Unique System for Underbalanced Drilling Using Air in the Marcellus Shale

Abstract

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 171024, ’Unique System for Underbalanced Drilling by Use of Air in the Marcellus Shale,’ by Chris Maranuk, SPE, Ali Rodriguez, SPE, Joe Trapasso, SPE, and Joshua Watson, SPE, Weatherford, prepared for the 2014 SPE Eastern Regional Meeting, Charleston, West Virginia, USA, 21-23 October. The paper has not been peer reviewed. Air drilling has become popular in the Marcellus and Utica shale reservoirs because of its higher rate of penetration (ROP) and less resulting formation damage. A unique drilling system incorporating the use of downhole mud motors, electromagnetic (EM) measurement-while-drilling (MWD), and air hammers has been specifically designed and ruggedized to address downhole shock and vibration encountered in air drilling. Use of this system has resulted in significant reduction of nonproductive time (NPT). Introduction While seeking alternatives to increase ROP and reduce drilling costs, a few operators in the northeastern US implemented batch-drilling practices from pad locations. This provides an attractive alternative by allowing multiple wells to share the same surface location, effectively reducing footprint and environmental impact. Common well design uses streamlined well construction, where low-cost rigs can drill the tophole sections and larger, more-expensive rigs drill the curve and lateral sections. The typical well plan incorporates surface, intermediate, curve, and lateral sections that, combined, may exceed 18,000 ft. The lateral sections are the most critical and range between 2,000 and 8,000 ft, depending on formation and well geometry. The goal for close-proximity-well design is to minimize well-to-well interference and maximize reservoir exposure. Air drilling provides a significant decrease in hydrostatic pressure over common mud types, resulting in an increased ROP. Additionally, significantly better hole cleaning can be achieved because of the high air velocities used to drill the well. Finally, mud- and cuttings-handling costs can be reduced because there are no chemicals to absorb and no cuttings-cleaning requirements on virgin formations. Early tests of this application proved it to be a viable option for the Marcellus and the Utica fields. Initially, hammer bits were used for air drilling, but significant challenges involving directional control emerged as well-plan trajectories became more advanced. The development of ruggedized mud motors and MWD tools capable of handling these challenges, and the use of specialized fluid-control systems, eventually allowed more-conventional bottomhole assemblies (BHAs) to be successful when used for air drilling.