ABSTRACT
Gulf of Mexico Miocene through Holocene stratigraphy exhibits general physical properties conducive to detailed geophysical investigation. Selected seismic attributes may be used directly to produce net gas sand thickness. Synthetic examples demonstrate the relationship between the energy of a sand-top reflected wavelet and the associated gas pay. Reflected seismic energy displayed as acoustic impedance sections are used to produce pseudo “net pay” isopach maps, which are used to predict gas sand thickness, gas distribution, and gas reserves.
The techniques and concepts used in this form of geologic analysis are demonstrated in the rediscovery and development of the Ship Shoal Block 134 gas field of offshore Louisiana. Using the properties of amplitude, acoustic impedance, and reflected energy to produce net pay isopach maps has led to 95% successful prediction of gas reserves within this study area and other areas. The thickness of gas sands estimated by impedance methods is substantially less than the accepted minimum thickness interpretable from conventional seismic sections. In this case study, gas sand thicknesses ranging from 1.5 m to 10 m have been reliably mapped.
