Completing the Bakken shale in North Dakota presents options that are varied and complex. To achieve optimum recovery, the Bakken formation needs to be drilled horizontally and hydraulically fracture-stimulated. If the wellbore is drilled in the orientation to achieve a longitudinal fracture treatment, only one fracture treatment is needed and the issue of frac-stage isolation is not an issue. If the stress orientation is unknown, or the wellbore is drilled in the orientation for transverse oriented hydraulic fracture direction, then frac-stage isolation is an important decision. In the past few years, numerous methods have been tried to achieve good frac-stage isolation in the Bakken. A brief review of completion success in the Bakken identifies one method that has the highest degree of success when completing transverse-oriented hydraulic fractures. The best wells have an uncemented liner and a compartmental completion technique. These compartments can be tailored to cover specific areas of the borehole so the treatment is placed near the best shows. The frac compartments are created with the use of swellable external casing packers and ball-actuated stimulation sleeves. In one pumping event, multiple frac-stages are pumped, separated by opening individual stimulation sleeves selectively from the toe to the heel. The completion of two wells are discussed that show positive proof of this concept from a completion and production perspective.

In recent years, the formation known as the Bakken Shale in eastern Montana and western North Dakota has seen enormous growth in oil and gas production. Scientists from the United States Geological Survey have commented that the area has the potential to become "the next Saudi Arabia." In most cases, the Bakken horizontal wells are fracture stimulated. However, with several thousand feet of formation, effective stimulation of the entire length has proven time-consuming and costly. In the past, a single-leg zone was fractured all at the same time, regardless of the varied permeability of the layers. Although this simple method of stimulation was seen as a success at the time, a new, more efficient method using swellable packers with reactive elements now promises to optimize total recovery and minimize fracturing cost. Case history data will show how employing multiple frac sleeves with swellable packers straddling each interval proves to be a cost-effective way to stimulate multiple zones and save days of rig time. Specific experience in the Bakken field provides an optimization model for worldwide well completion markets Unlocking Tight Oil Traditional methods for tight oil drilling often include several costly steps to open up new veins: multiple downhole trips, cementing, plugging, perforating and finally fracturing. With the reactive-element packer method, the open-hole packers segregate multiple frac sleeves used to set up and designate multiple fractures on a horizontal wellbore. This segmenting process allows for more fractures, reduces the time and cost for hydraulic fracturing, accelerates production and improves reservoir drainage. In the Middle Bakken formation at the Sanish Field, North Dakota, an independent contractor sought a frac stimulation procedure to increase overall production while reducing well construction and completion costs. The contractor selected a successful recent innovation - reactive-element (swellable) packers - to perform an eight-stage compartmentalized frac job. Challenges The efficacy of frac stimulation is diminished when laterals exceed 5,000 ft. running an eight-stage frac job at more than 5,000 ft. involved even greater challenges. Major pumping investments are often required for tight shale formations. Traditional methods include pumping frac fluid into the open hole or isolating separate zones of a horizontal wellbore. The former method typically results in the frac fluid flowing to areas of least resistance, which can reduce production along the rest of the wellbore. The latter method typically includes several steps (repeated cementing, plugging, perforating and fracturing) and will also require multiple trips as well as the expense of additional crew and equipment for the duration of the operation. Completing high-angle wells also becomes problematic when getting tools through doglegs and other restrictions. The packers in the selected frac system are shorter than standard tools, which allow them to navigate better through such tight spots.

Completion techniques in the Middle Bakken formation have evolved over the years, with cemented Plug & Perf becoming the most common technique in recent years. It relies on stimulation of multiple clusters of perforations, normally 3-5, at one time. As previously demonstrated by multiple papers (SPE 173363, 144326, 167726, 174943) up to 40% of the perforation clusters remain un-stimulated. A novel engineered diversion workflow was implemented in 687 intervals of 20 Williston Basin wells. The purpose of this workflow is to increase cluster efficiency by stimulating the previously un-stimulated clusters. Results from each step down test and engineered workflow evaluation indicate increased cluster efficiency by up to 80%. Moreover, the success criteria for diversion pressure (1000 psi) was achieved on 81% of the intervals. Due to the success of these wells, this workflow has now become the standard diversion technique for one major operator in the Williston Basin.

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.