珠江口盆地白云深水区储层AVO异常特征分析

An analysis of AVO anomaly for reservoirs in Baiyun deep-water area,Pearl River Mouth basin

珠江口盆地白云深水区储层含气、含水时AVO异常没有规律,并且AVO正演时部分储层出现第IV类AVO异常,无法用AVO异常类型来区分气层和水层。对白云深水区储层AVO异常特征进行了分析,认为当气层横波速度小于上覆高速盖层横波速度时,气层AVO异常是气层顶界面第III类AVO异常与高速盖层底界面第IV类AVO异常两者平衡的结果,即由于储盖组合的不同及调谐厚度的影响,气层顶界面可能为第III类或第IV类AVO异常,而水层也可能表现为较弱的第III类AVO异常,因此不能简单地以AVO类型来识别气层和水层,须对各种储盖组合进行模型正演分析,以提高储层含气性预测精度。

In Baiyun deep-water area. Pearl River Mouth basin, the AVO anomalies are not regular for gas or water bearing reservoirs, and they can not be used to recognize these two kinds of reser- voir, because Type Ⅳ of AVO anomaly will be ob served for a part of reservois when conducting AVO forwarding. By analyzing the features of AVO anomaly for reservoirs in the deep-water area, it is considered that the AVO anomaly for a gas-bearing reservoir may result from a balance between Type Ⅲ of AVO anomaly from the top of the gas bearing res- ervoir and Type Ⅳ of AVO anomaly from the bot- tom of the overlying high velocity layer, when S- wave velocity in the gas-bearing reservoir is lower than that in the overlying high-velocity layer. In oth er words, because of different combinations of reser voirs and overlying layers and the effect of tuning thickness, Type III and Type Ⅳ of AVO anomaly may be observed at the top of gas-bearing reservoirs, and a weaker Type Ⅲ of AVO anomaly may occur at the top of water-hearing reservoirs. Therefore, the types of AVO anomaly can not be simply used to discriminate a gas-bearing reservoir from a water- bearing one, and an analysis of model forwarding has to be conducted for different combinations of reser- voirs and overlying layers, in order to improve the accuracy of predicting gas-bearing reservoirs.