地球物理技术在页岩储层裂缝研究中的应用

近年来北美等国外页岩气勘探的巨大成功和我国在南方海相页岩(包括涪陵焦石坝、长宁-威远及昭通等)中获得的重大突破表明,泥页岩裂缝的研究尤为重要.裂缝的发育程度是决定泥页岩气藏品质的重要因素,一般来说,裂缝越发育,气藏的富集程度越高.地球物理方法和技术贯穿于页岩气勘探开发的始终,也是识别泥页岩裂缝的重要手段.在对国内外大量页岩储层测试数据和研究成果全面系统调研和深入分析总结的基础上,总结了常规测井技术识别裂缝的特点以及测井新技术裂缝识别的原理和方法.现今有关泥页岩裂缝识别的地震研究工作主要存在下面三种思路和方法:基于对裂缝敏感的属性直接分析、基于施工过程中的裂缝响应特征分析以及基于学科综合的定量化分析预测和识别裂缝.根据以上思路,全面系统分析了泥页岩裂缝识别的各种地震方法.综合测井和地震的地球物理方法准确确定裂缝产状、裂缝长度及空间展布特征等参数,对寻找页岩气富集"甜点区"有着重要意义.     

泥页岩油气藏水平井评价对策与实践

随着泥页岩油气藏勘探程度不断深入,水平井数量成倍增长,给水平井测井评价带来机遇与挑战,但水平并测井解释方法还停留在直井思维上,且水平并响应特征与直并存在较大差剐.而泥页岩储层砂泥薄互层发育,各向异性、非均值性非常严重,砂体横向上不连续,给测井解释评价造成很大困难.本文根据实际资料,采用交互式反演方法,以寻找井眼轨迹与目的层的精细关系为目的,探索了泥页岩油气藏水平井测井评价方法以及应注意的事项.     

地震与测井数据综合预测裂缝发育带

章针对前新生代海相残留盆地碳酸盐岩裂缝识别这一难题提出一种利用地震与测井数据综合预测裂缝发育带的方法.用测井资料标识出裂缝发育层段，同时利用地震资料具有空间上数据点多、分布均匀的特点通过地震多属性的人工神经网络方法将测井与地震数据结合起来综合预测裂缝发育带，充分利用测井资料和地震资料的各自优势，达到在剖面上和区域上预测裂缝发育带的目的.本方法经过实际资料的处理与预测证实比常规方法预测精度高.     

成像测井解释模式在基岩油气藏裂缝性储层的应用研究

基岩油气藏裂缝性储层具有复杂的储集空间和储层非均质性,为了实现对基岩油气藏储层的精细评价,以地层微电阻率扫描成像测井和井周声波成像测井资料为核心,通过岩心资料标定,结合录井、常规测井、试油、地质等实际资料,系统建立了基岩油气藏变质岩储层的成像测井解释模式.根据成像测井模式的识别实现了对基岩油气藏特征的认识、准确的裂缝分析和现今地应力场分析.分析结果表明,研究区基底变质岩地层中基本以基岩内幕油气藏为主;裂缝以中高角度缝、网状裂缝为主,其主要走向与井旁断层走向大致平行,属纵裂缝;裂缝主要发育在东西两侧靠近断层、近源的构造陡坡上;现今最大水平主应力方向主要呈NE-SW和NEE-SWW.成像测井解释结果与地质情况吻合较好.     

基于频变AVO反演的页岩储层含气性地震识别技术

结合地震岩石物理技术,研究了叠前频变AVO反演在四川盆地龙马溪组页岩储层含气性识别中的应用.首先,应用Backus平均理论将测井数据粗化为地震尺度储层模型,应用传播矩阵理论进行高精度地震正演及井震标定,分析页岩气储层地震响应特征.其次,基于岩心观测结果,应用Chapman多尺度裂缝理论设计页岩气储层理论模型,研究储层衰减、频散以及对应的地震反射特征.应用该理论模型测试频变AVO反演方法,计算结果表明：对于研究区地层结构和地震数据,区分流体类型的优势频率不是地震子波的主频,还受层间调谐干涉等储层结构因素控制,也进一步说明理论模型测试和标定的重要性.最后,将频变AVO反演技术应用到四川盆地龙马溪组页岩地层,计算得到的频散属性为页岩气储层含气性识别提供依据.     

储层裂缝识别与评价方法新进展

裂缝发育程度决定着低渗储层的渗流和产出能力,但由于裂缝发育机制的复杂性,故裂缝性油气藏一直是勘探的重点和难点.目前裂缝评价方法多以常规测井资料为主,结合其它分辨率较高的诸如FMI测井、地层倾角测井等.本文列举的计算机层析成像技术、ANN技术、灰色系统评判法是在裂缝研究领域相对有效的识别和评价方法,在油田的现场应用中取得了良好效果.     

