【作者】 兰慧田；

【导师】 刘财；

【作者基本信息】 吉林大学 ， 固体地球物理学， 2014， 博士

【摘要】 随着油气勘探开发程度的不断深入，裂缝性油气藏将在世界范围内的油气勘探与开发中占据越来越重要的地位。裂缝性储层介质的等效介质模型建立了地震数据与储层特征的联系。传统的等效介质模型未考虑岩石孔隙的存在，也无法对实际裂缝性储层中地震波的频散和衰减给出合理解释，利用基于传统的等效介质模型所建立的裂缝性储层地震波传播理论能够获得裂缝方位和裂缝密度信息，但无法获得裂缝的几何结构信息（如裂缝尺寸、裂缝开度）。然而，裂缝几何结构信息对裂缝性储层的渗透性具有重要影响。因此，为了实现裂缝性储层的精细描述，应采用更为完善的裂缝性储层介质等效介质模型来研究裂缝性储层的相关问题，进而力求通过所建立的地震波传播理论获得诸如裂缝几何结构信息等更多的储层信息，从而实现储层的定性评价以及储层参数的定量反演。裂缝性储层介质实际上是一种包含裂缝、岩石孔隙以及流体的含流体裂缝性孔隙介质，裂缝性孔隙介质的等效介质模型能够更精确地描述实际裂缝性储层介质的性质，通过相应的等效介质模型研究裂缝性孔隙介质中的波动现象，认清地震波传播规律和响应特征可为裂缝性储层预测、流体识别以及储层参数反演提供新的技术手段。本文分析了几种常见的裂缝性孔隙介质等效介质模型的特点，Chapman(2003)模型能够对地震波频散和衰减给出合理的解释，在描述裂缝性储层介质性质方面较其他模型更具有优势，而且，目前已有的实际应用研究表明，利用基于该模型所发展起来的储层参数反演方法能够从野外观测数据中反演出裂缝尺寸、裂缝密度和裂缝方位，该模型具有良好的应用前景。因而，本文对基于Chapman模型的裂缝性孔隙介质的相关问题进行了研究，主要包括裂缝性孔隙介质地震波传播特性分析、波场数值模拟、频变AVO分析以及储层参数反演。为了充分认识地震波在裂缝性储层中的频散、衰减、方位各向异性等特性，本文开展了基于Chapman模型的裂缝性孔隙介质中地震波传播特性的研究。首先，从HTI介质的频率域弹性波方程出发，通过假定各种波的平面谐波解，推导基于Chapman模型的三维HTI介质中的Christoffel方程。然后，通过求解频散关系方程确定复速度，并给出相速度和逆品质因子的表达式。在此基础上，研究入射角、渗透率、裂缝尺寸、裂缝密度和流体类型对频散和衰减的影响，并对频散和衰减的方位特性及其影响因素进行分析，同时，从横波分裂的频率相关性和Thomsen参数的频率相关性两个角度来分析裂缝性储层介质的频率相关各向异性特征。研究结果表明：拟P波和拟SV波在裂缝性孔隙介质中传播时，将诱导流体在裂缝与孔隙之间发生流动，从而发生速度频散和衰减，拟SH波由于不挤压裂缝，不会诱导流体流动，从而不发生速度频散和衰减；由于裂缝的定向排列，速度频散和衰减将表现出方位各向异性，进而地震各向异性和横波分裂将表现出频率相关性；入射角、裂缝密度、渗透率、裂缝尺寸和流体类型对于地震波频散和衰减具有重要影响；入射角、裂缝密度、裂缝尺寸和流体类型也将影响相速度和衰减的方位特性；同时，与频率相关的各向异性和横波分裂也将受到裂缝密度、裂缝尺寸和流体类型的影响。为了从波场正演角度揭示裂缝性孔隙介质中由地震波诱导的流体中观流动引起的地震波频散、衰减以及与频率相关的各向异性，研究地震波在裂缝性孔隙介质中的传播机理及其波场响应特征，本文提出了基于Chapman模型的裂缝性孔隙介质波场数值模拟的时间域方法。根据Chapman模型有效刚度参数是与频率相关的复数值这一特点，采用Zener粘弹性模型匹配这些有效刚度参数，进而通过求解与裂缝性孔隙介质等效的粘弹各向异性介质的波动方程进行波场数值模拟。数值模拟算例表明，所提出的数值模拟方法正确地模拟了裂缝性孔隙介质中地震波场的传播特征，从波场快照、波形图、合成地震记录中可以明显观测到地震波的频散和衰减特性。地震波反射问题是地震勘探研究中的最基本也是最重要的问题之一，是反射波地震勘探的核心问题。本文研究了裂缝性孔隙介质中波的反射问题。以Chapman模型描述裂缝性孔隙介质，根据粘弹各向异性介质与基于Chapman模型的HTI介质在频率域本构方程的一致性，将粘弹各向异性介质中的波反射、透射系数的计算方法与Chapman模型相结合，给出了基于Chapman模型的HTI介质的地震波精确反射系数的计算方法。同时，采用前人提出的衰减各向异性介质反射波近似反射系数的计算公式对基于Chapman模型的HTI介质的反射系数进行了计算，两种方法在近似公式适用的范围内具有很好的一致性，表明了两种方法的有效性。在此基础上，就重要的储层参数对PP波频变反射系数的影响进行了分析，并进一步分析了反射PP波的频变AVO和频变AVOZ特性，研究表明：PP波频变反射系数对于裂缝密度、裂缝尺寸和孔隙度的变化具有良好的敏感性；PP波的频变AVO特性与上、下层介质的波阻抗关系有关，通过三个模型算例的计算，并参照Ren等(2009)对斑块饱和含气储层的分类方式，按照PP波反射系数的频率相关性将储层分为低频暗点储层、相移储层和低频亮点储层；PP波反射系数及其频变性质随着方位角的变化而变化。对于裂缝性储层的研究，裂缝尺寸、裂缝密度、孔隙度以及裂缝方位都是储层识别和评价的关键参数，储层参数反演对于储层的定性预测和定量描述至关重要。本文根据PP波频变反射系数对裂缝密度、裂缝尺寸、孔隙度变化具有良好敏感性这一特点，开展了利用遗传算法通过裂缝性孔隙介质的频变AVO、频变AVOZ进行储层参数反演的研究。在已知裂缝方位的情况下，通过频变AVO数据反演了裂缝密度、裂缝尺寸和孔隙度；而在裂缝方位未知的情况下，通过频变AVOZ数据对裂缝方位、裂缝密度、裂缝尺寸和孔隙度进行了同时反演；针对裂缝性薄储层，通过频变AVO数据实现薄层厚度、裂缝密度、裂缝尺寸和孔隙度的同时反演。反演方法具有一定的稳定性和抗噪性，为裂缝性储层参数反演提供了新的技术手段。更多还原

【Abstract】 With the deepening of the degree of oil and gas exploration and development,fractured reservoirs will become more and more important in the worldwide oil andgas exploration and development. The relationship between seismic data and reservoircharacteristics is build with the equivalent medium model for fractured reservoirsmedia. Traditional equivalent medium model do not consider the existence of thepores of the rock, cannot give a reasonable explanation for seismic wave dispersionand attenuation in actual fractured reservoirs, the information about fracture azimuthand fracture density can be got with the use of seismic wave propagation theory infractured reservoirs which is established based on traditional equivalent mediummodel, but the information about fracture geometry (such as fracture size, fractureaperture) can’t be got. However, the information about fracture geometry has animportant effect on reservoir permeability. Therefore，in order to achieve sophisticateddescription of fractured reservoirs, the more perfect equivalent medium model offractured reservoirs media should be used to research issues related to fracturedreservoirs, and then by using the established seismic wave propagation theory toobtain more reservoir information such as the information about fracture geometry, soas to realize the qualitative evaluation of the reservoir and reservoir parametersinversion.In fact, fractured reservoir is a kind of fractured porous media containing