Hydraulics and Well Control Complications in Unconventional Shale Laterals

Abstract

Unconventional shale resources are drilled horizontally following the geologic bed dip upward or downward to maximize reservoir contact. Despite the efforts to control formation pressures, well control emergencies arise. Wellbore communication with high pressure zones through natural or induced fractures is a major cause of blowouts in unconventional shales. The philosophy of well control is to maintain the bottomhole pressure while balancing the formation pressure; however, it is a challenging process. The objective of this study is to investigate mud hydraulics and well control complications in unconventional shale laterals. This included the impact of wellbore configuration (inclined upward or downward laterals), drilling fluid type (water or oil based mud), and drillstring configuration (drillpipe, casing, or liner). This research employed an interactive drilling and well control full-scale simulator for more than 500 hours of real-time operations. It also utilized a robust steady-state hydraulics and multiphase dynamic well control program. A hydraulics base model was developed and verified with field data from a recently drilled Marcellus Shale well in Monongalia County, WV. In inclined upward laterals, gas bubbles migrated and accumulated at the lateral end. Consequently, the choke experienced lower pressure, volume, and gas discharge rate for extended periods of time. Thus, higher circulation rates and longer operation times were essential to flush-out the dispersed and trapped gas bubbles. The deeper and over-pressurized Utica Shale presents more challenges compared to Marcellus Shale wells. Well integrity was verified by monitoring surface choke, casing shoe, and bottomhole pressures throughout the entire well control operations. This research revealed that it is crucial to identify accurate hydraulics and well control complications for unconventional shale laterals. Some examples were drilling inclined upward and downward laterals using different string and fluid configurations. This improves rig and personnel safety and diminishes the environmental risks and hazards associated with blowouts.