Using a dynamic representation of sedimentary structural features in prestack inversion: A case study in a tight sandstone in the Sichuan Basin

Abstract

Tight sandstone gas is an important unconventional hydrocarbon resource. In the Sichuan Basin, tight sandstone gas is generally stored in channel sandstone reservoirs. Previous studies have shown that sandstone reservoirs have complex sedimentary features characterized by overlapping multistage channel sandstone and large lateral variations. However, it is challenging for conventional inversion methods to adapt to this strong variation. This hinders the accurate construction of the reservoir’s structural features. A prestack seismic inversion method constrained by a dynamic representation of sedimentary structural features has been used to predict the properties of a tight sandstone reservoir. First, an initial feature library (a set of structural features) is extracted from the well-log data. Second, reliable inversion results are obtained using prestack inversion near the well logs. Meanwhile, using the reliable inversion results as training samples, an online learning algorithm is introduced to dynamically update the feature library in real time. Finally, the sedimentary structural features are gradually and stably extended to areas far from the well logs. The results demonstrate that the structural features of multistage channel sandstones were inverted accurately using a dynamic representation method. Combined with petrophysical analysis, the density is used to predict the distribution of sandstone thickness. In addition, based on the reliable prestack inversion results, we predict the gas-bearing properties of sandstone using Poisson’s ratio. The prediction results indicate the effective size of the reservoir. This provides important information for deploying horizontal wells.