Abstract:

In order to obtain the transformational relations between shear wave slowness time and compressional wave slowness time and other statics parameters of the gypsum mudstone of Paleogene in An area of Tarim Basin at 20 kHz, we conducted indoor 1 000 kHz high frequency acoustic wave test, and extrapolate the acoustic wave velocity at 20 kHz based on the tested acoustic wave velocity, quality factor and dispersion equation. The comparative analysis of the acoustic wave or acoustic wave slowness time at these two kinds of frequencies shows that the compressional wave slowness time is closer to logging compressional wave slowness time value under simulated formation condition; the wave velocity and quality factor change slightly within 85 ℃, the changes of wave velocity can be ignored, and the quality factor ranges from 5% to 7%; both the wave velocity and quality factor increase with the increasing of net confining pressure; comparing with compressional under simulated formation conditions and atmospheric pressure, the compressional wave velocity increment is 2.7% to 8.4%, and the compressional wave quality factor increment is 27% to 58%, gypsum mudstone dispersion degree is 7.4% to 24.4% （average 15.12%）, with relatively large dispersion degree. By using the deformation of dispersion equation, we proposed an intuitive expression between quality factor and wave velocity decline of gypsum mudstone under simulated formation condition. According to the influencing factors of gypsum mudstone quality factor, the compressional wave of gypsum mudstone was divided intoⅠ, Ⅱ, Ⅲ three levels of dispersion from high to low, at last dispersion effect was discussed in the application of shear wave slowness time prediction. The results show that under the conditions of 1 000 kHz and 20 kHz frequency, the average relative error of shear wave slowness time predicted by compressional wave slowness time is only 2% within the variation range of gypsum mudstone acoustic time, and the error has the trend of increase with the increasing of gypsum content. The fitting formula of compressional wave slowness to shear wave slowness can be applied to the prediction of shear wave slowness under the two kinds of frequencies. Because the dispersion degree of gypsum mudstone is larger, and the acoustic slowness varies greatly under the two kinds of frequencies, so dispersion calibration should be applied in the actual application.

Key words: well, productivity, productivity index, nozzle productivity index, productivity curve, productivity test