ACOUSTIC CHARACTERISTICS OF HYDRATE-BEARING SEDIMENTS：A COMPARATIVE ANALYSIS OF EXPERIMENTAL AND NUMERICAL SIMULATIONS RESULTS
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摘要:
含水合物沉积物声学特性在水合物勘探中非常重要。针对含水合物沉积物声学特性，前人通过实验模拟及岩石物理建模已取得一定的进展，但基于实验条件开展的数值模拟及其结果的对比研究仍鲜有涉及。笔者拟采用实验室物理模拟与实验储层数值模拟相结合的方法，通过物理实验模拟获得水合物储层声学特征。在此基础上，以实验物理模型以及声波采集系统为基本构建对应条件下的近似地质模型和声波观测系统，分别在50 kHz和80 Hz频率条件下获得具有不同水合物饱和度储层的波形记录和波场快照，并获得不同时间点和饱和度条件下的储层速度，对比分析实验模拟与数值模拟获得结果的异同。研究表明在3种模拟条件下获得的不同时刻的含水合物储层声速对应关系良好，数值模拟结果很好地印证了实验室模拟实验的结果，表明在实验室内进行相应物理模型的岩石物理模拟实验具有可行性。将实验模拟与数值模拟结果同野外探测数据对比分析，具有一致的变化趋势，表明物理模拟实验和数值模拟结果对野外勘探数据分析具有重要的指导意义。
Abstract:Acoustic characteristics of hydrate-bearing sediments are very important in hydrate exploration. So far, some important research progresses have been reached in experimental simulation and rock physics modeling. However, the numerical simulation based on experimental conditions and comparative studies between the above are still lacking. This paper intends to obtain the acoustic characteristics of hydrate reservoir through physical experiment simulation by combining laboratory physical simulation together with experimental reservoir numerical simulation. On the basis, a geological model is constructed based on the simulated experimental device model, and the reservoir velocity results obtained at the frequencies of 50 kHz and 80 Hz under different hydrate saturation conditions, and the wave field snapshots at different time points and saturation conditions are obtained. Comparative analysis of the similarities and differences are carried out between the results obtained by experimental simulation and numerical simulation. The research shows that the correlation between the wave velocity of the hydrate reservoir at different times obtained under the three simulation conditions is good. The numerical simulation results confirm the results of the laboratory simulation experiments, suggesting that it is feasible to carry out corresponding rock physical simulation experiments in laboratory. Comparing the results of experimental simulation and numerical simulation experiment with field detection data, there is a consistent change trend, indicating that the results of physical simulation experiment and numerical simulation have important guiding significance for field exploration data analysis.
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表 1 实验样品各层
位在不同水合物饱和度条件下的数值模型输入参数 Table 1. The input parameters of the numerical model for each layer of the experimental sample under different hydrate saturations
时间 层位 Kf
/GPaKm
/GPaKdry
/GPaPm
/（g/cm3）ρf
/（g/cm3）κ
/（10−15 m2 )ϕ
/%0 h 层4 2.5 58.32 1.209 2.692 1.032 2.0 39.8 层3 2.5 58.32 1.334 2.692 1.032 1.53 38.3 层2 2.5 58.32 1.209 2.692 1.032 2.0 39.8 层1 2.5 58.32 1.334 2.692 1.032 1.53 38.3 54 h 层4 2.6 47.383 1.175 2.676 1.032 1.32 37.5 层3 2.57 50.319 1.28 2.684 1.032 1.18 36.9 层2 2.6 47.383 1.175 2.676 1.032 1.32 37.5 层1 2.53 53.656 1.288 2.686 1.032 1.34 37.6 148 h 层4 2.87 38.538 1.395 2.644 1.032 0.467 32.2 层3 2.87 38.806 1.509 2.656 1.032 0.363 31 层2 2.87 38.538 1.395 2.644 1.032 0.467 32.2 层1 2.87 38.806 1.509 2.656 1.032 0.363 31 245 h 层4 4.15 58.32 1.046 2.692 1.032 2.0 39.8 层3 4.35 58.32 1.155 2.692 1.032 1.53 38.3 层2 4.11 58.32 1.046 2.692 1.032 2.0 39.8 层1 3.89 58.32 1.155 2.692 1.032 1.53 38.3 注：表中Kf，Km，Kdry，ρm，ρf，κ和ϕ分别表示孔隙流体的等效体积模量，沉积物组成矿物的等效体积模量，沉积物骨架的等效体积模量，沉积物组成矿物的等效密度，孔隙流体的等效密度，沉积物的渗透率和沉积物的孔隙度。 
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表 2 实验模拟与数值模拟纵波速度对比
Table 2. Comparison of P-wave velocity between experimental simulation and numerical simulation
/(m/s) 实验模拟（超声频率50 kHz） 数值模拟（震源频率50 kHz） 数值模拟（震源频率80 Hz） 0 h 层4 1 905.97 1 984.13 1 946.17 层3 1 807.22 1 875.00 1 830.57 层2 1 880.87 1 971.09 1 868.79 层1 1 762.63 1 825.93 1 768.58 54 h 层4 1 996.00 2 068.97 2 028.15 层3 1 880.87 1 936.73 1 866.93 层2 1 977.58 2 061.86 2 017.17 层1 1 845.01 1 879.70 1 874.38 148 h 层4 2 084.78 2 161.38 2 068.21 层3 2 043.59 2 118.64 2 072.77 层2 2 105.26 2 172.34 2 126.70 层1 2 074.68 2 142.86 2 088.89 245 h 层4 2 504.17 2 497.92 2 520.11 层3 2 564.10 2 669.04 2 585.97 层2 2 469.13 2 535.93 2 503.33 层1 2 417.40 2 457.00 2 425.81
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