Fizz Gas Characterization Through Density Inversion: A Case Study in Deep-Water Sabah

Fizz gas detection is a critical step in field development as it is often difficult to differentiate it from commercial gas in reservoirs on acquired seismic data. In a shallow reservoir context, it is theoretically possible to observe a fizz gas effect through a joint analysis of P-wave velocity (Vp) and density (Rhob) properties. Although inverting density is routinely done in pre-stack inversion, it is generally too strongly coupled to Vp to achieve an efficient fizz gas characterization through a Vp versus Rhob crossplot. This paper presents a pre-stack inversion case study conducted in offshore North Sabah, Malaysia, to characterize Late and Middle Miocene clastic, gas-bearing deposits. Very high-quality pre-stack seismic data allowed for the possibility to partially decouple Vp and density through an adequate inversion parameterization. Supported by fluid change predictions coming from a petro-elastic model calibrated to the field conditions, a fizz gas characterization routine could be established through a joint analysis of the inverted Vp and Rhob properties, giving access to a potential fizz gas detection over the targeted reservoir.