Average semblance and maximum-likelihood spectral analyses are applied to syntheticand field full waveform acoustic logging data to determine formation velocities. Ofparticular interest is the ability of these methods to resolve the P and shear/pseudo Rayleigh arrivals in data from poorly-bonded cased boreholes. In synthetic open-holedata the velocity analyses yield results within 4% of the true velocities. Results fromsynthetic well-bonded cased hole data are generally as good as those from the open holedata. However, if the formation P-wave velocity is within roughly 10% of the platevelocity of the steel pipe (about 5.3-5.5 km/s), then there may be a resonance effectthat appears to slow down the P wave slightly (on the order of 6%). For cased-holemodels with no steel/cement bonding (the free-pipe situation), the measured P-wavevelocities are typically 6 to 8% less than the actual formation velocities. If the formation S-wave velocity is greater than about 2.5 km/s, the S-wave velocity estimate may also be 6 to 8% low. Furthermore, increasing the thickness of either the cement layer or the fluid layer between the pipe and the cement further decreases the formation velocity estimates. Also, if the P-wave velocity is within roughly 15% of the velocity of the steel arrival, the P wave may not be resolved by the semblance method unless the data is first low-pass filtered. Initial tests show that this filtering process may adversely affect the final P-wave velocity estimate, but the details of this type of approach have not been studied. The P wave is resolved. by spectral analysis of the original, unfiltered data. For cased-hole models with no cement/formation bonding (the unbonded-casing situation), formation S-wave velocities are estimated to within 3% relative error, and the formation P-wave velocity is estimated to within 2% error in a slow formation. However, for P-wave velocities between 3.4 km/s and 5.94 km/a, the P wave cannot be resolved by spectral analysis, and it is resolved by the semblance method only in the model with the low velocity (3.4 km/s).
展开▼
机译:将平均相似度和最大似然谱分析应用于合成和现场全波形声波测井数据,以确定地层速度。这些方法能够解决粘结不良的套管井的数据中的P和剪切/伪瑞利波到达问题,这尤其令人关注。在合成裸眼数据中,速度分析得出的结果在真实速度的4%之内。合成的结合良好的套管套管孔数据的结果通常与裸眼井孔数据的结果一样好。但是,如果地层纵波速度在钢管的板速度的大约10%之内(约5.3-5.5 km / s),则可能会出现共振效应,似乎会稍微放慢纵波(按顺序(6%)。对于没有钢/水泥粘结的套管孔模型(自由管情况),测得的P波速度通常比实际地层速度小6%至8%。如果地层S波速度大于约2.5 km / s,则S波速度估计值也可能低6%至8%。此外,增加管和水泥之间的水泥层或流体层的厚度进一步降低了地层速度估计。同样,如果P波速度在钢到达速度的大约15%以内,则除非先对数据进行低通滤波,否则P波可能无法通过相似方法解析。初步测试表明,该滤波过程可能会对最终的P波速度估算产生不利影响,但尚未研究此类方法的细节。 P波被解析。通过对未经过滤的原始数据进行频谱分析。对于没有水泥/地层粘结的套管井模型(未粘结套管的情况),地层S波速度估计在3%的相对误差内,地层P波速度估计在缓慢的2%以内编队。但是,对于介于3.4 km / s和5.94 km / a之间的P波速度,无法通过频谱分析来解析P波,并且仅在低速度(3.4 km / s)的模型中才能通过相似方法来解析P波。 。
展开▼