The main focus of this study is to relate successful production from the Niobrara Formation at Silo Field, Laramie County, Wyoming to geologic variables like porosity, mineralogy, TOC, natural fracture intensity and orientation, distance of wells from faults and thickness. Silo Field has over thirty years of Niobrara production data. Though the Niobrara has been the topic of much previous research, little attention has been paid in analyzing relationships between geological trends and production data in a quantitative manner. The goal is to build a geologic model of Silo field that will predict the locations of successful producing wells or " sweet spots". This paper presents progress made so far in relating porosity, mineralogy and natural fracture intensity to production at Silo Field.
The Niobrara Formation consists of interbedded chalks and marls deposited during the Late Cretaceous in the Western Interior Seaway. It extends throughout the Rocky Mountain region from Montana to New Mexico. The alternating chalk and marl strata contribute to the petroleum system potential of the Niobrara. Ductile marl units have higher organic carbon content, and act as both a source and seal while most reservoir capacity is in the brittle chalk benches. Natural fractures within the Niobrara are recognized as being important for storage and deliverability of hydrocarbons.
Silo Field, located in the Denver-Julesburg Basin in Laramie County, Wyoming (Figure 1a), has been producing from the Niobrara Formation since 1983. Cumulative production to date is 10.9 MMBO and 9,818 MMCFG. At Silo Field, the Niobrara Formation is ~300 ft. thick, lies at depths of 7000–8500 ft (2133–2590 m), and consists of the lower Fort Hayes Limestone Member and the upper Smoky Hill Member. The Smoky Hill Member is composed of the upper, middle and lower, or the A, B, and C chalk and marl intervals (Figure 1b). The B chalk bench is the main production target. Structurally, Silo Field is a westward dipping monocline. Drilling history at Silo can be grouped into three periods:
original 1980s vertical wells,
1990s horizontal wells and
modern horizontal wells drilled using multi-stage hydraulic fracturing technology (Figure 1c). Despite a long production history at Silo Field, it is not well understood why only a few wells are top producers while neighboring wells have very poor production rates.