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南海北部东沙隆起区广泛发育新生代碳酸盐岩台地,台地上原地生长的生物礁由于孔隙、裂缝的发育加之上覆泥岩盖层的阻挡,形成了非常好的油气储层。文章结合测井资料,利用谱分解方法分析了流花碳酸盐岩台地高孔隙度储层的地震时频特征,发现在孔隙极为发育的储层顶部地震波能量出现明显衰减,时频谱上表现为中心频率显著降低;但在分频剖面上,除了垮塌溶蚀层段可见低频强能量区外,未能在储层位置下方检测到表征能量衰减的“低频阴影”现象。研究结果认为:储层厚度较薄、碳酸盐岩平均速度较高、储层非含气高密度流体(油和水)的存在,是导致未检测到“低频阴影”的3个主要原因。其中,较薄的储层和速度较高的碳酸盐岩会引起衰减不足,而非含气高密度流体会导致顶底阻抗的差异不明显。另外,薄层的调谐效应使得地层在调谐频率处出现强振幅响应,这一峰值频率可以用来估计储层厚度。
The Cenozoic carbonate platform has been widely developed in the eastern part of the South China Sea uplift. The reefs originally formed on the platform have formed very good oil and gas reservoirs due to the development of pores and fractures combined with the blockage of the upper mudstone caprock. Based on the well logging data and using the spectral decomposition method, the paper analyzes the seismic time-frequency characteristics of Liuhua carbonate rock platform high porosity reservoirs. It is found that the seismic wave energy decays obviously at the top of the reservoir, and the time-frequency spectrum shows the center However, on the frequency division profile, “low-frequency shadow”, which characterizes the energy attenuation, can not be detected below the reservoir except for the low-frequency and high-energy region in the collapse-dissolution zone. The results show that the reservoir thickness is thin and the average carbonate rock velocity is high. The existence of non-gas-bearing high-density fluids (oil and water) in reservoirs is the main reason for undetected “low frequency shadow” the reason. Among them, thinner reservoirs and higher velocity carbonates cause insufficient decay, whereas non-gas-bearing high-density fluids lead to insignificant differences between top and bottom impedances. In addition, the tuning effect of the thin layer causes the formation to exhibit a strong amplitude response at the tuning frequency, which can be used to estimate reservoir thickness.