均质气层砂岩的声波吸收特征研究

Study on The Acoustic Absorption Characteristics of Homogeneous Gas-bearing Sandstone

岩石对声波能量的吸收与岩石的孔隙度、孔隙形状、孔隙中流体相态及性质、含流体的饱和度及岩石密度、弹性等因素有关。对均质气层砂岩的声波吸收特征进行了理论研究，分析了吸收系数与频率、波速及压力的关系。以此为基础，建立出2种均质气层砂岩声波吸收系数模型。第1种是以纵波速度及频率为变量的吸收系数模型，该模型中纵波速度在2～4km／s时，吸收系数变化最明显；第2种是以孔隙度、渗透率、饱和度等参数为变量的吸收系数模型，揭示了孔隙度、渗透率与吸收系数具有强相关性。砂岩在低含气饱和度时对吸收系数的影响不明显。研究认为纵波速度变化可以极大改变吸收系数。压力和温度会改变气体粘度和孔隙度，故对吸收系数也会有一定的影响。

The acoustic energy absorption of rocks is related to the rock porosity, the pore texture, the fluid-phase and the fluid properties/saturation, the rock density/flexibility and other influencing factors. Given is theoretical study on the acoustic absorption characteristics of homogeneous gas-bearing sandstone, analyzed the relationships among the absorption coefficient , the frequency, the compressional wave velocity and the pressure. Based on the above analyses, established are two acoustic absorption coefficient models for homogeneous gas sandstone. The variables involved in the first absorption coefficient model are P-wave velocity and frequency, and if the P-wave velocity is from the 2 km/s to 4 km/s, the absorption coefficients have the most obvious changes. The variables involved in the second absorption coefficient model are porosity, permeability and saturation, presenting the better relativity among the absorption coefficient , the permeability, the porosity and the saturation. For the gas-bearing sandstone, the impact of the low gas saturation on the absorption coefficient is not obvious. The result shows that the temperature and the pressure have some effects on the absorption coefficient.