Hydrocarbon reservoirs are increasingly recognized as spatially heterogeneous entities in terms of pore-fluid content, pore-fluid saturation, porosity, permeability, lithology, and structural control. Knowledge of these reservoir parameters and their spatial variation is critical in the evaluation of the total volume of hydrocarbon reserves in place, in understanding and predicting physical processes in the reservoir such as fluid flow and heat transfer, and in projecting and monitoring reservoir fluid production and recovery as a function of time.
Conventional approaches to estimating reservoir properties are mainly obtained through borehole measurements such as: rock cores, rock cuttings, geophysical well logs, and reservoir engineering pressure tests. These data are valuable in that they represent in situ measurements, but unfortunately only sample a very small fraction of the total reservoir volume [e.g., Nur, (1989)].
Surface seismic data, on the other hand, potentially sample the entire reservoir volume, although at a lower resolution and in a remote, as opposed to in situ, manner. Traditionally, surface seismic data are used as an imaging tool to make seismic-derived geologic maps of the reservoir target zone. These images are subsequently interpreted by reservoir geologists in terms of structure, stratigraphy, and major fault patterns, in order to provide some structural control to the reservoir model. However, relatively little work has been done to relate seismic reflection data directly to the reservoir mechanical property contrasts that develop due to hydrocarbon recovery.
Furthermore, a new diagnostic role for seismic has been proposed recently, in which several repeat seismic surveys are acquired in time-lapse mode to monitor reservoir production processes. This concept offers a method for better characterization of reservoir complexity by monitoring the flow of fluids with time in a producing reservoir. Additionally, monitoring provides a full reservoir volume analysis of production sweep efficiency, early prediction of injectant breakthrough, and location of bypassed (unproduced) hydrocarbons. Seismic monitoring of reservoir processes potentially offers a new dimension to the manner in which hydrocarbon reservoirs are currently developed and produced.