基于地震多属性融合的断层识别与评价——以塔里木盆地SHB地区碳酸盐岩缝洞型储层为例

塔里木盆地SHB地区的深部碳酸盐岩缝洞型储层主要发育于断裂破碎带,大多表现为断裂破碎形成的裂缝和后期溶蚀形成相互连通的断溶体。因此,断层的识别与精细评价成为该区缝洞型储层识别评价的基础。考虑到研究区处于沙漠腹部,深部地层的地震反射能量相对较弱,用单一地震属性难以实现断裂带的识别。本文针对研究区地震资料的地质-地球物理特征,提出融合多种地震属性的断层识别与评价方法。①利用地震剖面上“断裂+杂乱反射”特征,识别可能存在的断裂或裂缝带;②运用谱白化和倾角导向滤波方法,拓频并压制地震数据的随机噪声;③用去噪和拓频后的地震数据计算相干体、蚂蚁体等多种地震属性;④融合多种地震属性来识别和评价断层,并用剖面形态和平面切片的组合分析不同断裂系统的形成次序;⑤利用多种地震属性与稀疏脉冲反演结果综合进行缝洞体预测,与实钻结果对比具有良好的一致性。      

小波变换在裂缝识别和裂缝密度评价中的研究(英文)

通过常规测井曲线小波变换来评价裂缝参数是一个较新的研究课题。本文针对火山岩裂缝储层,对常规测井曲线做coif5、bior4.4和db5基小波的小波变换,通过变换后的分解信号与成像测井裂缝密度的对比研究,寻找出与裂缝密度相匹配的基小波,再将常规测井曲线在这个基小波下的分解信号与曲线变化率法相结合建立裂缝指示曲线来识别裂缝发育段,最后通过裂缝指示曲线与成像测井的裂缝密度之间的量化关系来比较准确的评价裂缝密度。将裂缝指示曲线法在松辽盆地南部进行了应用,通过裂缝指示曲线求取的裂缝密度与成像测井的裂缝密度之间的相对误差为0.53。     

频变AVO含气性识别技术研究与应用

在常规AVO理论的基础上,频变AVO属性计算方法利用多尺度裂缝介质模型中物性参数具有频变特征的优势,基于Zoeppritz方程建立反射系数与频率之间的数学关系,推导出截距、梯度、碳氢检测因子、流体检测因子、拟泊松比等AVO属性与频率之间的数学关系.应用地震反演方法,综合地质、地震、测井等数据,反演出高精度的频变AVO属性,在天然气敏感属性分析的基础上建立起频变AVO含气性识别技术.将该技术应用到川西新场陆相深层须家河组碎屑岩储层的含气性识别中,在孔隙度通常在1%~4%,渗透率普遍低于0.06×10^-3µm²的致密背景下,较准确地预测了孔隙度大于4％、渗透性偏高的富气优质储层分布带,为该区含气性识别难题的解决和钻井成功率的提高,提供了重要的技术支撑.     

页岩岩相测井表征方法——以准噶尔盆地玛湖凹陷风城组为例

页岩油气藏作为重要的非常规油气藏，富含巨大的油气资源潜力，且常形成于深湖-半深湖沉积体系.页岩中复杂的矿物成分以及沉积组构类型对于页岩储层物性、含油性和可动性具有重要的影响，因此“矿物成分+沉积组构”的岩相划分与识别是页岩储层油气勘探开发的关键所在.但由于目前常规测井纵向分辨率有限导致无法实现页岩中毫米尺度的沉积组构精细描述，在页岩“矿物成分+沉积组构”岩相的识别方面尚未形成完整的方法理论体系.本文由此将利用岩心刻度测井的方法，通过岩性扫描测井与微电阻率成像测井相结合的方法，对玛湖凹陷风城组页岩层段的矿物成分和沉积组构类型进行连续识别，实现单井页岩段“矿物成分+沉积组构”岩相类型划分.通过岩相划分结果与现场试油试采资料相对照，发现薄层状与厚层状长石-石英质泥页岩相叠置发育的岩相组合产能最佳，因此可作为风城组页岩层段的优势岩相组合进行深入研究，为后续勘探开发提供参考．     

Fluid identification based on P-wave anisotropy dispersion gradient inversion for fractured reservoirs

