Effective Options Utilized to Reduce or Eliminate Non-Productive Time in Case of Severe and Total Losses While Drilling Unconventional Horizontal Wells

Abstract

The horizontal wells in an unconventional area of interest are designed with a combined 8-½-in vertical/curve/lateral sections. The section is typically drilled with oil-based mud (OBM). Severe to total losses might occur while drilling through (or bellow) potential loss zone (depleted zone) in the vertical section. When losses happen, drilling further to the well total depth (TD) stops. Conventional ways to cure the losses are time-consuming. By applying the presented practices in this paper, the losses are successfully cured in most cases to allow drilling ahead to well TD. The results are less overall risk, less non-productive time (NPT), and more cost savings when compared to the traditional methods. Typical applied traditional methods to cure the severe/total losses are tripping out of the wellbore to change the bottom hole assembly to allow pumping higher loss-circulation materials (LCM) pills, setting a cement retainer inside the previous 9-⅝-in casing, and squeezing cement below the retainer to the loss zone. When the cement retainer is run, an additional cleanout BHA is needed to drill out the cement retainer and cement below it to continue to drill the remaining section. The worst-case scenario when the losses are not cured is running and cementing a 7-in liner to cover the loss zone. This option is very expensive and time-consuming. The team applied new strategies to reduce the NPT required to cure the losses, and to attempt to eliminate the losses from even happening while drilling through the potential loss zone. The NPT reduced dramatically when compared with wells drilled using the conventional methods, and it is eliminated in most of the newly drilled wells. The drilling fluid system (also called mud system) is modified to reduce the associated cost of the fluid lost to the loss zone. Furthermore, circulating sub is used in the bottomhole assembly (BHA) to allow pumping high concentration LCM pills without the need to trip out to change the BHA configuration. The developed pump-and-pull (P&P) cementing technique is used instead of the cement retainer when pumping cement is required. However, the most important practice is strengthening the potential loss zone while drilling through and below it to eliminate the NPT completely. A note to mention is that the loss zone in some areas in the unconventional area of interest is highly fractured to the point where even the developed methods are not successfull. Nevertheless, the success rate of these newly applied operational practices is high across the majority of the area of interest.