冻土带天然气水合物岩石物性及地震电磁响应特征研究

发布时间：2018-05-24 23:18

本文选题：冻土带天然气水合物 + 广义混合率　；参考：《中国科学技术大学》2017年博士论文

【摘要】：天然气水合物是可持续发展的清洁能源,然而受开采技术等制约,全球水合物开发基本处于室内试验和室外资源普查、试采阶段。相比海域天然气水合物,陆域水合物的勘探开发似乎更容易,然而目前世界上仅麦索雅哈气田是唯一实现工业性开采的陆域水合物藏。作为世界第三大冻土国,我国的陆域天然气水合物资源前景广阔,但是由于起步晚,对陆域冻土带天然气水合物的成藏模式及其勘探技术均研究薄弱,至今仅青藏高原北部木里地区钻获水合物样品。本文从复杂多相介质声学、电学性质岩石物理模型出发,建立起适合冻土区岩石物性的水合物模型。然后通过数值模拟,研究冻土带天然气水合物的地震学响应和电磁响应,探索我国冻土带天然气水合物成藏模式及综合地球物理勘探标志。岩石物性是地球物理勘探的基础。已有的天然气水合物岩石物理模型适用于高孔隙度的海域沉积层,且多考虑为球状孔隙。本文针对我国冻土带沉积层孔隙度低的特点,利用广义混合率模型研究任意孔隙形状的多相介质声学、电学性质,获得了广义混合率模型参数的变化规律及其与微观结构的关系,与广泛应用的差分有效介质(DEM)模型和自洽(SC)模型比较,具有更好的普适性,其结果获得大量实验数据的验证。相对于在测井上应用广泛的Archie公式,广义混合率可以解决Archie公式参数多、仅限一项介质导电、且仅适用于导电流体包围固体颗粒(Water-wet grains)结构,而不适合弱导电流体包围固体颗粒(Oil-Wet grains)等问题,第一次给出了关于弱导电流体包围固体颗粒类型的广义混合率参数表达式,并通过对已有的几种水合物导电模型进行数值模拟,结合水合物电导率实验数据表明,水合物导电机制为导电流体包围在固体颗粒表面,推测水合物赋存模式为非固结型。含天然气水合物储层表现为高声波速度和高电阻率特点,这是陆域天然气水合物勘探识别的基础。本文根据已有地质、地球物理资料和岩石物理模型,建立了陆域天然气水合物模型,并通过数值模拟研究其地震学、电磁学响应特征。弹性波振幅随偏移距变化(AVO)正演模拟结果表明,含天然气水合物储层在近偏移距处的P波一次反射震相以及垂直地震剖面数据中直达P波震相的振幅均较弱,这种AVO弱振幅特点为陆域水合物地震响应特征。电磁法在低阻金属矿勘探中取得明显效果,由于陆域天然气水合物为高阻体,可控源电磁(CSEM)法目前尚未取得好的勘探效果。本文第一次将海洋CSEM的方法原理应用于陆域天然气水合物勘探中,数值模拟结果表明,其电场的振幅随偏移距变化(MVO)在储层位置获得更大的振幅。因此,地震AVO相对弱振幅与可控源电磁MVO的强振幅结合,有可能构成陆域冻土带天然气水合物综合地球物理勘探的指示特征。直流电阻率法一般很少应用于冻土带地区的地质勘探,因为电流难于穿透高阻的覆盖区。我们对线电极源使用电流密度分配公式CDA(Current DensityAllocation),发展了基于CDA的任意长电极直流电阻率三维非结构有限元数值模拟,并在此基础上,借鉴已有线电极模型处理测量电极的方法,使用线电极代替圆柱体电极,形成了基于CDA方法的线电极供电、线电极接收的长电极三维电阻率模拟方法。本文将该方法应用于陆域冻土带天然气水合物勘探中,结果表明,长电极在穿过水合物储层上方,具有明显的高阻异常。本文研究了裂隙对陆域水合物勘探中地震波速度的影响。结合岩石物理模型,实验数据以及测井响应,计算了沿测井纵向剖面的裂隙密度,结果表明陆域水合物的赋存状态与裂隙密切相关。地震波在裂隙介质中传播的数值模拟表明,当裂隙中流体(气体或液体:)不连通时,地震波速度基本与频率无关,而受裂隙形状影响较大。而当裂隙中流体处于连通状态时,地震波速度基本不受裂隙形状影响,而与频率有关。裂隙中流体通过裂隙相互连通的类型,其地震波速度与频率的响应为:高频低速、低频高速。裂隙中流体通过渗透性良好的孔隙骨架连通时,则表现为:低频低速,高频高速。根据冻土带特点,建立了水合物储藏的裂隙模型,研究其地震剖面的AVO和频率特点,并与实际地震勘探响应对比,结果表明流体通过裂隙相互流通的裂隙模型符合冻土带天然气水合物的储藏特点,可为冻土带天然气水合物成藏机制提供一些新的认识。
[Abstract]:Natural gas hydrate is a clean energy for sustainable development. However, under the restriction of mining technology, the development of global hydrate is basically in the laboratory test and the survey of outdoor resources and trial production. Compared with the marine natural gas hydrate, the exploration and development of land hydrate seems to be easier than that of marine natural gas hydrate, but at present, only the maajakaha gas field in the world is the only one. As the third largest permafrost in the world, the land area natural gas hydrate resources in China are very promising. However, because of the late start, the reservoir formation model and exploration technology of the natural gas hydrate in the continental permafrost zone are all weak. The complex multi-phase medium acoustics and electrical properties of rock physics model set up the hydrate model suitable for the rock physical property of the frozen soil area. Then through numerical simulation, the seismological response and electromagnetic response of natural gas hydrate in the permafrost zone are studied, and the reservoir model and comprehensive geophysical prospecting mark of the natural gas hydrate in the permafrost zone are explored. Rock physical property is the basis of geophysical exploration. The existing petrophysical model of gas hydrate is suitable for high porosity marine sediments and more considered spherical pores. In this paper, in view of the characteristics of low porosity in the deposited layer of the permafrost zone in China, the multiphase medium acoustics with arbitrary pore shape are studied by the generalized mixing rate model and the electrical properties are studied. The variation of the parameters of the generalized mixture rate model and its relationship with the microstructure are obtained. Compared with the widely used DEM model and the self consistent (SC) model, the generalized mixture rate model has a better universality and the result is verified by a large number of experimental data. The generalized mixing rate can be solved compared with the widely used Archie formula in the log. The Archie formula has many parameters, only one medium is conductive, and it is only suitable for conducting fluid to encircling solid particles (Water-wet grains) structure, but not suitable for the weak conducting fluid to encircling solid particles (Oil-Wet grains). Several existing models of