Abstract

Recent improvements in coiled tubing technology and reliability have resulted in an impressive participation of coiled tubing units in drilling / completion operations and well services such as stimulation, liquid nitrogen lifting, testing, logging etc. for oil and gas wells.

This paper presents an operational overview of ZADCO experience in applications of coiled tubing (C/T) as follows:

  • velocity strings in weak flow well,

  • pack off strings for corroded production tubings

  • acid conveyer for stimulating deviated and horizontal wells.

The case history of running C/T as a velocity string in two ZADCO wells has resulted in a continuous flowing wells and a marginal improvement in the wells' productivity.

The program for utilizing C/T as pack off string in ZADCO wells was not implemented yet due to logistics problems and changes in the workover program. However, a brief theoretical plan / running procedure is highlighted.

Also, this paper presents the benefits of using C/T for placing acid across low permeable sub-reservoirs which results in maximizing the well's oil production.

Introduction

Zakum Development Company (ZADCO) is operating one of the largest oil-fields in the Gulf Area (Offshore). Since the start up of the production / injection in December 1982, ZADCO has experienced problems in some wells such as:

  1. Non/intermittent flow due to depleted reservoir pressure.

  2. Tubing leaks due to corrosion which resulted in high unsafe annulus pressure.

  3. Ineffective stimulation jobs due to different permeabilities of sub-reservoirs.

Since coiled tubing units have become reliable and cost effective means to perform light workovers, ZADCO has used the C/T as a viable option to solve these problems at a minimal cost.

Velocity Strings
Applications:

Oil and gas wells which suffer from declining reservoir pressure and increased water production cause liquid to accumulate at the bottom of the well and exert back pressure on the formation. This restricts or in some cases prevents fluid entry into the wellbore from the formation.

To return the wells to flowing status, one of the available technique is to reduce the production tubing size by running a concentric string through the existing tubing. This reduces the effective flow area and increases the flow velocity. However, by applying this technique the reservoir monitoring can't be achieved due to restriction in wells' configurations. Also the life and performance of C/T in sweet and sour environment has not been well established.

Applications:

Oil and gas wells which suffer from declining reservoir pressure and increased water production cause liquid to accumulate at the bottom of the well and exert back pressure on the formation. This restricts or in some cases prevents fluid entry into the wellbore from the formation.

To return the wells to flowing status, one of the available technique is to reduce the production tubing size by running a concentric string through the existing tubing. This reduces the effective flow area and increases the flow velocity. However, by applying this technique the reservoir monitoring can't be achieved due to restriction in wells' configurations. Also the life and performance of C/T in sweet and sour environment has not been well established.

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