Dear Colleagues:

It’s been alleged that transition zones (TZs) rather than residual oil zones (ROZs) of imbibition reservoirs hold most of the oil reserves recoverable by CCUS projects, including those in the Permian Basin. Posts appearing in other TIGS titled “Buoyancy and Breach of Caprock Seals” offer a technical basis for this allegation.

This post shares what some (apparently many) in our industry consider to be “science”. Was the conceptual model of Mother Nature’s Waterflood offered to us in jest?

Herd Mentality

Herd mentality is the tendency of people in a group to think and behave in ways that conform with others in the group rather than as individuals. Perhaps “group think” can be a good thing. How could this be? Well, it keeps it all going. What does this mean? Here's an example:

A Fairytale

Once upon a time we were told by researchers at the University of Texas of the Permian Basin that ROZs hold a vast energy resource, billions of barrels of oil recoverable as a result of CCUS activity. Their claim was based on a magical model presented at a West Texas Geological Society symposium, whereby ROZs are said to form via viscous forces resulting from tectonic uplift, changed hydrodynamic flow within aquifers and lateral sweep of oil columns (Lindsay 2001).
By promoting this enchanting story as science and ignoring the long-held belief that a ROZ and its overlying TZ form by vertically acting buoyancy forces in leaking reservoirs, a myriad of consultants and academics solicited and received vast sums of public funds from the Fossil Energy Department of the U.S. DOE over a period of years to mature their fairytale.

All was going well for the fairies until those incredible entrepreneurs from West Texas revealed that they were purposely landing their horizontal completions in the TZs overlying the ROZs, not in the ROZs themselves! Then researchers at Texas Tech presented a paper (SPE 187482) concluding that production wells claimed to be completed in the upper portion of San Andres ROZs are "unlikely to be true ROZ producers and are more likely to be completed in the Transition Zone (TZ)."

That the TZs are holding the prize rather than the ROZs should not have been a surprise - it was predictable for reasons clarified by Lucia (2000) and Adams (2002 and 2003), and in the book "Reservoir Modeling: Pitfalls in Practice and Projects Gone Wrong" (Amazon Books 2019).
Herd mentality accepted and continues to accept this fairytale that has been dubbed Mother Nature's Waterflood. To not be part of the herd is dangerous. As an academic in the petroleum industry, not buying into the fairytale would likely mean the loss of public funding and a shrinkage in university petroleum engineering and earth science programs. Seemingly, group think and a "wink of the eye" kept - and likely will continue to keep - it all going, employing thousands given massive government subsidies.

How could reducing unemployment in the absence of real opportunity be other than a good thing?

Jim Dietrich
Member SPE / AAPG
Pasadena, CA, USA