The Application of Permanent Completion Techniques To Offshore Operations
Authors: King T.G. 
Published: December 2007

To reduce the cost of workovers at offshore locations, several techniques using concentric tubing strings and/or wireline methods, and/or treatments (excluding installation of gas lift valves or acidizing) performed directly down the production tubing have been field tested. Low fluid loss cement slurries have been used to complete deeper below a single zone production packer by squeezing the existing perforations, washing out excess cement and perforating the new zone with an expandable gun. higher recompletions (both below and above a single zone production packer) have been successfully accomplished using the same principles. Sand production has been stopped through the use of epoxy resin solutions displaced either through concentric tubing strings or directly down the production tubing. Plugback operations using dump bailers have been disappointing, but further work in required before this method can be condemned. Results to date are encouraging, and open a way to reduce production maintenance costs at distant deepwater locations.

Introduction

The average oil or gas field occurring in the Miocene and Pliocene sediments of the offshore U. S. Gulf Coast contains multiple reservoir. Realizing maximum returns from investments requires optimization of two quantities:

reduction of direct operating costs. and maintaining all wells in a continuously producing capacity until all horizons are depleted.

To attain this ideal, recompletion of depleted zones or, if economically feasible, the reestablishment of production from the existing completion must be undertaken at minimum cost and with a minimum of delay. During extensive development programs, primary drilling activity tends to take precedence over production maintenance which results in an insufficient number of deepwater rigs being available for the work at hand. While capital expenditures for new development may enable production to maintain an over-all upward trend, production from older fields frequently declines to a level that is lower than necessary because deficient or off-production wells have not been worked over promptly. Rig availability is not the only factor responsible for such delays. The cost of moving an offshore rig into a field is high (between $10,000 and $50,000, depending on the length of the move and type of rig). Single well workover programs may not be economical and it is often necessary to accumulate a series of projects before a profitable workover program can be attempted. To help in solving the problems created by these restraints, workover operations using permanent completion techniques have been adapted for use at marine locations. In this paper, permanent completion techniques are defined as remedial operations which can be conducted without physically disturbing the original downhole mechanical condition of the well. This type of workover involves the use of concentric macaroni tubing strings and/or wireline methods and/or treatments (other than installation of gas lift valves or acidizing) performed directly down the production tubing. Small rigs or pulling units capable of handling the necessary tubular equipment and easily installed on well jackets or platforms are available with little delay at relatively low cost. The small units usually work 12 hours a day, handle tubing in singles and can be installed on location for about $5,000. Research into cement technology has developed low fluid loss slurries which retain fairly constant properties throughout their entire pumping time. Physical properties of such cements enable them to be pumped safely through small openings and small diameter (3/4 in. ID) work strings. Successful recompletions above and below existing perforations have been made, sand controls installed and repaired and small milling operations undertaken. These procedures have resulted in the profitable acceleration of recompletions at reduced costs and the restoration of production from sanded up wells. They have also enabled high-risk recompletions to be attempted in zones which, but for these lower cost techniques, would have been abandoned without testing. Permanent completion workover operations offer attractive economic advantages over conventional methods and enable high risk zones to be exploited.

JPT

P. 1031ˆ