Abstract: The Hari sag is located in the northern part of the Yingen-Ejinaqi Basin. The exploration level is relatively low. At present, the main exploration targets are such unconventional oil- and-gas reservoirs as grey mudstone and dolomitic mudstone. The sag belongs to the small and complex fault depression and its lithology is complex and diverse. The lithology of the target layer changes rapidly and the longitudinal span is large. Many lithologies, as thin sand layer, dolomitic mudstone and grey mudstone, are difficult to identify with conventional prediction methods. In order to solve the above problems, through repeated trials and tests, broadband seismic data acquisition and processing is used. A three-dimensional seismic-sedimentary-facies model is established through the technology of well seismic identification and virtual slice analysis. The optimization technology under strict three-dimensional "phase"-boundary control and the inversion, based on pseudo-acoustic curve reconstruction, of phase-controlled frequency division are adopted. These technologies have effectively improved the accuracy of identification of grey mudstone reservoirs. Thus, a simple, effective and economical identification system for small-scale, complex-filled-basin grey mudstone gas reservoirs has been formed. Consequently an area of 128 square kilometers of grey mudstone gas reservoirs has been identified in the Bayinggebi Formation of Hari sag. The wells drilled have achieved better results of shale gas exploration in the target layer. It has been proved that the identification technology for complex fractured shale gas reservoirs based on broadband seismic data is valid and practical.