In-situ stress is a common stress in the exploration and development of oil reservoirs. Therefore, it is of great significance to study the propagation characteristics of borehole acoustic waves in fluid-saturated por...In-situ stress is a common stress in the exploration and development of oil reservoirs. Therefore, it is of great significance to study the propagation characteristics of borehole acoustic waves in fluid-saturated porous media under stress.Based on the acoustoelastic theory of fluid-saturated porous media, the field equation of fluid-saturated porous media under the conditions of confining pressure and pore pressure and the acoustic field formula of multipole source excitation in open hole are given. The influences of pore pressure and confining pressure on guided waves of multipole borehole acoustic field in fluid-saturated porous media are investigated. The numerical results show that the phase velocity and excitation intensity of guided wave increase significantly under the confining pressure. For a given confining pressure, the phase velocity of the guided wave decreases with pore pressure increasing. The excitation intensity of guided wave increases at low frequency and then decreases at high frequency with pore pressure increasing, except for that of Stoneley wave which decreases in the whole frequency range. These results will help us get an insight into the influences of confining pressure and pore pressure on the acoustic field of multipole source in borehole around fluid-saturated porous media.展开更多
A lot of previous experimental studies on ultramafic rocks(SiO2 unsaturated system)(Ringwood and Major, 1971;Irifune et al., 1986;Gasparik, 1989;Ono and Yasuda, 1996) have demonstrated that characteristics of Si-rich ...A lot of previous experimental studies on ultramafic rocks(SiO2 unsaturated system)(Ringwood and Major, 1971;Irifune et al., 1986;Gasparik, 1989;Ono and Yasuda, 1996) have demonstrated that characteristics of Si-rich and Al-deficient in garnet are resulted from coupled substitution of SiⅥ+MⅥ=AlⅥ+AlⅥ and SiⅥ+NaⅧ=AlⅥ+MⅧ(M=Mg, Fe, Ca) at ultrahigh pressures(UHP)(>5 GPa). The degree of substitution will be enhanced by increasing pressure which has a positive correlation with the content of SiⅥ, but a negative correlation with the content of AlⅥ in supersilic garnet. These experimental results established a theoretical foundation for further understanding the formation mechanism of the exsolution of pyroxene in garnet observed in deep mantle xenoliths and some ultrahigh pressure rocks, and also for estimating the pressure conditions of the formation of supersilic garnet before exsolution(Haggerty and Sautter, 1990;Sautter et al., 1991;van Roermund et al., 1998;Ye et al., 2000). Although some experimental studies on SiO2 saturated system have been reported(Irifune et al., 1994;Ono., 1998;Dobrazhinetskya and Green.,2007;Wu et al., 2009), the stability conditions of supersilic garnet are still lack of unified understanding. Therefore, HP-HT experiments were carried out on felsic rocks under conditions of 6–12 GPa and 1000℃–1400℃. Combined with previous experimental data, we try to figure out the minimum stable pressure and geological significants of supersilic garnet in SiO2 saturated system. Our experimental results from SiO2 saturated system show the minimum stable pressure of supersilic garnet should be ≥10 GP of stishovite stability field. These results are similar as that from experiments using starting composition similar to average upper continental crust reported by Irifune et al(1994) who yielded that garnet gradually became supersilic and Al-deficient as pressures increased above 10 GPa, especially in a pressure interval between 13 and 18 GPa. Moreover, experiments with different s展开更多
基金Project supported by the National Natural Science Foundation of China (Grant No.42074139)the Natural Science Foundation of Jilin Province,China (Grant No.20210101140JC)。
文摘In-situ stress is a common stress in the exploration and development of oil reservoirs. Therefore, it is of great significance to study the propagation characteristics of borehole acoustic waves in fluid-saturated porous media under stress.Based on the acoustoelastic theory of fluid-saturated porous media, the field equation of fluid-saturated porous media under the conditions of confining pressure and pore pressure and the acoustic field formula of multipole source excitation in open hole are given. The influences of pore pressure and confining pressure on guided waves of multipole borehole acoustic field in fluid-saturated porous media are investigated. The numerical results show that the phase velocity and excitation intensity of guided wave increase significantly under the confining pressure. For a given confining pressure, the phase velocity of the guided wave decreases with pore pressure increasing. The excitation intensity of guided wave increases at low frequency and then decreases at high frequency with pore pressure increasing, except for that of Stoneley wave which decreases in the whole frequency range. These results will help us get an insight into the influences of confining pressure and pore pressure on the acoustic field of multipole source in borehole around fluid-saturated porous media.
基金granted by the National Natural Science Foundation of China(Grant Nos.41430209)the Chinese Ministry of Science and Technology(Grant No.2015CB856100)the MOST Special Fund from the State Key Laboratory of Continental Dynamics(Grant No.201210133)
文摘A lot of previous experimental studies on ultramafic rocks(SiO2 unsaturated system)(Ringwood and Major, 1971;Irifune et al., 1986;Gasparik, 1989;Ono and Yasuda, 1996) have demonstrated that characteristics of Si-rich and Al-deficient in garnet are resulted from coupled substitution of SiⅥ+MⅥ=AlⅥ+AlⅥ and SiⅥ+NaⅧ=AlⅥ+MⅧ(M=Mg, Fe, Ca) at ultrahigh pressures(UHP)(>5 GPa). The degree of substitution will be enhanced by increasing pressure which has a positive correlation with the content of SiⅥ, but a negative correlation with the content of AlⅥ in supersilic garnet. These experimental results established a theoretical foundation for further understanding the formation mechanism of the exsolution of pyroxene in garnet observed in deep mantle xenoliths and some ultrahigh pressure rocks, and also for estimating the pressure conditions of the formation of supersilic garnet before exsolution(Haggerty and Sautter, 1990;Sautter et al., 1991;van Roermund et al., 1998;Ye et al., 2000). Although some experimental studies on SiO2 saturated system have been reported(Irifune et al., 1994;Ono., 1998;Dobrazhinetskya and Green.,2007;Wu et al., 2009), the stability conditions of supersilic garnet are still lack of unified understanding. Therefore, HP-HT experiments were carried out on felsic rocks under conditions of 6–12 GPa and 1000℃–1400℃. Combined with previous experimental data, we try to figure out the minimum stable pressure and geological significants of supersilic garnet in SiO2 saturated system. Our experimental results from SiO2 saturated system show the minimum stable pressure of supersilic garnet should be ≥10 GP of stishovite stability field. These results are similar as that from experiments using starting composition similar to average upper continental crust reported by Irifune et al(1994) who yielded that garnet gradually became supersilic and Al-deficient as pressures increased above 10 GPa, especially in a pressure interval between 13 and 18 GPa. Moreover, experiments with different s
