Rock physics and AVO studies of PL 348 (Norwegian Sea)

Abstract

The block, PL 348 is situated on the Halten Area in the Norwegian Sea. This license contains four discoveries Galtvort, Galtvort South, Gygrid and Tau and number of potential prospects that bear similar AVO anomalies on seismic data as were observed in the drilled structures. The aim of this thesis was to investigate whether these AVO anomalies are caused by the presence of hydrocarbons in the structures or other factors that are causing the anomalies. Combination of Rock Physical and AVO techniques were used to study the problem. Avseth, P. et al., in their book "Quantitative Seismic Interpretation" have shown number of Rock Physics techniques in order to study the the effect of hydrocarbon bearing sands and water bearing sands on the well logs. Based on this knowledge cross-plots of existing wells were modeled using Vp, Vs and density logs."Gassmann Fluid Substitution Technique", available in RockDoc, was used to simulate different fluid scenarios and the results were cross plotted again to study the changes in logs due changes in fluid type saturating the reservoirs. The results obtained by Rock Physical studies suggested that the elastic parameters i.e. Vp, Vs and density of the reservoirs are affected by the type of fluid in the reservoir. The main AVO techniques used in this report are the product stack of "Near" and "Far" partial stacks, the product stack of "Far - Near" and "Far", the product stack of "Far - Near" and "Near" and crossplotting"Far - Near" versus "Near". The results from these techniques confirm the presence of hydrocarbon bearing AVO anomalies. At the end it was concluded that the type of fluid in the reservoir effect the elastic behavior of all the expected reservoirs and hence the AVO anomalies indicate presence of hydrocarbons in the prospect