Acoustic analysis of overpressure: from modeling to wireline observation

Abstract

A comparison between acousto-elastic modeling, surface seismic, and wireline responses to overpressure suggests that acoustic responses to overpressure are not uniform among the data of different sources. Acousto-elastic modeling underestimates the effect of the in-situ formation pressures on acoustic properties of waves. That seismic energy decreases with increasing pore pressure is evident for either very low overpressure or extremely high overpressure, but becomes less definite for moderate overpressure. Sonic logs in conjunction with wireline pressure measurements in a number of wells are used to establish a common understanding of acoustic-pressure relationship in the Muderong Shale of the northern Carnarvon Basin. The velocity-pressure relationship in the Muderong Shale seems to be controlled by stratigraphic factors. In the same stratigraphic category, acoustic velocity changes across wells are found to be consistent with pore-pressure variations in our examples. Investigation of velocity-pressure relationships for the Muderong Shale indicates that pore-pressure prediction should be based on the detailed lithologic classification.