Abstract: Acoustics tests are conducted on deep tight sandstone reservoir samples in Tazhong area. A new method is developed for quantitatively evaluating the microcrack stress sensitivity of tight sandstone reservoir using inversion of acoustic data. The fracture density and the aspect ratio are inversed by using the Biot consistent model and the DEM model, and the variations of and are discussed under different confining pressures. The stress sensitivity of microfractures are also evaluated. The results show that, with the increase of confining pressure, decreases and increases, mainly due to the closing of the microfracture. According to the reducing amplitude of under different confining pressures, the percentage of fractures that close or open can be determined. Samples with a larger under high confining pressure represent low stress sensitivity. Otherwise, the stress sensitivity is higher. This paper defines the point, where the pore-fracture in the rock changes greatly, as the turning point. The values of corresponding to the turning points of different samples are similar. This phenomenon can be seen as the common characteristics of tight sandstone reservoir fractures, and it can also act as the contrast indicator of the fracture development degree. The correlations of (with a confining pressure of 65 MPa) and turning pressure with rock porosity are discussed, which shows that they both have a very good positive correlation. For the deep low permeability sandstone reservoir in this region, the favorable fracture that has weak stress sensitivity is influenced mostly by physical properties of rock.

Key words: Tazhong area, acoustics, inversion, tight sandstone reservoir, microcrack, stress sensitivity