利用声波资料计算天然气水合物饱和度的可靠性实验

Reliability experiment on the calculation of natural gas hydrate saturation using acoustic wave data

为了探讨利用声波速度数据计算天然气水合物(以下简称水合物)饱和度的可靠性,通过岩石物理实验测量非固结砂泥沉积物中水合物生成过程中的纵、横波速度及其变化值;利用物质平衡方程,结合pVT状态方程及其测试条件,建立了实验过程中水合物饱和度的计算模型;在此基础上,分析了非固结沉积物声波速度随水合物饱和度增加的变化规律,利用修正的Lee权重声波公式,计算了水合物的饱和度,并与实验得到的饱和度数据进行了比较。研究结果表明:(1)在水合物含量达到一定程度的情况下,可以利用声波资料计算水合物的饱和度;(2)随着沉积物中水合物含量的不断增加,非固结砂泥沉积物的纵、横波速度也随之增大,二者之间具有较好的线性相关性;(3)利用声波资料计算所得的水合物饱和度数值与实验室测试得到的结果可比性较高、误差较小。结论认为,该研究成果为利用实际声波测井资料计算水合物的饱和度提供了依据。

In this paper, compression wave velocity, shear wave velocity and their change during the formation of natural gas hydrate in unconsolidated sand and mud sediments were measured through petrophysical experiments to discuss the reliability of calculating natural gas hydrate saturation by using acoustic velocity data. Then, a computation model of natural gas hydrate saturation during the experiments was established based on the material balance equation, combined with the p–V–T state equation and its test conditions. On this basis, the changing law of the acoustic velocity of the unconsolidated sediments with the increase of natural gas hydrate saturation was analyzed. Finally, natural gas hydrate saturation was calculated by using the modified Lee＇s weight sonic formula, and was compared with that measured in the experiments. And the following research results were obtained. First, the acoustic data can be used to calculate the natural gas hydrate saturation when the content of natural gas hydrate reaches a certain extent. Second, the compression and shear wave velocities of unconsolidated sand and mud sediments increase with the rise of their natural gas hydrate content, and they are in a good relationship of linear correlation. And third, the natural gas hydrate saturation calculated based on the acoustic data is close to that measured in the laboratory with much smaller errors. It is concluded that the research results provide a basis for the calculation of natural gas hydrate saturation using the actual acoustic logging data.