SEISMIC DATA CAN IMPROVE STOCHASTIC FACIES MODELING

Heterogeneous reservoir units comprised of fluvial channel sandstones that alternate vertically and laterally with finer grained, nonreservo ir lithologies pose a serious problem to production drilling and field development planning. The interwell position of each reservoir sandst one body can be assessed, in most cases, only indirectly through conve ntional geological well-correlation and mapping, and the potential of drilling unsuccessful production wells is usually present. The scope o f this paper is to present a new technique that ensures that informati on obtained from 3D seismic surveys is fully utilized in the discrete facies modeling of fluvial sandstone bodies in a heterogeneous reservo ir unit. In our study area, we show that there is a useful, empirical relationship between seismic impedance and the facies (channel sandsto nes/nonreservoir). Notably, there is a high probability of obtaining c hannels in low impedance regions, whereas high impedance areas have a lower probability of channels. An opposite impedance behavior may occu r in other reservoir environments. This relationship is utilized to gu ide the discrete modeling of channels. An example from a fluvial North Sea reservoir is presented. The use of seismic data as an additional source of conditioning data reduces the uncertainty in the stochastic reservoir model, because the uncertainty in the reservoir description in the interwell areas is reduced significantly.