基于电-力-声多物理场耦合数值模型的含水合物多孔介质声速和衰减特性研究

在物理模拟实验中对水合物微观赋存模式和饱和度进行准确控制和评价尚存在技术困难,仅依赖实验技术研究含水合物沉积物声学特性、建立储层参数解释模型存在局限性。采用基于有限元的数字岩石物理技术,针对悬浮、接触和胶结三种典型的水合物微观赋存模式分别建立多孔介质的三维电-力-声多物理场耦合模型,考察了微观赋存模式和水合物饱和度对多孔介质声速和衰减的影响规律,对比了声速数值模拟与理论模型计算结果,建立了声波衰减参数与水合物饱和度之间的关系式。研究结果表明：（1）对于三种水合物赋存模式,由于水合物相比孔隙水具有更高的弹性模量,多孔介质的声速随着水合物饱和度的增大而增大;水合物的存在导致声波在传播过程中遇到更多不连续的声阻抗界面,声衰减随着水合物饱和度的增大而近似线性增大;（2）悬浮和接触赋存模式条件下,水合物饱和度对多孔介质的声速和衰减影响规律基本一致;对于相同的水合物饱和度,胶结模式条件下含水合物多孔介质具有更高的声速和更小的声衰减;（3）通过合理选择参数值,利用权重方程与Lee改进的Biot-Gassmann Theory（BGTL）模型估算的含悬浮和接触模式水合物多孔介质的声速较为准确;通过等效介质理论模型C计算的含胶结模式水合物多孔介质的声速更为准确。研究结果可为获取复杂条件下含水合物沉积物的声学特性提供数值建模方法,为基于声波测井数据的水合物储层精细评价提供理论支撑。

Sound Velocity and Attenuation Characteristics of Hydrate-Bearing Porous Media Based on Numerical Model of Electrical-Mechanical-Acoustic Multi-Physics-Field Coupling

There are still technical difficulties in accurately controlling and evaluating the micro-distribution mode and saturation of hydrate in physical simulation experiments. Limitations exist in the experimental technologies for investigating the acoustic characteristics of hydrate-bearing sediments and establishing interpretation models of reservoir parameters. Three-dimensional numerical models were established for hydrate-bearing porous media based on digital rock physics technology. For the three kinds of hydrate micro-distribution modes (suspension, contact, and cementation), finite-element models were established individually based on the method of electrical-mechanical-acoustic multi-physics-field coupling. The effects of micro-distribution mode and hydrate saturation on sound velocity and attenuation of porous media were examined. The results of sound velocity from the numerical and theoretical models were compared. The relationship between acoustic attenuation parameters and hydrate saturation was established. It was demonstrated that: (1) for the three micro-distribution modes, the sound velocity of porous media increased with the increase of hydrate saturation due to the higher elastic modulus of hydrate compared with pore water; the existence of hydrate caused the sound wave to encounter more discontinuous acoustic impedance interfaces in the process of propagation, thus the sound attenuation increased approximately linearly with the increase of hydrate saturation; (2) under the conditions of suspension and contact modes, the influence of hydrate saturation on sound velocity and attenuation in porous media was quite similar; under the condition of cementation mode, the sound velocity was higher and the sound attenuation was lower for the porous media with the same hydrate saturation; (3) based on a reasonable selection of parameters, the sound velocity of hydrate porous media with suspension and contact modes of hydrate estimated by the weighted equation and Biot-Gassmann Theory modified by Lee (BGTL) model was more accurate; the sound velocity of porous media containing cemented hydrate calculated by the effective medium theoretical model C was more accurate. This study may provide a numerical modeling method for obtaining the acoustic characteristics of hydrate-bearing sediments under complex conditions, and provide a theoretical support for the fine evaluation of hydrate reservoirs based on acoustic logging data.