Integration of geological and technological factors influencing production in the Bakken play, Williston Basin

Abstract

A great variety of factors can influence production, and it is often difficult to discriminate how significant the impact of a single factor is. The unconventional nature of the Bakken tight oil play requires considering both geological and technological aspects, as completion designs evolved at a rapid pace over recent years. Based on an integrated and correlative approach this study aims to understand why certain areas in the Bakken play are considerably more productive than others, and to identify the responsible factors. 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. The Bakken is a technology-driven play and a clear trend of increasing production rates over time is evident as drilling techniques and the completion design of wells are progressively becoming more sophisticated. Since 2010 the majority of operators employ massive hydraulic fracturing treatments with up to 40 stages and millions of pounds of proppant. However, numerous older wells outperform younger wells despite technological advancements, suggesting that geological factors have a larger impact on production than the completion design. Geological factors influencing productivity can range from reservoir quality and thickness, structural and stratigraphic framework, rock-mechanical properties, natural fractures, to pore-overpressure distribution, organic geochemical parameters, and trapping mechanisms. The interplay of hydrocarbon generation potential and maturity results in tremendous overpressuring, and creation of fracture permeability and secondary porosity. Secondary migration of hydrocarbons, driven by overpressure, into up-dip located traps can lead to the occurrence of large-scale accumulations, such as Sanish-Parshall and Elm Coulee. The comprehensive and integrated analysis of technological and geological data allowed identification of different Bakken play types, which are productive for different reasons. The knowledge and understanding of where and why sweetspot and low productivity areas occur is invaluable for both current development and future exploration.