Carbonate reservoir characterization using seismic diffraction imaging

Ordovician Model

Our first synthetic model is based on the very deeply buried (5,500-6,500 m) Ordovician limestone strata in Northwest China's Tarim Basin, which features anomalous seismic amplitude bright spots. The amplitude bright spots correspond to high-gamma-ray, low-velocity zones in wireline logs and have been interpreted by Zeng et al. (2011a) as paleokarst features. A geocellular model was built to study the seismic response of the paelokarst in detail (Zeng et al., 2011b; Janson et al., 2010). The synthetic model uses the Ordovician unconformity surface (boundary between a basal Ordovician interval and an overlying Silurian siliciclastic interval) that was mapped from subsurface seismic data (Figure 1). Collapsed paleocaves with cave sediments were modeled by randomly distributing low acoustic impedance (AI) circular geobodies that measured 300 $\times$ 300 m in the horizontal dimension and 18 m in vertical dimension. The AI (approximated by acoustic velocity using constant density) is distributed using a sequential Gaussian simulation with parameters derived from a sonic log in the cored well (Zeng et al., 2011b; Janson et al., 2010; Zeng et al., 2011a).

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Figure 1. Ordovician velocity model.

Carbonate reservoir characterization using seismic diffraction imaging