Abstract

Oil and gas fields near the eastern margin of the Midland Basin in eastern Irion County are productive from sandstone reservoirs informally referred to as “Canyon” sandstones. These sandstones occur between Wolfcampian and Strawn limestones within a 2000 feet thick section of predominantly shale and sandstone. Within this section, zones of predominantly sandstone are separated by spiculitic or cherty, calcareous shale/mudsones. The calcareous shales are less resistive than shales associated with the sandstones and are easily correlated in this area. Based on these correlations the “Canyon” is subdivided into upper, middle, and lower “Canyon” sandstones.

With the exception of wells along the Irion-Tom Green County line most “Canyon” production is from the upper and/or middle “Canyon” and most wells do not penetrate the lower “Canyon”. Upper “Canyon” oil and gas fields include Rock Penn, Christi, Irion West, and Lucky Mag. Middle “Canyon” production comes from Zan Zan and some wells in the Brooks Field.

The vertical and areal position of these fields suggest a prograding shelf margin and at least two episodes of lowstand deposition. A third lowstand, represented by sandstone near the top of the upper “Canyon” in the Clark Field may also have occurred but a third lowstand system tract has not been recognized. This may be indicative of a less significant relative sea-level fall. Sandstone reservoirs in the area are typically from these lowstand systems, however, the productive sand of the upper “Canyon” Lucky Mag Field is interpreted to be within a highstand system. The sand quality and production of these reservoirs is relatively poor.

An upper “Canyon” fairway of lowstand reservoirs has been well defined and heavily explored. The discovery of Zan Zan in 1988 demonstrated that a middle “Canyon” fairway may also be present and that additional reservoirs may be located in this trend in Irion County.