AVO Research on Coalbed Methane Reservoirs in East Ordos Basin

Abstract

DESCRIPTION:In east Ordos basin, there are plenty of coalbed methane (CBM) resources. However, the coalbeds are of strong heterogeneity due to laterally variant thickness and gas contents. Consequently, the heterogeneity gives rise to the great challenges for fine reservoir prediction and evaluation in seismic exploration. For the purpose of applying AVO to CBM prediction, in this paper, combining with geological and geophysical characteristics of CBM reservoirs NO. 5 coal seams from drilling, logging and the relationship between elastic parameters and gas contents in the lab, we established a set of thin coalbed models with different thickness and gas contents to model AVO using reflectivity method. Subsequently, AVO responses to gas contents and thickness of CBM reservoir are systematically investigated. APPLICATIONS:Our researches are theoretical discussion about the relationships between AVO responses and coalbed thickness and gas contents. These relationships can be applied to exploration of CBM reservoirs in practice. RESULTS AND CONCLUSIONS:Through the research on AVO intercept/gradient and spectrum of AVO responses, some conclusions are drawn as following:1) the attribute of AVO intercept/gradient has a linear relation with gas contents and a quasi-linear relation with thin bed thickness.2) the values of peak amplitude increase with gas contents linearly and with thin bed thickness gradually, but the values of peak frequency change little with both of them.3) high frequency components of AVO gradient trace spectrum increase when gas contents and thin bed thickness increase. 4) low frequency components of AVO gradient trace spectrum become less if the range of incidence angle is narrower. TECHNICAL CONTRIBUTIONS:1) Our researches are the further insights of AVO responses to high accumulation CBM reservoirs.2) Our conclusions provide a meaningful guide and an obvious evidence for detecting CBM reservoirs. TX 75083-3836, U.S.A., fax +1-972-952-9435