AVO Influence Factors And Spatial Propetries Of HTI Coal Bed

In the coal field seismic prospecting, AVO is one of the feasible techniques that can detect thearea rich in coal gas. Recnetly, the coal field geo-structure and the target strata are complex and thedifferent between the target and neighbouring layers is great so that AVO can not meet demandsfrom the industry and AVO should be improved more precisely. In areas rich in coal gas, HTItectonic coal is very common. When tectonics occurred, HTI coal is the result of the effect ofgeostress on the native coal. Gas rush has a close relationship with the development of tectonic coal.The traditional AVO methods contain Aki-Richard, Shuey and Thomsen. Aki-Richard isapplied to regional anomaly by AVO intercept distance and gradient. Shuey by sin angle ofincidence square and intercept distance.Simplified Thomsen parameters to inverse velocity, densityand NMO velocity. All mentioned above are well used in petro-prospecting except coal-prospectingbecause the common characteristic is that the difference between target strata and neighbouringlayers is small and coalbed is against the characteristic, letting alone the anisotropy. That’s whyAVO equation should be corrected precisely.For a more accurate AVO method, my paper has a deep analysis of HTI and the contents areas follows: firstly we discuss the relationship between phase velocity and group velocity of TTI,find a way to get the transmitted angle and velocity knowing the ray parameter and finally makesure the velocity in AVO equation is precise.Then calculate Hooke matrix according to Cheng (1993)and discuss factors, including fracture density, thickness, fracture aperture, bulk modulus, that affectAVO curves greatly. At last deduce the accurate AVO equation and give AVO spatial curves whosecharacters help us pinpoint the fracture azimuth. Compare our results with Liu Yang’s and at thesame take into account the symtry axis angle.Besides the above contents, my paper also does extra research, such as explain how todeduce the approximate AVO equation, compare the approximate AVO equation with the accurateequation, methods to calculate the complex Hooke matix and difference of the methods, deduce thethin interbed equations by displacement vector and displacement, compare the results, Successfullysynthesize seismic data, etc.