Fluid identification in fractured reservoirs is a challenging issue and has drawn increasing attentions. As aligned fractures in subsurface formations can induce anisotropy, we must choose parameters independent with azimuths to characterize fractures and fluid effects such as anisotropy parameters for fractured reservoirs. Anisotropy is often frequency dependent due to wave-induced fluid flow between pores and fractures. This property is conducive for identifying fluid type using azimuthal seismic data in fractured reservoirs. Through the numerical simulation based on Chapman model, we choose the P-wave anisotropy parameter dispersion gradient (PADG) as the new fluid factor. PADG is dependent both on average fracture radius and fluid type but independent on azimuths. When the aligned fractures in the reservoir are meter-scaled, gas-bearing layer could be accurately identified using PADG attribute. The reflection coefficient formula for horizontal transverse isotropy media by Rüger is reformulated and simplified according to frequency and the target function for inverting PADG based on frequency-dependent amplitude versus azimuth is derived. A spectral decomposition method combining Orthogonal Matching Pursuit and Wigner–Ville distribution is used to prepare the frequency-division data. Through application to synthetic data and real seismic data, the results suggest that the method is useful for gas identification in reservoirs with meter-scaled fractures using high-qualified seismic data.     

Azimuthal anisotropy analysis of walkaround vertical seismic profiling vertical seismic profiling: a case study from Saudi Arabia

Understanding fracture orientations is important for optimal field development of fractured reservoirs because fractures can act as conduits for fluid flow. This is especially true for unconventional reservoirs (e.g., tight gas sands and shale gas). Using walkaround Vertical Seismic Profiling (VSP) technology presents a unique opportunity to identify seismic azimuthal anisotropy for use in mapping potential fracture zones and their orientation around a borehole. Saudi Aramco recently completed the acquisition, processing and analysis of a walkaround VSP survey through an unconventional tight gas sand reservoir to help characterize fractures. In this paper, we present the results of the seismic azimuthal anisotropy analysis using seismic traveltime, shear‐wave splitting and amplitude attenuation. The azimuthal anisotropy results are compared to the fracture orientations derived from dipole sonic and image logs. The image log interpretation suggests that an orthorhombic fracture system is present. VSP data show that the P‐wave traveltime anisotropy direction is NE to SW. This is consistent with the cemented fractures from the image log interpretation. The seismic amplitude attenuation anisotropy direction is NW to SE. This is consistent with one of the two orientations obtained using transverse to radial amplitude ratio analysis, with the dipole sonic and with open fracture directions interpreted from image log data.     

Contributions of non-tectonic micro-fractures to hydraulic fracturing—A numerical investigation based on FSD model

Shale gas has been discovered in the Upper Triassic Yanchang Formation, Ordos Basin, China. Due to the weak tectonic activities in which the shale plays, core observations indicate abundant random non-tectonic micro- fractures in the producing shales. The non-tectonic micro-fractures are different from tectonic fractures and are characterized by being irregular, curved, discontinuous, and randomly distributed. The role of micro-fractures in hydraulic fracturing for shale gas development is currently poorly understood yet potentially critical. Two-dimensional computational modeling studies have been used in an initial attempt toward understanding how naturally random fractured reservoirs respond during hydraulic fracturing. The aim of the paper is to investigate the effect of random non-tectonic fractures on hydraulic fracturing. The numerical models with random non-tectonic micro-fractures are built by extracting the fractures of rock blocks after repeated heating and cooling, using a digital image process. Simulations were conducted as a function of: (1) the in-situ stress ratio; (2) internal friction angle of random fractures; (3) cohesion of random fractures; (4) operational variables such as injection rate; and (5) variable injection rate technology. A sensitivity study reveals a number of interesting observations resulting from these parameters on the shear stimulation in a natural fracture system. Three types of fracturing networks were observed from the studied simulations, and the results also show that variable injection rate technology is most promising for producing complex fracturing networks. This work strongly links the production technology and geomechanical evaluation. It can aid in the understanding and optimization of hydraulic fracturing simulations in naturally random fractured reservoirs.     

利用地震叠前数据预测火山岩裂缝的方法和效果分析——以松辽盆地北部徐家围子断陷营城组火山岩为例

裂缝问题是火山岩复杂岩性油气藏勘探开发中必须考虑的重要因素之一.火山岩储层裂缝预测的准确性直接影响着油气的产能、钻井工艺和增产改造措施等.本文主要根据等效HTI介质(扩容各向异性介质)的特性,立足地下介质各向异性理论,利用三维地震叠前P波在HTI介质中的属性分布特征来检测裂缝的发育情况.利用三维地震叠前P波裂缝检测技术在松辽盆地北部徐家围子断陷深层营城组火山岩中尝试开展了储层裂缝发育预测研究.通过研究建立了火山岩裂缝地震叠前预测方法,并对营城组火山岩裂缝发育情况进行预测,结果表明裂缝主要分布在工区中部构造高部位,发育方向以北北西向为主.最后利用测井资料和钻井产能资料等进行效果分析,证实该技术对于认识火山岩储层裂缝发育具有实际应用价值,说明应用地震资料开展储层裂缝预测具有横向分辨率高、实现井间分布描述和宏观空间分布规律清楚等特点.     

