气层和异常高压带地震特征的超声波实验研究

ULTRASONIC WAVE EXPERIMENTAL RESEARCH ON THE SEISMIC CHARACTERISTICS OF GAS RESERVOIRS AND ABNORMAL HIGH PRESSURE ZONES

利用超声波观测方法在实验室内分别研究了砂岩露头岩样在不同孔隙流体压力和含气 (水 )饱和度条件下所引起的地震响应 ,由实验观测得出如下结论 :①纵横波速度、品质因子、主频均随孔隙压力从低到高而逐渐减小。②随含水饱和度的增加或含气饱和度的减小 ,纵波速度在低含水饱和度基本保持不变 ,而当含水饱和度达到一定程度时 ,纵波速度明显增大 ;而随含水饱和度的增加 ,横波速度略有降低或基本保持不变 ;③砂岩部分气水饱和时 ,纵波品质因子和主频最小 ;而横波品质因子在低含水饱和度时 ,随含水饱和度的增加 ,横波品质因子和主频降低较快 ,当含水饱和度达到一定值后 ,横波品质因子和主频基本保持不变。这些认识可以作为利用地震方法来检测异常高压带和含气层的标志 ;同时也指明了用地面地震资料来检测异常高压带和含气层时应该使用的参数和方法。

Caused by different pore fluid pressures and different gas (water) saturations,the seismic response to sandstone outcrop samples was respectively studied in laboratory by use of ultrasonic wave observation method.Through experimental observation,it is concluded that ① the velocities,Q values and master frequencies of compressional wave and shear wave all decrease with the increase in pore fluid pressure;② along with the increase in water saturation or the decrease in gas saturation,the compressional wave velocity is basically constant in low water saturation,then obviously increases as the water saturation reaches to a certain value;along with the increase in water saturation,the shear wave velocity slightly decreases or basically maintains constant;and ③ when the sandstone is partially saturated by gas and water,the Q value and master frequency of compressional wave are of the minimum values;when the water saturation is low, the Q value and master frequency of shear wave rapidly decrease with the increase in water saturation;and when the water saturation reaches to a certain value,the Q value and master frequency of shear wave are constant.All these mentioned above may be taken as the criteria of detecting abnormal high pressure zones and gas reservoirs by use of seismic methods.Meanwhile it is also pointed out that the parameters and methods should be adopted as the surface seismic data are used for detecting abnormal high pressure zones and gas reservoirs.