fractures,pore space of rocks and fluid. The equivalent medium models for fractured porousmedia can describe the property of the actual fractured reservoirs media moreaccurately. To research wave phenomena and recognize seismic wave propagation law and the response characteristics in fractured porous media through the correspondingequivalent medium model can provide new technical ideas for fractured reservoirprediction, fluid identification and reservoir parameters inversion. This paper analyzesthe characteristics of several common equivalent medium models for fractured porousmedia, the equivalent medium model of Chapman (2003) can give a reasonableexplanation for seismic wave dispersion and attenuation in fractured reservoirs, It hasmore advantages than other models on the description of the property of fracturedreservoirs media, moreover, the existing investigation for some practical applicationsshow that fracture size, fracture density and fracture azimuth can be inverted fromfield observation data with the use of the reservoir parameter inversion methodadvanced based on this model, this model has good application prospect. Therefore,this paper researches the issues related to fractured porous media based on Chapmanmodel, such as the characteristics analysis of seismic wave propagation in fracturedporous media, numerical simulation of wave field, frequency-dependent amplitudeversus offset analysis and reservoir parameter inversion.In order to fully understand seismic wave dispersion, attenuation, azimuthanisotropy and other characteristics in fractured reservoirs, this paper carry outseismic wave propagation characteristics research in fractured porous media based onChapman model. First, begin with frequency domain wave equation for HTI media,the Christoffel equation in the three-dimension HTI media based on Chapman modelis derived by assuming plane harmonic solution of various wave. Then, throughsolving the dispersion relation equation to determine the complex velocity and givethe expressions of phase velocity and quality factor. On this basis, researching theeffect of incidence angle, permeability, fracture size, fracture density and fluid type onseismic wave dispersion and attenuation, and analyzing the azimuth characteristics ofdispersion and attenuation and its influencing factors, meanwhile, through frequency-dependent shear wave splitting and the frequency-dependent property of Thomsenparameters to analyze frequency-dependent anisotropy characteristics of fracturedreservoirs media. The results show that when quasi P wave or quasi SV wave througha fractured porous rock, It will induce fluid flow occurs between fractures and pores result in velocity dispersion and attenuation, as to quasi SH wave, It will not squeezethe fractures and induce fluid flow, thus no velocity dispersion and attenuation.Because of the fractures are aligned in space, then velocity dispersion and attenuationwill show azimuth anisotropy, and then seismic anisotropy and shear wave splittingwill show frequency-dependent. Incidence angle, fracture density, permeability,fracture size and fluid type have important effect on seismic wave dispersion andattenuation. Incidence angle, fracture density, fracture size and fluid type have alsoeffect on the azimuth characteristics of phase velocity and attenuation. Meanwhile,frequency-dependent anisotropy and shear wave splitting will also be affected byfracture density, fracture size and fluid type.In order to reveal seismic wave dispersion, attenuation and frequency-dependentanisotropy caused by wave-induced mesoscopic fluid flow in fractured porous mediafrom the angle of the wave field forward modeling, and then to study the mechanismof seismic wave propagation and seismic response characteristics in fractured porousmedia, this paper advances a time-domain numerical simulation method of wave fieldin fractured porous media based on Chapman model. According to the characteristicsthat the effective