Thin-Oil-Column Extended-Reach Drilling at Sakhalin

Abstract

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 163487, ’Case History of a Challenging Thin-Oil-Column Extended-Reach- Drilling Development at Sakhalin,’ by Vishwas P. Gupta and Shea R. Sanford, SPE, ExxonMobil Development Company; Randall S. Mathis and Erin K. DiPippo, SPE, Exxon Neftegas; and Michael J. Egan, AIPC, Consultant to Exxon Neftegas, prepared for the 2013 SPE/IADC Drilling Conference and Exhibition, Amsterdam, 5-7 March. The paper has not been peer reviewed. ExxonMobil, operator for the Sakhalin-1 project, planned an additional drilling campaign at the Chayvo field, Sakhalin Island, Russia. The focus of this campaign was to develop a thin-oil-column reservoir by use of extended-reach drilling (ERD). This overview describes the planning of these wells at the edge of the ERD envelope, the associated technical and operational challenges, and the complexity of targeting a thin oil column in an ERD environment. Planning of these wells involved building upon the operator’s previous experience and the use of additional tools and methods to address unique challenges. Introduction The Sakhalin-1 project comprises the Chayvo, Odoptu, and Arkutun Dagi fields off the east coast of Sakhalin Island, Russian Federation, as shown in Fig. 1. Development drilling at the Chayvo field started in 2003 with extended-reach wells drilled from an onshore wellsite pad with the Yastreb drilling rig. In 2005, further development drilling commenced from the offshore Orlan platform. In 2008, the Yastreb rig was moved approximately 75 km north to the Odoptu onshore wellsite pad and drilled nine ERD wells as part of the initial-stage development of Odoptu. Following the Odoptu campaign, the Yastreb rig was moved back to the Chayvo onshore wellsite in 2011 for further development and infill drilling of the Chayvo reservoirs. As of October 2012, 15 of the 20 longest ERD wells in the world had been drilled in the Sakhalin-1 project, with the recently completed Well Z-44 at Chayvo field setting a new measured-depth (MD) record at 12 376 m. Significant well-design parameters, tools, and techniques that enabled these challenging wells are detailed in the complete paper. The technical challenges included uncertainties in the location of the oil column and fluid contacts, the need for very accurate well placement for effective reservoir drainage and for preventing early gas/water breakthrough, completing long horizontal intervals, and high-torque/drag effects. The geologic uncertainties and wellbore-positioning challenges were addressed with a combination of a single near-horizontal pilot hole to locate the fluid contacts and a novel technique to minimize vertical-position uncertainty by use of formation-pressure measurements while drilling. Extensive torque/drag modeling and wellbore-stability modeling were performed to design the wells and equipment and define operational parameters. Completion designs were optimized to ensure successful placement in long horizontal intervals.