Abstract:

Against the backdrop of continuously growing global energy demand, tight sandstone gas, as an important unconventional hydrocarbon resource, exhibits significant exploration and development potential. The development of microcracks in tight sandstone reservoirs can substantially influence reservoir permeability, thus, predicting microcrack zones is crucial for identifying high-permeability tight sandstone reservoirs. This study establishes a microcrack indicator for tight sandstone reservoirs and a pre-stack seismic inversion method. Based on rock physics analysis, an AVO equation is derived, linearly parameterized by the microcrack indicator, shear-wave impedance, and density. Further, an elastic impedance inversion method based on this AVO equation is developed to directly predict the microcrack indicator and other parameters from pre-stack seismic data. The research yielded the following key findings: 1) The microcrack indicator can reliably predict microcrack porosity and is unaffected by gas saturation. 2) Theoretical model tests confirm that the AVO equation for the microcrack indicator achieves reasonable accuracy. The equation can be further used to predict the microcrack indicator from pre-stack seismic data. 3) Real data application results show a strong correlation between the predicted microcrack indicator and permeability logging data, validating the effectiveness of the proposed method. 

Key words: tight sandstone gas, reservoir microcrack, rock physics, AVO, seismic inversion