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萨克拉门托(Sacramento)盆地上的两次野外试验和在格林河(Green River)盆地上的一次野外试验证明,利用纵波和横波共深度点地震对比剖面方法,可以直接检测天然气砂岩储集层。萨克拉门托盆地地震测线布置在正在生产的气田上方,目的是为了与纵波剖面上的振幅异常对比。在岩性界面上纵波和横波剖面为强度相当的反射;但在含气层界面上引起纵波的亮点振幅异常,而横波剖面上却未显示出同样的异常。这些响应与实验室观测结果是一致的,即纵波速度对进入含液体孔隙中的天然气比横波速度要敏感得多。格林河盆地地震测线布置在比较深的气田上方,天然气产自超压储集层,这个超压储集层却未引起常规的纵波亮点。该储集层的纵波反射强度只比横波反射强度大50%,而其他主要反射层的纵波强度和横波强度相当。这三次野外试验表明,在横波同相轴上无异常振幅时,可证实相应纵波亮点是由于含天然气引起的,这一技术对于证实微弱的和强的振幅异常都是有用的。
Two field tests in the Sacramento Basin and a field experiment in the Green River Basin have demonstrated that sandstone reservoirs can be directly detected using the method of cross-section comparison of P-wave and S-wave common-depth points. The Sacramento Basin seismic line is positioned above the gas field in production for the purpose of contrasting with the amplitude anomalies in the longitudinal wave profile. In the lithologic interface, the P-wave and S-wave profiles are fairly strong reflection; however, the bright-spot amplitude anomalies in the gas-bearing interface are caused at the gas-bearing interface, while the same anomalies are not observed in the S-wave profile. These responses are consistent with laboratory observations that the P-wave velocity is much more sensitive to the velocity of the S-wave entering the liquid-containing pores. The geochemical survey of the Green River basin is arranged above the deeper gas fields. Natural gas is produced from overpressured reservoirs. The overpressure reservoir has not caused the conventional longitudinal wave bright spots. The compressive strength of the longitudinal wave of this reservoir is only 50% greater than that of the transverse wave, whereas the compressional and shear wave intensities of the other primary reflectors are comparable. These three field tests show that there is no abnormal amplitude in the shear-wave events and that the corresponding P-wave highlights are due to the presence of natural gas. This technique is useful for verifying weak and strong amplitude anomalies.