Abstract

Plastic coating that is applied on the internal surface of production tubing is intended to protect the tubing from contact with corrosive production fluid to avoid corrosion. In most cases the use of plastic coating is successful only when the coating is perfect, because experience shows that damaged coating may make localized corrosion more aggressive at the point of damage. This paper presents VICO Indonesia's experience in using plastic coated tubing.

VICO Indonesia, the operator of Sanga-Sanga Block in East Kalimantan, Indonesia, has 4 (four) major gas fields which produce an average of 1.6 BSCFD (45.3 x 10⁶ m³ per day). Most of the wells are dually completed. Approximately 38% out of 642 tubing strings are internally plastic coated. Many wells have been worked over due to tubing-annulus communication from corrosion. Most of the tubing failures were found to be caused by localized corrosion at coating damage areas or aggressive corrosion on uncoated crossovers or pup joints that were installed in a coated tubing string. This corrosion phenomena is caused by galvanic corrosion that is aggravated by the large ratio of cathodic area (surface of good coating) to anodic area (surface of damaged coating or uncoated metal). There is also an effect of the morphology and dimension of the connection as a certain shape of the connection is susceptible to coating damage by wireline work, and may cuase turbulence.

Based on VICO's experience, several corrective actions and future design considerations to prevent further corrosion and to avoid tubing failure have been identified and implemented.