利用分频地震属性进行古风化壳岩溶储层预测--以千米桥潜山凝析气田为例

Prediction of Ancient Weathering Crust Karst Reservoirs Using Separate Frequency Seismic Attributes

古风化壳岩溶储层的主要储集空间是长期暴露及淡水溶蚀作用形成的有效缝洞空间,其岩性特别是灰岩的基质孔隙度总体很低,储层的渗流通道主要依靠裂缝,因此以灰岩为基础的古风化壳岩溶储层的有效储集空间主要是大中型溶洞以及相互沟通的裂缝系统,而以白云岩为基础形成的古风化壳岩溶储层则表现出较高的基质孔隙及渗透率,其中的缝洞系统特别是大中型溶洞则没有灰岩古风化壳岩溶储层那样发育,时而会出现粘土含量相对较高、油气产量不稳定的情况。为了有效区分裂缝储层和粘土含量的响应特征,分析了振幅统计类、复地震道统计类以及相关统计类10余种地震属性的特征,并与已钻井的各种动、静态资料进行了对比,发现低频异常与含气储集层渗透率较高有关,高频振幅异常通常提示粘土含量较高。该方法在千桥潜山凝析气田的古风化壳岩溶储层预测中取得了很好的效果。

Effective fractures and pores developed from exposure over a long period of time and corroded by fresh water occupy the main space in the ancient weathering crust karst reservoir. The matrix porosity is always very low in this kind of the lithology, especially in limestone; and the flow matrix depends on fractures. So the effective space in the ancient weathering crust karst reservoir characterized by limestone are big-and middle-sized dissolved caverns and interconnected fractures. But the ancient weathering crust karst reservoir characterized by dolomite generally exhibits high matrix porosity and permeability, and the fractures and caverns, limestone, and appears especially big- and middle-sized caverns, are not developed effectively as those in to have high content of clay and non-stabilized rate. In order to distinguish the response features of the fractured reservoir and the content of clay, the authors analyzed about 10 kinds of the seismic characteristics of the amplitude, complex seismic trace and so on, and compared them with different dynamic/static state data of drilled wells. The results show that the abnormally low frequency has strong connection with high permeability of the gas-bearing reservoir, while the abnormal high frequency amplitude generally indicates high content of clay. Good results have been achieved in the application to predicting the ancient weathering crust karst reservoir in the burial hill of Qianmiqiao in the Dagang oilfield.