Abstract
Unconventional reservoirs require innovative completion techniques and technology to become more economical. Formations vary drastically in lithology, lateral lengths, completion methods, and financial drivers. The two most popular stimulation techniques are ‘plug-n-perf’ and multistage openhole packer/sleeve completions.
The Williston Basin consists of two primary oil- and gas-producing formations: Bakken and Three Forks. As frac sleeve designs have improved, the capabilities to offer operators an ever-increasing number of stages in a one-trip system have vastly increased the effective flow area created by staged hydraulic fracturing, thus resulting in better production.
Over the years, hybrid systems have been installed in horizontal wellbores to increase the number of compartmental sections for hydraulic fracturing because of the limitations of ball-actuated frac sleeves. These hybrid systems place ball-actuated frac sleeves along sections of the wellbore starting at the toe. Once the maximum number of frac sleeves has been spaced out using openhole packers for isolation, the additional sections of the wellbore are separated without sleeves using only openhole packers. During the frac, balls are used to shift open frac sleeves and provide isolation from the previously treated sections. Once all the sleeves have been opened and the fracs placed, composite frac plugs are pumped down and set to isolate and treat additional stages using the ‘plug-n-perf’ method. Experimenting with hybrid systems provides operators with the ability to optimize spacing of frac stages along the horizontal section when sleeve technology alone did not allow for the desired number of stages. The costs are higher for operators to perform a hybrid-type completion, and this has driven enhanced sleeve technology to allow for all sleeve completions.
Working relationships between operators and service companies have enabled the advancement of current technology to provide solutions that increase efficiencies and production. This paper outlines information from specific case histories on current well construction/design, historic overviews showing the progression of openhole completions used within the Williston Basin, how spacing is determined between stages based on reservoir characteristics, and how technological advancements and working relationships have enabled a record number of sleeves to be installed in a single wellbore where tighter frac spacing is required.
