Ultra-Narrow Annular Tubing Drilling Deployment
Authors: Diaz Leonardo , Alves Sandro Batista , Krasuk Raul Miguel , Tisera Leonardo David , Luna Ruben Fabian 
Published: March 2022

Abstract
Two formation pressure regime shifts coexists on Bajada del Palo field subsurface leading to an additional casing seat to keep well design and execution aligned with well control requirements. A massive field development demands well-construction costs fine tuning and optimization to ensure competitiveness, and in this regard a big-bore well program jeopardize the business. This paper portrays how expertise on Casing Drilling technologies and slim-hole drilling challenges management are put together into a successful ultra-narrow annular Tubing Drilling implementation, with well objectives met and development cost reduced.
Lotena formation, a gas producer reservoir rock, is tipically overlained by the potentially over-pressurized and naturally fractured Quintuco-Vaca Muerta system in the East side of the field. As this formation is characterized by a normal pressure regime, a conservative well design requires Quintuco-Vaca Muerta isolation to overcome potential drilling challenges such as limited mud-weight window, high formation pressures, influxes, and fluid losses. This additional intermediate interval enlarges every section upwards with well cost been dragged up consequently.
Historically, Lotena Gas wells design considered two intermediate casing seats (on Quintuco formation top and on Vaca Muerta base). Optimized well design consist of removing one intermediate interval and slimming down all open hole and tubular sizes to an ultra slimhole well design, i.e., clearances being from 6 to 8 mm for tubular body, and 2 or less than 1 mm for tool-joints, on the production section.
Tubing Drilling on ultra slimhole design enables well cost optimization but brings onboard its intrinsic related and own set of challenges. From Tubing Drilling side, these are: torque and drag management, non-viable directional control, weight on bit limitations, tripping restrictions and impacts, well barriers concerns, and electric-log program constraints. On the other hand, an ultra-narrow annular clearance adds the followings: drilling fluid design, lubricity requirements, ECD management, hole cleaning concerns, losses control, and cementing quality assurance. The paper discusses the key engineering design and operational aspects to focus on an operation with such challenges combination as well as summarizes the implementation results from the wells where this unusual design took place.
This paper concludes with some of the lessons learned from this successful experience, which was a result of well planning and operational efforts focused on logistics, tubing selection and integrity assurance, torque management procedures, ECD control, fluid properties with lubricity approach, and rig crews prowess to handle and drill with a string much different than the one they are used to. Understanding and managing drilling hazards on this environment provides the encouragement to include ultra-slimhole geometry on the standard well design portfolio, leaving aside the preconception of it been perceived as an unworkable design.