Proactive Geosteering in Safaniya Sands in KSA (World’s Largest Offshore Oilfield)
Safaniya oilfield operated and owned by Saudi Aramco is the largest offshore oilfield in the world, located in Persian gulf, Saudi Arabic. The Safaniya is primary supplier of heavy oil at an average API gravity of 27 according to Wikipedia.
The geosteering objective was to optimize the horizontal wellbore placement within reservoir intervals and to maximize the net pay utilizing the real-time distance to bed boundary analysis.
- Vertical seismic uncertainty.
- Thinning and truncation of good sand facies.
- Channel sand deposits.
- Local features such as scouring or wedging create high angle departures from the reservoir.
- Baker’s Deep Azimuthal Resistivity (AziTrak) tool.
- Density image.
- Triple combo.
The wellbore was landed by the geosteering experts in the target sand and was geosteered to maximize the wellbore exposure within the target zones utilizing the Azimuthal Propagation Resistivity (APR) signals and distance-to-bed-boundary (DTBB) calculations. 400KHz and 2MHz attenuation and phase curves were utilized to generate DTBB and resistivity modeling. The density image was significant in calculating formation dips and dip predictions ahead. The target layers thickness change was obvious on APR inversions and the timely decisions made to reduce the wellbore exposure to unwanted zones while entering the next reservoir layer. The thickness of the target layers was 4-10 feet with reservoir / shoulder bed resistivity contrast of 1:20. The wellbore length was increased to the depth where wet zone no-go limit was reached with structural bending of the reservoir into the wet zone.
Overall, wellbore objectives were achieved in optimizing wellbore placement within the target zone with minimum doglegs and reduced exposure to shoulder beds.
- AziTrak distance to bed boundary enabled the optimum wellbore placement within the target zones.
- Minimized doglegs severity due to prompt decisions made in advance.
- The boundary mapping tool added value in precise well placement within zone with reduced exposure to unwanted zones.
- Knowledgeable personnel were the key for accurate interpretation and wellbore placement.