stiffness coefficients of Chapman model are complex andfrequency-dependent, by using Zener models to fit the stiffness coefficients, and thencarrying out numerical simulation of wave field by solving the wave equation inviscoelastic anisotropic media which is equivalent to fractured porous media. Thenumerical simulation examples show that the advanced numerical simulation methodsimulates correctly seismic wave propagation characteristics in fractured porousmedia, seismic wave dispersion and attenuation characteristics can be observedclearly from the wave field snapshots, waveform and synthetic seismogram.Seismic wave reflection problem is one of the most basic and most important issues,It is the core issue of the reflection survey. This paper studies reflection problem ofwaves in fractured porous media. By using the Chapman model to describe thefractured porous media, according to the consistency between constitutive equationfor viscoelastic anisotropic media in frequency domain and the HTI media based onChapman model, combining the calculation method of reflection and transmission coefficients of waves in viscoelastic anisotropic media and the Chapman model topresent the calculation method of exact reflection coefficients of seismic waves inHTI media based on Chapman model. Meanwhile, by using the approximate formulasof the reflection coefficients in attenuative anisotropic media to calculate thereflection coefficients in the HTI media based on the Chapman model, two methodshave good consistency within the scope of the approximate formula applicable, whichshow that two methods are both effective. On this basis, analyzing the effects ofimportant reservoir parameters on PP-wave frequency-dependent reflectioncoefficient and further analyzing the frequency-dependent AVO characteristics and thefrequency-dependent AVOZ characteristics of reflected PP-wave, the researches showthat the PP-wave frequency-dependent reflection coefficient is sensitive to variationsof fracture density, fracture size and porosity; frequency-dependent AVOcharacteristics of reflected PP-wave have some connection with the relation of waveimpedance between the overlying formation and underlying formation. Through thecalculations of three model examples, and referring to the classification method forpatchy-saturated gas reservoirs advanced by Ren et al (2009), according tofrequency-dependent property of PP-wave reflection coefficient, classifying fracturedreservoirs into three classification, they are low-frequency dim-out reservoirs,phase-shift reservoirs and low-frequency bright-spot reservoirs. PP-wave reflectioncoefficient and its frequency-dependent characteristics vary with changes in azimuth.As to the studies on fractured reservoirs, fracture size, fracture density, porosityand fracture azimuth are all the key parameters in reservoir identification andevaluation, and the reservoir parameters inversion plays the significant role onqualitative prediction and quantitative description of fractured reservoirs. On the basisof the characteristics that PP-wave frequency-dependent reflection coefficient hasgood sensitivity to the variations of fracture density, fracture size and porosity, thispaper adopts genetic algorithm to carry out reservoir parameter inversion by using thefrequency-dependent AVO or frequency-dependent AVOZ in fractured porous media.In the case of known fracture azimuth, fracture density, fracture size and porosity areinverted by frequency-dependent AVO data. While in the case of unknown fracture azimuth, the fracture azimuth, fracture density, fracture size and porosity are invertedsimultaneously. For the thin fractured reservoir, the thickness of thin lay, fracturedensity, fracture size and porosity are inverted simultaneously. The advanced reservoirparameters inversion method in this paper has a certain stability and noise immunity,provides new techniques for reservoir parameters inversion in fractured reservoirs.更多还原