Maximising recovery from thin oil columns, Part 2: Using geophysics for improved reservoir quality prediction and better drilling performance. 9th Middle East Geosciences Conference, GEO 2010.

Petroleum Development Oman (PDO) is currently developing a Cretaceous (Shu’aiba Formation) matrix carbonate reservoir with a transitional thin oil column of 10 to 15 m as a waterflood with over 1,000 m long horizontal producers and injectors. In-depth geophysical studies added significant value in a number of areas: improved understanding of the reservoir extent, pre-drill prediction of porosity and fractures from quantitative interpretation (QI) work and borehole seismics to accurately predict the distance from the horizontal producers to the top reservoir. An improved velocity model utilizing regional wells from a 40 km radius greatly reduced the depth uncertainties to < 0.5% and predicted an extension of the field to the southeast, resulting in a stock tank oil initially in-place increase of 20%. Quantitative interpretation volumes provided rock property and reservoir quality prediction for well placement and sequencing. The porosity distribution predicted from acoustic impedance (AI) ahead of the main drilling campaign was confirmed by the drilling results and continues to guide the well lengths and sequencing successfully. Semblance and discontinuity extractions predicted sub-seismic faults and fractures along the planned wells and improved well placement and reduced drilling risks. Borehole acoustic reflection survey, based on seismic data acquired post-drilling in the borehole with a sonic tool, proves useful in validating distance from borehole to reservoir top and recognizing sub-seismic faults. The results are used in subsequent side-track strategy, nearby well placement to reduce unswept attic oil and understanding production behavior. In conclusion, geophysics has demonstrated impacts on field extension, reservoir modeling and optimal oil production beyond routine formation structure and fault definitions.