Abstract

A number cores from Foster, East Goldsmith, Goldsmith, and H.S.A. Fields were examined to evaluate the platform-wide stratigraphy of (almost) all intervals in the San Andres These cores have been correlated to the “classic” interpretation of the San Andres across the Central Basin Platform. The classic interpretation refers to the L-7 an L-8 as the “Holt” which rapidly floods the Glorieta eroded surface with deeper water, open marine dense carbonates. ROZ’s are often present in the “Holt” interval. The L-7 and L-8 package is capped by the McKnight Shale Maximum Flooding Event (G-1). The McKnight Shale is probably equivalent to the El Centro Member of the Cutoff Formation in the Delaware Basin and the P-4 Maximum Flood event on the Northwest Shelf. ROZ’s are typically not present in this interval. The McKnight Formation (G-2) is represented by deep water open marine limestones with significant quantities of chert. Minor ROZ’s are present in this interval. The “Intermediate” (G-3 & G-4), as defined in Crane County, is also composed of deeper open marine carbonates, primarily limestone and dolomite with minor to extensive ROZ potential. The top of this interval is correlated to the Pi Marker, and Brushy Canyon Bypass Surface on the Northwest Shelf. The Judkins Formation (G-8) transitions from thick, homogeneous open marine cycles to thin subtidal cycles with tidal flat caps. This interval has extensive ROZ potential on the east and west flanks of the platform. The Judkins also is the first unit to have been exposed and heavily eroded across the “spine” of the platform which extends from the Ft Stockton Uplift to the Hobbs High.

The Lovington/Post Lovington (G-9) is absent over large portions of the Spine of the platform due to the major erosional event associated with the top of the San Andres. ROZ’s can be present in the G-9 on the flanks of the platform. In many areas, there is a “double whammy” with the 2 erosion and karst events (G-8 & G-9) superimposed on the “top” of the San Andres, removing thick sections of the upper San Andres, and creating a deep, vertical karst, which results in connectivity issues in both waterfloods and CO2 floods of many San Andres reservoirs on the platform. A classic example of this is the McCamey Field where the San Andres is exceptionally thin and heavily karsted and has been characterized as a “Big Tank” with similar vertical and horizontal permeabilities.