Numerical evaluation of the shear stimulation effect in naturally fractured formations

In shale gas fracking, the stimulated natural fracture system is often critical to the gas production. In this paper, we present the results of state-of-the-art modeling of a detailed parametric evolution of the shear stimulation effect in discrete fracture network (DFN) formations. Two-dimensional computational modeling studies have been used in an attempt towards understanding how naturally fractured reservoirs response in hydraulic fracturing. Simulations were conducted as a function of: (1) the in-situ stress ratio; (2) internal friction angle of DFN; (3) DFN orientation with the stress field; and (4) operational variables such as injection rate. A sensitivity study reveals a number of interesting observations resulting from these parameters on the shear stimulation in natural fracture system. This work strongly links the production technology, geomechanical evaluation and aids in the understanding and optimization of hydraulic fracturing simulations in naturally fractured reservoirs.     

碳酸盐岩裂缝性储层测井识别及评价技术综述与展望

由于碳酸盐岩裂缝发育机制的复杂性,开展碳酸盐岩裂缝性储层的识别与评价一直是测井分析的热点和难点.本文基于大量文献调研,梳理了碳酸盐岩裂缝的定义、成因和分类,系统归纳了碳酸盐岩裂缝性储层的测井响应特征及评价方法,并进行了实例分析.研究表明,常规测井方法对碳酸盐岩裂缝均有不同程度的揭示,基于不同原理的常规测井方法对碳酸岩盐裂缝的响应程度差异显著,利用常规测井方法对碳酸岩盐储层裂缝识别应遵循综合识别原则;碳酸盐岩裂缝成像测井识别方法中,电阻率成像测井、偶极声波测井和核磁共振测井反映裂缝较为直观,但成本高;基于常规测井资料的灰色关联识别方法、神经网络识别方法、小波多尺度识别方法等非线性数学方法,弥补了常规测井和成像测井识别碳酸盐岩裂缝的不足,并且取得较好的应用效果.     

The 3D shear experiment over the Natih field in Oman: the effect of fracture-filling fluids on shear propagation

This is the final paper in a series on the 3D multicomponent seismic experiment in Oman. In this experiment a 3D data set was acquired using three-component geophones and with three source orientations. The data set will subsequently be referred to as the Natih 9C3D data set. We present, for the first time, evidence demonstrating that shear waves are sensitive to fluid type in fractured media. Two observations are examined from the Natih 9C3D data where regions of gas are characterized by slow shear-wave velocities. One is that the shear-wave splitting map of the Natih reservoir exhibits much larger splitting values over the gas cap on the reservoir. This increase in splitting results from a decrease in the slow shear-wave velocity which senses both the fractures and the fracture-filling fluid. Using a new effective-medium model, it was possible to generate a splitting map for the reservoir that is corrected for this fluid effect. Secondly, an anomaly was encountered on the shear-wave data directly above the reservoir. The thick Fiqa shale overburden exhibits a low shear-wave velocity anomaly that is accompanied by higher shear reflectivity and lower frequency content. No such effects are evident in the conventional P-wave data. This feature is interpreted as a gas chimney above the reservoir, a conclusion supported by both effective-medium modelling and the geology.
With this new effective-medium model, we show that introduction of gas into vertically fractured rock appears to decrease the velocity of shear waves (S2), polarized perpendicular to the fracture orientation, whilst leaving the vertical compressional-wave velocity largely unaffected. This conclusion has direct implications for seismic methods in exploration, appraisal and development of fractured reservoirs and suggests that here we should be utilizing S-wave data, as well as the conventional P-wave data, as a direct hydrocarbon indicator.     

塔河油田碳酸盐岩缝洞型储层的测井识别与评价方法研究

塔河油田奥陶系以碳酸盐岩为主，油气的主要储渗空间为裂缝和溶蚀孔洞，具有很强的非均质性．本文利用常规及成像测井资料，对碳酸盐岩缝洞型储层的识别与评价方法进行研究．为了综合各种测井方法识别裂缝，建立了综合裂缝概率模型，计算综合裂缝概率指示裂缝的发育程度．利用地层微电阻率扫描成像测井资料进行裂缝和溶蚀孔洞的定性、定量解释．定量计算的裂缝参数为：裂缝密度、裂缝长度、裂缝平均宽度、平均水动力宽度、裂缝视孔隙度；定量计算的溶蚀孔洞参数有：面孔率、孔洞密度．根据缝洞型储层孔隙空间类型及其中子孔隙度、补偿密度、声波、双侧向电阻率的测井响应物性特征，建立缝洞型碳酸盐岩储层复杂孔隙介质解释模型，用于确定裂缝、溶蚀孔洞孔隙度和评价储层．     

基于Choi-Williams时频分布的阵列声波测井信号时频分析

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