Detailed analysis of seismic reflection characteristics of tight sandstone reservoirs in the Upper Paleozoic of the Ordos Basin: a case study of Block X

Tight sandstone gas represents a crucial domain for augmenting reserves and boosting oil and gas production in the Ordos Basin. Currently, the primary focus for development lies in the Upper Paleozoic tight sandstone gas located in the southwestern Ordos basin. The gas reservoirs in this area present distinct characteristics, including significant burial depth exceeding 4000m, modest-scale sand bodies, an average thin reservoir thickness of 5.8m, and rapid lateral variations in sand body distribution. These factors contribute to challenges in establishing a clear correlation between reservoir scale and seismic reflection patterns, leading to uncertainties in reservoir prediction. In this study, three types of seismic reflection characteristics of the bottom interface associated with the development of the S13 reservoir in Block X have been summarized by using Forward modeling: (1) strong reflection of peaks on seismic sections; (2) weak reflection of troughs on seismic sections; and (3) strong reflection of complex waves with the bottom of the Shanxi Formation. The main factors that cause the above seismic reflection characteristics include the thickness of the lower coal seam, the spatial distribution and thickness of the reservoir. The above analysis breaks the inherent understanding that traditional strong seismic reflections are indicative of reservoir development, and instead, based on the three types of seismic reflection waveforms, waveform clustering is used to realize the differentiation of zones in the study area. Furthermore, combining with the facies-controlled high-resolution inversion, we achieved high-precision identification of tight sandstone reservoirs in Block X. This approach can be applied to similar reservoirs both at China and abroad.