致密碳酸盐岩跨频段岩石物理实验及频散分析

Multi-frequency rock physics measurements and dispersion analysis on tight carbonate rocks

致密碳酸盐岩在成岩和后成岩过程中形成了复杂的孔隙结构特征,其速度等地震弹性参数不仅与孔隙度有关,而且还与孔隙结构特征密切相关.为了进一步研究致密碳酸盐岩内部流体相关的速度频散特征,针对致密碳酸盐岩进行实验室的频散测量与频散理论分析尤为重要.本研究选用了一块典型的致密型碳酸盐岩样品,在对样品进行了精细的包括CT扫描与镜下薄片的孔隙结构描述基础上,进行了实验室跨频段(从地震频段-超声频段)的频散测量与频散响应分析.比较实验室跨频段岩石物理频散测量可以获得如下认识:1)较之于典型的"喷射流"机制,改进的"喷射流"模型可以半定量地解释频散测量的结果,这大大提高了对致密碳酸盐岩频散响应的理解与认识;2)改进的"喷射流"模型还不能完全精确地匹配实验室频散测量结果,这说明除了微观尺度下的"喷射流"机制,还存在着其他控制频散与衰减的机制;3)本项工作对研究致密碳酸盐岩储层中不同频段地震波响应以及对储层预测与流体识别提供了理论依据.

Tight carbonate rocks have formed complex pore structure through diagenesis and postdiagenesis.Their elastic properties are not only related to porosity,but also closely related to pore structure.In order to further study the velocity dispersion characteristics of fluid correlation in tight carbonate rocks,it is very important to measure the dispersion and analyze the dispersion theory in the laboratory.In this study,a typical tight carbonate rock sample is selected.Based on the detailed description of the pore structure of the sample,including CT scanning and microscopic thin section,the laboratory cross frequency(from seismic frequency band to ultrasonic frequency band)dispersion measurement and dispersion response analysis are carried out.Comparing laboratory cross-band measurement results and dispersion curve from theoretical modeling,we can obtain the following understanding:1)Compared with the typical squirt flow mechanism,the improved squirt flow model can semi-quantitatively explain the results of frequency dispersion measurements,which greatly improves the understanding of the dispersion response of tight carbonate rocks;2)The improved squirt flow model still cannot exactly match laboratory dispersion measurement results.This shows that in addition to the microscopic squirt flow mechanism,there are other mechanisms that control dispersion and attenuation;3)This work provides a theoretical basis for studying seismic wave responses in different frequency bands in tight carbonate reservoirs for reservoir prediction and fluid identification.