Abstract

Silo oil field is located seventeen miles northeast of Cheyenne, Wyoming in townships 15 and 16 north, ranges 63, 64 and 65 west. It was discovered by Amoco in 1980. Horizontal drilling commenced in 1990 and 53 horizontal wells were completed by 1994. It has produced over 10 MMBO and 989 MMCFG through January 2010. Most of the production was from horizontal wells however some vertical wells in the center of the field produced over 300 MBO. Oil is primarily produced from the Niobrara Formation (Upper Cretaceous), a complicated reservoir consisting of four limestone benches layered with organic rich shale. Silo has been considered somewhat unique because following its discovery the search for analogs was unsuccessful. Production is enhanced by natural fractures and previous authors have differing hypotheses regarding the origin of the fractures. Permian salt solution, horizontal compression, and reactivation of basement wrench faults have been proposed. The fracturing that enhances production rates appears to dissipate outward from the center of the field but the extent of the fractured area is not completely delineated. Early operators targeted development of the “B” bench in the field. Additional reserves probably remain and could be exploited in the “A” and “C” benches.

Falling oil prices in the late 1990’s led to the cessation of drilling before the limits of the field were fully defined. Horizontal drilling was in its early stage of development and most of the wells encountered problems in drilling and completing. Wells early in the field development flowed oil while drilling and later wells experienced lost circulation. Horizontal drilling and hydraulic fracturing technology have progressed markedly in recent years. Recent drilling successes, primarily in Northern Colorado have renewed interest in the Denver Basin and may ignite new exploration. Advances in horizontal drilling and hydraulic fracturing that have been made in recent years would likely improve results of future development. The ownership of the lands within the field until recently was controlled by several operators which made field development competitive and therefore problematic. Fewer operators currently control the field which should mitigate land and logistical issues.