Horizontal fracture stimulated completions remain the de facto method of producing from shale formations. The vast majority of wells are completed using the "Plug and Perf" fracturing technique which later requires either a drill string or coiled tubing (CT) with a positive displacement motor (PDM) to remove the composite plugs. An estimated 6,000 to 8,000 wells are completed each year, with between 100,000 to 140,000 composite plugs installed in them in the U.S. alone. In extended reach horizontal completions, plug removal using CT becomes less efficient since end load forces transmitted to the PDM from the coiled tubing decrease as well depth increases.Currently many operators rely on 'word of mouth' to design and perform extended reach CT jobs, resulting in 'nonengineered' and poorly executed plug milling operations. However, one new method to extend the operating envelope of efficient coiled tubing plug milling utilizing a water hammer tool has gained significant momentum. Several water hammer tools are in common use and there is significant anecdotal evidence that their application has improved job efficiencies. This paper reviews plug milling efficiencies and general best practices from milling operations conducted in shale formations across the US (Eagle Ford, Bakken, Haynesville, Barnett and the Marcellus). The scope will cover operations completed with three different fluid hammer tools and base cases conducted without these tools.The paper will also discuss milling efficiencies, number of stalls, stuck pipe incidents, speed and frequency of wiper trips and fluid selection associated with plug milling operations. The authors believe that the information presented in this paper will provide relevant analytical data to assist operators in improving the overall efficiency of the completion process.

Traditional multi-stage high rate fracture treatments have been used in many shale and conventional formations. These treatments typically rely on composite bridge or frac plugs, run on wireline to provide zonal isolation. In a typical frac treatment, rates of up to 100 bpm are normally divided between four to six pre-perforated clusters per stage. Typical spacings between clusters are 50 to 100 ft. In theory, fluid would divide equally between each perforated cluster, however that is an unlikely scenario since stimulation treatments will follow the path of least resistance. To improve production results, targeted fracturing operations are gaining in popularity in many formations. Some targeted operations utilize abrasive perforating via coiled tubing (CT), followed by the fracture treatment down the annulus. The treatment flush is modified to include an underdisplaced dense slurry stage to act as the isolation mechanism. In vertical wells, proppant settles by gravity covering the recently treated interval. In horizontal wells however, a plug enhancement additive (PEA) can be used to achieve isolation, partially mitigating gravity effects. Moreover, instead of splitting flow between four to six clusters, most horizontal treatments target only one discreet cluster/zone at a time. Significant gains in fracture control are obtained with this method. Initial targeted operations were applied to 300 ft of frac spacing, thus reducing the number of stages per well when compared to the 50 to 100 ft cluster spacing on higher rate frac operations. This paper describes one targeted operation in a horizontal well where the spacing was reduced to 60 ft. In all, forty-three stages were successfully stimulated using enhanced sand plugs for zonal isolation.

Horizontal completions continue to increase in popularity throughout the industry. In North America the majority of horizontal wells are drilled in shale gas formations. These formations require fracture stimulation for economic production. The majority of these stimulations are completed by fracturing four to six clusters of perforations simultaneously at high rates followed by a mechanical isolation with a composite bridge plug. As the horizontal wells increase in length the number of plugs required increases, with up to twenty plugs not being uncommon. These plugs are removed with a positive displacement motor (PDM) and mill run on either coiled tubing (CT) or jointed pipe. In longer-reach horizontal completions, plug removal using CT becomes more challenging as the efficiency of surface end loads transmitted to the mill are reduced. Quite often the deepest plugs can not be reached with standard coiled tubing, instead requiring larger-diameter, more costly, coiled tubing or jointed pipe. The need to extend the operating depth to effectively operate PDMs and reach the deepest plugs has led to development of several tool systems. This paper will discuss the engineering, design, testing and initial field trial results of a variable fluid hammer extended-reach tool; how it was used to improve plug milling performance, to give superior control of weight on bit, to extend coiled tubing reach in the horizontal section and to reduce operational time. These field results will be compared with results using other methods of friction reduction, such as pipe-on-pipe friction reducers.