The subsurface geological formations demonstrate a range of porosity including cracks. This characteristic significantly affects the propagation of elastic waves in rocks. In this context, Tang's method relies on crack density and aspect ratio as two important parameters. In this new theory, the crack density and aspect ratio can be obtained by inverting the measured velocities (Vp, Vs) of rocks versus different effective confining pressures under dry and fluid-saturated rocks conditions, which is one way to get the crack density value. Another way to calculate the crack density directly is using X-ray CT images to count the cracks in the core plug rock samples. Finally, after using the two different ways to get crack density value, the relationship between crack density value results in two different methods could be revealed.

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