Goldsmith Landreth San Andres Unit (GLSAU) #203RW (Injector Offset Well Core): Proof of Mobilized Oil from the Residual Oil Zone

Steve Melzer¹ and Bob Trentham¹

¹University of Texas of the Permian Basin, Melzer CO2nsulting

Abstract

As part of the commingled Goldsmith Landreth Main Pay (MP) and Residual Oil Zone (ROZ) CO2 flood in the Goldsmith (San Andres) Field, a core was taken in both the MP and ROZ with a partial objective to demonstrate the sweep efficiency of the MP and ROZ flood. The well, #203 RW GLSAU, was a replacement for one of the original injectors in the initial producer-centered five-spot pilot. Oil response was excellent and very rapid in the pilot and, early in the injection history, it was determined that for conformance reasons, it was necessary to plug back from the fast processing lower unit of the ROZ (LROZ), and concentrate the injection in the upper member of the ROZ (UROZ). The operator's most desirable solution was to replace the original well (#203W) and drill and core a replacement well (#203 RW). The new well was drilled ~135' from the original well, just outside the original pattern. Both the MP and ROZ was cored and it became apparent that there were elevated oil saturations (So) in the LROZ when compared to other cores taken before the inception of the CO2 flood. These elevated So values just outside the pilot pattern serves as proof of oil 'bank' development in LROZ that had provided the fast response inside the pattern and was caught in the act just outside the pilot pattern. As CO2 had been injected in the lower ROZ for a brief period, the flood front had advanced to the center producer but not moved far beyond the location of the replacement well (#203 RW) outside the injector.

The reservoir portion of the ROZ is composed of 2 parasequence sets of fusulinid rich outer shelf mud rich to mud poor packstones (in both the UROZ & LROZ). An interval of deeper water fusulinid dominant wackestone to mudstone separates the two ROZ CO2 targets. The base of the ROZ is coincident across most of the field with the transition from predominantly limestone below to dolomite above. This transition is often seen to be associated with the base of the ROZ, as is the presence of native sulfur. The faster processing LROZ represents a heavily dolomitized and leached sequence just atop the limey base of the ROZ. The MP is composed of an overall shallowing upward sequence, from open marine to tidal flats, where there are a series of individual shallowing upward individual cycles, many of which have Solid Hydrocarbon Residue (SHR) at the base of the cycle suggesting each cycle acts as a separate flow unit.

AAPG Datapages/Search and Discovery Article #90190©AAPG Southwest Section Annual Convention, Midland, Texas, May 11-14, 2014