Abstract:

Systematic study of composite reflectance coefficient of solution cavity shows that the seismic response is characterized by strong amplitude, low velocity and harmonization. This paper discusses the conditions of occurrence of strong reflectance and the reflectance signatures of cavities with different filling materials, and believes that strong reflectance waves can be observed in seismic data with normal frequency (20～30 Hz). According to the relationship between height of cavity,property of filling material and signal frequency, a frequency difference prediction and analysis technology is developed on the basis of wave equation. Its application in Tahe oilfield shows that this technology can get amplitude-frequency and velocity-frequency anomalies in cavities filled with fluid at a burial depth of over 5000 m, with over 100 m width and over 3 m height from normal seismic data with predominant frequency of 20～ 30 Hz. The anomalies appear in different zones and different layers with vertical and lateral comunications. They can be used as the basis for determining the existence of cavities, their distribution and estimating their heights.

Key words: carbonates, cavern-type reservoir, composite reflectance coefficient, frequency difference analysis, Tahe oilfield