Despite their low porosity and permeability, tight gas-bearing sandstones contain substantial oil and gas trapped within their dense matrix. These unconventional reservoirs have been developed through advanced drilling and hydraulic fracturing technologies, unlocking new energy supplies and offering a sustainable solution to the growing global demand for energy. However, seismic exploration of these reservoirs presents unique challenges. The tight nature of the sandstones means that conventional seismic methods often struggle to provide the necessary details for successful exploration. Special interpretation strategies are required to accurately identify potential hydrocarbon-bearing zones due to the subtle contrasts in acoustic impedance between the tight sandstones and the surrounding beds. In our exploration of deep tight gas-bearing sandstone from northwestern China, we find that the matrix shear modulus effectively distinguishes between sandstone and mudstone lithologies, making it a useful parameter for describing tight gas-bearing sandstone. We develop a novel amplitude-variation-with-angle (AVA) inversion method to obtain matrix shear modulus. First, under deep tight geologic conditions with porosity less than 10%, the modulus of relatively cleaner sandstone reservoirs, saturated with a two-phase mixture of gas and water, is approximately equivalent to the dry modulus. Based on this, we approximate the saturated modulus in the Gray AVA approximation as the dry modulus. Next, we introduce the Nur critical porosity model to establish an AVA approximation using the matrix modulus, achieving the Aki-Richards approximation accuracy. Then, using this approximation, we establish a Bayesian inversion method for the matrix modulus. Theoretical model testing and practical data inversion demonstrate that this method is theoretically sound and practically feasible. After estimating Nur’s critical porosity parameter using logging data and core measurements, the inverted matrix shear modulus parameters successfully describe the vertical and lateral distribution of the deep tight sandstone.

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