气体垂向运移体系下天然气水合物声学特性模拟实验研究

发布时间：2018-04-26 11:41

本文选题：天然气水合物 + 饱和度　；参考：《中国地质大学》2017年博士论文

【摘要】：天然气水合物具备巨大的资源潜力,在世界范围内广泛分布,在我国海域和陆上冻土带中也逐渐发现了水合物。当前,以地震波技术为主的地球物理勘探技术仍是海洋天然气水合物勘探的主要手段。由于野外获取的数据难以在水合物饱和度和声速之间建立关系,因此人们通常用实验的方法将水合物饱和度和声速之间建立相应的关系并进行速度模型验证。在合适的模型基础上希望利用获取的地震波参数和声波测井数据对储层资源量进行估算与评价。已有研究大多在封闭体系下对天然气水合物生成分解过程中声学响应特征进行研究,对更接近水合物实际成藏过程的气体运移条件下声学响应特征了解甚少。因此,采用实验模拟的方法研究气体垂向运移体系中水合物储层的声学特性,将对水合物地球物理勘探和资源评价具有重要意义。本文通过模拟气体垂向运移条件下水合物在沉积物中生成和分解过程,利用超声探测技术和时域反射技术(TDR),实时探测水合物的声速和饱和度变化,确定不同甲烷通量对水合物饱和度、声学响应特征的影响。通过上述模拟实验获取动态体系中声速随水合物饱和度的变化规律,验证速度模型在各种条件下的适应情况。在此基础上,同封闭体系下水合物形成过程中声学特性进行对比,揭示不同体系下含水合物沉积物的声学响应特征差异,根据理论模型和声学数据探讨水合物生成模式。通过相应的研究,一方面在技术方面取得创新,另一方面在不同体系下水合物的声学响应、速度模型的选取和水合物微观分布方面取得了新的认识,也为更加逼真模拟水合物的形成和真实理解水合物成藏过程提供了重要实验依据。在实验技术方面,采用数字示波器优化和改进了实验技术的数据采集系统,将数字示波器替代A/D数据采集卡应用到超声数据采集系统,相比数据采集卡数字示波器具有同等的数据存储和采集功能,并且在实验过程中能对待测波形进行直观观测,应用取得良好的效果。在实验装置中实现气体垂向运移体系,使用压差控制系统为气体的流动提供驱动力,为防止沉积物中水分的散失和气体运移通道的堵塞,将微孔烧结板、防水透气砂和下气室加热底板应用到实验体系,保证实验过程的顺利进行。将BROOKS质量流量控制器应用到实验体系,实现对反应体系的气体流量控制。系统地获得了气体垂向运移体系中水合物生成和分解实验的声学和饱和度数据,建立了气体垂向运移体系下声学和水合物饱和度的关系。对气体垂向运移体系下水合物声学特性研究表明水合物生成过程中的纵横波速度大于分解过程中的纵横波速度。在气体垂向运移体系下,当水合物饱和度在0-20%时,发现声速有一个小幅度的快速增加。当水合物饱和度在20%-60%时,声速的增加幅度变慢。当水合物饱和度大于60%时,声速的增加再次变快。发现含水合物沉积物声速随水合物饱和度的增加呈现出快速-慢速-快速增加的变化趋势。在此基础上,对进气端甲烷通量进行控制,探索了不同甲烷通量的水合物生成模拟实验。通过实验获取了不同甲烷通量对水合物生成速率及水合物生成量的影响:即甲烷供应通量越小,生成最大水合物饱和度所需时间越少;甲烷通量越大,生成最大水合物饱和度用时越长。在一定时间内,甲烷通量越大,越易形成高饱和度水合物。甲烷通量供应模式下声速同气体垂向运移体系下声速变化呈现出相似趋势,在水合物生成初期,声速有相对较快的增长;之后在水合物生成阶段,声速呈现出较为平缓的增长趋势;在水合物饱和度50%-60%左右,声速的增加速率明显变快。为了进行动态、静态体系水合物形成差异性对比,在二维实验装置中进行封闭体系模拟实验,并得到水合物生成过程中空间分布的初步认识:即水合物生成初期,水合物优先在粗粒沉积物中生成;水合物生成末期,粗粒和细粒对沉积物饱和度及声速影响不大。在沉积物中纵向上离气源越近,越易生成水合物,随着时间推移各层水合物饱和度逐渐趋于一致;在横向上水合物优先在反应釜周边生成,随后在反应釜内部生成。实验获得Vp-Vs间的经验公式,与野外同类型储层实地数据具有良好对比性,可为储层纵横波速度和水合物饱和度估算提供依据。将封闭体系下和气体运移体系下水合物声学特性进行对比分析,得出在封闭体系中,声速的增加较快,没有明显阶段性变化。在气体垂向运移体系下,声速体现出快速-慢速-快速增加的趋势。将南海北部陆坡实测声速同水合物饱和度数据与实验结果对比,结果表明气体运移体系下声速与水合物饱和度间关系同南海实测数据结果较为一致。在进行不同体系实验的基础上,将适应于水合物饱和度预测的速度模型进行验证。结果表明,在气体垂向运移体系下,适应的速度模型为权重方程、BGTL理论和等效介质理论,权重方程的预测值同实测值有较好一致性。由于本实验为松散沉积物体系,通过验证得知权重方程并不适应实测横波速度值。当水合物饱和度在20%-60%时,实验结果同等效介质理论模式A的计算结果相近。在甲烷通量供应模式下,适应的速度模型为BGTL理论和经过调整的等效介质理论。在权重方程中,权重方程预测的纵波速度值同实验测试值有相近的趋势,但计算值同实际值之间有一定差值。在等效介质理论中,当水合物饱和度为25%-55%时,实验结果同等效介质理论模式B计算结果相接近。当水合物饱和度为60%-70%时,实验测得结果同等效介质理论模式A结果相一致。在水合物饱和度大于80%以后,实测值趋向于等效介质理论模式C的计算值。BGTL理论和等效介质理论对南海沉积物中水合物饱和度预测有一定适应性。综上可知,速度模型在各体系下具有不同的适应性,由于水合物对沉积物声学影响较复杂,单一参数选择难以适应不同条件。BGTL理论和等效介质理论在各体系下具有较好的适应性。在高甲烷通量体系下,气体对沉积物声速的影响需要考虑,经过调整的等效介质理论模型不仅能对水合物饱和度进行估算,还能对水合物微观分布模式产生指导意义。改进和完善了水合物成藏的微观理论模型,根据理论模型并结合CT实验数据探讨了水合物在不同体系下的微观分布模式。在气体垂向运移体系下,水合物生成初始阶段,水合物优先在颗粒接触处和气泡表面以胶结方式形成,沉积物颗粒通过水合物壳相互结合在一起。之后水合物主要在孔隙流体中生成。随着水合物饱和度的增加,流体中的水合物同沉积物颗粒相互接触在一起,水合物充填满孔隙空间。在高甲烷通量渗漏体系下,水合物主要以颗粒接触模式生成,之后水合物会在孔隙流体中生成。随着水合物饱和度的增加,流体中的水合物同沉积物颗粒相互接触在一起,水合物以胶结模式生成。
[Abstract]:Natural gas hydrate has great resource potential and is widely distributed worldwide, and hydrates have been found in the sea area and the continental permafrost zone. At present, the geophysical exploration technology based on seismic wave technology is still the main part of the exploration of marine gas hydrate. The relationship between degree and sound velocity is established, so people usually establish the relationship between hydrate saturation and sound velocity by experimental method and verify the velocity model. On the basis of suitable model, we hope to estimate and evaluate the source of reservoir by using the obtained seismic wave parameters and acoustic logging data. Most of the research has been done. In the closed system, the acoustic response characteristics of the gas hydrate formation and decomposition process are studied. The acoustic response characteristics of the gas migration under the actual gas hydrate formation process are little understood. Therefore, the experimental simulation method is used to study the acoustic characteristics of the hydrate reservoir in the gas vertical migration system, and the hydrate will be used to hydrate the gas hydrate reservoir. Geophysical exploration and resource evaluation are of great significance. In this paper, by simulating the formation and decomposition process of hydrates under the condition of vertical migration of gas, ultrasonic detection and time domain reflectometry (TDR) are used to detect the velocity and saturation of hydrate in real time, and determine the