Solid Expandable Tubulars Enable Practical Well Re-entry in Mature Fields
Authors: Itoua-Konga Félix , Coluccia Giovanni Itoua , Congo Eni , Felix Vasco 
Published: October 2008

Abstract
The lack of available slots on offshore platforms necessitated consideration of a new approach to well re-entry programs in mature fields. An infilling drilling campaign in the offshore Zatchi and Loango fields in West Africa led an operator to explore a more economical and practical approach that reduces drilling time and maximizes the use of existing assets. Prior to initiating the plan, an analysis was made on the available alternatives to the retrieving and milling operations that often resulted in a long and difficult ordeal. Two alternatives considered included:New drills with slot recoveryRe-entry with solid expandable tubulars
The first alternative required further studies on the platform to use the slot-recovery deflecting tool. This process also appeared more expensive than the solid expandable tubulars and would require additional time to get the wells back on production.
This paper will introduce the results of the application of solid expandable tubular technology on the two wells in the Loango and Zatchi fields, the difficulties of the operation and how they were overcome. An actual case history will be used to describe the safe and successful installation of solid expandable tubular systems through windows opened in existing casings. This paper will also explain how solid expandable tubulars facilitate enough hole diameter to install the necessary electric submersible pumps (ESP) without having to mill existing casing or find recovery platform slots.

Introduction
Due to a lack of available platform slots, the infilling campaign previously conducted on the Zatchi and Loango fields consisted of re-entering existing wells with retrieving and milling operations. Prior to starting the 2005 drilling campaign, the operator conducted an internal analysis on previous results and on available alternatives to the previous recovery methods used, which on several occasions resulted in time-consuming and laborious operations. The target reservoir consists mainly of sand, sandstone and shale. The shale's tendency to swell presented a challenge; sometimes preventing the casing from reaching total depth (TD). Milling operations also presented a challenge in that it took longer than forecasted. After analyzing past operations and offset data, the operator identified only two viable methods-slot recovery, which involves sidetracking high in the slot and drilling a new well or sidetrack lower in the wellbore and use solid expandable tubular systems to preserve hole size.
The slot recovery option was rejected for this application because the technology was not available at the time. Furthermore, use of this option required studies as to the compatibility of the slot-recover deflecting tool and the platform. When the operator factored in the timeframe that would be required to put the well back on production preliminary analysis showed this approach was not as economically feasible as using solid expandable tubulars. Therefore, the solid expandable tubular system was identified as the most viable alternative considering its cost-effectiveness and technical contribution.