The Study On Extracted Absorption Parameter And Applied Of Borehole Seismic

Seismic wave propagation in the medium, as the medium attenuate the wave, it lead to reduce the basic frequency of seismic wave and narrow the frequency band. Through the analysis of the seismic data, can get the attenuation information and use it recovery the attenuation of data to increase the basic frequency and broaden the bandwidth, so as to improve the seismic resolution. In addition, by analysis it can be concluded that, variation of attenuation is correlated with the reservoir lithology and physical properties and variation of reservoir fluid properties, therefore, can predict porosity, permeability, saturation and oiliness of reservoir by calculating the variation of attenuation of reservoir.By analysis it can be concluded that, rapid variations of low velocity layer lead to the large attenuation of seismic wave, reducing or eliminating the effects is very important for improving the resolution of seismic wave filed and describing the reservoir. Comparing the borehole seismic with the surface seismic that the seismic wave just pass through halfway of the shallow low velocity layer or not, so with less influenced by the shallow, shown by the attenuation characteristics are concerned with the attenuation of high-speed strata. By analysis of the attenuation characteristics of borehole seismic data that, extracting reservoir attenuation information can be more effectively help for reservoir comprehensive evaluation research.This paper is based on the borehole seismic wave field includes conventional VSP and cross-well seismic. Analysed and deduced two common frequency domain methods of extracting the attenuation parameters, i.e. spectrum ratio method and centroid frequency shift method. Programmed and calculated the attenuation parameters by using the zero offset VSP downgoing wave field, calculating the forward record and actual data record for test, the result is correct.According to the characteristics of cross-well seismic, considered the characteristics of the two methods above comprehensively, analyzed and deduced SIRT(Simultaneous Iterative Reconstruction) and LSQR(Least Squares QR-factorization)'s attenuation tomography method is based on centroid frequency shift method in cross-well seismic, namely according to centroid frequency shift method to calculate the attenuation's similar line integral form, further deduced the correction term of normal tomography line integral form, changed the travel time tomography imaging algorithm into attenuation tomography imaging algorithm. Use SIRT method and LSQR method respectively, calculated the distribution of the interval velocity and ray path by the first arrival velocity tomography imaging in cross-well seismic. Obtained the Q value tomography profile according to attenuation tomography imaging by using the first arrival's centroid frequency shift and ray path. Calculated by the theoretical and practical records, found the results of formula deducing and algorithm programming are correct, Comparatively, the result of LSQR's attenuation tomography imaging is better than SIRT's.This paper shows the two methods have their own feature, the most important factor to affect the inversion of Q value is the quality and frequency characteristics of the records, so that the high resolution and fidelity in process of the borehole seismic pre-stack records is the key of the Q value accurate inversion.