Diagnosis of “fizz-gas” and gas reservoirs in deep-water environment

“Fizz-water” or “Fizz-gas” is a rather ill-defined and misused concept. For some, it refers to gas in solution with brine; for others, it is defined as small amounts of free gas phase. This small, uneconomic gas content then gives rise to seismic bright-spots or other Direct Hydrocarbon Indicators (DHIs). Unfortunately, it is often the culprit of choice when no other reason can be found. However, progress has been made in assessing the problem. We have systematically examined physical properties of fluid and rock, and fluid interaction with rock to examine gas saturation effect on acoustic velocities, especially in deep-water sands of the Gulf Mexico . Furthermore, we have reviewed the current AVO and Rock physics interpretation techniques to propose optimum DHIs. Several promising techniques of seismic evaluation of gas saturation are in development.