New Gas Play in Fractured Pennsylvanian Strata in the Eastern Paradox Basin of Colorado and Utah

Rasmussen, Donald L.1, Dalton L. Rasmussen2 (1) Paradox Basin Data, Denver, CO (2) Platte River Associates, Inc, Boulder, CO

An emerging new play in the Paradox Basin is for gas trapped in micro-porosity and fractures within strata of the sub-salt (Pinkerton Trail) and salt-bearing (Paradox) Pennsylvanian horizons. Greatest potential for gas in the Pinkerton Trail is in structures along the Uncompahgre Uplift where thick organic-rich shales were interbedded with carbonates, evaporites, and siliciclastics during the late Morrowan and earliest Atokan. These strata were subsequently fractured in the late Paleozoic by wrench and thrust faulting and again during the early Tertiary Laramide event by reactivated folding and faulting. Hydrocarbon generation began possibly as early as the late Paleozoic and continued into the Tertiary. Gas potential in the Atokan and Desmoinesian Paradox organic-rich shales and dolostones and their siliciclastic interbeds is greatest within trends of maximum thickening or where interbedded between Paradox salts. Fracturing of these strata began during post-depositional folding and faulting, primarily during excavation of salt intervals to adjacent anticlines or diapirs, and was reactivated during hydrocarbon generation and tectonism in the Cretaceous and Tertiary.