3. Oseberg Sør Many areas of bad data… But we have great production wells C J
4. Series of down stepping fault blocks Thin reservoirs – often little or no seismic expression Increasing erosion of Brent to east Omega G-Central Tune BCU Draupne /Heather UTarbert MT2 MT1 LT UNess LNess Coal Channel Sandstone J-Structure C-structure G-East BCU Draupne /Heather UTarbert MT2 UNess Coal Channel Sandstone Geological cross section through Oseberg Sør West East
5. C-structure F-12, F12A and F-12 B. 30/9-6 Exploration well 1 km F-12 B: Success! F-12: Water wet F-12 A: No sand 3 wells, payback time 80 days
17. (11) (3) (5) (7) (1) Number of Azimuths FOLD 25 75 125 175 225 Model stack of Top Shetland with different numbers of azimuths Conclusion: Minimum 7 well spaced azimuths required
18. What is OBC? Seismic receivers are on the seafloor Records both P-wave (compression) and S-wave (shear) We shoot crossline to get multiazimuth coverage from PGS Receivers Shot points
Complex rift zone Nine structures Many compartments Significant uncertainy on depth and fluid contacts State the total number of wells. Total production 37.45 Sm3 since 1988. BUT the geophysical limits reached. Need to image much better than our conventional approaches – and if we can then there are considerable rewards. Highly mature large area. The easy drilling is done. The seismic image and reservoir models need to be much better to continue the recovery. Excellent economic potential if we can solve the problems
Animated slide
Animated slide F-12 B: 900 Sm 3 /day Costs: F-12 drilling and completion: 67 MNOK F12 A and B drilling and completion: 78 MNOK Total costs: 145 MNOK In the C area, we had drilled the 30/9-6 exploration well and the 30/9-F12, which was supposed to be the first producer. The seismic was awful. The well did not come in on prognosis and did not find sand.
Oligocene sands are the main reason for the poor image. The two wells are a kilometer apart showing the rapid
The problems are due to the Oligocene anomalies and their rapid variations. These are tur
NH9802 on the left, NH0402 on the right same location running E-W through the 30/9-6 well
Conclusion: Minimum 9 well spaced azimuths required Modelled effects assuming a flat Top Shetland
Animated slide
Oligocene anomalies: NH0506 volume peak reflectivity 1188 msec to 1976 msec (viewed as volume in HydroAVI)
OBC survey shot in 2005 model ready 2007
Our management recognised that we had made a substantial imporvement. We capitalised on the success quickly. J block also had awful data. In fact J had needed 12 sidetracks to obtain 2 producers, some of them due to seismic problems. We checked the acquisition parameters of 200 X 250 by decimating the C data in various ways and concluded that we could use a 300 X 300 configuration. This was a big saving in time and was one of the factors that resulted in the cost of the survey dropping by 50%.
J 12 two geological sidetracks, J 11 two sidetracks