difference of methane flux to hydrate saturation and acoustic noise. The variation of sound velocity in the dynamic system with hydrate saturation is obtained by the above simulation experiments, and the adaptation of the velocity model under various conditions is verified. On this basis, the acoustic characteristics of hydrate formation under the closed system are compared to reveal the acoustic response of the hydrate deposits in different systems. On the basis of theoretical model and acoustic data, the hydrate formation model is discussed. On the one hand, innovation is made on the one hand, and on the other hand, the acoustic response of hydrates, the selection of velocity model and the micro distribution of hydrate in different systems are new, and the more realistic simulation of hydrates is also made. In the experimental technology, the digital oscilloscope is used to optimize and improve the data acquisition system of the experimental technology. The digital oscilloscope is applied to the ultrasonic data acquisition system instead of the A/D data acquisition card. Compared with the data acquisition card digital oscilloscope, the digital oscilloscope has the same data. The storage and acquisition function, and can be used to observe the measurement waveform in the experimental process, and achieve good results. In the experimental device, the vertical migration system of gas is realized and the pressure difference control system is used to provide the driving force for the flow of gas. In order to prevent the loss of water in the sediment and the blockage of the gas migration channel, the micropores are burned. The BROOKS mass flow controller is applied to the experimental system and the gas flow control of the reaction system is applied to the experimental system. The acoustic and saturation data of the hydrates generation and decomposition experiments in the gas vertical migration system are systematically obtained. The relationship between acoustics and hydrate saturation under the vertical migration system of gas is established. The study of the acoustic characteristics of hydrates under the vertical migration system shows that the velocity of the longitudinal and transverse waves in the process of hydrate formation is greater than that in the decomposition process. Under the vertical migration system of gas, when the hydrate saturation is at 0-20%, the velocity of sound is found. A small amplitude increases rapidly. When the hydrate saturation is at 20%-60%, the increase of sound velocity slows down. When the hydrate saturation is more than 60%, the increase of sound velocity becomes faster. It is found that the velocity of the hydrate content of the hydrates shows a fast slow fast increasing trend with the increase of hydrate saturation. On this basis, the intake end is on the intake end. The methane flux is controlled and the simulation experiment of hydrate formation with different methane flux is explored. The effects of different methane flux on hydrate formation rate and hydrate formation are obtained by experiments. The smaller the methane supply flux is, the less time it takes to generate the maximum hydrate saturation; the greater the methane flux is, the greater the formation of the maximum hydrate is full. In a certain time, the greater the methane flux, the higher the formation of high saturation hydrate. The sound velocity in the methane flux supply mode is similar to that under the vertical migration system, and the sound velocity increases relatively quickly at the early stage of hydrate formation, and the sound velocity appears relatively flat in the hydrate formation stage. The slow growth trend; the rate of sound velocity increased obviously at the hydrate saturation of 50%-60%. In order to make the dynamic, the static system hydrate formation difference contrast, the closed system simulation experiment in the two-dimensional experimental device, and the preliminary understanding of the space distribution in the process of hydrate formation, namely, the early formation of hydrate formation, hydration. At the end of hydrate formation, coarse particles and fine particles have little effect on the saturation and sound velocity of the sediments. The closer to the gas source in the