The Bakken Shale located in North Dakota has seen large increases in oil and gas production. The contributing technologies that have aided in the increased production are the recent advances in openhole packer and sleeve completions. These completions have enabled operators to isolate and fracture up to 24 stages using a one-trip openhole packer and sleeve completion.The use of multilaterals enables operators to save capital investment by accessing production from two laterals while drilling a single vertical wellbore. Greater drainage access across a section is also achieved by using this technology. Coupling multilateral and openhole packer/sleeve technologies together allows for multiple-stage hydraulic fracturing operations of both laterals. This paper will show how employing openhole packer and sleeve completions coupled with a fracturable multilateral junction provides a cost-effective way to drill, complete, and stimulate wells in the Bakken. The experience gained in the Bakken will be applicable worldwide as operators look to optimize openhole completions in their unconventional reservoirs.

We characterize cutting sequences of infinite geodesics on square-tiled surfaces by considering interval exchanges on specially chosen intervals on the surface. These interval exchanges can be thought of as skew products over a rotation, and we convert cutting sequences to symbolic trajectories of these interval exchanges to show that special types of combinatorial lifts of Sturmian sequences completely describe all cutting sequences on a square-tiled surface. Our results extend the list of families of surfaces where cutting sequences are understood to a dense subset of the moduli space of all translation surfaces.Comment: 28 pages, 12 figures. Minor revisions and corrections. To appear in Geometriae Dedicat

Unconventional reservoirs require innovative completion techniques and technology to become more economical. Formations vary drastically in lithology, lateral lengths, completion methods, and financial drivers. One of the most common techniques is the ‘plug-n-perf’ method. In the Eagle Ford, long-string completions are the norm, with the production casing cemented in place along the horizontal section and up the vertical section, providing isolation between frac stages and from other formations above and below the zone of interest. The Eagle Ford shale is a formation that produces gas, liquids, and oil, depending on the area in South Texas being drilled. Operators are looking for ways to reduce cost and gain efficiencies when completing wells in unconventional reservoirs. One way of reducing cost is eliminating coiled-tubing-deployed perforations for establishing reservoir communication on the first stage of multistage frac operations. Technology has been developed which provides operators the option of placing a pressure-actuated valve above the shoe track, allowing for standard cementing practices. The new valve provides operators the ability to pressure test the casing and, through the use of applied pressure from the surface, activate into the open position. Once opened, information about the reservoir can be gathered that will influence the frac design before assembling the required pumping equipment. This paper presents multiple case histories showing different applications of the cemented pressure-actuated valve. The development history, reliability, and inherent accuracy are presented. This interventionless access technique has been proven effective in the Eagle Ford and Haynesville formations and is applicable in other unconventional reservoirs requiring multistage hydraulic fracturing.

Unconventional reservoirs require innovative completion techniques and technology to become more economical. Formations vary drastically in lithology, lateral lengths, completion methods, and financial drivers. Since reservoir conditions typically mandate the use of hydraulic fracturing for economical production results, a significant amount of resources are focused on making the fracturing process more efficient and lowering its environmental impact. This case history includes an operational review focused on a novel technique to rapidly perform targeted annular hydraulic fractures by deploying an activation tool on coiled tubing (CT) to open frac sleeves in a horizontal well. The paper covers results and information gathered from the first operation of its kind in Montana's Bakken Formation – where a total of 19 stages were fractured in the shaley dolomite. The new technology does not involve dropping balls or setting composite plugs to isolate stages. Rather, the technique utilizes frac sleeves that are activated using a CT bottomhole assembly to save time between stages. The sleeves can be cemented in place if desired and have a full-bore internal diameter that does not require post-treatment composite plug millouts, further reducing overall completion time and time to production. Additional capabilities of the system enable the use of memory gauges to monitor downhole pressure and temperature characteristics. The operator preferred this method due to its targeted nature, efficiency, and fluid savings. As opposed to multicluster fracturing methods (such as ‘plug-n-perf"), a single entry point during the frac job promotes increased fluid velocity, enabling a more aggressive sand ramp and reduction in required hydraulic horsepower. Similarly, the single entry point ensures that a fracture is generated at each port, as opposed to the possibility that some clusters are not treated. In addition, no composite plugs or diverting devices are required to be pumped down the wellbore, so water usage is reduced considerably. The system, already used in thousands of fracturing stages in Canada, speeds up the completion process, uses less fluid, minimizes risks, and reduces overall downtime.

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.