AVO analysis of thin coalbed with dirt band

Abstract

Zoeppritz equations can only describe the reflection and transmission of plane waves incident on a single interface. It cannot deal with the thin bed case. The presence of dirt band in thin coalbed makes the problem even more complicated. We present an AVO (amplitude variation with offset) analysis of thin coalbed with dirt band. We derive equations to calculate the exact solution of reflection and transmission coefficients. Two models are built, one contains a single thin coalbed and the other one insert a dirt band into the coalbed. Both P-P and P-S reflection coefficients are analyzed with varying incidence angle, dominant frequency of plane wave, thickness and position of dirt band. We conclude: (1) dirt band has great effect on the reflection coefficients; (2) the dominant frequency and thickness of dirt band have greater effect on the reflection coefficients; (3) the position of dirt band may be difficult to be obtained using AVO response because it has little effect on the reflection coefficients. Keywords—AVO; thin coalbed; dirt band;