The Shannon Sandstone is a Late Cretaceous (Campanian) marine shelf sand within the Cody Shale of Wyoming's Powder River Basin. It lies above the Niobrara Formation and below the Sussex, Parkman and Teapot sands, and like them it is charged mainly by the Mowry Shale source rock beneath the section. The Wyoming State Geological Survey lists the Shannon and Sussex members of the Cody Shale among the basin's unconventional reservoirs, though not among the five most productive in 2024 (those are the Frontier, Niobrara, Parkman, Turner and Mowry).

The Shannon is best understood as a secondary, shallower target that adds a completion zone to pads already drilling the Niobrara and Turner. That is how it appears in Kingdom Exploration's current Powder River program: two wells in the proven Niobrara and a third in the Shannon above it, all from one pad.

Shannon production began with conventional vertical wells in higher-permeability shelf sand bodies and has continued for decades. The federal Table Mountain Unit in Johnson County, operated by Prima Exploration, still produces from the Shannon through a mix of conventional and horizontal wells under waterflood. Horizontal drilling has extended the productive footprint into tighter parts of the sand, usually as part of multi-zone pad development rather than as a standalone program.

The Shannon Sandstone Member of the Cody Shale was deposited in a marine shelf environment during the Campanian age. The formation comprises fine to medium-grained sandstone with interbedded marine shales indicative of fluctuating water depths and sediment supply.

The Shannon is commonly developed with the Sussex Sandstone, which lies stratigraphically above. Both formations represent marine sand bodies encased in organic-rich Cody Shale.

Shannon sandstones exhibit moderate reservoir quality with porosity of 12-18% and permeability of 0.1-5 mD. Higher permeability zones can be prolific producers while tighter intervals require stimulation.

Oil gravity ranges 36-44 API with moderate solution gas. The marine depositional setting creates laterally continuous sand bodies favorable for horizontal development.

Shannon output is incremental to the basin's main zones. Public reporting does not break out Shannon-only volumes; the Wyoming State Geological Survey groups it with the other Cody Shale sands as an unconventional reservoir outside the 2024 top five. Horizontal Shannon wells are typically drilled alongside Niobrara or Sussex wells so that one pad, one set of tanks and one pipeline tie-in serve several zones.

Because the Shannon is shallower than the Niobrara and Turner, a Shannon lateral is less expensive to drill than a Niobrara lateral from the same pad. Operators do not publish per-well Shannon costs. Basin-wide, two-mile laterals are standard and completions average more than 2,000 pounds of proppant per lateral foot (Enverus). The practical advantage is shared infrastructure: where a pad already has production facilities, a Shannon well sells oil from first production without new surface investment.

Shannon economics rest on cost sharing rather than headline rates. A shallower target drilled from an existing pad carries a lower cost than the Niobrara well beside it, so a modest producer can still pay out. The trade-off is reservoir quality: the Shannon is a conventional-style marine sand with more variability in thickness and permeability than the Niobrara, so results depend more on local sand development. Enverus's basin breakeven range of roughly $55 to $65 a barrel applies to the Niobrara and Mowry; the Shannon is not separately benchmarked.

The Shannon will continue to be developed opportunistically as a stacked-pay zone wherever Niobrara and Turner pads make it cheap to add. Its lateral continuity as a shelf sand supports horizontal development, and waterflood experience at Table Mountain shows the sand responds to secondary recovery.

The Shannon Sandstone is a supporting act in the Powder River Basin: not a play driver, but a shallower, cheaper zone that improves pad economics when it is drilled alongside the Niobrara. In a program that already has a proven Niobrara well, pad and pipelines in place, a Shannon well is the lower-cost, higher-uncertainty third leg.