RE: 2P: 12 MMboe (~80% oil) with ONLY 11% recovery
To understand better, the importance of WATERFLOOD, check out Ghawar.
As FORBES notes, the secret to Ghawar longevity is water injection. I quote from FORBES:
https://www.forbes.com/2010/01/21/biggest-oil-fields-business-energy-oil-fields.html
"The once and future king of the world's oil fields, Ghawar, in Saudi Arabia, ranks first on our list. It is thought to have had more than 100 billion barrels of recoverable oil in place. At 160 miles long and 16 miles wide it confounds even the most experienced geologists. With something on the order of 60 billion produced over the past 60 years, you'd be excused for thinking that Ghawar was sliding into its twilight years. Yet the Saudis insist that Ghawar is still going strong, producing 4.5 million bpd from six main producing areas with the ability to do 5 million bpd if called upon.
The secret to Ghawar's longevity is water injection. Starting in the 1960s Saudi Aramco began injecting water underneath the oil around the outer borders of the field. Today the water flood is up to millions of barrels a day, with the oil floating up to the top of the reservoir on sea of water. In conversations with Forbes in 2008 Aramco executives insisted that by continuing to treat Ghawar with kid gloves they'll be able to coax 4 million bpd out of her for many years to come".