The use of sonic method to detect reservoirs with secondary porosity (fissures and cavities) was due to the high effect of this porosity on the elastic waves. The generalization of the experimental results helped to construct a diagram to be used in detecting reservoirs with secondary porosity in the wells. A joint analysis of the data of the sonic method and other well logging methods, such as boreborehole diameter log, natural radioactivity log, natural log and micro and deep resistivity log...etc, was achieved. The wave spectrum was analysed for a relatively long period so that it included Lambi waves. The detection of these reservoirs was achieved by using the correlation between all available results, which led to the determination of the presence of the secondary porosity and the suggestion of a new calculation method. In addition to the secondary porosity some other factors which affect the sonic measurements were mentioned.