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在裸眼井中,不论地层声速高低,大都可以获得地层信号,这是由于地层声速一般高于泥浆声速,从而可能在地层中产生滑行波的缘故。但固井后的情况和裸眼井不同,有些地层的横波声速低于套管横波声速,因而不可能在地层中产生滑行横波和Rayleigh波。声测资料[1]证实,并非对所有地层都能获得Rayleigh波信号。如果个别地层的纵波声速也低于套管横渡声速,那就也不能获得地层纵波信号。本文试图从理论上探索,寻求措施,以便在固井后仍然能够获得低声速地层的地层信号。
In open-hole wells, most of the stratum signals can be obtained regardless of the sound velocity of the formation, which is due to the fact that the sound velocity of the formation is generally higher than the velocity of the sound of the mud, which may cause the formation of a gliding wave in the formation. However, after cementing, unlike the open-hole wells, the shear-wave velocity in some formations is lower than the casing-shear-wave velocity, so it is not possible to generate both sliding and Rayleigh waves in the formation. Acoustic data [1] confirm that Rayleigh signals are not available to all formations. If the individual longitudinal wave velocity is also lower than the casing cross-sound velocity, it can not get the formation of longitudinal wave signal. This paper attempts to theoretically explore and seek measures to obtain formation signals of low-sound-velocity formations after cementing.