To Mill or Not to Mill: A Fully Retrievable Multistage Fracturing System

Abstract

Abstract With the increase in horizontal wellbore lengths, effective hole cleaning and efficient milling practices play a critical role in coiled tubing (CT) extended reach applications. Multistage hydraulic fracturing of unconventional reservoir plays has focused horizontal completion techniques on one of two primary types: plug-and-perf or ball-and-seat liner systems. The introduction of ball-and-seat technology in the middle of the last decade was a breakthrough in the horizontal stimulation completion process and significantly impacted the ability of operators to economically develop shale and tight oil reservoirs. Most current completion systems require post-fracturing milling interventions to restore full wellbore access and remove flow restrictions. To address the challenges associated with plug milling or opening ball seats up to the full liner drift diameter, fully retrievable single-trip systems have been developed. These next generation systems require no post-stimulation milling or drilling while maintaining the benefits of both the plug-and-perf and the ball-and-sleeve completion methods through the use of retrievable isolation plugs and ball seats. Workover time can be decreased over 40%, eliminating costly milling operations. The uncertainty in both milling efficiency and the removal of debris is replaced with a simple set-down and release mechanism which leaves the wellbore unobstructed for any future well interventions. The retrievable seat system has the added advantage of leaving behind a shiftable sleeve which can be activated numerous times. Over 600 stages of the retrievable seat system have been successfully installed and retrieved within the last 12 months while providing operators the future ability to shut off zones which may unfavorably affect production by water or gas break through. This paper will address sleeve and plug retrieval versus milling, comparing job times, cost, operating efficiencies and equipment requirements.