Prediction of Ancient Weathering Crust KarstReservoirs Using Separate Frequency Seismic Attributes
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

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, especially big\| and middle\|sized caverns, are not developed effectively as those in limestone, and appears 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.