Rejuvenating Understanding of Structure and Sand Distribution in a Difficult and Declining North Sea Area

Oseberg South area has produced oil for more than 10 years from Heather, Tarbert and Ness sands but with poor to very poor seismic images. An Ocean Bottom Cable seismic shot in 2010 has overcome the problems caused by overburden sands with very high acoustic velocities that disrupted the signal. The results obtained from a fast-track process were exceptional, with major improvements in the seismic image and the inversion data everywhere. The inversion data identifies Ness channel sands for the first time, one of which has just been drilled, shows large volumes of previously unrecognized Heather sands and clearly locates the highly deformed Oligocene sands where drill cuttings are being injected in the shallow section. The considerable improvements in the deep section were also very useful: the Statfjord was easily mapped and provides new exploration targets.