Q Extraction Methods Study Based On Full-waveform Acoustic Logging

The subsequent intrinsic attenuation when acoustic wave propagates through the earth is a very important kind of reservoir rock physic characteristics,and its influence could be quantified by Quality Factor(Q).Many laboratory core experiments show that the intrinsic attenuation is much more sensitive to reservoir properties such as gas-bearing than the velocity.However,it is still very difficult to accurately and stably estimate the intrinsic attenuation from the seismic and well logging data,which has become the biggest constraint to the application of intrinsic attenuation information on detecting oil and gas directly.This paper focuses on the methods and challenges of estimating P-wave attenuation information from monopole full-waveform acoustic logging.The specific research content is as follows:Firstly,this paper utilizes the theory of acoustic wave propagation in the borehole to calculate the monopole acoustic logging synthetic records with the real axis integration method,analyzes the type and characteristics of wave modes propagating in the borehole,and discusses the various factors affecting the amplitude in the process of the refracted Pwave propagation.Secondly,the theoretical foundations of the four acoustic logging Q value estimation methods,spectral ratio method,centroid frequency shift method,spectral peak method,and statistical averaging method,are introduced.The implementation of the statistical averaging method is introduced with emphasis.The seemingly complex statistical averaging process is analyzed,and it is proposed that the statistical averaging method is based on the absolute amplitude difference to estimate the Q value.Therefore,it is necessary to correct other elastic factors that affect the amplitude to accurately estimate the intrinsic attenuation.Based on a deep understanding of the statistical averaging algorithm,the theoretical framework and technical process of the previous statistical averaging algorithm are integrated,and the unreasonable hypothesis is abandoned.The optimized statistical averaging Q value estimation method is then formed.Again,the real axis integration method is used to calculate the elastic and viscoelastic simulation records for different models and different excitation parameters.The effect of disturbance factors such as geometrical spreading,the complex interference between first arrival of P-wave and subsequent multiple arrivals,and the transmission losses of P-wave at the borehole wall on the stability and accuracy of the four Q-value estimation methods are further studied.Finally,the four Q value estimation methods are applied to process the real acoustic logging data.Analysis of the results leads to a similar conclusion with the synthetic data test.That is,the spectral peak method and the statistical averaging method are more stable than the spectral ratio method and the centroid frequency shift method in the borehole environment.The estimated Q value with spectral peak method and statistical averaging method can basically agree with each other,and the results are similar to the Q value measured with rock physics experiments through resonance bar method.The optimized statistical averaging method further improves the Q estimate compared with the spectral peak method,and could act as a quantitative measurement for reservoir and fluid evaluation,oil recovery and carbon dioxide sequestration monitor.