Seismic attributes and acoustic impedance inversion in interpretation of complex hydrocarbon reservoirs

Seismic attributes along with seismic inversion are used to study a challenging reservoir facies from Boonsville field in north central Texas. Two thin reservoirs, Upper Caddo and Lower Caddo, separated by a nonproductive thin limestone formation are investigated. Seismic was not an unambiguous indicator of the Caddo reservoir. The Caddo event exhibits doublet character reflections when productive facies are present. However, this character proved to be a false diagnostic of the Caddo reservoir. Wells drilled on interpreted doublet reflections turned out to dry holes penetrating two thin limestone units instead.First, some modern poststack processing techniques are used to remove incoherent noise and improve the data resolution and interpretability. Seismic instantaneous attributes (i.e., amplitude, phase, and frequency) are then calculated to infer seismic expressions of the reservoir and the limestone formations. Next, spectral decomposition is performed to study the frequency responses of the different lithotypes. Interestingly, the attribute images and frequency maps could distinguish between the different investigated units. However, some limestone units show up similar to the Lower Caddo formation in the frequency images. Model-based acoustic impedance inversion is carried out on seismic lines spanning both zones. Acoustic impedance sections reveal that producing wells and dry wells penetrate different formations. The cosine of instantaneous phase attribute along with impedance sections supports the above interpretations and displays more clearly where the Caddo reservoir is traversed and where it is not. This study demonstrates that integration of modern poststack processing and novel seismic attributes can lead to extract more key information about challenging reservoirs with less ambiguity.