Abstract

The Upper Leonardian (L-6, L-7, and L-8) are important contributors to production in the Permian Basin, but are typically glossed over when reviewing the middle-late Permian fields and stratigraphy. The Leonardian (L-6), the Glorieta (GLRT) and/or San Angelo (SAGL), is productive on the platforms, however, it is often a ‘teaser” with good porosity, oil shows, and potentially productive calculated Sw’s. In the North Ward Estes (N.W.E.) area, a new pool discovery in 1991, the W. A. Estes (Holt), found the Leonardian (L-6) productive from tighter, restricted marine, subtidal to intertidal dolomites, while the better quality open marine facies formed the Residual Oil Zone (ROZ). At W. A. Estes Field, the Leonardian (L-6) top is eroded, however, it does not exhibit major karsting, perhaps due to the lack of permeability in the uppermost subtidal to intertidal cycles retarding infiltration of meteoric water. In the field area, the basal San Andres (L-7) transgression is so rapid that a crinoid, bryozoan, bivalve, gastropod rudstone rests on an eroded, dolomitized Leonardian (L-6) restricted marine, shallow subtidal to tidal flat cycle.

Thirty miles to the northeast, across the spine of the platform, in the East Goldsmith Field, the top of the upper Leonardian (L-6), is also identified by the sharp transition from eroded, dolomitized restricted marine to tidal flat faces below, to deep, open marine Holt Limestone (L-7) above. The L-6 main pay at East Goldsmith is mostly shallow subtidal to tidal flats (similar to the W. A. Estes Field), with a producible interval shallow and an ROZ deep.

The “Holt Pay” was named for the first production from the zone in the North Cowden “Deep” pool. The Gulf #1 Holt, Section 1, Block A, PSL, Ector County. Jones, 1953, identifies the “Holt Pay” in Ector County as a clean, porous limestone about 140’ thick above the top of the subsurface Glorieta. Jones continues “this pay was once considered to be of Leonardian age, then as Early Guadalupian (Skinner)”, Wilde considers the interval to be Leonardian (1991). The use of the term “Holt Pay” in Winkler County for the productive dolomite below the top of the subsurface Glorieta is a PATENT ERROR” according to Jones.

The Maximum Flood of the San Andres (Guadalupian G-1) is represented by the McKnight Shale in Ector and southern Andrews County. It is a shale in name only elsewhere on the CBP, and can be correlated to the P-4 Maximum Flood on the Northwest Shelf, and the El Centro Member of the Cutoff along the northern margin of the Delaware Basin. The “true” shale would be expected to have developed in the low areas on the SAGL surface, however, the shale is well displayed across the Goldsmith, and East Goldsmith Fields associated with the “spine” of the CBP, suggesting post-depositional tectonic uplift in that area. In the North Ward Estes area, the “McKnight Shale” is a deeper marine, dark gray to black, crinoid-rich wackestone with significant percentages of chert, as nodules, filling matrix porosity, and replacing skeletal grains. In Ward County, the McKnight Shale lacks the true shale gamma ray signature but does present as a correlatable “dirty” carbonate.