycles and soil types on geometrical structure of surface shrinkage cracks in clayey soils, special software Crack Image Analysis System (CIAS) for analyzing shrinkage crack patterns was developed. Eight groups of soil samples were prepared and subjected to drying to crack in laboratory. The number of crack segments and intersections, average crack length, width and aggregate area, crack intensity factor (CIF), and the corresponding probability density functions (PDF) of these parameters were determined by analyzing several crack patterns derived from different experimental conditions. The results show that the soil cracking behavior and the geometrical structure of crack patterns are significantly influenced by these considered factors. There is a tendency of crack length, width, aggregate area and their most probable value (MPV) related to the PDF increases with temperature increase. With thicker soil layers, the average crack length, width, aggregate area and CIF are increased, and the main distribution ranges of crack length, width and aggregate area are increased also. When the soil is subjected to multiple wetting–drying cycles, the soil surface generates more irregular and coarse cracks. The number of short and narrow crack segments increases significantly, and the CIF decreases with an increase in wetting–drying cycles. It is also observed that the extent of cracking is directly related to the soil fines fraction and its plasticity index (I_P). The greatest CIF and crack width are observed in the soils with the largest fines fraction and highest I_P. In addition, the ratio of numbers of crack segments to intersections ranges from 1.5 to 2, and cracking mainly takes place in three stages: main-cracks initiation stage; sub-cracks initiation stage; terminal stable stage.     

砂土中单桩竖向抗压承载机制的离散元分析

将单桩视为平面问题,采用二维离散单元法分析了砂土中单桩竖向抗压承载机制。首先利用离散元模拟地基的形成、挖孔灌注桩的成桩过程以及地基土的双轴压缩试验;然后通过离散元模拟单桩竖向抗压静载试验,分析其承载机制。结果表明：随着桩的沉降增大,桩端阻力一直增大,桩侧摩阻力先增大后达到稳定值;单位桩长侧摩阻力从桩顶到桩端呈非线性增长趋势;当荷载达到桩的极限承载力时,桩端发生刺入破坏,导致桩侧与桩端附近土体的转动场梯度、应力场梯度增大,主应力发生大角度旋转。     

粉煤灰混凝土桩钻孔压灌工艺在软土地基上的应用

介绍了粉煤灰混凝土桩及钻孔压灌工艺的特点,指出了粉煤灰混凝土桩钻孔压灌工艺在软土地基施工中应注意的问题,并列举了２个工程实例。