WELL LOG DATA CONDITIONING USING A ROCK PHYSICS MODELING APPROACH: EXAMPLES FROM THE BANYU URIP FIELD, CEPU KKS, EAST JAVA BASIN

摘要

Establishing decent seismic/well ties is crucial for quantitative geophysical applications such as seismic attribute analysis, seismic inversion, AVO analysis, 4D seismic monitoring, and interpretation of multi-component seismic data. Well logs, particularly sonic and density logs, tend to be problematic in carbonate environments for a variety of reasons that include invasion effects and bad borehole conditions. In this paper we propose the use of a robust and practical carbonate rock physics model to address various log quality issues in a predictive manner. The predictive power of this carbonate model has been demonstrated through significant improvements in well-seismic ties for 4 wells from the Banyu Urip field in Mobil Cepu Ltd.'s Cepu KKS, East Java Basin.Resistivity log data (deep, shallow, and micro resistivity) from Banyu Urip wells show strong mud filtrate invasion within the carbonate reservoir section in comparison with the overlying clastic section. While invasion effects on density logs is well known, our quantitative data analysis shows that the fluid invasion effect on sonic logs is strong enough to impact the quality of Banyu Urip well-seismic ties. For instance, our rock physics model gave a much better prediction of measured S-wave logs (and hence Vp/Vs) when assuming 100% mud filtrate invasion, indicating that sonic log tools measure within the invaded zone of the carbonate section. Pronounced invasion effects on sonic and density logs are also seen in the shallow gas-bearing clastic section that overlies the Banyu Urip carbonate reservoir. Logs in the clastic section are also affected by washout, and by anisotropy where boreholes are highly deviated.Significant improvements in seismic/well ties were achieved following editing of measured well logdata. These improved well ties will be used for a variety of quantitative geophysical applications that hitherto have been challenged due to seismic and well log data quality issues.