Simultaneous AVO inversion and seismic lithology cube estimation by using PP and PS angle stack seismic data of the Oseberg Field, North Sea

Abstract

Converted seismic wave data is not yet commonly used in oil industry. In an offshore environment Ocean Bottom Cables (OBCs) are needed to register the converted S-waves in addition to the P-waves which makes the acquisition of converted seismic waves very expensive. Nevertheless, converted seismic waves may provide additional information to the P-wave seismic which may justify the extra costs in acquisition, processing and interpretation. This thesis focuses on the joint PP & PS AVO inversion on the Oseberg Field, North Sea. A 2D seismic model is created to analyze the behavior and reliability of AVO inversion by using different sets of P and S angle stack data, different wavelets and multiple algorithms. Based on this result a joint PP & PS AVO inversion is applied to the Oseberg Field data. The result (P-, S- impedance and density) is critically compared with the well log data. In addition, synthetic seismic sections are derived from the inversion results and compared with the angle stacks. The next step consists of analyzing the well logs in order to find log sets including rock moduli derived from the well logs to discriminate between the different lithological units. This leads to differentiate between hydrocarbon sand, carbonate and shale. Based on these results the seismic inversion attributes are converted to a seismic lithology cube limited by the top and the base of the reservoir. That cube allows to map the hydrocarbon sand of the reservoir.