Abstract

The long-term service life outcomes were compared for similar natural gas storage wells operated with either no cathodic protection or partial cathodic protection. Cathodic protection for storage wells is not mandated by regulation and industry practice varies so the outcomes for more than 350 wells were assessed based on casing inspection logs, historical failure rates and service lives. Casing inspection logs indicated a higher prevalence of external corrosion on the wells without cathodic protection. Furthermore, of the wells that had been remediated/abandoned, those operated with partial cathodic protection were found to have increased service lives when compared with the wells operated without cathodic protection. A higher percentage of the wells operated without cathodic protection also required remediation/abandonment. Overall, the data supported a conclusion that partial cathodic protection lead to improved service life outcomes and reduced external corrosion.

Introduction

When two long-time operators of natural gas storage wells in southwestern Ontario merged, it was an opportune time for the combined company to evaluate the effectiveness and impact of cathodic protection (CP). Staff from both legacy operators expressed general satisfaction with the longevity of their storage wells, typically 30+ years, but they had relied on two different approaches to corrosion control: one had isolated wells from flowlines and operated without CP, while the second had resistively bonded wells to cathodically protected flowlines. For the second operator, typical well currents were in the range of ∼3 A.

Lending weight to the ‘no CP’ approach were internal studies from the 1990's shared by other storage well operators in the vicinity that had concluded that CP was not beneficial and could even be detrimental. This detrimental effect was attributed either to interference between clustered wells or to current discharge on a single well from one well casing to another, such as from the production casing to the intermediate casing (see Figure 1 for terminology). Based on these interference concerns and well lives exceeding 20 years without CP – which was attributed to conditions not being aggressively corrosive – these other storage well operators had subsequently removed CP from their wells. It was noted at the time that the cost of CP was relatively low and was not a factor in the decision.

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