The Sable Field, South Africa — Lessons Learnt in Producing Oil and Gas from Offshore Deep-Marine Reservoir
William McAloon and Frank van Baarsel
New Ventures:East and West Africa, PetroSA, Cape Town, South Africa
The SABLE oil and gas field is located approximately 95 km off the southern coast of South Africa in approximately 100 metres of water. The field is presently producing from two reservoirs: the E-BD undersaturated oil reservoir and the underlying E-CE oil and gas reservoir. The field was brought on production in August 2003. By the end of November 2007 the field had produced over 22 million barrels of oil. More than 113 Bcf of gas had been re-injected into the E-CE reservoir and 13.5 million barrels of water into E-BD.
The E-BD reservoir section of the SABLE field is interpreted to comprise deep-marine sandstones within a lowstand channel-fill complex. The channel underwent significant post-depositional erosion by cross-cutting younger channels. These clay-filled channels, in conjunction with intra-formational shales within the reservoir, were identified during pre-development studies as possible baffles to fluid flow over production time.
Early production data from the E-BD reservoir suggested that there was a problem with vertical communication within the reservoir, which quickly resulted in declining reservoir pressure and a potentially low recovery factor.
During production operations reservoir simulations indicated that the drilling of a dumpflood well would increase SABLE oil recovery by a significant amount. The well was successfully drilled and completed in May 2004. The desired crossflow from the overpressured water injection zone to the shallower depleted oil layers was achieved. The well was the first of its kind drilled offshore in South Africa.
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