Possibilities of Weber Stratigraphic Traps, Rangely Area, Northwest Colorado

Abstract

The purpose of this study is to determine the possibilities of stratigraphic hydrocarbon accumulation in the Weber formation, especially in the general area of Rangely, Colorado. Outcrop descriptions, core analyses and descriptions, sample examinations, flowmeter surveys, production data, and test data were utilized in drawing conclusions. During early Pennsylvanian time a shallow trough extended from the geosynclinal Oquirrh basin eastward upon the broad shelf. Apparently this east-trending seaway intermittently connected the Oquirrh basin with the central Colorado trough. The Morgan and Weber formations are believed to be shelf-deposited equivalents of the Permo-Pennsylvanian geosynclinal Oquirrh formation. As such, the Weber transects the Permo-Pennsylvanian time boundary. The Uncompahgre and Park Range uplifts became very active in early Des Moines time. Clastics from the Uncompahgre uplift spread north, and northwest into the shallow trough and westward into the Oquirrh basin. The arkosic Maroon formation forms a wide belt around the uplift areas. The Maroon interfingers with and is overlapped by the relatively cle n quartzose sandstone of the Weber. Therefore, the Maroon formation is essentially a near-source facies variation of the Weber formation. The Weber formation contains beds with more favorable reservoir characteristics than the Maroon. Consequently the possibility of significant stratigraphic trapping of hydrocarbons along the Weber-Maroon facies change is good. Both Rangely and Thornburg fields are located within this facies change, and may have been in areas of general oil accumulation prior to the formation of local structural traps by Laramide folding.