Published by the DTI Oil & Gas Directorate for the reservoir engineering and IOR community in the UK.
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Evidence for Success - Demonstrable Field Evidence for Increased Recovery From the Prudhoe Bay Miscible Gas Project

In the last edition of this newsletter it was noted that BP would shortly release a new DVD illustrating demonstrable field evidence for increased recovery from the Prudhoe Bay Miscible Gas Project. The DVD is now available and has been reviewed by RML’s Dave Sherrard.

"Miscible gas is demonstrably reducing oil residuals in contacted rock from 20% to less than 5% in layers with high throughput”, proclaims Andrew Cockin in the introduction to BP’s new DVD extolling the achievements the world’s largest miscible flood.

The real star of this 60 minute DVD is Prudhoe Bay itself, stretching over the arctic landscape, beautifully photographed and refuting the notion that oil field developments can only blot the landscape. At Prudhoe 8 billion cubic feet of gas is stripped of rich hydrocarbons every day for sale and for injection back into the reservoir. Half a billion cubic feet alone is used for enhanced oil recovery.

The story begins with a 1980s fibreglass cased observation well. Repeat resistivity and neuton logging has tracked alternating waves of water and gas as they drive through the rock 1000 feet away from one of the injection wells. Observed vertical conformance has surpassed expectations and oil residuals have dropped from a waterflood value of circa 30% down to 10%.

This analysis is bolstered by the story of the design and analysis of a single well tracer test to corroborate the indirect logging measurements. Again oil residuals are reduced to very low levels.

Buoyed by this technological success, two wells were sidetracked in the 1990s and cored through a swept zone close to an injector and a region of swollen oil close to a producer. Gas chromatograph measurements of the composition of the residual and swollen oil reveal the subtle complexities of the miscible process in the reservoir, with both condensing and vaporising processes occurring.

The final chapter uses the measurable changes in produced oil composition to segregate waterflood oil from miscible oil allowing the total benefit of the project, in terms of additional oil reserves, to be identified and quantified.

These measurements span 20 years of work by the Prudhoe operators. DVD is a great medium to convey the high level messages with the key technical references also supplied on the disk. Cockin and McGuire are ardent and media friendly presenters with the experience to pull together years of work by many contributors. One slight regret is that little credit is given to the companies that preceded BP at Prudhoe and had the courage to initiate these projects in an era when enhanced oil recovery was unproven technology. Thanks to them, and publications such as this, the decision to implement such schemes is getting easier."

Copies of "Evidence for Success" can be ordered by sending an email to Jeane Drewett; drewetj@bp.com

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