Historic Oil Field
Cottonwood Creek Field lies about fifteen miles northeast of Worland in Washakie County, Wyoming, and it broke the mould for the Bighorn Basin. Where nearly every earlier field in the basin was found by drilling a visible surface anticline, Cottonwood Creek was discovered in 1953 by deliberately testing a stratigraphic trap in the Permian Phosphoria — a change in rock quality rather than a fold. The result was a broad, low-relief accumulation spread over roughly sixty square miles of reservoir dolomite that has been produced under injection for decades.
By the early 1950s the obvious structures of the Bighorn Basin had been drilled. Cottonwood Creek was the product of a different idea: that oil could be trapped where porous Phosphoria dolomite passes laterally into tight rock, with no fold required. The 1953 discovery is often described as perhaps the first major Wyoming field drilled specifically as a stratigraphic trap prospect, and its success changed how operators looked at the basin’s Permian section, redirecting exploration toward facies changes rather than toward the anticlines that had defined the previous forty years.
Development revealed a field unlike the basin’s anticlinal giants. Instead of a compact crest with steep flanks, Cottonwood Creek covers a wide area of modest thickness, so it required many wells to drain and careful attention to where reservoir quality actually existed. Contemporary AAPG work on the field concentrated on exactly that problem — mapping the carbonate reservoir and the geologic heterogeneities that controlled its behaviour — and later studies identified a separate Tensleep fault trap component within the same field outline.
The operating history since has been the ordinary Rocky Mountain sequence of unitization, waterflood, and repeated attempts to squeeze more from an aging carbonate. Published engineering work describes acid refracturing programs in the Cottonwood Creek Unit that added reserves by restoring injectivity and productivity in wells whose perforations had tightened over decades. Carbon dioxide recovery in Bighorn Basin Phosphoria reservoirs has been studied more broadly, and Cottonwood Creek appears in that literature, though owners should not assume a flood is running without confirming it.
Cottonwood Creek produces from Permian Phosphoria dolomite in a stratigraphic trap, with production also documented from a Tensleep fault trap within the field. The reservoir is a broad sheet of porous carbonate that grades laterally into rock too tight to produce, so the field boundary is a facies boundary rather than a structural contour. Roughly sixty square miles of reservoir rock is involved, and reservoir heterogeneity — where porosity is developed and where it is not — controls well performance far more than depth or structural position does. That is why individual wells vary so much across a single lease.
Water injection has carried Cottonwood Creek through most of its producing life, maintaining pressure across a low-relief reservoir that has no strong natural drive to lean on. Engineering literature on the unit describes acid refracturing campaigns that increased recoverable reserves by reopening flow paths in wells that had lost injectivity or productivity — an unglamorous form of enhanced recovery that matters enormously in tight carbonate. Carbon dioxide flooding of Bighorn Basin Phosphoria reservoirs has been evaluated in regional studies, and Cottonwood Creek is among the fields discussed as a candidate rather than as an established CO2 project.
Because Cottonwood Creek is a stratigraphic field, ownership value varies more across the field than it would on an anticline: two tracts the same distance from a good well can sit on very different reservoir. Production is late-life, injection-supported, and slow-declining, which is a durable profile but one that income-multiple pricing handles poorly. Washakie County interests are also commonly fractionalized among heirs several generations removed from the original lessor. We buy minerals and royalties in Washakie County and provide free written offers.
County-level well data, production charts, and selling guides for the counties this field spans:
It is a trap formed by a change in the rock itself — porous reservoir passing into tight rock — rather than by a fold or fault. Cottonwood Creek is one, which is why the field covers a broad, low-relief area and why reservoir quality varies so much from tract to tract.
It has been produced under water injection, and carbon dioxide recovery in Bighorn Basin Phosphoria reservoirs has been studied with Cottonwood Creek among the fields discussed. Treat it as a candidate rather than an operating CO2 project unless your operator has told you otherwise.
Because the reservoir is a carbonate sheet with uneven porosity development. In a stratigraphic field, a few hundred feet can be the difference between good dolomite and rock that will not flow, which is exactly the variability that has to be modeled when valuing an interest here.