Control of corrosion in oil and gas production tubing

Abstract

Controlling corrosion in production tubing is essential for maintaining production and for preventing loss of well control. Materials for use downhole have to meet criteria for corrosion resistance and also mechanical requirements. The potential corrosion rate can be estimated and the risks of sulphide stress corrosion cracking assessed on the basis of the anticipated environmental conditions and flow regime. Material options for tubing can then be considered on the basis of published corrosion test data and also field experience. Candidate materials may be tested under the precise field conditions expected in order to ensure that overconservative choices are not made. Corrosion inhibitors, coated carbon steel, and fibre reinforced plastic tubing have temperature, flow regime, and mechanical limitations. Specific corrosion resistant alloys (CRAs) have environmental limitations with respect to temperature, hydrogen sulphide, and chloride content. Details of field experience with all of these material options are given. There exists a large amount of experience with CRAs for downhole applications. Correctly selected CRAs have a good track record of service, even for hostile, H₂ S containing conditions. There are a few limited examples of CRA clad tubing. This product may be one that needs re-evaluation as it offers potential for economic use of costly but effective CRAs.