Affiliation:
1. Key Laboratory of Coalbed Methane Resources and Reservoir Formation Process of the Ministry of Education, China University of Mining and Technology, Xuzhou 221008, China
2. School of Resources and Geosciences, China University of Mining and Technology, Xuzhou 221116, China
3. Huayang New Material Technology Group Co., Ltd., Yangquan 045000, China
4. Beijing Tan Chuang Resources Technology Co., Ltd., Beijing 100160, China
Abstract
We investigated the frequency dependence of Poisson’s ratio
in partially/fully fluid-saturated rocks. Based on one dominant fluid flow mechanism at each condition, we theoretically summarized that (1) when a rock is partially saturated or transits from drained state to undrained state at full saturation,
increases monotonously with frequency, and the associated attenuation
is positive with one peak. (2) When the rock transits from undrained state to unrelaxed state at full saturation, there are three cases: 1)
increases monotonously with frequency and has positive
with one peak, 2)
keeps constant with frequency and has no attenuation, 3) and
decreases monotonously with frequency and has negative
with one peak. In this condition, the dependence is influenced by the concentrations of stiff and soft pores, the aspect ratio of soft pores, and the pore fluid bulk modulus. (3) When it comes to the transition from drained state to unrelaxed state at full saturation,
can exhibit two shapes with frequency: 1) step shape with two positive attenuation peaks and 2) bell shape with one positive attenuation peak and one negative attenuation peak. Then, we conducted a numerical example to indicate the effect of influence factors (the concentrations of stiff and soft pores, the aspect ratio of soft pores, and the pore fluid bulk modulus) on Poisson’s ratio from undrained state to unrelaxed state, and validated the theoretical analysis by the published experimental data. In addition, based on
, we reanalyzed and validated the relationship between different attenuation modes (i.e., bulk attenuation
, P-wave attenuation
, extensional attenuation
, and S-wave attenuation
): (1) when
is positive, the relationship between them is
; when
is 0, the relationship between them is
; and when
is negative, the relationship between them is
. The relationship between different attenuation modes does not depend on saturation state (partial or full saturation) or
but on
. This research provides the frequency dependence of Poisson’s ratio in partially/fully saturated rocks, which helps better understand Poisson’s ratio at different frequencies and saturation states and can be used to improve the accuracy of geophysical data interpretation, such as lithology identification, hydrocarbon characterization in conventional reservoir, and brittleness evaluation of shale/tight sandstones in unconventional reservoir.
Funder
National Natural Science Foundation of China
Subject
General Earth and Planetary Sciences