sediments, the more easily the hydrate is generated, and the hydrate saturation gradually tends to be consistent with the time. The empirical formula between the Vp-Vs and the field data of the same type reservoir in the field is well contrasted, which can provide the basis for estimating the velocity of the longitudinal and transverse waves and the hydrate saturation of the reservoir. The acoustic characteristics of the hydrate under the closed system and the gas migration system are compared and analyzed, and the sound velocity in the closed system is obtained. In the vertical migration system, the sound velocity reflects the trend of rapid, slow and rapid increase. Compared with the experimental results, the measured velocity of sound and hydrate saturation in the northern slope of the South China Sea is compared with the experimental results. The results show that the relationship between sound velocity and hydrate saturation under the gas migration system is the same as the measured data of the South China Sea. The results are consistent. On the basis of different system experiments, the velocity model adapted to the prediction of hydrate saturation is verified. The results show that the velocity model adapted to the gas vertical migration system is the weight equation, the BGTL theory and the equivalent medium theory are in good agreement with the measured values. This experiment is a loose sediment system. Through verification, it is found that the weight equation does not adapt to the measured shear wave velocity. When the hydrate saturation is at 20%-60%, the experimental results are similar to that of the equivalent medium theoretical model A. Under the methane flux supply model, the adaptive velocity model is the BGTL theory and the adjusted equivalent medium theory. In the weight equation, the longitudinal wave velocity predicted by the weight equation has a similar trend with the experimental test value, but there is a certain difference between the calculated value and the actual value. In the equivalent medium theory, when the hydrate saturation is 25%-55%, the experimental results are close to the results of the equivalent medium theoretical model B calculation. When the hydrate saturation is 60%-70%, the actual result is true. The results of the test are in accordance with the A results of the equivalent medium theory model. After the hydrate saturation is more than 80%, the measured values tend to be the equivalent medium theory model C value.BGTL theory and the equivalent medium theory for the prediction of hydrate saturation in the sediments of the South China Sea. Because of the complex effect of hydrate on sediment acoustics, the single parameter selection is difficult to adapt to the different conditions and the.BGTL theory and the equivalent medium theory have good adaptability. Under the high methane flux system, the effect of gas on the sound velocity of sediment needs to be considered, and the adjusted equivalent medium theory model can not only be considered. The estimation of hydrate saturation can also provide guidance for the micro distribution pattern of hydrates. The micro theoretical model of hydrate formation is improved and perfected. According to the theoretical model and the experimental data of CT, the micro distribution pattern of hydrate under different systems is discussed. Under the vertical migration system of gas body, the initial order of hydrate formation is formed. The hydrate is formed in the form of cementation at the particle contact and the surface of the bubble, and the sediment particles are combined together through the hydrate shells. Then the hydrate is generated mainly in the pore fluid. As the hydrate saturation increases, the hydrate in the fluid is contacted with the sediment particles, and the hydrate fills the void void. In the high methane flux leakage system, hydrates are generated mainly in the particle contact mode, and then hydrate will be generated in the pore fluid. With the increase of hydrate saturation, the hydrate in the fluid is exposed to the sediment particles, and the hydrate is produced in the cementation model.

【学位授予单位】：中国地质大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P618.13

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