hydrate conduction are simulated, and the experimental data of the conductivity of hydrates show that the gas hydrate conducting mechanism is surrounded by solid particles on the surface of the solid particles, and it is speculated that the mode of hydrate accumulation is non consolidation. The gas hydrate reservoir containing natural gas is characterized by high acoustic wave velocity and high resistivity, which is the natural gas of land domain. Based on the existing geological, geophysical data and rock physical models, a land domain natural gas hydrate model has been established in this paper, and its seismological and electromagnetics response characteristics are studied by numerical simulation. The results of the elastic wave amplitude with the offset variation (AVO) show that the gas hydrate reservoir is near the bias. The amplitude of the direct P wave phase in the P wave and vertical seismic profiles at the distance is weak, and the weak amplitude of the AVO is characterized by the seismic response of the land domain hydrate. The electromagnetic method has achieved obvious effect in the exploration of low resistivity metals, because the land domain gas hydrate is a high resistivity body, and the controllable source electromagnetic (CSEM) method has not yet been found. For the first time, the method principle of marine CSEM is applied to the exploration of natural gas hydrate in the land domain. The numerical simulation results show that the amplitude of the electric field increases with the shift distance (MVO) in the reservoir position. Therefore, the relative weak amplitude of the earthquake AVO is combined with the strong amplitude of the controllable source electromagnetic MVO, and it may be constructed. The direct-current resistivity method is generally rarely applied to geological exploration in the permafrost zone, because the current is difficult to penetrate the high resistance coverage area. We use the current density distribution formula CDA (Current DensityAllocation) for the line electrode source to develop the CDA based arbitrarily. On the basis of the three-dimensional non structural finite element numerical simulation of the long electrode DC resistivity, and on this basis, using the wire electrode model to deal with the measuring electrode, using the wire electrode instead of the cylinder electrode, the three dimensional resistivity simulation method for the line electrode received by the wire electrode based on the CDA method is formed. This method is applied to this method in this paper. In the exploration of natural gas hydrate in the continental permafrost zone, the results show that the long electrode has obvious high resistivity anomalies over the hydrate reservoir. The effect of the crack on the seismic wave velocity in the exploration of land hydrate is studied. The results show that the occurrence of the marine gas hydrate is closely related to the fissure. The numerical simulation of the seismic wave propagation in the fractured medium shows that when the fluid (gas or liquid) is not connected in the fissure, the velocity of the seismic wave is irrelevant to the frequency, but is greatly influenced by the shape of the fissure. It is not affected by the shape of the fissure, but it is related to the frequency. The response of the fluid through the crack interconnected in the crack is the response of the velocity and frequency of the seismic wave: high frequency and low frequency, low frequency and high speed. When the fluid through the porous skeleton is connected by the good permeability in the fissure, the fluid is characterized by low frequency, low speed, high frequency and high speed. According to the characteristics of the permafrost zone, the hydration is established. The AVO and frequency characteristics of the seismic profile are studied and compared with the actual seismic response. The results show that the fissure model flowing through the fissure conforms to the storage characteristics of the natural gas hydrate in the permafrost zone, and can provide some new understanding for the gas hydrate formation mechanism of the permafrost zone.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P618.13

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