The unconventional wells in Marcellus are becoming increasingly longer and more complex which involves a number of challenges on the drilling side. But we should also not forget about the performance and implications of the subsequent drill-out of plugs in the commonly used plug and perf approach for completions in the Marcellus basin.
The main challenges in assessing drill-out scenarios lies in the smaller outside diameter (OD) pipes that can be conveyed inside the production casing, and in the fact that torque and drag (T&D) models should allow enough margin to compensate for any deviation in the directional plan during the drilling operations.
The main uncertainty in the calculations comes from the Friction Factor (FF) associated to the particular scenario of cased hole applications and the potential use of Snubbing units (and coiled tubing (CT) to a certain level) which allows to push the pipe and effectively reduces the FF (additional force to gravity); the purpose of this paper is to provide real expectations of achievable Friction Factors using data from real drilled-out wells in the field and its comparison against simulations using the Friction Factor as calibration parameter.
The Marcellus basin is mostly comprised of extended reach horizontal wells, the most common completion methods in the area is the plug and perf approach (Blake et al, 2018), which implicates the requirement of post-stimulation plug drill-out once the entire lateral section is finished.
Particularly in Marcellus basin, the wells have become longer in lateral section in the past few years, increasing the average lateral length with the objective of reducing the cost of each foot (Koperna et al, 2021). But with this increase in lateral length there is also increase in complexity to deploy tubulars used in the well construction process that require a more demanding evaluation for the torque and drag. While this issue is typically addressed during the drilling phase of the well it is commonly overlooked during the drill-out of plugs after well stimulation.
The plug drill-out operations are performed in cased hole with a relatively small OD tubular string that can be conveyed inside the production casing using a Snubbing unit, the smaller size of this string reduces the mechanical properties and limits for the drill-out operations.