The Niobrara can be classified as a self-contained petroleum system due to that it serves as a hydrocarbon source rock as well as containing reservoir rocks. Reservoirs are low permeability chalks, shales, and sandstones (<0.1md). The Niobrara petroleum system is present in most of the Rocky Mountain Region and development is prospective in many areas, depending on thermally mature spots. In the Powder River Basin (PRB) of Wyoming, the Niobrara thickness ranges from 50 feet in the eastern side of the basin to a maximum of 600 feet along the western flank. The basin average is around 400 feet thick. Niobrara depth is between 6,000 to 10,000 feet, TOC in the range of 1-8% and porosity is 8-10%.
Natural fractures are important in locating sweet spots in certain fields of Niobrara development. According to the USGS, Niobrara production is delivered through a network of fractures and faults which can control rates and distribution of fluids. Multiple studies have stated the regional structural orientation is northwest-southeast and northeast-southwest in the PRB. There may be different orientations locally, but are considered minor contributions to regional patterns. Percolation theory supports the idea of high fracture density with an increase in reservoir permeability, but only if fracture length improves the connectivity of a given area. Since this is merely a short blog post and since most locally generated fractures are connected by a regional system, I am only crudely observing the entire PRB.
Higher peak liquid production or MaxIP is clearly evident on the southern portion of the basin in central Converse County, on the map below. Production data provided from DI Desktop, basin areal extents from DI Analytics, and fault shapefiles from the USGS Mineral Resources On-Line Spatial Database. It would appear major faulting trends only follow the outline of the PRB.
Then by just taking a quick look at the image below, there appears to be no correlation between sweet spots and lineament zones in the PRB. Assuming the sweet spot areas are mapped correctly, Niobrara production rates in the PRB are not dependent on faults and fractures.
However, the caveat here to me is the basin edges. Once again, by looking at the first map image, one can see a well spot location trend following the basin margins along the southern and southeastern extents. The generalized cross section below portrays the faulting scenario involved here.
For more information on geology of the Niobrara in the PRB as well as the DJ Basin, check out the Niobrara folder inside the Drillinginfo DNA section. Also, check back periodically to the Niobrara Unconventional Reservoir Blogs for a follow up on this topic or other various activity in the play.
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