Factors Influencing Productivity in the Bakken Play, Williston Basin
Cosima Theloy and Stephen Sonnenberg
A great variety of factors can influence production, and it is often difficult to discern how significant the impact of a single factor is. This study aims to understand why certain areas and /or fields in the Bakken play are considerably more productive than others, and to identify the responsible factor(s). The late Devonian to early Mississippian Bakken Formation in the Williston Basin is a world-class petroleum system and represents the most prolific tight oil play known to date. The source rocks in this unconventional system are the highly organic-rich Lower and Upper Bakken shale members. The silty, dolomitic Middle Bakken member, sandwiched in-between the shales, and Upper Three Forks member, underlying the Bakken Formation are the main target horizons for production. Parameters, which may potentially have a strong influence on productivity, are numerous and include both geological and technological aspects. Geological factors reach from reservoir quality and thickness, over the structural and stratigraphic framework, to pore-overpressure distribution and organic geochemical parameters. Natural fractures are suspected to play a key role in recovering oil and gas at economic rates from the tight reservoir rocks. Deep-seated faults, tipping out in the underlying Prairie Salt, cause folding at Bakken level and thus may enhance the natural fracture density. Gas shows and drilling mud weights were used to investigate this relationship. Production increased over time as drilling techniques and the completion design of wells are progressively becoming more sophisticated. Initial production rates drastically improved with the advent of horizontal wells in the 1990s. Further augmentation in productivity was observed during the transition from dual and triple laterals to long single laterals with high number of hydraulic fracturing stages. However, often older wells outperform younger wells despite technological advancements, suggesting that geological factors have a far larger impact on production than the completion design. Based on an integrated and correlative approach it seems that migration of hydrocarbons and trapping mechanism may be the key to identify sweet spot areas within the Williston Basin.
AAPG Search and Discovery Article #90156©2012 AAPG Rocky Mountain Section Meeting, Grand Junction, Colorado, 9-12 September 2012