Next Generation of Sakhalin Extended-Reach Drilling
Authors: Denney Dennis 
Published: February 2015

This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 99131, "The Next Generation of Sakhalin Extended-Reach Drilling," by R.A. Viktorin, SPE, J.R. McDermott, R.E. Rush Jr., SPE, and J.H. Schamp, SPE, ExxonMobil, prepared for the 2006 IADC/SPE Drilling Conference, Miami, Florida, 21-23 February.
Six of the longest-reach wells in the world have been drilled in Chayvo field on Sakhalin Island. Revised completions used standalone screens (SASs), pre-drilled liners, and swell packers to achieve a low-damage, sand-free completion with zonal isolation. Bit designs, bottomhole-assembly (BHA) configurations, and operations practices were modified to minimize the amount of backreaming, improve the overall rate of penetration (ROP), and achieve a "one-pass trippable hole" (OPTH). Improving rotary-steerable-system (RSS) reliability could eliminate trips to replace the tools.

Introduction
The Chayvo field development plan comprises 15 onshore extended-reach-drilling (ERD) wells with measured-depth (MD) reaches of 8 to 10 km and 18 offshore directional wells drilled from an ice-resistant platform. The focus of this paper is the Chayvo onshore ERD operations that began in July 2003. At the time this paper was written, eight of the 15 land-based ERD wells had been drilled from the Chayvo wellsite (Fig. 1). The full-length paper details design changes and operations optimization that evolved into the next generation of ERD wells at Sakhalin. The typical Chayvo ERD well design is shown in Fig. 2.

Completion Design Evolution
The original completion design met the following objectives.Low-damage completion capable of producing 25,000 BOPD.Providing zonal isolation to mitigate risk of gas and/or water breakthrough.Sand-free completion.Provide low-risk interventions.
The first four Chayvo completions were designed to achieve these objectives by use of a rotated and cemented 7-in. liner tied back with 7-in. tubing. These 7-in. monobore completions enabled oriented underbalanced perforating with coiled tubing, thereby reducing potential for sand production and providing a low-skin completion.
Although this design achieved all the objectives, implementation proved difficult because of liner-cementing and perforating problems. Running the 7-in. liners on the first four wells was trouble-free. However, problems occurred in two wells while filling the liner with mud, and the other two wells had cementing problems.
Redesign. Completion redesign focused on reducing nonproductive time (NPT) caused by failures in the liner installation and problems with perforating. Design options included openhole completion, openhole gravel pack, cased-hole gravel pack, and SAS. Fig. 3 compares the new and old completion designs. The new design uses external-isolation swell packers and SASs with inflow-control devices (ICDs), which were not proven or available for the original completion designs. The new design positions SASs across the weaker, more permeable formation to provide a sand-free completion. These SASs use ICDs (or chokes) to reduce flow from the high-permeability formations that could produce gas or water if allowed to produce unrestricted. The high-permeability intervals are isolated from the low-permeability intervals with swell packers. The higher-strength low-permeability intervals are completed with a predrilled liner. Swell packers replaced cement for zonal isolation, and ICDs replaced selective perforating to control flow from high-permeability zones. The key to successful zonal isolation was positioning swell packers and screens precisely across the high-permeability zones.