3-D Finite Element Seismic Modeling of Hydrocarbon Drainage in a Gulf Coast Mini-Basin: The Role of Seismic Modeling in 4-D Seismic Technologies

Wei He, Roger N. Anderson, Xuefen Wang, and Yu-Chiung Teng

4-D seismic technologies are to promote hydrocarbon recovery efficiency. Carefully processed seismic amplitude differences from two time-elapse 3-D seismic surveys are very useful in finding gas caps, and more importantly, bypassed hydrocarbons in existing oil fields. However, it is extremely difficult to quantify the amount of these new reserves. Using stochastic simulation in reservoir characterization to associate acoustic impedance inverted from 3-D seismic data to reservoir physical properties that are derived from well data, we are able to construct individual reservoir models in the Eugene Island Block 330 Field in the offshore Gulf of Mexico. These quantified reservoir models in terms of lithology, porosity, pore fluid pressure and fluid saturation are then used t form acoustic models by using modified Gassman's equations to accommodate multi-phase fluid conditions. By applying 3-D finite element seismic modeling technique to each individual acoustic model, the observed seismic amplitude differences are modeled accordingly. The production data, i.e., gas and oil ratio, pressure depletion, and oil-water contact are used to constrain the seismic modeling process. Preliminary results applied to two 3-D seismic sub-volumes acquired seven years apart in the study area suggest that the delay in travel time caused by newly developed gas caps may substantially affect the seismic response of the reservoirs below them. Reservoir parameters deciphered from seismic modeling to fit the observed seismic differences must be subject to constraints from productio history data, or the estimated reservoir parameters may not be realistic because the acoustic models are substantially controlled by many reservoir physical parameters. The proposed technique may be useful in estimating the new reserves found in old oil fields.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California