Abstract

Cement packer well work is a rig-less intervention method for accessing reserves above and between production packers. It is used to isolate a target completion interval from other hydrocarbon or non-hydrocarbon zones. Cement packer is used as an alternative to the conventional production packer. The key benefit of cement packer application is the cost savings (in the order of $MM) realized instead of using a major rig workover to achieve the same objective of isolation of a target interval. A key challenge however is the attendant increased skin caused by reduced perforation efficiency through the extra layer of cement plug. This paper addresses this issue by showing the work-around adopted by one of the Assets in Chevron Nigeria JV to improve well productivity.

Well-AA was evaluated and proposed for a zone switch non-rig workover intervention of the production interval from N-AA/Well-AA to K-AA/Well-5X reservoir in November 2012 using cement packer to isolate existing completion and recomplete in the new target reservoir. The zone switch and perforation were executed successfully via a cement packer operation but didn't flow after perforation. Several attempts to bring the well on production such as swabbing were made with no success. The outcome of the attempts indicated there was poor or lack of connectivity between the wellbore and the sand-face.

A well performance lookback was done to identify the well problem and it was recommended to re-perforate the proposed interval of the well and initiate gas lift. The recommendation for re-perforation was based on productivity index analysis of previous cement packer completions and the perforation gun performance with respect to the required penetration through the cement plug, tubing/casing and the formation. Estimated productivity index (PI) from two previous cement packer operations were the basis of the recommendation. Well-BD (was perforated twice) with calculated PI of 2 Bbls/Day/Psi and Well-CX (which was perforated once) with calculated PI of 0.3 Bbls/Day/Psi.

This paper will discuss the lessons learnt and best practice from re-perforation of Well-AA with a bigger and deeper penetrating perforation gun that restored initial production from 0 BOPD to 550 BOPD at natural flow condition via a SEWOP barge operation.

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