The Upper Cretaceous Codell and Niobrara formations are primary targets in the Wattenberg field (Figure 1) of the Denver-Julesberg basin in northwest Colorado. Although initial discovery of producible hydrocarbons in the Codell occurred in 1955, it was not until the early 1980s when larger scale completion began for the Codell and Niobrara wells throughout the field. Since the early 1980s, there have been more than 10,000 Codell and Niobrara completions in the Wattenberg field.
Originally, the Codell and Niobrara formations were completed individually within the same well. In the early 1990s, operators introduced a limited-entry style stimulation technique in an effort to effectively stimulate both formations with one hydraulic fracturing treatment. Although there is currently significant activity in the field with regard to horizontal well completion in both the Codell and Niobrara formations, extensive vertical well completion still exists. Various completion strategies are currently employed for vertical well completion, including individual stimulation of the Codell and Niobrara formations, limited-entry completion of both formations, and completion of only one of the producing horizons, leaving the other behind pipe. Furthermore, there are many cases of recompletions where an operator has re-entered a Codell-only well at a later date to complete the Niobrara.
Spatial sampling was employed to assess the effectiveness of various completion strategies in one area of the Wattenberg field. Spatial sampling is a documented method for comparing large groups of wells with their direct offsets. The original intent of the spatial sampling method was to identify underperforming wells; however, the method has also been employed as a way to compare various completion or stimulation techniques.
The Codell and Niobrara formations are two of the primary producing horizons in the Wattenberg field of the Denver-Julesburg basin located in northeastern Colorado. Although discovered earlier, few wells were drilled in the Codell or Niobrara before 1981 (Wright 1988). Since that time, there have been more than 10,000 wells drilled in the Codell and/or Niobrara (COGCC 2013).