Abstract

Assessing the Cathodic Protection (CP) performance of well casing is part of well casing Corrosion Management to ensure its integrity. CP is essential in managing well casing integrity by mitigating external corrosion, preventing well casing leaks, reducing operating/capital costs and maximizing total production over the life cycle.

Petroleum Development Oman (PDO) has reviewed the corrosion management strategy to ensure proper mitigation of well casings external corrosion in several clusters. This paper will detail the review process followed for two clusters; which included: i) confirmation of total amount of wells (with and without CP) within the clusters, ii) re-visit the requirement of external protection for well casings without CP, iii) identify historical failures relevant to external corrosion in well casing (with and without CP) to confirm barrier effectiveness and/or future requirement, iv) assessment of CP performance (protection level, cause of failure/lack of protection and recommendation for reinstatement).

Introduction

Oil and gas wells represent a large capital investment. It is imperative that corrosion of well casings be controlled to prevent loss of oil and gas, environmental damage, and personnel hazards, and in order to ensure economical depletion of oil and gas reserve.[1] Wells placed in external corrosive environment shall be protected by appropriate barriers such as additional cemented casing, cathodic protection and coating to assure well casing integrity. It should be recognized that no one solution fixes all and a combination of these may be required and a final decision must be based on history of corrosion problems in analogous fields/ wells, economics (high volume producers, long design life, repair like scabbing), HSSE (high pressure, sour wells, populated areas) over the lifecycle of the well. As per Company standards, the following combinations are considered to be reliable barriers to protect the well casing from external corrosion:

1. Coating + Cathodic protection (recommended for high sour/gas/critical wells with long design life > 25 years)

2. Sacrificial casing + coating

3. Coating + fully assured cementing (with cement log to verify), recommended for low risk wells

4. Thicker casing/Corrosion allowance + coating for clusters/areas identified as low corrosion severity/reduce service life (repairs).

5. Non metallic/corrosion resistance material (primary barrier)

Keywords:
pipeline corrosion, riser corrosion, ampp, materials and corrosion, upstream oil & gas, cathodic protection, flowline corrosion, production chemistry, material protection, requirement
Subjects:
Production Chemistry, Metallurgy and Biology, Pipelines, Flowlines and Risers, Materials and corrosion, Corrosion inhibition and management (including H2S and CO2)
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