--> --> Impact of geology on development of the Niobrara and Codell resource play in Wattenberg Field, CO

AAPG Rocky Mountain Section Meeting

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Impact of geology on development of the Niobrara and Codell resource play in Wattenberg Field, CO

Abstract

The combined Niobrara/Codell resource play is a major target of current oil & gas development in Wattenberg Field, CO. Enerplus Resources is currently developing a position on the northern edge of the field. During our development phase, we developed a hypothesis that the geometry and character of faulting and in situ stress anisotropy can be detrimental to both our ability to stay in zone and our ability to complete wells. To test this hypothesis, we identified faults in a fully developed 9-section study area using vertical well logs and from re-steering horizontal wells. Re-steering wells also allowed us to calculate the percentage of wellbore in target intervals. The 9- section study area – located in the southeastern part of Wattenberg Field – contains 143 vertical wells and 70 horizontal wells, and was selected to minimize the impact of other variables (e.g., reservoir thickness, porosity) on drilling and production. We picked 71 large faults (throw > 50 ft), 100 medium faults (50 ft > throw >20 ft), and 117 small faults (throw < 20 ft). Correlating fault picks resulted in identification of 51 large faults across the 9-section area. The orientation and quantity of faults are similar to fault traces interpreted from seismic data. Large faults appear to cut both the Niobrara Formation and Codell Sandstone, and the geometry of these faults reveals the presence of flower structures that appear related to basement strike-slip faults. Medium and small faults appear to only cut the Niobrara Formation and may be associated with polygonal faulting. Horizontal wells that cross through flower structures are more likely to be “out-of-zone” than wells that do not pass through these structures. Furthermore, wells that are >80% in chalk appear to produce more oil over 12 months than wells that are >80% in marl. This study advances our predictive capabilities regarding the behavior of faults in both Niobrara and Codell target intervals and has changed how Enerplus completes wells in our acreage on the northern edge of Wattenberg.