AAPG Southwest Section

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The relationship between the San Andres regional setting and Residual Oil Zones (ROZs) in the Permian Basin


Residual Oil Zones (ROZs) in the San Andres have gone from a “one off” a decade ago to established, economically producible reservoirs today. The science of ROZs have been documented over the past decade with DOE and RPSEA supported projects. There are now a variety of different methodologies used to produce oil from ROZs: co-mingled and separate “brownfield” ROZ and Main Pay CO2 floods, CO2 EOR ROZ floods peripheral to existing fields, “greenfield” CO2 EOR ROZ floods without an associated main pay. Recently, horizontal depressuring (DUROZ) projects where horizontal wells target uneconomic classic vertical pay zones and ROZs together, have been developed on the Northwest Shelf and northern Central Basin Platform.

Despite the fact that there is now a decade of research into ROZs, and close to 20 projects producing oil for the ROZ, we need to step back and evaluate the relationship between ROZ targets and the complex depositional and diagenetic history of the San Andres to avoid the pitfalls associated with developing any new play. Assuming that the environment of deposition and diagenetic overprint are the same will lead you down that same garden path. Ditto for the fluid's properties in the ROZ.